Listening Ability as Related to Duration of Exposure to High Level Noise

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P U R D U E U N IV ER SITY

T H IS I S TO C E R T IF Y T H A T T H E T H E S IS P R E P A R E D U N D E R MY S U P E R V IS I O N

Georg© Lewis Shaffer

e n title d

Listening Ability as Related to Duration of Exposure to High Level Noise

C O M P L IE S W IT H T H E U N IV E R S IT Y R E G U L A T IO N S O N G R A D U A T IO N T H E S E S

A N D IS A P P R O V E D B Y M E A S F U L F IL L IN G T H IS P A R T O F T H E R E Q U IR E M E N T S

FO R THE DEG REE OF

Doctor of Philosophy

P r o f e s s o r in C h a r g e o f T h e s is

H ead of S chool or D epartm ent

19

.SO

TO T H E L IB R A R IA N :---tS=^ T H IS T H E S IS I S N O T TO B E R E G A R D E D A S C O N F ID E N T IA L .

GRAD, SCHOOL FORM O—3 .49 — 1M

LISTENING ABILITY AS RELATED TO DURATION OF EXPOSURE 10 HIGH LEVEL NOISE

A Thesis Submitted to the Faculty of Purdue University by George Lewis Shaffer

In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

August, 1950

ProQuest N um ber: 27714184

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ACK^CTOEDGEMENT

This study was undertaken in conjunction with work at the Voice Science Laboratory, Purdue University, Project 20-K-l, Contract N6ori-104, for the United States Navy, sponsored by the Purdue Research Foundation, PRF 339, appreciation to:

The writer wishes to express his

Professor M. D, Steer for his valuable guidance

from the inception through the writing of this research; Dr, T. D, Hanley who offered many constructive criticisms regarding the analysis of the data and the preparation of the manuscript; Dr. H. G. Wood who gave frequent counsel on the statistical treatment of the data; Professor A. H* Monroe for his interest and assistance during the period of graduate study; and the staffs of the Voice Science Labora­ tory and the Speech and Hearing Clinic who helped in collecting and processing the data* Finally, the writer pays recognition to his wife for constant encouragement throughout graduate study.

TABLE OF CONTENTS Page ABSTRACT............................................

. «*

i

..........................*................

1

History of Intelligibility Tests ...................

2

History of Speech Intelligibility

6

INTRODUCTION

inHigh Level Noise .

DEFINITION OF THE PROBLEM........ .........................

14

EQUIPMENT AND PROCEDURE..........................

15

Item Analysis of VCL 24-Word Multiple Choice Intelligibility Tests .... ..... Subjects ............ Apparatus

15

.........

........... .

15

.... ....

15

Method ..........................................

15

Analysis of the Data

16

........

...........

Listening Ability as Related to Duration of Exposure to High Level Noise Subjects Apparatus

20

•••

20

....

20

Method

....

Analysis of the Data RESULTS

«

....... *............

..............

26 27 31

SUMMARY OF RESULTS.......

65

CONCLUSIONS..............................................

6?

IMPLICATIONS

68

..................................

BIBLIOGRAPHY..........

71

APPENDIX A Administration of VCL Tests

.....

74

TABLE OF CONTENTS (Continued) Page APPENDIX B Administration of L-i-N Tests.......

77

APPENDIX C Item. Analysis of VCL Tests

.....

88

APPENDIX D An Analysis of Matched Subjects

..............

108

LIST OF FIGURES Page FIGURE I Simplified Block Diagram of Equipment Arranged for Investigation of Listening to SpeecJa-in-Noise. .,*«•.. *

21

FIGURE II Seating Position of Subjects in Experimental Room ........

24

FIGURE III Mean Listener Scores for L-i-N Tests

.....

42

FIGURE IV Mean Listener Scores for L-i-N Tests in Relation to Time Spent in Testing Situation .....

46

Mean Listener Scores for L-i-N Tests in Relation to Time Spent in Testing Situation. Tests Adminis­ tered in 1, 2, 3, 4 Order at One Hour Intervals .......

51

FIGURE V

FIGURE VI

Mean Listener Scores for Four L-i-N Test Lists Administered in 1, 2, 3, 4 Sequence to ÎVro Experimental Groups (50 Minute and 3 Hour Exposures) . ...

57

FIGURE VII Mean Listener Scores for Four L-i-N Test Lists Administered in 1, 2, 3, 4 Sequence to Taro Control Groups (50 Minute and 3 Hour Exposures) ..........

60

LIST OF TABLES Page TABLE 1 List I Comparison of Predicted and Obtained Intelligibility Values for Items in the L-i-N 50 Word Lists ............

32

TABLE 2 List II Comparison of Predicted and Obtained Intelligibility ........ Values for Itemsin the L-i-N 50 Word Lists

34

TABLE 3 List III Comparison of Predicted and Obtained Intelligibility Values for Items in the L-i-N 50 Word Lists ........

36

TABLE 4 List IV Comparison of Predicted and Obtained Intelligibility Values for Items in the L-i-N 50 word Lists .....

38

TABLE 5 Significance of Differences Among L-i-N Test Lists (Theoretical Means ) ........

40

TABLE 6 Significance of Differences Among L-i-N Tests and Among ...... Experimental Croups : Observed Data

43

TABLE 7 Significance of Differences Among L-i-N Tests and Among Control Croups : Observed Data ....................

43

TABLE 8 Significance of Differences (wtn test) Between L-i-N Test List Means: Experimental Subjects

44

TABLE 9 Significance of Differences ("t” test) Between L-i-N Test List Means : Control Subjects ...

.44

TABLE 10 Significance of Differences ("t" test) Between Experimental and Control Subjectsf Listening Scores on L-i-N Test Lists ••..

45

TABLE 11 Significance of Differences in Mean Score for L-i-N Tests Civen Successively (increase of exposure time to noise)i Experimental Subjects.....

47

TABLE 12 Significance of Differences in Mean Score for L-i-N Tests Civen Suecessively: Control Subjects •••••...............

48

LIST OF TABLES (Continued) Page TABLE 13 Significance of Differences ("t" test) Between Tests Administered at Successive Points in the Time Sequence (increase of exposure time to noise): Experimental Subjects..., 49 TABLE 14 Significance of Differences ("t” test) Between Tests Administered at Successive Points in the Time Sequence: .............. Control Subje c t s

49

TABLE 15 Significance of Differences (”ttf test) Between Experi­ mental and Control Subjects with Respect to Tests Administered at Successive Points in the Time Sequence (50 minute sequence).. 50 TABLE 16 Significance of Differences in Mean Score for L-i-N Tests Civen Successively (increase of exposure time to noise, three hour period) : Experimental Subjects.....

52

TABLE 17 Significance of Differences in Mean Score for L-i-N Tests Civen Successively (three hour period): Control Subjects ....... 52 TABLE 18 Significance of Differences (”tM test) Between Tests Administered at Successive Points in the Time Sequence (three hour period): Control Subjects ....

53

TABLE 19 Significance of Differences ("t" Test) Between Tests Administered at Successive Points in the Time Sequence (three hour period) : Experimental vs. Control Subjects ....... 53 TABLE 20 Significance of Differences in Mean Score for L-i-N Tests Civen Successively: Experimental Subjects (Twenty Members of 50 Minute Croup who Heard Tests in 1, 2, 3, 4 Order) *....... 55 TABLE 21 Significance of Differences in Mean Score for L-i-N Tests Civen Successively: Control Subjects (Ttoenty Members of 50 Minute Croup who Heard Tests in 1, 2, 3, 4 Order) .....

55

TABLE 22 Significance of Differences ("t" test) Between Tests Adminis­ tered at Successive Points in Time Sequence: Experimental Subjects (Twenty Members of 50 Minute Croups who Heard Tests in 1, 2, 3, 4 Order) ..............

56

LIST OF TABIES (Continued) Page TABLE 23 Significance of Differences ("t" Test) Between Tests Adminis­ tered at Successive Points in tüe Time Sequence: Experimental vs. Control Subjects (Twenty Members of each of the 50 Minute Groups who Heard Tests in 1, 2, 3, 4 Order) ..........

58

TABLE 24 Significance of Differences ("t" test) Between Tests Adminis­ tered at Successive Points in Time Sequence. Three Hour Group vs. 20 Members of 50 Minute Group who Heard Tests in 1, 2, 3, ..... 4 Order; Experime ntal Sub jects

59

TABLE 25 Significance of Differences ("t” test) Between Tests Adminis­ tered at Successive Points in Time Sequence. Three Hour Groups vs. 20 Members of 50 Minute Group who Heard Tests in 1, 2, 3, 4 Order: Control Subjects... ...

61

TABLE 26 Significance of Differences in Mean Listening Score in Relation to the Seat Occupied Relative to Sound Source : Experimental Subjects

62

TABLE 27 Significance of Differences in Mean Listening Score in Relation to the Seat Occupied Relative to Sound Source; Control Subjects ••••..................

62

TABLE 28 Significance of Differences ("t,T test) Between Seating Positions Relative to Sound Source :Control Subjects ...... 63 TABLE 29 Correlation Coefficients for L-i-N Test Lists; Subjects. (N = 80) .......

Experimental

TABLE 30 Correlation Coefficients for L-i-N Test Lists: Control Subjects. (N = 80) ............ ................

. 64

64

i

ABSTRACT

Shaffer, George L. Listening Ability as Related to Duration of Exposure to High Level Noise♦ August 1950* 30 tables, 7 figures 112 pages, 4 appendices, 40 titles in bibliography. This research is concerned with

two studies, an item analysis

of the VCL TWenty-Four Word Multiple Choice Test and listening ability as it is related to duration of exposure to high-level aircraft-type noise. Data for the item analysis were collected from two previous studies conducted at the Purdue Voice Science Laboratory.

The

analysis indicated that the VCL test items ranged in intelligibility from 13 per cent to 90 per cent on a scale where 100 per cent is equal to no failures.

Ninety-two per cent of the items fell within the 25

per cent to 75 per cent intelligibility range.

The ability to pass a

given item seemed to be unrelated to total listening score since 93 per cent of the items produced rb^g for this relationship of .50 or less. The range for rb^g for the 456 items considered was from -.44 to 87. By selection of items six theoretically equated lists of 50 words each were constructed.

Four of the lists, referred to as Listen­

ing-in-Noise (L-i-N) test lists, were used in the second study under consideration. The study which was concerned with listening ability as related to high-level noise was divided into two sections, a 50 minute experi­ mental period and a three hour experimental period.

For the shorter

section 160 subjects, 80 experimental and 80 control, were used, while in the longer section 38 subjects, 19 experimental and 19 control, were

il

used.

All subjects were male students attending Purdue University who

volunteered to participate.

A statistical analysis of the data revealed

that no significant differences existed among the groups of subjects with respect to the listening ability variable. In the practical testing situation, only 24.67 per cent of the 200 items oh the four L-i-N tests performed as predicted with respect to theoretical and obtained intelligibility values.

The test lists

were found too unequal in difficulty, with Test 2 being easier than all other tests for both experimental and control subjects and Test 4 being easier than Test 1 for the experimental subjects. When inequality in difficulty of the tests was taken into ac­ count, it was found that for both the experimental and control subjects listening ability improved for the first three tests and then leveled off.

This phenomenon was true for both 50 minute and three hour experi­

mental conditions; however, the initial test and subsequent tests yielded higher listening scores for those subjects, both experimental and control, who participated in the three hour portion. When the effect

of seating position in relation to the sound

source was considered it was found that for the experimental subjects no position was significantly better than any other.

This was not true

for the control subjects, some positions being found to yield significantly higher scores than others. Estimated reliability among the L-i-N test lists used in this portion of the experimentation gave correlation coefficients of from ,56 to .80.

LISTENING ABILITY AS RELATED TO DURATION OF EXPOSURE TO HIGH LEVEL NOISE

INTRODUCTION

Within the pest decade there has been an increasing interest in the problems involved in conmainication in the presence of high-level noise*

Particularly between or among military units, but no less signi­

ficantly in the industrial situation, the necessity for accurate, relatively rapid voice communication of ideas, commands, warnings, etc., has grown in the recent past.

As Steer (32, 216) states, the four

basic components of all voice communication are: (1) a message, (2) a talker, (3) a transmitting medium, ranging in complexity from air to highly developed radio-telephone circuits, and (4) a listener.

With the

transmission system being limited to some degree by the environment in which it is employed, a great deal of the research has emphasized the other three components as they are related to the best available equipment. These remaining attributes have been the subjects of much of the recent research published in the current speech and acoustical journals. With the developing interest in problems involved In communication in highlevel noise, a primary need of investigators was a series of tests which could be used to gauge the effectiveness of voice communication.

After

the development of such tests, the second fundamental objective of re­ searchers in this area was a definition and exploration of the specific problems confronting the speaker and/or listener who had to use the available transmission systems in high-level noise.

All speech character­

istics of the individual as he performed under such conditions were

2

studied and many of the results were used as bases for the armed forces training programs in speech intelligibility. History of Intelligibility Tests The testing of speech intelligibility had its origin in the test­ ing to establish thresholds for pure tones.

Hudgins,et al., (14, 60) in

discussing the development of recorded auditory tests for measuring hearing loss for speech pointed out that in 1904 Bryant had developed a monosyllabic test which he recorded on wax cylinders.

The relatively

crude phonographic equipment of the day, however, limited the use of this test.

The Bell Telephone Laboratories in 1926 developed an auditory

test using speech.

This test, known as the Western Electric 4-A, used

records on which digits were recorded in pairs or threes, with a gradual decrease In the intensity of the recorded signal.

Although still in use

as a screening device, an important disadvantage is that each digit (seven is omitted) contains a different vowel sound, so that the ability to recognize the vowel alone will enable the listener to give the cor­ rect response. Dr. Harvey Fletcher (9j, in the early 1920»s, devised syllable, word, and sentence tests for the evaluation of telephone equipment. Fletcher+s "Standard Articulation Testing List," which is made up of a list of nonsense syllables, is still considered to be one of the most valid of the tests of auditory discrimination, since the listener must repeat syllables exactly as he hears them.

Because of the complexity of

administration, the test is not widely used today. Just prior to and during World War II the Harvard Psycho-Acoustic Laboratory^ (18, 4) continued along the same lines as Fletcher in develop1

The Harvard Psycho-Acoustic Laboratory will be identified as PAL.

3

jpg word and sentence tests in equivalent forms to be used in different­ iating between different pieces of equipment and to measure the per­ formance of listeners and talkers in the presence of high level-noise. As indicated by Kelly (15, 12) four conditions were suggested to govern the construction of an intelligibility test; (1) the lists of items should be long enough to give reliable scores and short enough to avoid fatigue or boredom; (2) the tests should be constructed so that a mean score of 50 per cent could be achieved (the reliability of the test is maximal when the test is neither too difficult nor too easy); (3) every list should provide an adequate sample of the common sounds of the language; and (4) familiar words are easier to understand.

If the word

is repeated in the test, it is easier when it is heard the second time. There are two ways of avoiding familiarity— the use of nonsense material and the avoidance of repetition of words. The first Harvard tests were composed of 11 lists of 100 words each and 68 lists of 20 sentences each. The word tests were made up of one- and two-syllable words, varying in common usage, but within the vocabulary of college sophomores. Proper nouns, pronouns, articles, homonyms, slang,and regional terms were excluded from the lists.

An

attempt was made to balance the words of each list for phonetic content. The reliability of the word lists with 23 talkers was .89.

The sentence

tests were made up of rearranged and improved sentences developed by Fletcher.

The reliability of the sentence lists with 24 talkers was .82.

In two different experiments, using 24 and 28 talkers, the correlations between average word score and average sentence score were *47 and .73 respectively (27, 1-5).

Consistency between scores made on the word

lists and the sentence lists, both Harvard*s and Fletcher's, was taken

4

as evidence of the validity of the word intelligibility tests. The Voice Communication Laboratory1 at Waco Army Air Field, Texas, in developing a training program to improve the speaking intelli­ gibility of students, found the Harvard lists too long for testing and training of students in talking and listening.

The VCL (£3, 2) proposed

the following requirements for a suitable word intelligibility test: (1) test administration should be brief; (2) there should be many forms of the test, equivalent in mean intelligibility value and range of difficulty; (3)

the materials should be familiar to aviation cadets; (4) it should be

simply and rapidly scored by unskilled personnel ; (5) it should be easy to construct, standardize, and revise; (6) it should discriminate degrees of speaking skill within the laboratory; and (7) it should predict the intelligibility of the speaker under flight conditions. The first VCL intelligibility tests were made from a master list of 5,000 familiar one- and two-syllable words taken from Webster*s Collegiate Dictionary (Fifth Edition). Words were selected at random from the master list and grouped into six lists of 100 words each. These lists were read to a panel of enlisted men from the armed forces by one untrained and two trained speakers.

Listeners* responses were

scored and the words were ranked according to the number of times each word was heard correctly.

From this, 22 lists of 24 words each, with

about the same mean intelligibility scores and standard deviations, were constructed.

When the tests were checked using 318, 162, and 322 speakers

no significant differences were found among the 22 lists and they were therefore considered equivalent forms.

An odd-even reliability coeffic­

ient of .86 was obtained for 346 subjects who served as both speakers 1 The Voice Communication Laboratory wi 11 be identified as VCL.

5

and lis tenara, while a coefficient of *94 was obtained for 169 speakers who spoke to a constant listening panel exclusive of themselves. In developing the final VCL test lists Haagen (12, 5) indicates that the following criteria were followed as closely as was practicable in the selection of words: 1. Use of one and two syllable words. 2* Use of words with Thorndike ratings of 10 or less. 3. Use of words that in trial tests were pronounced correctly at least 90 per cent of the time. 4. Use of words that on trial tests were between 20 and 80 per cent intelligible. (The intelligibility value of a word is the proportion of times it is heard correctly when spoken by many speakers.) 5. Avoidance of homonyms. 6. Avoidance of words with alternative stress patterns. The 24-item word lists were later shortened to 24 twelve-word lists.

These were standardized using 50 speakers with 450 listeners, all

from the population from which the tests were constructed.

Further re­

finement of the above tests brought about the development of the 24-Word Multiple-Choice test. words each.

Here the listener heard eight groups of three

For each word he had to make a choice from a list of four

words, the correct word and the three most frequently substituted words, based on previous write-down tests.

Haagen (12, 6) states that the

following indexes relate to the adequacy of the tests: 1. The mean intelligibility score for a sample of 169 un­ trained speakers under laboratory conditions was 50.0, S.D., 12* 2. Split-half correlations, corrected for length, of the measures of individual speakers were .86 to .94. 3. Relative Intelligibility values of test items as deter­ mined at different training centers correlated .86 to .92. 4. Ho significant differences were found between the means of word lists. Doyne (6) investigated the application of the VCL Twenty-Four

6

Word test (each, word given separately and responded to orally) as a speech reception test of hearing ability and compared it to the PAL intelligibility test, comprised of Spondaic words, known as Test No. 9 (14) and the PAL intelligibility test, which is also used as a measure of speech sound discrimination ability, known as the EB-50 test (Phonetically Balanced lists).

The PB-50 lists are made up of lists

of 50 monosyllabic words of equal average difficulty with each list equated as to phonetic composition.

In addition, the words are in com­

mon usage and the lists contain sounds in the same proportion as they occur in ordinary English speech.

Thurlow, et al., (37 , 55) report a

correlation of .82 between thresholds obtained for the FB-50 and the No. 9 tests.

Doyne concluded that there was a high inter-relationship

among the tests used, but that the test means obtained were significantly (statistically) different.

She found that the VCL test resembled the

Spondee test (Test No. 9) but was harder (less easy to hear).

The most

difficult test was the PB-50. History of Speech Intelligibility Research in High Level Noise Fletcher (9J and subsequent researchers until the time of World War II developed speech intelligibility tests as a means of evaluating the performance of radio-telephone equipment. and later used in relative quiet.

This equipment was tested

As Steer (32, 217) points out, many

of the voice characteristics of superior speakers under normal conditions result in poor intelligibility when employed in the presence of noise while using radio-telephone equipment.

A few of these characteristics

are: (1) low pitch (average 115 c.p.s.); (2) wide pitch variations (two or more octaves); (3) variations in loudness (17 to 23 decibels); (4) variations in accent, stress and pauses; and (5) rate (140-180 w.p.m.).

7

The first research with emphasis on the communicator and his speech problems in high-level noise was conducted by the National Research Council Committee on Selection and Training of Aircraft Pilots.

Much of

this early work on pilot training was carried on at Purdue University (55, 217).

The outgrowth of this exploratory research was the establish­

ing of training and research programs in the area of speech intelligi­ bility by the United States Navy.

Tie first of these training programs

was conducted at Pensacola, Florida.

In September, 1941, the Navy Depart­

ment, Bureau of Aeronautics commissioned the National Research Council to investigate the area of speech intelligibility and to study methods of improving the speech intelligibility of aircraft intercommunication com­ ponents under simulated flight conditions (18)♦ The outgrowth of this request resulted in the establishing of two laboratories at Harvard University, the Electro-Acoustic and the Psycho-Acoustic.

The Psycho­

logical Corporation under contract with the Office of Scientific Research and Development carried on studies in speech intelligibility at the Voice Communication Laboratory, Waco Army Air Field, Texas, from 1945 to 1945 (2, 1). As has been mentioned before, certain characteristics of the superior speaker in a normal environment are detrimental to a speaker per­ forming in noise; however, speakers tend to make adjustments which are appropriate in kind,if not in degree,when confronted with the noise barrier (40).

Likewise, it has been discovered that standard articulation

tests for weeding out defective speakers are of negligible value. When such tests were administered to a group of 124 flight instructors, only 0.8 per cent were classified as definitely defective in speech.

However,

8

more than 20 per cent were classified as defective speakers under simu­ lated flight conditions (52, 217)•

In a report titled "Subjective

Ratings of the Intelligibility of Talkers in Noise," PAL states (27, 2) : Ratings made on the basis of a standard speech interview, appropriate to the requirements of a college course in speech, are of limited validity for the peculiar situation of a military talker who must make himself intelligible in noise. Only a part of the criteria for superior speech in the absence of noise seems applicable in determining this type of intelligibility. In the case of the listeners it was also noted that the conven­ tional medical tests for measuring the acuity of hearing cannot be used as a basis for selecting good listeners for communication in noise (20, 14). Against a background of noise the signal-level is raised to such an ex­ tent that it exceeds the hearing threshold of all but the most seriously acoustically handicapped.

Fowler in a text edited by Davis (4^ 69) points

out that in the noisy place those with conductive deafness are not greatly handicapped.

In fact, a person with a pure conductive loss of moderate

degree can hear conversation just as well as or better than a person with normal hearing, while in the presence of a loud noise.

In noise the

handicapped individual hears only faintly, if he hears at all, the back­ ground noise which makes listening difficult for the person with normal hearing.

In such a noisy environment, the average individual usually

speaks louder in order to hear himself and hence the person with a con­ ductive loss is a t m advantage.

It is not possible to discriminate be­

tween good and poor listeners in noise by using the conventional articula­ tion tests (speech sound discrimination) conducted under relative quiet (20, 15). In considering the effect of noise on the listener, it is reported

9

{13, 7) that when five subjects were submitted to noise similar to that of a bombing plane (llOdb to llSdb) for periods of from one-half hour to eight hours, hearing losses occurred. from 3,000 c.p.s. to 5,000 c.p.s.

Loss was greatest in the region

After eight hours of exposure loss as

great as 20db occurred at frequencies as low as 250 c.p.s.

In all cases

studied, hearing impairment was temporary (complete recovery from four hours or longer), but the mere fact of occurrence indicates the strain imposed on the auditory mechanism in loud aircraft-type noise. Knowing that the techniques used by superior speakers in quiet were ineffective in noise, investigations were carried on in two general areas— the proper use of existing equipment and the speaking techniques which give the best intelligibility in high-level noise. In investigating the proper use of equipment for maximal per­ formances, it was found that when using the hand-held carbon microphone (T-17) best results were obtained when the speakers held the microphone squarely over the mouth and touching the lips.

In the same study, a

voice signal of 4.2 volts at the listener’s headset was found to be best. As the number of phones increased or decreased, the loudness level of the speaker had to vary to maintain this level of 4.2 volts.

By use of the

sidetone, optimum loudness of the voice signal could be maintained. Further, it was found that when the listener did not attenuate the voice signal reception for voice in high-level noise was better (30, 9-13). Studies in speech intelligibility in high-level noise covered such aspects as pitch, loudness, rate, and articulation. Research on the voice variable known as pitch indicates that use of the "normal* speaking pitch is best for highest intelligibility.

PAL

10

found that any advantages gained from raising pitch were apparently due to the increase in loudness (28, 18) * This conclusion was based on a study using 47 talkers when the correlation between pitch level and talking at a conversational level was *18 as compared to the correlation between pitch level and talking at a high voice level of *35.

In

another study (28, 18) it was found that a rise in decibels correlated with the rise in frequency by *47. VCL has also substantiated these findings.

In their experiments (3) they found that in the presence of

noise and loud speech the pitch tends to rise.

They also state that

training in using a pitch other than that which results from instruction in loudness is not warranted, since intelligibility

for "high" and "very

high" pitch was found to be significantly less than

for "normal" or "low"

pitch. If a favorable speeeh-to-noise ratio is to be established, an in­ crease in loudness of speaking must take place.

In summarizing experi­

mental work on loudness PAL concludes (28, 7): The primary requirement for a good talker is an ability to speak loudly. Any military talker, no matter how well qualified in other respects, will be ineffective if he does not speak loudly enough to be heard above background noises. In its final report VCL makes the following statement which sup­ ports previous findings (50, 3): The high loudness levels, found to be most effective in noise, were necessary to produce favorable signal-to-noise ratios. Where noise pick-up of the microphone is less in­ tense, the gain in intelligibility with increased loudness levels is either small or absent. This is indicated by the equivalent mean intelligibility scores, at 4 levels of loudness, earned by students using the ANB-M-C1 microphone, shielded from noise by an oxygen mask. However, in the majority of cases in AAT voice communication, the speaker talks with the microphone open to high-level noise and, to be understood, must speak loudly.

11

All studies seem to indicate that for the highest intelligi­ bility in high-level noise, the talker must speak louder than normally and less loud than shouting (17, 18).

As has been pointed out before,

optional loudness may be learned and maintained by use of the sidetone in the speaker1s headset. The rate of speaking has been thought to be related to intelli­ gibility of voice transmission, and hence, it was recommended that a rate of 120 w.p.m. be used.

However, VCL reports (30, 4) no signifi­

cant differences in intelligibility between slow rate (103.7 w.p.m.) of speaking and normal rate (141.3) of speaking when 60 subjects were used. In a second experiment (30, 5) they report that in an experiment involv­ ing 20 subjects, no loss in intelligibility occurred until a rate of 150 w.p.m. or more was reached.

In a third experiment (30, 5) with 23

subjects using the T-17 and the T-30 microphones, the only significant difference was found in using the T-30 microphone between 120 w.p.m. and 180 w.p.m.

We can conclude that the only rates which might interfere

with intelligibility are rates much faster than those used in normal con­ versation. Research at VCL reported by Draegert (J7) indicates that training for good articulation patterns is superior to training which attempts to improve the pronounciation of "difficult*1 sounds only.

Experimentation

indicated that when the hand-held microphone (T-17) was used, significant improvement in intelligibility was brought about by having the talkers stress the final consonants. No significant improvement was observed when sibilant sounds were stressed.

In a second study by the same re­

searcher, significant improvement was observed in a one-hour training

IS

period when subjects were told to "read back" messages they had received* Although no specific instructions were given, improvement took place. Such improvement probably was brought about by the talkers f desires to perform well in a difficult situation and hence produce better articula­ tion. It has been found that two periods of two hours each, where the various attributes of good speech for high intelligibility is stressed, produced significant improvement in intelligibility (26, 5).

Kelly (15)

also found that both trained and untrained speakers improved in intelli­ gibility in the experimental situation; however, the trained subjects improved significantly more.

This improvement persisted after periods of

65 and 100 days with the trained speakers being significantly more in­ telligible on the basis of the tests used than the untrained speakers. In a VCL study, when the listener was considered per se, it was found that the diversity in ability to receive a message was such that the best listener was able to identify correctly almost twice as many words as the worst listener (20, 3) • When 10 listeners listened to three speakers each reading four lists of 100 words each daily for a period of seven days, a marked improvement took place in listening ability until the fifth day, when a leveling-off effect took place.

Nevertheless, all 10

listeners kept the same relative positions as to ability in relation to the other listeners that they held on the original test.

This would seem

to indicate that an initial test might furnish an adequate index to future listening ability.

In a second experiment (30, 17) four listeners

heard ten 100-word lists daily. the same speaker.

Of these lists, five were always read by

Improvement was based on the gains made for these five

tests only. The average listening score improved 15 per cent after a

13

single practice of ten readings• A relatively small amount of training, therefore, may be predicted to yield a considerable increase in listening ability*

It required about 40 readings to achieve the maximum level of

performance*

In a report prepared by YCL (30» 14) where listeners and

speakers were trained in one of these two attributes of communication for a three-hour period, listeners made an 8*2 point gain in ability as contrasted to a 17,0 gain for the speakers*

The gain of 8,2 for the

listeners is not as meaningful when we realize that tests administrated initially and finally were the same.

Steer, Hadley and Kerr (35) tested

four groups of flight students at the beginning and end of an experi­ mental period with a test designed to measure listening ability in flight. On four days two groups received systematic listening training periods of a half hour each, which consisted of listening to records made under flight conditions.

The remaining two groups received no training.

the experimental and the control groups made significant gains.

Both

However,

the experimental group made gains which were significantly higher than the control group.

Since the tests used in this experiment were known

to be reliable, the improvement of the control group was attributed to the learning factor involved in taking the initial test. From the foregoing reports of research, it is evident that both speaking and listening ability can be improved in the presence of loud noise.

However, gains in speaking ability are more clear-cut than those

in listening ability.

It has been reported also (21) that the correla­

tion between speaking and listening ability is low.

For two groups of

enlisted army personnel of 419 and 597 men, the correlations were .27 and .41 respectively.

14

DEFINITION OF THE PROBLEM The present investigation is concerned with two aspects of voice communication*

The first, designated an analysis of the VCL 24-

Word Multiple-Choi ce Intelligibility test, is concerned with subjecting this test to item analysis*

In order that test words might be used in

other arrangements and that different lists might be assembled which might, in a given population, be predicted to yield intelligibility scores of given values, the following questions are asked about each test word in each list: 1. What is the intelligibility value (per cent of correct re­ sponses) of this word? 2. How does success in identifying this word correlate with total listener performance on the intelligibility test? 3. What are the central tendency and variability of listener scores of subjects who successfully identify this word in an intelligi­ bility test? 4. Can equated 50-word L-i-N (Listening in Noise) test lists be constructed from data obtained? 5* When such L-i-N test lists are administered in an experimental situation, do predicted intelligibility values of individual items differ significantly from obtained intelligibility values? The second major aspect of this problem, designated listening ability as related to duration of exposure to high-level noise, is con­ cerned with the ability of subjects to understand spoken messages after varying lengths of exposure to loud, aircraft-type noise.

The following

questions are asked about the testing of subjects exposed to noise for

15

varying lengths of time: 1. Do the several L-i-N test lists measure listening ability equally well? 2, How well do students perform in listening ability as related to duration of exposure to loud noise? 5, Is the seating position in the testing room, relative to the sound source, of any consequence in test scores obtained?

EGALEMENT AND PROCEDURE Item Analysis of VCL 24-Word Multiple Choice Intelligibility Tests Data for this aspect of the study were collected from two pre­ vious researches conducted by Project 20-K-l, Contract N6ori-104, T.O. II (3^; J59).

The following conditions prevailed in

1* Subjects.

theseinvestigations :

Male undergraduates enrolled in an elementary

course in public speaking at Purdue University served as subjects.

No

known bias was operative in the selection of class sections of the public speaking course, nor in the selection of male subjects from within the sections.

Hence, though statistical randomization was not followed,

selection of subjects was essentially random. 2. Apparatus.

In testing the intelligibility of the subjects,

the following apparatus was used: carbon microphones, Navy type T-38C; Magnetic headphones, type ANB-H-l; and an amplifier with built-in noise generator. Navy Device 8-1, the Portable Interphone Trainer described by Nordyke (j5). 3. Method.

VCL 24-Word Multiple-Choi ce Intelligibility tests

16

were administered to the subjects of the two investigations under con­ trolled conditions1* Form A of the VCL test was administered to naive subjects. test.

That is, the subjects had no previous acquaintance with the

Fona B was administered to control subjects who had previously

been tested with Form A and to experimental subjects who had undergone intelligibility training in addition to having been tested with Form A. Data collected for the two test forms are not, therefore, directly com­ parable since increments in intelligibility scores were observed for both experimental and control subjects in the retest situation.

A

statistical treatment designed to equate the two test forms was employed* Application of the treatment will be described below. Analysis of the Data* A. Test reliability.

Reliability of the VCL tests (Form A and

Form B) was determined by the split-half method, corrected for atten­ uation.

A standard formula for this statistic was employed (11, 4llf). B. Listener score.

An individual subject's listener score was

calculated as follows: Wjl + w

3

+

:

.

.

+ wn

n x 24 Where : WgL = words correctly heard and marked by the listener for the first speaker, Wg = words correctly heard and marked by the listener for the second speaker, Wa ” words correctly heard and marked by the listener for the nth speaker, 1 For specific step-by-step description of the administration of these tests see Appendix A.

17 n « the number of speakers heard by the listener, and 24 • the total number of words spoken by each individual speaker. C. Item intelligibility.

The index of intelligibility for an

individual item in a given word list was calculated as follows: s

y

* Number correct responses to word Total number responses to word

D. Ability of item to discriminate among successful and unsuc­ cessful listeners.

It was believed that three elements were contribu­

tory to this factor for each item.

They were:

1. Mean listener score of all listeners who correctly heard and marked the item. 2. Standard deviation of such listener scores (a smaller standard deviation being indicative of more homogeneity among listeners). 3. Biserial coefficient of correlation

between listener

score and the pass-fail dichotomy on each item.

It is to

be understood the r ^ ^ is a statistic which includes in its computation elements 1 and 2 noted above.

However, it is

believed that presentation of all three elements gives a more fully rounded picture for each item. r, . was by the following formula: bis r « Mp - Met x bis dt y Where: Mp = mean score of "pass" distribution Mq == mean score of "fail" distribution p

» proportion of cases in "pass" distribution

q ■ proportion of cases in "fail" distribution

Calculation of

18

dt «* standard deviation of total distribution y

= the ordinate of the normal distribution curve for the Corresponding values of p and q, when p and q as usual represent areas under the normal curve (11, 350).

E. Correction factor employed to equate difficulty of items in

Form B to difficulty of items in Form A.

This correction factor was a

means of compensating for speaker and/or listener improvement noted in the retest situation, using Form B.

The factor was obtained by divid­

ing the mean listener score for all subjects on Form A by the same statistic. Form B.

Each item Intelligibility score in Form B was then

multiplied by the quotient obtained* F. Construction of L-i-N Tests, The item analysis yielded an intelligibility score for each word"*". All words, 300 in number, with intelligibility scores of from 32.5 to 66.6 per cent were used to con­ struct the new list tests. These limits were used in order to meet the criterion of a test which is neither too easy nor too difficult.

Each

word was written on a card and the obtained intelligibility rating was added to the card.

The cards were then arranged in ascending order of

intelligibility values, and six test lists were assembled by dealing the cards into six piles in the following order: 1, 2, 3, 4, 5, 6, 6, 5, 4, 3, 2, 1, 1, 2, 3, 4, 5, 6, 6, 5, etc., until the entire 300 cards were used.

This procedure produced six lists of 50 words each.

When item

intelligibility values of items within a given list were summed and the total obtained divided by the number of items, 50, a mean predicted intelligibility score resulted.

In the investigation here reported, the

six test lists were found to have mean predicted intelligibility scores 1 See Appendix C

19

which differed by less than .05 on a 100-point scale.

(The four lists

used in the second section of this experiment were tested for significance of differences between these predicted mean scores.) As each list now stood, the more difficult words appeared first and the items in each list became progressively easier.

A table of random numbers was consulted for

assignment of each item to a position on its list.

The effect of this

procedure was to negate any systematic effects which might have resulted from progressive increases or decreases in item difficulty. G-. Test of Goodness of Fit.

As has been previously stated, each

item in each test list was assigned a theoretical intelligibility value based on previous use of the test items in other arrangements.

In the

present investigation, it was believed to be desirable to compare theoretical intelligibility values with obtained intelligibility values and to test the significance of the divergence of fact from hypothesis. Accordingly, intelligibility values for these items were recomputed on the basis of the test administration used in the second phase of this experiment.

As will be described later, each test list was administered

to naive subjects, to subjects who had been subjected to one previous test, to two previous tests, and to three previous tests.

In the compari­

sons of theoretical and obtained intelligibility values for individual items, results from test administration to naive subjects only were used. The Chi-square statistic (X2 = sKS-T-ffi,) ) then was applied to the theoretical and obtained data.

20

Listening Ability as Related to Duration of Exposure to High Level Noise A. Subjects.

One hundred and Ninety-eight male undergraduate

students between the ages of 19 and 32 served as subjects.

(Ninety-nine

of these students served as experimental and 99 as control subjects. subject served in both groups.)

No

These students were volunteers from be­

ginning and advanced public speaking classes and from University housing units.

No known bias was operative in the selection of subjects.

The

only qualifications imposed were (1) that the subject have "normal" hear­ ing, and, (2) should not have participated in previous experiments involv­ ing listening- and/or speaking-in-noise. B. Apparatus. As described above, six lists of 50 words each, designed to be equally difficult, were prepared from the results of the item analysis of the 24-Word Multiple Choice Intelligibility test. Four of the six lists were used in this portion of the experiment. phonograph recording containing these 50-word lists was prepared.

A This

stimulus record was achieved by first recording the test lists on mag­ netic tape while the speaker monitored his voice at a predetermined level of 70 db as measured by a General Radio, Model 759B, sound level meter.

The record was 2ater transferred from the magnetic tape to a

lacquer-coated disc.

The magnetic tape recorded employed. Magnecorder,

Model PT6-J, had an overall response for record-reproduce operation of 40-8,000 c.p.s., - 3 db, and the 15,000 c.p.s. response was down 8 db below the 1,000 c.p.s. point.

Copying from tape to disc was accomplished

by means of a Presto 92-A power amplifier and a Presto 1-D cutter.

The

record used was a 16 inch red-label Audio disc, and the stimulus material occupied the outer 3-1/2 inches of the disc. the stimulus disc was 33-1/3 r.p.m.

Turntable speed for cutting

SPEECH

LU

< X o

LU

en o

LU

LU

to LU

Q Z)

LU

LU

s O

< cr

z

tr

< ce

LU

u>

LU

LU

>

Z>

O en S P E E C H -IN -N O IS E .

LU

o TO

u. ARRANGED

FOR

INVESTIGATION

tz> cr

EQUIPMENT

LU

LISTENING

OF

X o LU LU Q.

DIAGRAM

IS

lO

^ lO I S

toO

^ to O- ^ H

00 t O rH

rH H

02 H

to tO H tO 03 04 CO 04 CM CO rH t o tO 04

o

to to to to 04 CM

rH

CM Ht rH rH tO rH lO 04 04 rH rH rH 00

CO

CM CM Ht

to

H


rH rH

rH 00

rH rH CM CM

• to

rH

rH t> 0 0 0 > t> 0 2 C O m

to 04 o to

pH

I 0 0 > n t0 t0 t0 0 2 0 0

IS

m o

03

CM

to IS 00 I S CO 04 CM CM

rH H

•

to

IS rH to o> I S tO

to S # 02 $ IS

to

O• O* 03 03

to

O'. to

O

Cl 02

td to

. 8to.

§

H ai rH04 tO o o +»

+> c t

64

significant at the one per cent level of confidence between six and five and at the five per cent level of confidence between positions six and eight, and positions six and ten). It should be recalled that for the 80 experirontal subjects exposed to noise for a 50 minute period, List 2 was easier than the other lists and list 4 was easier than List 1.

For the 80 control sub­

jects in the same portion of the experiment. List 2 was easier than the other lists.

Correlation coefficients, employed in a modified test-

retest estimate of reliability, were calculated among the four L-i-N test lists.

Correlations ranged from .56 to .75 for the experimental

subjects and .62 to .80 for the control subjects.

These results are

tabulated in Tables 29 and 30.

Table 29. Correlation Coefficients for L-i-N Test Lists: Experimental Subjects. fN « 80) Tests 1 2 3 4 1 2 3

.75

.65 .56

.59 .60 .71

Table 30. Correlation Coefficients for L-i-N Test Lists: Control Subjects. (N » 80) Tests 2 3 4 1 1 2 3

.69

.76 .63

.62 .64 .80

65

SUMMARY OF RESULTS The following numbered paragraphs constitute a summary of the results of this investigation.

Conclusions and implications based upon

the summary of results follow in succeeding sections. 1. An item analysis of the VOL test gives a range in intelligibility from 13 per cent to 90 per cent. 2. Ninety-two per cent of the VCL items fall within the 25 per cent to 75 per cent intelligibility range. 3. Success in passing a given item, has little or no rela­ tion to total listening score, since 93 per cent of the items are found to have indexes for this relationship (r^^g) of below .50. 4. The range of r^^g for the 456 items considered was —.44 to .37. 5. Four L-i-N test lists constructed from the results of the item analysis of the VCL tests yielded theoretical means which differed at the most by 0.03 per cent. 6. The four L-i-N test lists were found to be theoretically equal in difficulty. 7. When the 200 items on the four L-i-N tests were subjected to a testing situation only 24.67 per cent performed as predicted. 8. L-i-N test List 2 was found to be easier than the other four tests for all subjects.

List 4 was easier than List 1 for the

experimental subjects. 9. No significant differences existed among the groups participating in the experiment.

66

10*

Both expérimental and control subjects improve in

listening ability for the first three tests and then level off in performance*

This observation was noted both for the subjects

who participated in the 50 minute testing sequence and for those who took part in the three hour portion of the experiment. 11.

Mean listening scores on the initial test (and subsequent

tests) were higher for the subjects participating in the three hour portion of the experiment than for subjects in the shorter session. 12.

Seating position within the testing room was not

significantly (statistically) different for the experimental subjects; however, certain positions were advantageous for the control subjects. 13.

Estimated reliability calculated among the four L-i-N

test lists gave correlation coefficients from .56 to .80.

67

CONCUJSIONS

Within the limits of the population sampled and the procedures employed in this investigation the following conclusions may be noted: 1. An item analysis of the standard VCL intelligibility tests is now available. 2.

The item analysis of the VCL tests reveals a range in intelligibility scores which is greater than that reported by the authors of the tests. However, the majority of the items in the VCL tests are within the range of intelligi­ bility scores reported for the tests.

3.

Listening ability on a given test list is no index of listening ability for a given item within that list*

4.

Theoretically equivalent intelligibility tests have been constructed and are now available*

5.

Theoretically equivalent intelligibility test lists con­ structed from an item analysis of the VCL tests are not necessarily equivalent when applied in a test situation.

6*

Successive L-i-N test lists yield scores reflecting gradual improvement, followed by a leveling off.

7.

Subjects exposed to more or less prolonged periods of noise do not yield significantly different scores than those achieved by subjects not exposed to noise.

8. Duration of exposure to noise is not related to L-i-N test scores attained by experimental and control subjects.

68

IMPLICATIONS From the item analysis of 456 words, it was possible to con­ struct six test lists which were theoretically equated as to difficulty. However, when four of these six lists were used in a practical situation it was demonstrated that the lists were not equal in their ability to measure listening, either in the experimental or the controlled situa­ tion.

Initially, words which were analyzed were each spoken by 32 to

357 speakers and the analysis was based upon averages for these speakers. f The equated word lists were recorded by one speaker, who monitored his voice at a predetermined level.

It is possible that even though the

loudness level of the speaker's voice was held constant, other voice variables, not measurable at the time of the recording, may have changed enough to alter the intelligibility values of individual items. Evidently, the technique as described is somewhat inadequate for the con­ struction of equated word lists, at least for the listening-in-noise situation.

If it were possible to control all the voice variables in

the recording of such test lists, it is conceivable that the technique described might be adequate.

Again, inter-relationships of the words in

different contexts may account for the differences obtained.

Also, it

will be remembered that the VCL word lists were spoken three words at a time while the L-i-N words were spoken individually. Previous research has indicated that test taking in and of itself is sufficient to improve the listening ability of subjects.

A

number of explanations have been offered for this phenomenon, such as learning, adaptation to the testing situation and becoming familiar with the context of material being used in testing.

Other research has

69

indicated that exposure for long periods to loud noise produces a temporary hearing loss, as measured by pure-tone audiometer.

In the

present research, exposure, regardless of length, did not produce sufficient loss to hinder the improvement from testing period to test­ ing period.

Since both experimental and control subjects followed

the same pattern, further research should be carried out with a larger number of subjects where the exposure time is increased to as much as eight to ten hours. It will be recalled that both experimental and control subjects participating in the three hour portion of the experiment performed at a higher level than those of the 50 minute group (this was also true for the limited number of subjects matched on initial performance, Appendix D). One is at a loss for an explanation of these results un­ less, as has previously been hypothesized, only subjects strongly motivated to assist in research of a military character responded to the appeal for volunteers for a three hour testing session. the number of subjects available was limited.

Here, too,

An experiment designed to

use a greater number of subjects over a longer period of time would be desirable.

An attempt to overcome the motivation factor might be

attempted by having enlisted military personnel assigned to one testing situation and a highly motivated civilian group to another. Although both the experimental and control subjects performed the same on each test list and from test to test in the time sequence, it was found that certain seating positions in the testing room were advantageous to the control group.

Here the subjects were exposed to

ambient noise only during the testing situation; between tests they

70

sat in relative silence.

Apparently there is a period of adjustment to

the noise used which gives certain positions an advantage over others in the control situation.

It should be noted that the seats found to

be advantageous were located in the back half and center of the rever­ berant room.

It might be possible to overcome the advantage of one

position over another by having the subjects change seating positions for each exposure.

71

BIBLIOGRAPHY 1* An Experimental Comparison of 5 Conditions for Voice Training. Purdue Research. Foundation, Project 20-K-l, Contract N6ori-104, Technical Report No. SDC 104-2-4, Lafayette, Indiana, 1947. 2. Black, John W, Studies in Speech Intelligibility: A Program of War-Time Research. Speech Monographs, Vol. XIII, No. 2 1946, 1-3. 3. Brackett, I.P. Intelligibility Related to Pitch. Monographs, Vol. XIII, No. 2, 1946, 24-31.

Speech

4. Davis, H. Hearing and Deafness. Murray Hill Books, Inc., 1947, Chapter 4. 5. Directions for Installation and Operation of Voice Communication Equipment Utilizing Device 8-1. Purdue Research Foundation, Project 20-K-l, Contract N6ori-104, Technical Report No. SDC 104-2-2, Lafayette, Indiana, 1947. 6. Doyne, Marcella Pepper. Studies in Speech Reception Testing. M.S. Thesis, Purdue University, June 1950. 7. Draegert, G. L. Intelligibility Related to Articulation. Monographs, Vol. XIII, No. 2, 1946, 50-53. 8. Egan, James P. Articulation Testing Methods. 58, No. 9, 1948, 955-991. 9. Fletcher, Harvey.

Speech and Hearing.

Speech

Laryngoscope, Vol.

Van Nostrand, 1929.

10. Frequency Distortion in the Device 8-1 Portable Interphone Trainer. Purdue Research Foundation, Project 20-K-l, Contract N6ori-104, Technical Report No. SDC 104-2-1, Lafayette, Indiana, 1947. 11. Gilford, J. P.

Psychometric Methods.

McGraw-Hill, New York, 1936.

12. Haagen, C. Hess. Intelligibility Measurement. Vol. XIII, No. 2, 1946, 4-7.

Speech Monographs,

13. Handbook of Human Engineering Data for Design Engineers. Technical Report No. SDC 199-1-1. Tufts College Institute for Applied Experimental Psychology, Part IV, Chapter IV, Section II. 14. Hudgins, C. V., Hawkins, J.E., Karlin, J. E., and Stevens, S. S. The Development of Recorded Auditory Tests for Measuring Hearing Loss for Speech. Laryngoscope, Vol. 57, 1947, 57-89. 15. Kelly, James C. Effects of Training on Speech Intelligibility through Synthetic Noise Barriers. Ph.D. Thesis, Purdue University, January, 1948,

72

16*

Lindquist, E. F. Statistical Analysis in Educational Research. Houghton Mifflin Co., Boston, 1940.

17.

Moore, Paul. Intelligibility Relative to Loudness. Monographs, Vol. XIII, No. 2, 1946, 13-18.

18.

National Research Council Committee on Sound Control. Articulation Testing Methods. February 1, 1942.

19.

OSKD 383. National Research Council Committee on Sound Control : Report on Articulation Testing Methods. February 1, 1942.

20.

OSRD 987. The Problem of Selecting and Training Personnel for Communication in Intense Noise. November 10, 1942.

21.

OSRD 1769. Speech Communication Project; Selection and Training of Telephone Talkers; A Speech Interview for Selection of Telephone Talkers. Report No. 1, August, 1943.

22.

OSRD 3105. Response Characteristics of Interphone Equipment IV. January 1944.

Speech Report on

23. OSRD 3748. Intelligibility Measurements ; Techniques and Proce­ dures Used by the Voice Communication Laboratory. May 1944. 24.

OSKD 3516. Auditory Tests of the Ability to Hear Speech in Noise. September 1, 1944.

25.

OSRD 3802.

26.

OSRD 3862. Can Intelligibility of Voice Communication be Increased by Training in Voice Techniques? July 5, 1944.

27.

OSRD 4023, IC 69. Speech in Noise; A Study of the Factors Determining its Intelligibility — The Use of Words and Sentences in Testing the Intelligibility of Telephone Talkers. September 1944.

28.

OSRD 4023, IC 81. Speech in Noise; A Study of the Factors Determining its Intelligibility. September 1944.

Articulation Testing Methods II.

29. OSRD 5567. Intelligibility Measurement; Choice Tests. September 11, 1945. 30.

November 1, 1944.

Twenty-Four Word Multiple-

OSRD 5568. Final Report in Summary of Work on Voice Communication. September 11, 1945.

31. Phonetic Considerations in the Selection of Words for Best Intellig­ ibility. ,Bell Telephone Laboratory Report, August 5, 1941. 32.

Steer, M. D. Speech Intelligibility in Naval Aviation* Speech Disorders, Vol. 10, No. 3, 1945, 215-219.

Journal of

73

33.

Steer, M. D. end Hadley, J. M. Ihe Speech Intelligibility Program in Naval Aviation: Historical Summary, quarterly Journal of Speech. Vol. 32, No. 2, 1946, 217-228.

34. Steer, M. D., Hadley, J.M., and Kelly, J. C. Development and Evaluation of Techniques to Measure Speech Intelligibility of Flight Personnel. Research Report: Naval School of Aviation Medicine, U. S. Naval Air Training Bases, Pensacola, Florida, February 1946. 35.

Steer, M. D., Hadley, J. M., and Kerr, W. A. Listening Training Aids for Pre-Flight and Primary Flight Students. Research Report: Naval School of Aviation Medicine, U. S. Naval Air Training Bases, Pensacola, Florida, September 22, 1945.

36. Stevens, S. S., Egan, ing Spectra. Journal 19, 1947, 771-780.

J. P., and Miller, G .A. Methods of Measur­ of the Acoustical Society of America, Vol.

37.

Thurlow, W. R., Silverman, S. R., Davis, H., and Walsh, T.E. A Statistical Study of Auditory Test in Relation to the Fenestration Operation. Laryngoscope, Vol. 58, 1946, 43-66.

38.

Voice Communication: Retention of Improved Intelligibility. Purdue Research Foundation, Project 20-K-l, Contract N6ori-104, Technical Report No. SDC 104-2-5, Lafayette, Indiana, 1948.

39.

Voice Communication: Retention of Improved Intelligibility II. Purdue Research Foundation, Project 20-K-l, Contract N6ori-104, Technical Report SDC 104-2-9, Lafayette, Indiana, 1948.

40.

Effect of Level of Distracting Noise Upon Speaking Rate, Duration, and Intensity. Purdue Research Foundation, Project 20-K-l, Contract N6ori-104, Technical Report No. SDC 104-2-14, Lafayette, Indiana, 1949.

74

APPENDIX A

ADMINISTRATION OF VCL TESTS

75

Administration of VCL Tests Subjects, wearing headphones, are seated in test booths. structions in the use of hand-held microphones are given.

In­

Each subject

is provided with a microphone, a VCL Test Answer Booklet, and a cafd on which is typed the list of words he is to read when his turn comes. The following specific instructions are then communicated to the sub­ jects, either by "live voice" or by means of a phonograph disc and playback; Please examine the cover page of the test booklet as I explain the procedure for this test. The directions state: When you hear "Number 1; mortar, shut, assist" you are to mark your paper, with lines through the words mortar, shut, assist in the group of words to the right of the number One. And when you hear "Number Two, blimp, injure, knob," you are to draw lines through those three words in the word group to the right of the number Two. And when you hear "Number Three, gliding, battle, ignite" you are to draw lines through those three words in the word group to the right of the number Three. For the remainder of this sample exercise, you are to cross out each word as it is read by the sample exercise speaker. This will indicate to you the method to follow in marking the test sections which appear on succeeding pages. As each group of three words is read, cross out each of the words that you hear. You will now hear the sample exercise in its entirety, spoken against a background of noise. Note that mortar, shut, and assist are the first three words spoken by the sample exercise speaker. Get ready for the sample exercise. exercise: (Noise in) "Number One Number Ttoo Number Three Number Four Number Five Number Six Number Seven Number Eight

mortar blimp gliding rapid boat towel pillow wither

Here is the sample

shut injure battle bamboo brutal mood ruler drastic (Noise out)

assist knob ignite monkey graceful funny swap turtle"

76

Now check your answers when the words are spoken without the noise background* (Word list repeated without noise) If your concentration and listening ability were good, you have pencil lines through all of the words just read to you. In the following tests each of you in turn will have an opportunity to read a list similar to the one you just heard. While one man on a circuit reads a word list, the other cir­ cuit members should respond to the talker by marking out, in the manner just completed in this sample, the words which are spoken. The exercise is not easy. The barrier of noise makes concentration imperative. At this point you should turn to page two of the test booklet and be ready for Speaker One in your circuit. All those except Speaker One will mark their answer sheets in the manner just practiced. Speaker One will take up his micro­ phone, depress the push-to-talk button, and say: "This is Speaker One, Speaker One. My name is . ..... and he will give his name. Then he will read the word list which is pasted in his answer booklet. When Speaker One finishes his word list, he will say: "Over" and prepare to mark his answer booklet when Speaker Two begins. Speaker Two will perform the exercise just as Speaker One did, beginning by saying : "This is Speaker Two, Speaker Itoo." He then announces his name and reads the word list pasted in his test booklet. Each speaker in the circuit will follow in turn, introducing himself and reading the word list. Listeners will write the names of the speakers on the appropriate lines. Speakers must remember to read the number which precedes each group of three words, for example, "Number One, mortar, shut, assist. Number Two, blimp, injure, knob," and so on. Speaker Number One will begin just as soon as he hears the noise barrier in his headset. Ready now for the noise barrier. (Noise in) The subjects then perform the test in the manner indicated in the instructions.

APPEND DC B

ADMINISTRATION OF L-i-N TESTS

78

Administration of L-i-N Tests

Experimental Group Subjects are first instructed in the proper manner of wearing the headphones to get the best seal against ambient noise.

They then

removed their headsets and the following specific instructions were read to them; This is a test of listening ability in noise.

We are interest­

ed infinding out how well a person can understand language in the presence of loud aircraft-type noise.

This is not as loud as that pro­

duced by many of the large four-motored bombers in which missions of from four to twelve hours are made. a warning.

Before each test you will be given

At that time make sure that your headphones are securely

placed over each ear.

Tests will be administered at five and ten

minute intervals (one hour intervals). noise without your headphones on. in the testing room. equipment.

Between tests you will hear the

At that time you will be at leisure

Please do not compare papers or play with the

As soon as a test is completed remove your headphones and

place them on your chair.

At the warning signal make sure you are in the

same position and wearing the same headphones you were when you began the experiment. Since the words which you are to hear come quite rapidly, it willbe

necessary to be alert at all times.

mark it out in the appropriate place.

As soon as you hear a word,

Should you miss a word or if you

are unable to find the word you think you heard, do not spend time trying to figure out a correct answer. you are to do a good job.

It is necessary to keep up if

Should you mark out a word you hadn't

79

intended, place an "X" beside that word and mark out the correct word. On the first page you will find an example of the type of tests you will be taking. Please turn to the first page and read the instructions with me. This is a sample test section demonstrating the manner in which all test sections in this booklet are to be marked. You w i H note that to the right of number 1 is a group of four words. One word has been crossed out. That indicates that that word was spoken in the test list. For example : Ho. 1 would read, wrench. You will note that wrench, repast, fifth, rapid, attempt, sealed, coat, firmer, perceive, and thunder are crossed out. Thus in numbers 1 to 10 those words vrould be read by the test speaker. In the following portions of the sample list you are to cross out each word as it is read by the sample exercise speaker. This will indicate to you the method to follow in marking the test sections which follow on succeeding pages. As each word is read, cross out each of the words that you hear. If you pay careful attention, we will now do this example in order that any question which you might have can be cleared before we start testing.

When the last word of the example has been read

and the noise is "cut off" DO HOT remove your headphones.

At that time

you will hear the correct answers and will be able to see how well you performed.

The example starts with word number one.

Please put

on your headphones and we will listen to the example. (Noise in) "Number Number Number Number Number Number Number Number Number Number Number Number Number

one two three four five six seven eight nine ten eleven twelve thirteen

wrench repast fifth rapid attempt sealed coat firmer perceive thunder paint warm cur

Number Number Number Number Number Number Number Number Number Number Number Number (Noise out)

fourteen fifteen sixteen seventeen eighteen nineteen twenty twenty-one twenty-two twenty-three twenty-four twenty-five

gentle dead cheese stood superb attire shoe elk firm away decide hold

80

Answers are checked without noise.

Any questions on pro cedure

are answered at this time. (Noise in) First test heard. Tests administered at various intervals with noise present from beginning of first test until the completion of the last test.

Subjects

remove headsets between tests.

Control Group Subjects are first instructed in the proper manner of wearing the headphones to get the best seal against ambient noise.

They then

removed their headsets and the following specific instructions were read to them: This is a test of listening ability in noise. We are interested in finding out how well a person can understand language in the presence of loud aircraft-type noise.

This noise is not as loud as that pro­

duced by many of the large four-motored bombers in which missions of from four to twelve hours are made. Before each test you will be given a warning.

At that time make sure that your headphones are securely placed

over each ear.

Tests will be administered at five and ten minute inter­

vals (one hour intervals).

Between tests there will be no noise.

that time you will be at leisure in the testing room. compare papers or play with the equipment.

At

Please do not

As soon as a test has been

completed and the noise is "cut off" remove your headphones and place them on your chair.

At the warning signal make sure you are in the same

position and wearing the ssme headphones as you were when you began the experiment.

81

Since the words which you are to hear come quite rapidly, it will be necessary to be alert at all times. mark it out in the appropriate place.

As soon as you hear a word,

Should you miss a word or if you

are unable to find the word you think you heard, do not spend time trying to figure out a correct answer. you are to do a good job.

It is necessary to keep up if

Should you mark out a word you handft in­

tended, place an f1X,f beside that word and mark out the correct word. On the first page you will find an example of the type of tests you will be taking.

Please turn to the first page and read the instruc­

tions with me. This is a sample test section demonstrating the manner in which all test sections in this booklet are to be marked. You will note that to the right of number 1 is a group of four words. One word has been crossed out. That indicates that that word was spoken in the test list. For example: No. 1 would be read, wrench. You will note that wrench, repast, fifth, rapid, attempt, sealed, coat, firmer, perceive, and thunder are crossed out. Thus in numbers 1 to 10 those words would be read by the test speaker. In the following portions of the sample list you are to cross out each word as it is read by the sample exercise speaker. This will indicate to you the method to follow in marking the test sections which follow on succeeding pages. As each word is read, cross out each of the words that you hear. If you will pay careful attention, we will now do this example in order that any question which you might have can be cleared before we start testing.

When the last word of the example has been read and

the noise is "cut off" DO NOT remove your headphones.

At that time

you will hear the correct answers and will be able to see how well you performed.

The example starts with word Number One.

Please put your headphones on and we will listen to the example. (Noise in)

82

"Number Number Number Number Number Number Number Number Number Number Number Number Number

one two three four five six seven eight nine ten eleven twelve thirteen

wrench repast fifth rapid attempt sealed coat firmer perce ive thunder paint warm cur

Number Number Number Number Number Number Number Number Number Number Number Number

fourteen fifteen sixteen seventeen eighteen nineteen twenty twenty-one twenty-two twenty-three twenty-four twenty-five

gentle dead cheese stood superb attire shoe elk fira away decide hold"

(Noise out) Answers are checked without noise.

Any questions on procedure

are answered at this time. (Noise in) First test heard. Tests administered at various time intervals with "noise out" between tests.

Subjects removed headsets between tests

83 Name

Date

Local Address

Phone Number

Hour

FILL IN THE BLANKS ABOVE IMMEDIATELY INSTRUCTIONS This is a sample test section demonstrating the manner in which all test sections in this booklet are to be marked. You will note that to the right of num­ ber 1 is a group of four words, One word has been crossed out. That indicates that that word was spoken in the test list. For example : No. 1 would be read, wrench. You will note that wrench, repast, fifth, rapid, attempt, sealed, coat, firmer, perceive, and thunder are crossed out. Thus in numbers 1 to 10 those words would be read by the test speaker. In the following portions of the sample list you are to cross out each word as it is read by the sample exercise speaker. This will indicate to you the method to follow in marking the test sections which follow on succeeding pages. As each word is read, cross out each of the words that you hear. SAMPLE EXERCISE 5.

preempt exempt except attempt

proceed peree-ive precise preside

10.

plunder thunder blunder lumber

14.

dental gentle simple dimple

15.

head bed dead fed

disturb absurd disperse superb

19.

aspire acquire attire admire

20.. cute suit shoe chute

away assay await awake

24.

bedside seaside beehive decide

25.

1. French drench weneh trench

2.

prepay repay defray repast

3.

stiff fifth sniff gift

4-

rabid rapid rabbit ravage

sealed yield shield field

7.

eeat coach coke coax

8.

former farmer firmer foreman

9.

paint quaint plain quake

12.

warm warn work worm

13.

purr cur purge curve

tease cheese keys ease

17.

could hood good stood

18.

health elk felt help

22.

firm yearn adjourn gem

23.

21.

bold hold mold fold

84 Name

Date

Hour

Local Address

Phone Number List 1_

1.

kernel curdle turtle hurdle

2.

held bell fell tell

3.

heart barge lard hard

4.

swim twin swift twist

6.

yawn jump junk young

7.

grain grange range train

8.

fine mine bind find

9.

stretcher pressure treasure precious

10.

field feel heel eel

5.

relieve receive relief release

11.

kitchen mission friction fiction

12.

guard hearten garden bargain

13.

joy going join dawn

14.

head bed dead fed

15.

train crane strain terrain

16.

screech preach reach street

17.

beast beat meat least

18.

neglect deflect reflect reflex

19.

pun punch pond punt

20.

grope grove grow glow

21.

why wine wire wise

,22.

plant clamp cramp tramp

23.

ship skip gift shift

24.

motor mortar order odor

25.

dirty thirty sturdy pretty

26. milk

27.

shock shook shot shop

28.

scream screen green stream

29.

cross cough cloth claw

30.

harbor Harvard harvest horrid

31* willing wallet women woolen

32.

contest oontend content contempt

33.

needle fetal eagle beetle

34*

beside seaside beehive decide

35.

single jingle cycle sprinkle

36.

stardom pardon garden autumn

37.

late laden lazy lady

38.

adding addict acting attic

39.

burst hurt first birch

40.

occur absurd observe conserve

41.

stretch threat dread bread

42.

coast cost cough caught

43.

cute suit shoe chute

44.

gorge forge ford board

45.

hear steer near deer

46.

unpack attack compact relax

47.

happy handy candy envy

48.

fault vault dog fog

49.

normal formal corporal fumble

50.

left list lisp lid

built felt belt

35

Name

Date

Hour

Local Address

Phone Number List 2 2.

eye high tie hide

3.

revolve involve resolve dissolve

4.

wad wash squad squash

5.

6.

fasten passion fashion passing

7.

rabid rapid rabbit ravage

8.

baker major maker banker

9.

turf surf first thirst

10.

cape hate take tape

11.

leather lever letter lather

12.

budget bucket bunion budge

13.

abscess absent accent absurd

14.

fancy brandy sandy candy

15.

hard card cord harsh

puddle muddle muzzle puzzle

17.

court course cord cork

18.

action matching magic smashing

19.

yes jet get yet

20.

broke throw throat boat

2 1 .

blurred were word bird

22.

pier pierce fierce spear

23.

storage porridge shortage story

24.

lift rift drift list

25.

reason region legion legend

26.

main fame fade maid

27.

capture captor chapter captain

28.

banking flanking lanky blanket

29.

barge dark barred guard

30.

cash catch patch pitch

31.

pope pulse pulp pump

32.

brink bridge brisk brick

33.

prone cone tone thrown

34.

seed speed bead greed

35.

pelvis eldest elder welder

36,

top hop pop prop

37.

protrude conclude construed include

38.

chat chap shack shaft

39.

tassel tackle cattle pastel

40.

quicker flicker slicker liquor

41.

petal mettle meadow settle

42.

bubble tumble stumble fumble

43.

coat coach coke coax

44-

flame blame claim plane

45.

leap leaf lease leave

46.

fair bare care pair

47.

gale jail dale bail

48.

foreign forest forehead force

49.

choose fuse shoes huge

50.

paste pace paid paint

O''

option auction object action

i—i

1.

misuse diffuse dispute confuse

86

Name

Date

Hour

Local Address

Phone Number List 3

1*

dive side died guide

2.

glow blow below low

3.

enact impact relax intact

4.

naval Mable table able

6.

brain drain braid grade

7.

plunder thunder blunder lumber

8.

balance ballot gallons valid

9.

tonight ignite unite goodnight

10.. pain paint plank tank

11.

death debt depth deaf

12.

repeat receive recede reprieve

13.

crater traitor trainer treasure

14.

annual ample amble apple

15.

porch torch scorch court

17.

detain obtain attain maintain

18.

uncle buckle knuckle stucco

19.

contact unpack attract attack

20.

strange bring rain brain

16. process protest profess possess

5.

rocking locker rocket locket

21.

bath vast fast grasp

22.

paint quaint plain quake

23.

fair tare hair pair

24.

hold old ode hoed

25.

verse first burst hurt

26.

carve car tarred tired

27.

formal forebode foremost promote

28.

able stable fable table

29.

black track slack flak

30.

taken bacon vacant beacon

31.

confirm confer conserve concern

32.

tack tact pact pack

33.

break rake great grape

34.

nothing shopping message jumping

35.

bad bed mad fed

36.

exact retract detract attack

37.

band span spend bend

38.

skate state date gate

39.

dental gentle simple dimple

40.

blind grind shrine rind

41.

open oboe opal oval

42.

warm warn work worm

43.

egg edge hedge head

44.

roller polar molar colder

45.

week wheat wink weep

46.

could hood good stood

47.

fence dense bench bent

48,

license light lighten liken

45.

found down gown brown

50.

coal tone toe cold

87 Name

Date

Hour

Local Address

Phone Number List 4

16.

hard part harsh heart

2.

form warm s wam storm

3.

dodge dark dot dock

4.

tenant senate sentence tennis

game gain gage gang

7.

depend detain be came retain

8.

away assay await awake

9.

wrap rent lamp ramp

10.

quarter porter water order

5.

campus canvas pamphlet panther

bridal final vital title

12.

unheard concurred converge conserve

13.

heading sitting knitting fitting

14.

why wide wise wives

15.

duel fuel pool jewel

lunge lunch punch plunge

17.

banner manner mother batter

18.

table total stable fable

19.

boat boast booth both

20.

start dart starch dark

drag flag lag rag

22.

disturb absurd disperse superb

23.

graft draft drab grab

24.

compress contract contact contrast

25.

add have ax ask

folly volley polish trolley

27-

deluxe collect select elect

28.

hear ear year gear

29.

pack patch catch cat

30.

rumor roamer rubber rover

past pass path pad

32.

keep feet pe»p heat

33.

envy empty entry ending

34.

barn bond born bomb

35.

eight ache hate bake

ugly hungry country concrete

38.

hit it hip itch

39.

system pistol distant piston

40.

he re car air error

downbeat 37, stampede false teeth southeast proclaim domain cocaine profane

12.

dungeon cousin dozen doe snft

43.

bandit banded banquet bandage

44.

firm yearn adjourn germ

45.

tattle tackle paddle cattle

calm come comb cob

47.

remote promote provoke revoke

48.

angle amber anger anchor

49.

lotion motion ocean notion

50,

blast flat flak black

88

APPk:æiX G ITEM ANALYSIS OF VCL TS3TS

89

Table 1-A Item. Analysis, Form A - List 1^

[tern #

Word

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

swarm canvas quart airport bark tassel group flicker beef legion wonder horn threat deer garden curtain export final rage city all knuckle dress screech

Mean Listener Intelligibility Score of "Pass" (Percent) Distribution2 38 59 18 69 15 47 69 62 27 48 50 46 49 35 65 33 76 80 38 55 46 55 71 50

47.67 48.69 49.27 49.02 52.67 50.26 49.10 48.71 48.67 49.74 49.84 48.78 49.99 51.11 49.38 50.63 48.72 48.74 51.53 49.49 49.38 50.40 49.70 49.73

S.D. of "Pass" Distribution 14.20 10.23 11.60 10.47 10.87 10.52 10.56 10.23 11.60 9.44 10.13 10.34 10.53 10.44 10.29 10.41 9.90 10.22 9.82 9.98 13.06 9.37 10.30 10.30

rbii .01 .16 .11 .26 .30 .29 .27 .17 .08 .24 .26 .13 .28 .31 .29 ♦26 .26 .31 .37 .25 .19 .36 .41 .25

1 Number of responses to words in this list ■ 356, 2 Mean of all the subjects who correctly identified the word. 5 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

90

Table 2—A Item Analysis, Form A - List 2

*

Mean Listener Intelligibility Score of "Pass" S.D. of "Pass” T* bis fPercent) Distribution 2 Distribution

[tern #

Word

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 34

skid mood twist profane thin receive hard fasten anger joke shaft knitting course balance rank lanky horror unfold pipe beast spray drift concern first

76 35 52 49 28 65 45 53 60 66 36 63 18 42 57 33 66 42 57 50 61 26 41 48

48.47 49.87 50.40 50.67 50.09 48.62 50.83 49.58 49.25 48.34 50.32 48.20 52.17 49.72 48.50 50.30 49.77 49.55 48.67 49.68 49.14 50.42 50.12 49.82

9.51 10.03 10.11 9.87 9.94 10.13 9.58 10.15 10.24 10.33 9.98 7.23 7.85 9.89 10.40 9.85 9.50 10.68 10.32 10.52 10.01 10.58 10.26 9.63

.27 .25 *38 .39 .22 .22 .38 .29 .28 .18 .27 .14 .31 .24 .16 .25 .41 .22 .19 .28 .27 .23 .28 .29

1 Number of responses to words in this list = 355* 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

91

Table 3-A 1 Item Analysis, Form A - List 3

Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word feed conclude train virtue hire patch dinner envy rumor spear goal mettle fault birch praise slack kernel drab go lady break chain ten heart

Mean Listener Intelligibility Score of "Pass" (Percent) Distribution^ 21 67 51 58 56 40 69 43 63 33 28 49 60 47 33 40 40 49 70 67 43 53 17 40

9.43 10.49 10.50 10.09 10.71 10.99 10.55 11.13 10.09 10.02 11.12 10.70 10.67 11.04 9.77 10.23 10.79 9.89 10.19 10.19 10.42 10.30 9.78 10.84

52.27 49.41 47.99 50.27 49.59 48.99 48.48 49.22 49.91 51.02 49.85 49.30 48.41 48.97 51.35 51.05 47.60 49.36 49.43 49.98 51.09 49.61 51.55 49.04

1 Number of responses to words in this list

S.D. of "Pass" Distribution rbis' .34 .38 .09 .43 .31 .17 .23 .21 .42 .32 .21 .24 .17 .19 .35 .37 .37 .24 .41 .47 .40 .30 .27 .18

■ 356.

2 Mean of all the subjects who correctly identified the word* 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

92

Table 4-A Itea Analysis, Form A - List 4^

Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 35 16 17 18 19 20 21 22 23 24

Word pardo n ball double top cruel storage eight dissolve needle fable recline volley shade infect card brain squad tramp plan lift behoid glory not force

Mean Listener Intelligibility Score of "Pass" (Percent) Distribution 65 35 50 65 51 48 58 45 44 33 63 39 75 30 51 42 52 60 29 52 67 59 69 26

50.15 51.40 51.03 48.35 49.98 49.34 47.80 51.04 49.03 51.45 50.32 49.40 49.56 51.93 49 .48 50.66 49.70 49.90 49.56 50.14 49.93 49.28 49.26 51.85

S.D. of "Pass" Distribution rbis 9.53 10.09 9.68 9.94 10.74 10.14 10.27 9.60 10.51 9.66 9.04 9.98 9.85 9.85 8.96 10.24 9.47 9.31 10.40 9.62 9.78 10.54 9.58 9.46

1 Number of responses to words in this list = 357. 2 Mean of all the subjects who correctly identified the word. 3-A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

.45 .35 .42 .15 .30 .22 .46 .39 .16 .34 .45 .19 .46 .36 .24 .33 .28 .36 .17 .33 .43 .26 .33 .33

93

Table 5-A 1 Item Analysis, Form A - List 5

Item # 1 2

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word crook fair amble brick dim matching shook opal trail flame were relief plot kind sleeping eighty swoop quit world handy dot unfit reverse budget

Intelligibility (Percent) 48 55 46 35 18 55 78 49 46 58 28 59 21 35 72 71 36 19 65 54 45 31 54 65

Mean Listener Score of "Pass” S.D. of "Pass” Distribution Distribution rbis3 48.76 48.90 49.67 50*58 53.51 49.60 48.11 50.59 50.60 48.92 51.72 48.57 47.79 50.06 49.21 48.38 50.86 50.35 48.97 49.42 49.55 53.49 50.37 50.22

10.58 11.30 10.31 10.55 10.20 10.64 10.72 10.02 9.88 10.24 9.82 10.56 11.85 10.34 10.50 10.50 9.65 10.56 9.99 9.96 10.07 9.34 9.97 9.65

.16 .20 .25 .31 .39 .29 .20 .37 .35 .22 .34 .18 .32 .24 .38 .21 .31 .20 .27 .26 .24 .50 .38 .47

1 Number of responses to words in this table = 356. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

94

Table 6-A Item Analysis, Form A - List 6

[tern. # 1 2

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word term hate commit proud waist meaning deflect law jobber tell invite flat faithful suit became rural noon save edge binding prince desk vote young

Intelligibility (Percent)

Mean Listener Score of "Pass" Distribution*

48 30 42 25 45 28 55 27 74 37 64 33 52 40 33 51 21 40 64 76 31 74 22 53

50.09 48.29 49.24 53.28 51.28 50.99 49.81 51.14 48.88 51.57 49.64 49.74 49.44 49.80 49.96 49.48 53.15 50.50 49.38 47.80 49.02 48.18 48.51 49.77

S.D. of "Pass" T1 ' Distribution bis 9.37 10.06 9.86 8.81 9.81 8.04 10.07 9.13 10.50 9.75 9.89 11.70 10.61 8.65 11.36 10.71 9.80 9.74 10.23 10.36 10.53 10.93 11.31 11.11

.28 .06 .17 .42 .39 .27 .29 .27 .29 .37 .34 .19 .23 .22 .21 .23 .37 .29 .29 .06 .12 .14 .07 .28

1 Number of responses to words in this table « 356. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

95

Table 7-A Item Analysis, Form A - List 71

Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word chisel bond dream forge seal notion verse harvest tight guide jungle blunt pun seed hail eat pad depth wife rocket keep content fork ask

Mean Listener Intelligibility Score of "Pass" (Percent) Dis tributi on 54 56 50 58 28 47 20 64 19 40 83 60 59 56 64 75 41 53 46 59 35 35 13 48

51.65 50.49 49.85 50.12 51.35 51.51 52.63 50.49 51.02 51.12 49.77 49.88 49.30 50.83 50.65 49.66 50.96 50.55 49.99 49.70 50.67 51.23 51.49 51.60

S.D. of "Pass" Distribution bis 8.92 10.20 10.30 9.87 9.73 9.36 8.83 8.99 8.81 9.56 9.15 9.49 9.25 9.45 9.39 9.49 10.60 9.38 9.74 9.57 8.62 10.38 10.46 9.56

.42 .28 .17 .24 .23 .35 .29 .33 .17 .27 .42 .21 .12 .33 .36 .27 .25 .27 .17 .18 .20 .25 .18 .37

1 dumber of responses to words in this table = 326. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

96

Table 8-A Item Analysis, Form A - List 8

Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word

Mean Listener Intelligibility Score of "Pass" (Percent) Distribution**

gadget why belt sandy power fit attic main describe cattle heel tare ring option class killer span thimble dozen guard chapter wealth prevent foremost

77 37 39 46 23 23 36 39 57 34 36 49 32 40 53 45 67 27 44 40 57 52 37 57

50.07 50.56 50.37 51.04 50.60 49.10 52.57 50.60 51.83 51.33 50.12 50.02 50.53 50.45 48.61 51.61 49.92 48.79 51.26 51.22 49.99 50.67 52.01 50.40

S*D. of "Pass" Distribution 9.42 8.86 9.77 9.19 9.78 9.17 8.68 , 9.80 7.99 6.96 8.87 9.25 9.04 9.51 9.51 8.34 8.85 9.94 9.07 9.02 9.29 9.54 8.98 7.79

r « bis .20 .13 .12 .19 .10 .01 .28 .14 .34 .18 .09 .11 .12 .13 — .03 .24 .15 —.01 .21 .19 .12 .18 .24 .17

1 Number of responses to words in this table = 290. 3 Mean of all the subjects who correctly identified the word.

3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

97

Table 9-A Item Analysis, Form A - List 9

Item #• 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word endure calm absent bacon perfect decide fearful start gown drove thirty roller barge select pride light heading jump gift catch misfire fuel toe odor

Mean Listener Intelligibility Score of "Pass” S.D. of "Pass" (Percent) Distribution Distribution 82 55 62 64 74 75 40 42 47 28 48 58 90 57 49 18 26 67 48 64 40 51 33 52

51.75 52.26 51.08 52.05 52.39 51.74 53.70 51.61 52.42 52.80 50.68 50.80 49.72 49.97 51.63 55.70 53.65 50.85 53.54 51.61 53.02 51.02 53.62 52.35

8.98 8.85 8.97 9.02 8.44 8.90 8.44 10.19 8.12 8.79 9.64 9.78 10.15 9.77 9.67 9.34 9.59 9.06 9.17 9.39 8.36 9.12 9.38 8.95

„ rbis .63 .35 .22 .40 .61 .48 .42 .21 .32 .26 .12 .16 -.01 .04 .24 .42 .32 .21 .47 .32 .34 .17 .36 .34

1 Number of responses to words in this list = 165. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

98

Table 10-A Item Analysis, Form A - List 10"*"

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word recent confront lame perfume gamble what frame scatter harness you treason disgust talent cook musket gone plenty rub center less fox defeat some beach

57 51 40 79 70 35 14 54 63 63 71 43 75 44 63 56 59 29 29 33 63 41 41 32

52.19 51.44 53.60 50.46 51.93 50.68 58.22 52.12 51.75 48.15 50.62 50.70 49.98 53.18 50.55 51.23 49.65 52.78 52.61 53.71 52.38 47.96 51.50 50.05

S.D. of "Pass” Distribution 8.50 8.57 7.28 9.18 7.80 9.74 7.18 7.96 7.82 9.62 8.75 9.29 9.24 8.47 8.15 9.82 7.51 9.47 6.16 7.64 7.95 11.48 10.00 11.36

r 3 bis .40 to

Item #

Mean Listener Intelligibility Score of "Pass" (Percent) Distribution^

.44 .21 .49 .10 .60 .36 .38 -.31 .20 .11 .05 .43 .15 .23 -.02 .28 .27 .41 .50 -.31 .21 .03

1 Number of responses to words in this list ~ 63. 2 Mean of all the subjects who correctly identified the word. 3.A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

99

Table 11-A Item Analysis, Form B - List 1^

Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word piston film banner eve attain scream rupture tour medal ark spotter gain cannon detract made lumber case pierce jail glimmer ward nature enact old

Equated Intelli- IntelliMean Listener gibility gibility Score of "Pass" (Percent) (Percent) Distribution 58 67 61 30 61 39 88 34 35 17 83 64 92 80 52 44 38 73 65 41 71 52 55 62

48 55 50 25 50 32 72 28 29 14 68 53 76 66 43 36 32 60 54 34 59 43 45 51

60.23 58.76 58.52 60.61 59.81 61.17 57.92 56.86 59.11 63.94 58.06 58.64 57.84 59.19 60.00 60.41 60.78 58.96 58.88 61.60 58.95 60.22 60.14 59.38

S.D. of "Pass" Distribution rbis 9.50 10.52 10.67 10.71 9.74 10.04 10.66 9.72 11.40 10.17 10.05 10.15 10.29 9.74 10.21 11.48 10.17 11.72 13.15 10.99 10.19 9.38 10.57 10.76

.42 .27 .19 .27 .38 .38 .26 -.04 .17 .43 .24 .23 .35 .52 .34 .34 .34 .36 .27 .44 .34 .37 .38 .33

1 Number of responses to words in this list = 104. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

100

Table 12-A Item Analysis, Form B - List 2^

:tem # 1 2 3 4 5 6 7 8 9 10 H 12 13 14 15 16 17 18 19 20 21 22 23 24

Word Muzzle carve author scorch able cloth vision fumble groan cape lecture high possess blow single divide fiction maker leaf section rich traitor eastward join

Equated Intelli­ Intelli­ Mean Listener gibility gibility Score of "Pass" (Percent) (Percent) Distribution* 61 47 69 62 59 49 84 54 29 44 81 45 61 45 70 73 64 51 42 81 52 76 72 75

50 39 57 51 49 40 69 44 24 36 67 37 50 37 58 60 53 42 34 66 43 63 60 62

59.50 60.37 57.64 61.31 59.84 57.42 57.90 61.98 60.45 59.32 58.56 58.37 62.20 58.98 59.06 58.62 58.56 59.14 59.60 59.23 61.36 59.05 60.18 58.73

S.D. of "Pass" r 5 Distribution bis 10.42 9.06 10.45 8.66 7.59 11.71 9.96 7.66 10.41 8.44 10.02 10.09 6.88 9.87 9.05 9.52 9*26 11.07 8.32 9.49 8.78 9.09 8.35 9.65

.31 .33 .02 .61 .35 — .01 .12 .59 .24 .19 .31 .09 .73 .16 .31 .24 .17 .20 .22 .49 .49 .36 .56 .28

1 Number of responses to words in this list * 108. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

101

Table 13-A Item Analysis, Form B - List 3^

Item i£ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word traffic woolen swim can pulp eldest tank promote apt bad defend slight formal uhpack license socket find confuse quarter kit rummage lock bold grind

Equated Intelli­ Intelli­ Mean Listener gibility gibility Score of "Pass* (Percent) (Percent) Distribution 91 49 76 26 49 71 44 66 47 71 84 81 57 67 73 86 51 72 44 36 76 38 66 75

75 40 63 22 40 58 36 54 39 58 69 67 47 55 60 71 42 59 36 30 63 32 54 61

58.89 62.08 58.86 60.15 61.96 57.96 61.11 59.27 58.54 58.81 59.30 58.41 60.91 60.40 58.24 58.89 61.56 60.14 60.27 59.16 59.82 61.41 60.06 59.82

S.D. of "Pass" Distribution rbis: 9.99 9.52 17.22 9.07 8.94 9.31 9.02 9.61 9.90 9.33 9.57 10.21 9.84 9.49 9.68 10.20 8.88 9.61 9.77 9.34 10.14 8.71 8.61 9.74

1 Number of responses to words in this list » 102. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

.25 .45 .10 .14 .43 .10 .30 .15 .01 .07 .30 .02 .36 .36 .05 .17 .40 .36 .20 .07 .34 .30 .29 .32

102

Table 14-A Item Analysis, Form B - List 4^

[tern # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word tender beg swift wise nothing shark map full observe pace list contact unheard just grow range hungry fade confine boast white naval race discard

Equated Intelli­ Intelli­ Mean Listener gibility gibility Score of "Pass" (Percent) (Percent) Distribution 71 35 81 56 68 41 62 41 75 40 40 62 79 71 51 40 81 46 87 71 46 63 27 60

59 29 67 46 56 34 51 34 62 33 33 51 65 59 42 33 67 38 71 59 38 52 22 49

59.47 62.17 58.81 61.36 59.97 59.63 58.70 61.33 58.37 59.86 58.88 58.43 60.23 58.88 60.40 60.05 59.62 60.75 58.71 60.00 60.94 59.14 64.61 61.63

S.D. of "Pass" Distribution rM s : 10.09 9.33 7.03 10.22 9.42 10.70 9.98 7.86 10.40 9.31 13.24 11.13 9.03 10.84 10.87 10.34 9.75 16.84 9.83 9.69 10.25 9.83 8.43 9.54

1 Number of responses to words in this list « 104. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

.39 .41 .36 .51 .44 .21 .18 .38 .19 .23 .13 .14 .70 .27 .35 .25 .59 .35 .45 .49 .38 .26 .54 .60

103

Table 15-A Item Analysis, Form B - List 5"*"

Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word year prone forest stable blast visit oval shock cost tack vital mar glimpse bomb untied dike salute mock fort dance pirate nest release cold

Equated Intelli­ Intelli­ Mean Listener gibility gibility Score of "Pass” S.D. of "Pass" (Percent) (Percent ) Distribution Distribution rbis 40 52 73 67 63 36 54 69 53 43 64 19 19 58 64 35 59 22 32 45 64 63 41 51

33 43 60 55 52 30 45 57 44 35 53 16 16 48 53 29 49 18 26 37 53 52 34 42

60.15 60.19 58.39 59.45 61.48 61.24 60.50 60.08 59.22 58.82 58.91 55.65 61.35 60.10 60.47 64.81 59.08 60.87 61.06 57.96 59.85 59.40 58.48 59.45

9.08 10.10 8.89 9.51 9.27 10.32 9.79 9.44 8.78 7.15 10.47 6.76 7.47 10.71 9.52 7.68 9.50 10.34 11.42 10.03 9.76 9.95 8.84 9.10

.18 .23 — .16 .19 .51 .27 .28 .32 .10 .04 .08 -.20 .21 .25 .35 .61 .10 .18 .24 —.06 .24 .16 .00 .13

1 Number of responses to words in this list = 103. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item*

104

DaTale 16-A Item Analysis, Form B - List 6

Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word splash clock lag attack flavor gloom clap week this pause yet southeast drop arrest leather court fall navy bandit vast shatter word blame needy

Equated Intelli- Intelli­ Mean Listener gibility gibility Score of "Pass" (Percent) (Percent) Distribution2 72 39 45 71 66 50 35 41 37 36 71 80 50 74 64 61 36 74 78 45 86 45 37 77

60 32 37 59 54 41 29 34 31 30 59 66 41 61 53 50 30 61 64 37 71 37 31 63

58.47 59.70 61.21 59.30 60.73 58.96 58.52 62.05 60.31 59.94 58.73 59.55 61.68 59.53 60.18 58.40 61.56 58.74 58.07 57.98 57.48 62.52 64.23 59.69

S.D. of "Pass" Distribution rM s 10.30 11.49 9.92 10.18 9.67 10.36 11.70 10.07 10.07 10.39 9.95 10.09 9.66 9.93 9.62 9.31 9.88 9.52 11.01 10.66 7.81 8.75 9.83 9.40

1 Number of responses to words in this list = 94. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

.19 .21 .39 .35 ♦55 .17 .09 .46 .26 .22 .23 .54 .49 .44 .42 .13 .37 .26 .12 .04 .03 .54 .63 .51

105

Table 17-A Item Analysis, Form B - List 7

Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word tree pressure own cannon surf tonight ramp mold choose bench cancel arch senate got plunge harm flight drain fact throat it air gate outing

Equated Intelli- Intelli- Mean Listener gibility gibility Score of "Pass’ S.D. of "Pass" Distribution (Percent) (Percent) Lis tribution 54 60 33 82 60 60 60 40 57 66 44 68 63 33 61 18 36 64 34 51 43 74 43 60

45 49 27 68 49 49 49 33 47 54 37 56 52 27 50 15 29 53 28 42 36 61 36 49

59.37 58.59 58.17 56.50 58.41 58.96 59.41 56.78 57.92 58.17 59.63 60.05 58.40 57.73 56.55 56.63 58.09 57.45 57.68 56.37 57.21 57.54 57.51 56.61

10.13 9.12 7.63 10.47 8.44 9.64 9.24 7.93 9.65 10.25 9.29 8.54 10.45 7.90 9.38 11.13 8.43 10.37 10.59 10.48 9.87 9.64 10.07 10.82

1 Number of responses to words in this list -90. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

bis .40 .34 .17 .07 .32 .40 .46 .05 .23 .32 .36 .68 .34 .13 .04 ♦02 .17 .19 .13 .01 .10 .28 .13 .05

106

Table 18-A Iten Analysis, Form B - List 8^

Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word trench repay stiff rabbit exempt shield coach former preside blunder quaint worm purr dental bed keys good disturb aspire chute help germ await seaside

Equated Intelli­ Intelli­ Mean Listener gibility gibility Score of "Pass" (Percent) (Percent) Distribution 62 89 38 40 82 88 78 58 81 40 73 54 79 57 55 36 66 73 90 78 30 70 51 69

51 73 31 33 68 72 64 48 67 33 60 44 65 47, 45 30 55 60 74 64 25 57 42 56

59.16 60.10 61.18 59.28 60.11 58.79 61.74 61.65 60.72 63.00 60.49 61.58 60.93 60.53 61.37 59.75 60.36 59.14 59.74 59.91 65.81 60.45 58.40 61.05

S.D. of "Pass" Distribution rbis 9.13 9.24 8.85 6.53 9.51 9.12 7.98 7.39 8.49 8.66 2.17 9.42 8.57 7.65 7.98 8.95 9.45 9.91 9.42 8.75 6.35 8.20 8.97 7.92

.01 .49 .22 .02 .33 -.15 .73 .41 .51 .43 .32 .36 .53 .22 .34 .07 .24 .00 .34 .22 .62 .28 -.10 .40

1 Number of responses to words in this list = 89, 2 Mean of all the subjects who correctly identified the word, 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

107

Table 19-A Item analysis, Form B - List 9^"

Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Word call handle vacant dust wallet leave fruit bail pants dish sitting jolly replace hunter bath journal fluid none plate cabin acute suffer clown grim

Equated Intelli­ Intelli­ Mean Listener gibility gibility Score of "Pass” S.D. of "Pass” (Percent) (Percent) Distribution Distil bution rbis' 75 75 44 88 88 41 72 28 69 38 44 91 88 75 66 97 91 41 78 91 88 59 19 38

62 62 36 72 72 33 59 23 57 31 36 75 72 62 54 80 75 33 64 75 72 49 15 31

64.79 63.00 66.50 62.29 62.79 62.46 60.22 69.00 62.64 67.67 65.79 63.03 63.29 62.54 64.19 61.42 62.21 64.69 61.88 62.34 62.32 65.47 66.67 65.50

6.84 8.68 5.95 8.27 8.05 8.27 7.75 4.40 8.40 4.96 7.54 7.72 7.28 8.11 2.93 7.93 7.86 9.36 8.17 8.27 8.06 6.40 4.15 6.98

.81 .30 .61 .18 .43 .07 -.44 .71 .16 .68 .51 .71 .69 .17 .48 .87 .18 .35 — .02 .26 .19 .65 .40 .42

1 Number of responses to words in this list =32. 2 Mean of all the subjects who correctly identified the word. 3 A coefficient relating total listening score on an intelligibility test to the pass-fail dichotomy of a given item.

%C8

a p p r i s r: d

AÎTALYGIS CF l.lATCHdL SUB; ^CTS

109

APPENDIX D

When the 38 subjects (19 experlmntal and 19 control) who participated in the three hour portion of the experiment were com­ pared with the 40 subjects (20 experimental and 20 control) who participated in the 50 minute portion and who took the tests in the same order, it was found that those subjects participating in the longer section performed at a higher level for all four tests ad­ ministered*

Since all subjects were tested under the same conditions,

it was of interest to see how the groups compared when matched on initial test performance.

It was realized that no conclusions could

be drawn from this analysis, since the number of subjects available for matching was limited.

Eleven subjects for the three hour experi­

mental group were matched with eleven subjects for the 50 minute experimental group.

For the two control groups eleven pairs of

subjects were used also.

Each matched pair of subjects did not differ

in listening ability on the first test by more than three percentage points. An inspection of Table A indicates that the two experimental groups did not differ significantly (statistically) in performance. However, there was an increase in performance level for both groups as exposure time increased, significant at the one per cent level of confidence.

110

Table A.

Significance of Differences in Mean Scores for L-i-N Tests Given Successively to Matched Experimental Subjects (Exposure Times: 50 Minutes and Three Hours)

Source Groups Lists Interaction: L x G Between Cells Between subjects in same group Interaction: Pooled Subjects x Lists Within Cells Total Sum F

= VL

= 5.8378

V^-îSxL FL.05

d.f.

Sum of Squares

3 and 60) = 2.76

F- n_ (d.f. 3 and 60) » 4.13 Ju.U«L

Variance

432.11 1073.58

1 3

178.67 1684.36

3 7

13142.37

20

657.12

3677.99 16820.36 18504.72

60 80 87

61.30

V -------2---G between SxG

F

FG

05

FG.01

432.11 357.86

= .6561

(ü.f. 1 and 20) = 4.35 1 and 20) = 8.10

Table B shows that for the experimental group who were exposed to noise for three hours there was a gradual improvement in performance (after the discrepance of test^ List 2 is taken into account).

List 2

is so out of line that all significant differences are between that test and the other tests, except where List 3 and List 4 are significant­ ly higher than List 1.

Ill

Table B.

Significance of Differences("t" test) Between Tests Administered at Successive Points in the Time Sequence: Experimental Subjects (11, 3 hour subjects previously matched with 11, 50 minute group subjects on the basis of initial test score)_______________________ ______ 1 (64.82)

2

(78.55) 5.8160

1 (64.82) 2 (78.55) 3 (72.18)

3 (72.18) 3.1177 2.6983

4 (70.55) 2.4272 3.3888 .6905

(, ) = Mean Value "f.OSio - 2-228 "t"

. 0 1 1 0 = 3 -169

Table C indicates that for the 50 minute group List 2 has a higher listening score than List 1. ing value than List 1.

List 3 also has a higher listen­

Both of these differences are significant at

the five per cent level of confidence. All other differences are nonsignificant. Table C.

Significance of Differences ("t" test) Between Tests Administered at Successive Points in the Time Sequence: Experimental Subjects (11, 50 minute subjects matched ________ with 11, 5 hour group in Table B)______________________ 1 (64.00) 1 (64.00) 2 (70.00) 3 (66.91)

2 (70.00) 2.5416

3 (66.91) 2.5035 1.3089

4 (67.45) 1.4614 .9531 .2287

( ) * Mean Value "t" nP. = 2.228 •0510 "t" .Olio m = 3.169 Table D shows that the two control groups did not differ sig­ nificantly, nor were there significant differences among tests, even though List 2 held its relatively high position.

The control group

112

which participated in the longer portion of the experiment had higher mean scores on test List 2 and List 4«

Test List 1 (matched) and 3

are identical. Table D.

Significance of Differences in Mean Scores for L-i-N Tests given Successively to Matched Control Subjects (Exposure Time: 50 minutes anü 5 hours)

Source Groups Lists Interaction: L x G Between Cells Between Subjects in same group Interaction; Pooled Subjects x Lists Within Cells Total Sum

FL

(d.f. 3 and 60) = 4.13

d.f.

Variance

393.13 484.13

1 3

385.60 1262.86

3 7

13650.73

20

682.54

4933.27 18584.00 19846.86

60 80 87

82.22

V,G

Vi VjiSxL = 1.9628

FL 05 ^d#f* 3 aiia 6°^ = 2,76 F

Sum of Squares

V.between SxG

393.13 161.38

.5160

F

(d.f. 1 and 20) = 4.35 G.05 Fg q1 (d.f. 1 and 20) = 8.10

The analysis of date involving 22 matched pairs of subjects (11 experimental and 11 control) follows the trend previously reported, that those people participating in the longer portion of the experi­ ment have, in general, higher listening scores than those participating in the 50 minute portion.

VITA.

George Lewis Shaffer

Born August 19, 1913 Education:

High School Diploma. June 1932.

Midway High School;

Midway, Pennsylvania,

B.S. Degree. The Pennsylvania State College; State College, Pennsylvania. June 1936. M.A. Degree. State University of Iowa; August 1938, University of Minnesota;

Iowa City, Iowa.

Minneapolis, Minnesota, 1939-1941.

Experience; Teaching Fellow. University of Minnesota; Minnesota, 1939-1941,

Minneapolis,

Research Supervisor. State University of Iowa; conducted at Dubuque, Iowa, Summer of 1941.

Research

Speech and Hearing Therapist. Bloomington Public Schools; Bloomington, Indiana, 1941-1943. Instructor in Speech and Assistant Director of the Speech and Hearing Clinic. Indiana University; Bloomington, Indiana, 1943-1948. Research Associate. ERF 339 (Speech), Purdue University; Lafayette, Indiana, 1948-1950. Publications: Measures of Jaw Movement and Phonation in Non-Stuttered and Stuttered Productions of Voiced and Voiceless Plosives. Speech Monographs, Vol. VII, 1940. Some Suggestions for Elementary Speech. April 15, 1941.

Guidance in Missouri,

Transcription Service for Handicapped Students. The Crippled Child, Vol. XXIII, No. 4, December 1945. Editor, Speech and Hearing Therapist, 1945-1948.

Organizations:

Speech Association of America American Speech and Hearing Association Indiana Speech and Hearing Therapy Association