 

 

TIME- COMPRESSED SPEECH IN
HEARING AID EVALUATIONS

Thesis for the Degree of M. A.
MICHIGAN STATE UNWERSITY
SUSAN D. DALEBOUT
1975

 

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ABSTEXCT

TIME-CONPRESSED SPEECH IN
BIRING AID EVALUATIONS

BY
SUSAN D. DALEPOUT

A review of the audiologicsl literature indicates that
although hearing aid evaluation procedures are not standardized,
discrimination test scores serve as the primary basis for
the objective selection of hearing aids. Many audiologists
report, however, that conventionsl discrimination tests are
not difficult or realistic enough to produce differential
results among hearing aids. The scores frequently do not
reflect the cleetroueoustic quality of hearing aids, or the
listener's subjective impressions of them. The procedures
that have been suggested as alternatives to conventional
discrimination testing do not seen clinically feosible in
terms of time and convenience.

The purpose of this study was to investignte the potential
use of time—compressed monosyllables as a more difficult
listening task for hearing aid evaluations. Specifically,
the effects of aided listening on the percention of time-
compressed speech were examined. Also, the nntcntial of e
tine—compressed monosyllabic word ,est to produce differential
results among hearing aids end to reflect their electroneoustie
qualities was studied. '

Three lists of Form B of the Northwestern University
Auditory T.st No. 6 (NUﬁé) were compressed to levels of Adi
ﬁnd 60% using the Zenlin-modified version of the Feirbenks
Time Compressor. A 0% control Condition wen ilso used, resulting

in 2 total of nine eXperimental tenet. Seventy normal hearing

f.‘ »,,- Q. T“ .‘N
' ,wr‘n D. laleh1dt

s1d1jectr11 ere iﬂzcn IW1wlemlbr'1ssjfn1ed 'to er~1 1f rwrzcn cw:ccri-
nun1tsl. ccwuliti.u1s vﬂ1iel1 ecn“rern1ordfrl t") onr: 117 tht1 sijt rs"c~
selected exterinentsl heerinf aids er the unridcd fFOUU. The
aided corditions were charccterised hv the presentation of
the three lists at the three levels of time—eonnressio1 in

'c ﬂrom order st 0 _ee.1t1on level of 32 dB, re: the sided
sneeeh recention threshold (S‘T). All bids were worn at c
constert rein setting of 3O 8?, re: lﬂOO Us. Unhjccts in the
unaided croun received all three lists at ell three levels

1

of tine—concression st 3? d? nonﬁction level, w1: the nnniecd
"PT. Tiﬁht e1rr: were used exclusively and ell left ccrs

1:;ere e 11.70er 11'12'121-1 :1. pr otcci :ive e r mff throughout x1101 1*1'111 1,1 l
testinﬂ.

The results revenled that as the level of tin co rresc1mn
inercnscd, intellisibility dccrcsscd. A ricn1fi centlv wider
snrecd of menu hecring aid scores, however, wws not observed
"rith inert-1.1133111; levels of tine—c. 111.110. .si on. .‘v‘MTitiercllj',
the discrimination scores obtuircd both thr1urh henrinr ribs
end iJ1 the swnn1cfieléi emnlcrnxi in iﬂris stiﬁﬁ;' ere ffunwﬁ to lg.

lower than those obtained under earnhones Jy Beasley, 10hwiuncr,

\ J
3
1.)
NJ
3

far” Piﬁrtol"vrn1 (lfTYQ). EFNP'C drwn~1ssed lyr wesrr1 of
vd1er1 (ﬂatr1i11eﬁi iJ1 iﬂie :1ixlcéi r"1tl1e1* iﬂ1s11 thihix"(wl (~1nfliirice1.
Finally, n chance in raﬁk order for four of the six nids the
soon. This moons the t the Dids which nroduced the hes scores
at 0% timc— connression nrodneed the noorest scores st 607
time—co1nrension and the eids which nroduccd the noorcst scores
st 0% time-connrcssion produced toe best scores at 61” tine—
comnressien. Althonfh elect roecoustie moesvremcnts of the
0x11m_ﬁticntsl-r1ids rﬂ1owcd 1ﬂrvsicsl.(3iffcrwnweos 'roonpj ﬁnrn to
be nﬂirimsl, 'it urv1:found lﬂhlt thral1ect EXT? time-«nrnnrerwrisn
scores were eroduccd by the aids with the numerior electro—
ccoustic qualities.

The results of this study indiccted thet ti.e—comnrcssed

1‘1111111s3-‘llrihles did indeed corstitute :1. more diff 1e11lt listeninﬁ

‘ ‘ Susan D. Dalcbout

task which may be used efficiently and eXpediently in hearing
aid evaluations. It was also seen that time—compression
improved the ability of monosyllables to reflect the electro-
aeoustic quality of aids. This has important clinical impli—'
cations in that an aid which may be eliminated from selection.
on the basis of conventional discrimination test scores might
actually provide the best amplification for an individual in
more realistic listening situations. On the other hand, the
aid selected on the asis of conventional discrimination
scores might actually provide the noorcst annlification for
an individual in more difficult situations.

Time—comnression did not nr1duce differential results
among the scores for the six hearing aids. The range of mean
’scores for the six aids was increased by only one to two
words when the level of time—compr.ssion was increased from
0% to (Oi. Hence, it was recommended that time—compressed
monosyllahlcs be re—cvaluated using a hearing impaired nonu—
lation since the use of ajnoneal hearing penulction and the
lack of physical differences among experimental heiring aids

left no variable to create differential resh1un.

TIME—CUUPRESSEU STEHCV IN

E E MI INC A17) TVTLLUATI 3"???)

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73115fo D . -7 .elIﬂCT‘OUT

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Submitted to
Uichigcn Stote University
in nnrtisl fulfillment of the requirements
for the eegree of

NASTER OF APTS

Department of Audiology and SuOOCh 3CiPHC°9

Acceuted by the faculty of the Pensrtnert of NudiOlOCy

and Speech Sciences, College of Connunicstion Arts, Michisnn
3 ate University, in martial fulfillment of the requirements

for the Poster of Arts degree.

Thesis Connitte.

O
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This thesis is
dedieoted to

Mrs. Beverl'r Goodwin
.§ 3

time {free Wu) suxniort tﬂien i't Wﬂszieocdru’,

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I"'C)IIQT}¥ hlz.TTT '3

I a; yrs'eful for the onnortunity to thcnk some of the

{in’Vﬂ G \'.'. (“grime the

. wl‘ﬂc fVPCﬁ”T:lthﬁ rﬂ‘iﬂris thesis.
I tianV my co nmittee CCwmnI errtors, ‘hr. Penicl Pcssley end
Di". Fltewren 1?hj to, mid” m3? crrmniirtec: we ﬂlCl‘, It". Trinfba TuTu
suit?» 'Tor shﬁiﬁﬂi” theii‘ivrseorch lscomledrxwruml 1 WP)“YW‘CG
with We. Jneeiel thvnhs fees to Fr White for his friendshin,

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knowinr. 'u

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ten end best sudiolofists I hsve hed_the

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«so They Ph.‘ ntxderts vein "l.. vs «illins

t3 answer and nose cuestions

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They

offer‘lwel~vru~d

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to listen and to orcoursee. h've tsurht me

I iﬂisnKTIny Thﬂiendri, OSHH- cjnll ’hizsrnwe flvodvﬁ11, vﬁri
helped me msintein {urn} 'rits, heeywnufxww“r in_eersnective,
end not to rive in to discoursrenent.

List, hut most innortsntly, I wont to thenk my family

for their cessele ess love, encourufencnt, tolerance,

ﬁll my
annrecietcd more than they will ever hues.

ﬂlWl surniort.

Their enthusiasm end confidence in me and enlcsvors

is

TATE-‘.'} 0F COT‘TTST‘TTTB

I' IST 0F TADLEC; o o o o o o o o o o o o a o a
Chapter
I . INTRODUCTION . . . ,, . . . . . . .

Conventional Hesrins Aid Evolustion

Iwaeedures . .‘. . .. . . . . . .

The Effects of Amoliiicstion on
Intellisibility-. . . . . . . .
" eeech Tlis criminetion Testins .
Felinhility . . . . . . . .
Differential Sensitivity . .
“

Aliwerrmrtitwa ﬁeiﬂiodr= oi'TTeerﬁies

(301.00ti:3n o o o o o o O O O O 0
listwrted Snecch Tests . . . . . .

Tise— r‘rmrrtsm'o Cneech . . . .

Intellieihilitytof Time—Conercs
Tneech for Formal Listeners . .'

Tine—Comnressed Sncnsh Intellirf

for Innsired Listeners . . . .
:Stetcrnent of the Iro‘:l.::;.: . . .
II. EXP“”I“‘“T‘T ““0”‘“NWU” . . . . .
Tuhjects . . . . . . . . . . .
Stimulus Gererstion . . . . . .
Instrumentstion . . . . . . . .

'“'ncilf‘ﬁml'l Ii‘rvtjeerv‘es . . . .

(11'1”... ‘rn air: 0 o o o o o o o o o o
13(‘1' ' F1?”
III. PIAJJLL.) . . o o o o o o o o o o o

fixeecﬂi V(n1c*vtirni Tln“erﬂiolxi ...
Aided Discriminstion Scores st

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”10 EA, ii_e~oo erection . .

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Venn ﬁncrcnsc, rane, nnﬂ ntnnﬂnrd ﬁnvintion
in GB between unaiﬂod anﬂ niﬂcﬂ SPT'C for
each hnnrinC Cid rr3uh. 36

Mean ﬂiccriminqtion CcorCC, rCnC,n, and

stnndarﬂ ﬂovinfionm for e”ch hear TC 3i”

groun 8nd the unqiﬂeﬂ grown at e3oh level of
time—nomprCCCion. 37

LIFJT 01"

Table
9.

10.

11.

12.

TAB ES (cont'd):_ 4 o

P"! rr
be

Mean SpOCCh discriﬁinotion scores obtaincﬂ
under earphones by Reaslcy, Schwimner, anﬂ'
Rintelmnnn (1972), obtained through 311
hearing ai1e useﬁ in this study, ohtnincc
moneurnlly in the unﬂidcﬂ sounﬂfield used
in this etuey, and the differences between
them at 07, 40%, and 60% time— compression.

1e

L»

The r: nk ore er of the six execrimentnl
hearing 3103 pt oﬁ, 40}, end 60% levels of
tine—conoression.

'-
.. >
'.‘"

Ksrmonic distortion zvernﬂes for 500 HR
700 Hz, ORR Hz, enﬂ 1? >00 U? measureﬂ a
75 RP inhut on“ a coin refiirN oF 3R (R, r”:
100R T17. (11.11.), 111v“llROdUIr'IlOn c113 ortian
averages otxtnined xvith a vein setting of

30 RR, re: 1000 113 "1nd neireﬂ. input rzimmlr;
of 7? 03 (11.11.), effective Lnnﬁwiﬁth 021cm—
Wetcﬂ deceliing to R110 éI RF1_) s:ncciFicntiona
(UAFD/IDL I), IRI vn1ues IRI), enerzy peak

to n01k RIfIVVRVRPR (Pl/1p), the diFFr rence
ﬂC1T“C(N1 [£11 .err94je 91F crw2""wr ‘1; EFVW 7': '*WR
1000 Hz ﬁnd the cncroy at R')O) Hz (LC/*R),
and internal noise ﬁcecvrec et a ,jni.n setting
of 30 EB, re: 1000 Hz (I.V.\ For each exter—

I )
imentnl aid. 44

’cen air conﬁuction one home corﬂuction

thresho109, renﬁﬁﬁ, ﬁnd at nUH‘Ft ﬂev’otjons

For the yﬁgﬁrt and left awn”: of the 70 :tvﬂrjc cte. 54
Few scores of the 70 subjects at 0?, 43%,
and 60% time-compression. 62

vii

CHAPTER I

INTRODUCTION

In the past two decades, the literature in audiology has
indicated that a wide range of Opinion exists regarding the
kind of role the audiologist.should play in hearing aid eval-
uations, the procedures and methods to be used, the type and
efficacy 0f the instrumentation to be employed, and whether
the dividends of present day selection procedures justify the
audiologist's clinical efforts (Davis, Hudgins, Marquis, Nichols,
Peterson, Ross, and Stevens, 1946; Glorig, 1952; Fairbanks,
1958; Jeffers, 1960; McConnell, Silber, and McDonald, 1960;
Shore, Bilger, and Hirsh, 1960; Resnick and Becker, 1963;

Shore and Kramer, 1963; Jerger, Malmquist, and Speaks, 1966;
Jerger, Speaks, and Malmquist, 1966; Castle, 1967; Kreul,
Nixon, Kryter, Bell, Lang, and Schubert, 1968; Zink and Alpincr,
1968). While there is some consensus that the goal of hearing
aid evaluations should be to select ". . . the most appro-
priate electroacoustic amplification for those hearing impaired
individuals who can profit from such amplification . . ."
(Castle, 1967, p.1), there is no such consensus regarding the
validity or reliability of the methods currently employed to
accomplish this goal or the superiority of any of the methods
that have been suggested to replace them.

 

Conventional Hearinn Aid Evaluation Procedures

Burney (1972) surveyed practicing audiologists and reported'
that current hearing aid evaluation procedures follow one of

f‘ . o
(1 . a

three basic formats. The first format involved the administra-
tion of audiometric tests to a client while he wore a succession
of possibly beneficial hearing aids that had been pro-selected
by the audiologist. In the second format, audiometric tests
were performed without a hearing aid. Based on the results

of pure tone and Speech audiometry, the client was advised of'
the general nature of his hearing loss and the characteristics
of the hearing aid required to compensate for the deficit.

In the third format, a master hearing aid was used to measure
the client's maximum tolerance for intensity, his minimum gain
requirements, and the frequency reSponse needed for maximum
discrimination. The audiologist then reviewed the results and
recommended a hearing aid to the client based on this data.

Reportedly, 85% of the hearing aid evaluations conducted
at the time of Burney's survey followed the first format, while
the remaining 15% followed the second. Although many of the
institutions that reported had master hearing aids, no eval—
uations of the third type were reported.

Generally, the first method described by Burney was sim-
ilar to the procedure described by Carhart (1946) several years
earlier. According to Ross (1972), the most widely used
'modification of Carhart's method was characterized by three
basic parts. First, a complete audiologic evaluation was per—
formed to determine hearing aid candidacy. This evaluation
_was comprised of a case history interview and the audiologic
battery deemed necessary by the audiologist. If considered
a candidate, the client's aided and unaided performance in a
soundfield was sometimes evaluated and a personal earmold
sometimes made. On the basis of these results the ear to re-
ceive amplification, the hearing aid type, and the required
electroacoustic characteristics were determined. Client
counseling was emphasized. The second portion of the method
deScribed by Ross was a thorough otologic examination. The
third part was the hearing aid evaluation itself. Although

Burney found that Specific procedures varied from clinic to

1L5
clinic and from audiologist to audiologist, Ross reported that
typically three to six aids of the same generic family meeting
the tolerance, gain, and frequency reSponse requirements of
the client's hearing loss were selected. The electroaeoustic
properties of the aids were then checked against manufacturer'
Specifications and appropriate electroacoustic adjustments,
such as tone control or power control, were made by the aud—
iologist. Next, while Speech stimuli were presented at a
constant level approximating that of normal conversational
Speech, the client or the audiologist adjusted the gain of
the first aid to the level which was most comfortable.

Burney reported that an average of three to four tests
were administered during hearing aid evaluations. A small
number of the tests were eXpansions or modifications of measures
used in the audiologic differential diagnostic battery, for
example, Bekesy and recruitment testing. In order, the most
frequently used measures were speech discrimination (administered
either in quiet or both in quiet and noise), speech reception
threshold (SRT), tests of tolerance, and pure tone thresholds.
In addition, the use of subjective evaluations elicited from
the client, tone decay tests, and competing message tests were
reported. Successive aids were evaluated in the same manner_
and all results compared. Finally, after obtaining all pertin—
ent objective and subjective data, the audiologist again
. counseled the client. Based on the data, a referral was made
to one or more hearing aid dealers for, in some cases, a
specific hearing aid. A trial period was offered by most
dealers, after which the client returned to the clinic for a
hearing aid recheck, additional counseling, and the procuring
of aural rehabilitative services if desired.

I As mentioned by Burney, subjective evaluations elicited
from the client, either formally or informally, have frequently
played a part in the final selection of a hearing aid. These
subjective preferences have been found by some audiologists
to be valid and reliable indicators of the electroacoustic

4 . .
quality of aids. It has been suggested that perhaps they are
better indicators than objective test scores (Jeffers, 1960;
Witter and Goldstein, 1971). 'Jeffers reported that the pre—
ferences of conductively impaired individuals were indeed
valid and reliable. These persons were able to consistently
rank order a group of aids in terms of subjective preference.
Further, their judgements were found to correlate with the‘
electroacoustic characteristics of the aids. It must be noted,
however, that Jeffers made no physical measurements on the
aids used in her study but relied solely on manufacturer
Specifications. Still, the aids reputed to have superior
electroacoustic preperties, according to manufacturer specifi-
cations, were always preferred. Zerlin (1962) found that the
preferences of normal hearing subjects also yielded reliable
clear-cut choices among six hearing aids. He was unable to
relate subjective preference to the frequency response of the
aids, however, and he neglected to measure any characteristics
except that of frequency reSponse. Witter and Goldstein (1971)
reported findings similar to those of Jeffers and Zerlin for
their normal hearing subjects. They agreed with Jeffers in
concluding that subjective evaluations did reflect superior
electroacoustic characteristics in hearing aids. In various
combinations, the characteristics that most commonly influenced
the listeners' preferences were transient response, frequency
’range, and harmonic distortion. Transient response was described
as the overall measure of the system's linearity. The mea—
surement of transient response consisted of passing a square
wave through the electrical system while monitoring its out—
put to see what changes in the square wave occurred. In terms
of frequency response, Witter and Goldstein found that for ’
normal listeners, aids that amplified further into the high
frequencies than most aids correlated positively with behavioral
performance, while aids that amplified further into the low
frequencies correlated negatively with behavioral performance.-

The results of Burney's survey indicated that the procedures

;
5

most frequently employed in the selection of hearing aids

have changed little during the last 30 years. During that

time, however, substantial technologic advancements and im-

provements have been made in hearing aids themselves. These

improvements have taken the form of greater choices in micro—

phone type and placement, maximum power output (MPO) limiters,

receiver and earmold types, more external tone controls, less

distortion, increased frequency range, and better batteries.

Although the improvements may have diminished quality differ— .

ences among hearing aids, differences do remain and are sub-

jectively important to hearing aid users in real world situations

(Jeffers, 1960; Zerlin, 1962; Jerger, Speaks, and Malmquist,

1966; Chaiklin and Stassen, 1968; Rassi and Harford, 1968;

Zink and Alpiner, 1968; Haug, Baccaro, and Guilford, 1971;

Witter and Goldstein, 1971; Carhart and Tillman, 1972). Hence,

there is a need for updated procedures to evaluate the subtle,

yet important, differences among improved hearing aids.

i

The Effects 2: Amplification 33 Speech Intelligibility

 

 

 

 

Unfortunately, hearing aids in many cases serve to reduce
rather than to enhance speech intelligibility, as measured in
the test situation. Several investigators found that thresholds
for Speech and Speech discrimination scores were consistently
worse when obtained through hearing aids than when obtained
under earphones or in the soundfield, at the same sensation '
level (Zink and Alpiner, 1968; Tillman, Carhart, and Olsen,
1970; Zelnick, 1970). Bode and Kasten (1971) suggested that
the reduction in intelligibility could be attributed to the
better linear response of the earphones or the loudspeakers,
the increase in environmental noise when testing in the aided.
condition, the reduced frequency range of the hearing aid, and/
or the excessive harmonic distortion in the hearing aid. 6

Tillman, Carhart, and Olsen (1970) compared unaided sound-
field Speech reception thresholds and speech discrimination

6;;
scores to those obtained through hearing aids for normal lie—
teners, conductively impaired individuals, scnsorineurally
impaired individuals, and presbycusics. All hearing impaired
subjects had SRT's ranging from 23 to 49 dB. The soundfield
conditions were similar to those employed clinically, but the '
aided conditions were quite different. In the aided conditions
Speech was presented to an artificial head placed at a 45°
azimuth to the loudspeakers, on which two hearing aids were
mounted. The hearing aid transduced signal was then sent to
the subject who sat in a second test chamber wearing the
hearing aid receivers and earmolds covered by protective ear—
muffs. The gain for both hearing aids was set at 50 dB, re:
1000 Hz. In order to obtain aided discrimination scores,
monosyllabic words were presented through the loudSpeakers at
a level of 70 dB SPL. Before reaching the subject in the
second chamber a second attenuator was used to adjust the sig-
nal to a level of 30 dB sensation level (SL), re: the listener's
aided SET. Tillman, et al. found that for normal listeners,
aided speech reception threshelds were poorer by a mean of
12.4 dB than the corresponding unaided soundfield thresholds.
They attributed this result to the change from testing in the
soundfield to testing with insert receivers. A 12 dB decrease
for this change had been reported by Tillman, Johnson, and
Olsen (1966). Beyond the 12 dB decrease found for normal
listeners, aided SRT‘s were poorer than their correSponding
unaided SRT‘s by means of 2.6 dB, 5.7 dB, and 8.5 dB for
conductively impaired, sensorineurally impaired, and presbycusic
individuals, respectively. When aided discrimination scores
obtained in quiet were compared to unaided soundfield scores
obtained at the same sensation level (measured at the listener's
ear), mean reductions of 8.6%, 19.8%, 20.1%, and 14.1% were
found for normal listeners, conductively impaired individuals,
sensorineurally impaired individuals, and presbycusics, reSpec-.
tivcly. For normal hearing subjects, noise masked speech by
an additional 10 dB when it was heard in the aided rather than

7 .

unaided condition. Corliss, Kobal, and Berghorn (1960) had
reported that noise masked speech by an additional 7 to 12 dB
when heard in the aided rather than unaided condition. The
aided condition increased masking effectiveness by 17 to 18
dB for conductively impaired subjects and by even greater and
more variable amounts for individuals with sensorineural and I
presbycusic impairments.

Using aided conditions similar to those of Tillman, et a1.,
Zelnick (1970) reported a 10.8% decrease between discrimin-
ation scores obtained under earphones at 30 dB SL and those
obtained through hearing aids at 30 dB SL, for hearing impaired
listeners. Zelnick was not comparing earphone and hearing
aid discrimination scores for one listener, however, but ear-
phone scores for one group of hearing impaired listeners and
hearing aid scores for another group of hearing impaired listeners.

In spite of reported decreases in both aided SBT's and
aided discrimination scores, the objective hearing aid eval—
uation goals of some audiologists (Haug, Baecaro, and Guilford,
1971; Wilson and Linnell, 1972) were, first, to obtain an
aided Speech reception threshold that was within normal limits
and therefore better than that obtained under earphones, but,
second, to obtain an aided discrimination score that was only
equal to that obtained under earphones. This may be because
amplification tends to improve hearing sensitivity, or the
ability to hear sounds, but does not always improve the listener's
ability to make fine discriminations between speech sounds.

Speech Discrimination Testing

Although gain, as measured by comparing aided and unaided
Speech reception thresholds, and aided tolerance tests are '
taken into consideration, hearing aids are most often selected
on the basis of aided speech discrimination scores and sub—
‘jective preference (Zerlin, 1962; Ross, 1972). Discrimination

8
tests, as used in hearing aid evaluations, have therefore
become the subject of extensive research, criticism, and mod—
ification. According to both Zerlin and Ross, the method of
discrimination testing most widely accepted was the presenta—
tion of phonetically balanced monosyllables at a level of 20 .
to 40 dB SL or 40 to 50 dB hearing level (HL), in quiet or
against a competing message of Speech or noise. Unfortunately,
the scores from this test, which are serving as the primary
basis for the selection of amplification for an individual,
have been found by some to be unreliable and/or unable to pro-
duce differential results ameng hearing aids. Discrimination
scores are likely to be similar for all aids tested, even
those with demonstrable electroacoustic differences.

Reliability. Shore, Bilger, and Hirsh (1960) questioned the

 

reliability of conventional discrimination tests. Fifteen
hearing impaired subjects, five in each of three diagnostic
categories, were tested withﬂfour different hearing aids on
four different occasions. In addition to aided speech recep—
tion thresholds, aided Speech discrimination scores were ob—
tained with the Rush Hughes recordings of the Phonetically
Balanced (PB) 50 Lists (Egan, 1944) administered at 40 dB SL
in quiet and in noise. The test—retest variations were so
large that they concluded ". . . the reliability of these
measures is not good enough to warrent the investment of a
large amount of clinical time with them in selecting hearing
aids. . ." (Shore, Bilger, and Hirsh, 1960, p. 167). The use
of half lists might have confounded the reliability of the
results obtained in this study, however.

Conversely, McConnell, Silber, and McDonald (1960) compared
discrimination scores obtained in one session to those ob-
tained in a session two weeks later and found satisfactory
test-retest reliability. An aid of the same type, but not
the same aid, was used during the second session. Only the
discrimination results of the selected aid, however, were

.9-'
compared in this study. The rank ordering of aids was not
retested. McConnell, et al. also compared monosyllabic discrim—
ination test scores obtained in quiet by one clinician to
those obtained in quiet by another clinician, for the same
client. The scores were obtained with the same hearing aid,
on the same day, with the same test, and the results showed
good reliability.

Olsen and Carhart (1967) found good test—retest reliability
:hen monosyllables were presented in quiet and against two
types of competing signals, at four signal to noise ratios.
The listeners were three aids with known electroacoustic
differences. For the more difficult listening situations
(poorer signal to noise ratios and indirect listening condi—
tions) the aids were rank ordered on the basis of discrimin-
ation scores in the same way during two different sessions.
The investigators noted, however, that to demonstrate the re-
liability of rank order it is necessary to ensure a wide
range of scores, and hence, more difficult tests must be used.
Therefore, reliability was more easily demonstrated, statis~
tically, for subjects with sensorineural impairments since
their scores covered a wider range than those of conductively
impaired subjects. -

Cohen and Schleifer (1969) compared discrimination scores
obtained during clients' initial hearing aid evaluations to
those obtained during follow—up hearing aid reCheck evaluations.
They found that scores were reliable when the intervening
period between.test sessions was less than two months. A
slight discrepancy between results, in the direction of de—
creased scores, was noted when more than 63 days had passed.
The fact that the disparity continued to increase with time
led the authors to note the need for hearing aid recheck
appointments after one year.

- It appears, therefore, that discrimination tests are
potentially reliable measures for use in hearing aid evalua—
tions. Whether they are useful in differentiating among

.10;"

hearing aids, however, is another issue.

Differential Sensitivity. There is a concern among audiologists
that Open—ended monosyllabic word tests and the conditions
under which they are presented may serve to obscure rather than
to accentuate real differences among hearing aids. As a
result, Zink and Alpiner (1968) reported that they based
hearing aid selection on the known electroacoustic character-
istics of aids. It was their eXperience that discrimination
tests often produced similar scores for aids that spectral
analysis showed to be markedly different, in terms of distor—
tion and effective bandwidth. Not only are conventional
discrimination measures inefficient in terms of reflecting
physical differences among aids, but they frequently fail to
reflect subjective differences on the part of the listener.

In the previously cited study by Jeffers (1960), the consis-
tent subjective preferences of conductively impaired listeners
were not reflected in discrimination scores. In that study
seven out of 115 discrimination scores fell below 94% and only
two fell below 90%. Unfortunately, when all scores are ex~
cellent it is difficult to objectively select the most appro—
priate aid for a client. Zerlin (1962) also reported the
inability of conventional monosyllabic tests to reflect the
clear and definate subjective preferences of his listeners.
Chaiklin and Stassen (1968) reported a case in which ". . . an
extensive battery of audiometric tests was unable to reflect
the patient's perception of excessive distortion in her mod—
erately impaired poorer ear . . .' (Chaiklin and Stassen,
1968, p. 270) during a hearing aid evaluation.

Jerger, Malmquist, and Speaks (1966) assessed the sensi- ‘
tivity of different discrimination tests and test conditions
in current use. They presented the Psychoacoustical Laboratory
(PAL) 8 multiple choice sentence discrimination test (Hudgins,'
Hawkins, Karlin, and Stevens, 1947) under competing signal
conditions, the Central Institute for the Deaf (CID) W-22

€
11
monosyllabic word discrimination test (Hirsh, Davis, Silverman,
Reynolds, Eldert, and Benson, 1952) in quiet, the Consonant—
Nucleus-Consonant (CNC) word lists (Lehiste and Peterson, 1959)
in quiet, and the PAL PB 50 monosyllabie word lists processed
through a low pass filter. They found that the only test '
that clearly differentiated among aids was the sentence test.
This test produced differences of 30% among aids, while the
other tests produced differences only as great as 9%. They
concluded that monosyllabic tests as presently used ". . .
do not necessarily reflect meaningful hearing aid performance
differences . . ." (Jerger, Malmquist, and Speaks, 1966, p. 256).
This conclusion was in agreement with that of Shore, et a1.
(1960) who found that neither Speech reception threshold,
discrimination tested in quiet, or discrimination tested in
noise, were particularly effective in differentiating among
aids. _

Jerger, Speaks, and Malmquist (1966) demonstrated that
for normal listeners and listeners with sensorineural hearing
impairments, psychoacoustic tests could be devised to reflect
the electroacoustic differences among aids. Further, these
fairly stable differences were due to individual subject
interactions with hearing aids. They presented the PAL 8
sentence discrimination test to one ear of the subject and a
competing message of continuous discourse to the other car.
Each signal had been processed through each of three hearing
aid systems and recorded on one channel of a two channel tape
recorder at signal to noise ratios of -6 and ~12 dB. Aid
presentations were counterbalanced. It was found that the
aids could be rank ordered consistently on the basis of the
sentence test scores and that the rank order related to the
aid's measured amount of harmonic distortion. However, the‘
'fact that the eXperimental stimuli were presented via hearing
aid transduced tapes makes the validity of this method so a”
what questionable.

Another measure intended to be more sensitive involved

I, .
- K. - 6

the replacement of sentenCes for monosyllables. Speaks and
Jerger (1968) devised the synthetic sentence identification
test (SSI) which has received limited use in hearing aid
evaluations. Sentences are more like "everyday Speech"
(Harris, Haines, Kelsey, and Clack, 1961) and their inher-

ent redundancy permits a certain susceptibility to distortion.
Jerger and Thelin (1968) stated that ". . . the basic tech-
nique of sentence identification coupled with the competing
message concept can well be recommended as a point of departure
for the design of new approaches to hearing aid evaluation

in the clinical context . . Q" (Jerger and Thelin, 1968,

p. 183). Thus, it appears that an increase in stimulus
complexity may permit improved hearing aid evaluations.

Some modifications have been suggested for increasing the
effectiveness of monosyllabic word tests to distinquish among
hearing aids. Hood (1970) administered discrimination tests,
in quiet and in noise, at three intensity levels that approx—
imated soft, average, and loud conversational speech. He
reported a number of instances in which the scores of differ—
ent aids could not be differentiated at one intensity level,
but could be differentiated at a different level. However,
since this method is so time—consuming only a limited number

of words can be presented, or a limited number of aids evaluated.

alternative Methods of Hearing Aid Selection

 

 

Because of the lack of difficulty and reliability asso—
ciated with traditional hearing aid evaluation measures, a
number of alternative procedures have been suggested. As cited
previously, Jeffers (1960) used a paired-comparison method to'
differentiate among aids. In her study, 34 subjects with
conductive impairments listened to passages of cold running
speech that had been recorded through five different hearing
aids and sent through a loudSpeaker. The five aids with
markedly "good", "fair", and "poor" electroacoustic character—

istics, according to manufacturer specifications exclusively,

13
were ”Fr“r“o“ in four pairs, Each suljeet listenpd to speech
recorded through the first aid of a pair followed by sneeeh
recorded through the second ‘11"‘2.’:l‘:("r‘ of the pair. The subjects
were sole to differentiate amonr the aids and preferred the
aids with the objectively more desirable electroacoustic char-
acteristics. Jeffers concluded that subjective preference
on the part of the listener has a reliable predictor of hearing
aid suitability. It must be noted, however, that Jeffers
failed to counterlelance the order of aid presentation, and
hence, cannot account for the possible contributions of en
order effect upon her resultS. Further, only conductively
impaired {unijvets were used jji'mmls study and the Iwuuilts
might be different for subjects with sensorineural impairments.
Finally, the time requirements of this method would limit
its clinical practicality.

Zerlin (196?) also used a paired—comparison method to
differentiate among hearing aios. He presented 21 hearing
impaired listeners with tapes of conversational speech against
cafeteria noise at a signal to noise ratio of 5 dB. The
material had been recorded through s'x different hearing aid
systems. The subjects had access to w selector switch which
allowed them t) listen alternately to speech recorded through
two aids. The several aids were then compared to each other
in terms of preference. Following the paired—comparisons, each
subject was given a 25 word monosyllabic d'scriminntion test
(CID V~22) in quiet, which had also been transduoed throngs
the hearing aids. Zerlin found that his paired—comparison
procedure permitted differentiation among the aide, while the
tnonosyllabic word test did not. It would seem, however, that
the problems of recording, storage, rapid retrieva , playback,
and the amount of Clinical time involved with pairing every
n-td ill eliiric rrtock vsnild 1M? irmurrmo‘uitabltz.

Jerger (1967) also described a paired-comparison technique.'
Ile recorded two pure tones, are at 1000 Hz and one at 1609 Hz,

on.each channel of a two channel tape recorder. One signal

-14
was recorded directly and the other was recorded through a
hearing aid. Again, the subjects were asked to listen to pairs
and to make comparisons between the undistorted signal and
the signals recorded through aids with markedly different electro-
acoustic characteristics. Prior to the paired—comparison
test the subjects had been given the PAL 8 sentence intelli-
gibility test at a signal to noise level of -6 dB. This inter-
modulation distortion paired-comparison technique produced
the same rank ordering of aids as the sentence test. However,
as with the other paired-comparison techniques, the administra—
tive difficulties involved are noteworthy.

The measures discussed may be capable of differentiating
among hearing aids, but Jeffers (1960) and Jerger (1967) used
aids with exaggerated electroacoustic differences. These
differences were substantially more marked than those usually
encountered in the clinical situation and this may account,
in part, for the success of the measures used by Jeffers and
Jergcr. Further, as mentioned above, the validity of measures
in which the exnerimental stimuli consist of tape recordings
of hearing aid transduced speech is somewhat questionable.
‘This method is obviously less realistic than a method in which

snecch is presented directly to a listener through a hearing

J.'

J

aid. Also, in the process of recording alteration of the sig~
nal is unavoidable. We are left then with the need for a more
effective and clinically efficient way to reflect the electro-
acoustic and subjective differences among hearing aims.

h Tests

Distorted Speec
It has been shown that routine clinical tests of hearing
sensitivity and acuity are not adequate when diagnosing lesions
beyond the cochlea (Bocca and Calearo, 1963). The stimuli
used in these conventional tests are replete with extrinsic
redundancies and the multiple cues inherent in our language
(Harris, 1960). Therefore, even a severely disordered central

15
auditory system may be able to integrate and analyze the_sig—
nels, producing norms l or near normal test res ults. In addi—
tion, the pathways in which the message travels in the central
11ervous system are intrinsically redundant in terms of the
Zlarge number of duplicate neural fibers and interneural connec-
tions. Consequently, accurate identification of Spoken
rnessages is possible even if part of the neurologie pepulation
is destroyed. In order to override the intrinsic redundancy
(Teatini, 1970), the extrinSic redundancy of the Speech signal
must be reduced via some form of signal modification,or degra-
dation. i I
' In recent years speech has been degraded and distorted in
'various ways so that it mi ght constitute a more difficult
listening tas 1c. Jergcr (1960) hypothesized that beyond the
peripheral auditory system the auditory pathways increase in
complexity and the tasks needed to assess their function must
likewise increase in complexity and difficulty. To this end,
speech has been masked, interrupted, filtered, and alternated
between ears. An intact auditory system can compensate for
the distortion, but an auditory system that is deficient in
some way may be unable to process Speech information that has
been altered. One means of signal alteration that has been
studied is that of time—compressed Speech.

Time—Compressed Speech

 

Time—compressed speech has been useful in the diagnosis
of central auditory lesions. Several methoM have been devised
for the compressing of SpeeCh and these methods have been used
to increase the difficulty of discrimination measures as well
as the difficulty of other audit01y perceptual processing
measures. .

The simplest method of time—compressing Speech is for the.
speaker to talk more rapidly than normal. While this procedure
has the advantage of requiring no special equipment,-it has

‘3

16
the disadvantage of introducing the undesirable qualities
associated with a Speaker attempting to temporally alter his
normal verbal output. The Speaker deviates from normal habit—
ual inflection and intonation patterns, consonant/vowel dur-
ations, pauses, and articulatory productions. Not only are
undesirable and unintentional changes in the talker's Speech
unavoidable, but the method is limited in that a Speaker can
only shift his rate of Speaking by about 30% (Beasley and
Maki, 1975). '

Some investigators have employed the "Speed changing"
method. With this method Speech is reproduced at a faster
rate than that at which it was originally recorded. This method
has some significant advantages in that it is simple to per—
form, requires no Special apparatus, and can be modified to
allow the Speed of reproduction to be continuously variable.
Unfortunately, the primary disadvantage outweighs all the ad-
vantages; the procedure produces a frequency shift in the end-
product that is preportional to the change in playback speed.
Frequency variation interacts with temporal variation and
this interaction may introduce error into the data obtained
with this method (Beasley and Maki, 1975).

The most effective form of time—compression that has been
develOped is that of interval discard, described by Fairbanks,
'Everitt, and Jaeger (1954). In this process the taped sample
is cepied onto a tape 100p from which 18 to 20 millisecond
(msec) segments of the signal are randomly discarded. The re-
xnaining sampled'portions of the signal are electromechanically
arbutted in time to form a continuous message. This method
Ines the advantage of preserving the original pitch of the
zsignal while allowing for continuously variable percentages
of time-compression. The original electromechanical apparatus
(described by Fairbanks, et a1. has been modified and now takes?
idle form of a small computerized mechanism, which is the sire
of a.portable cassette recorder (Lee, 1971), known as the
liexicon VariSpeech I. The Lexicon device has been shown to

17
produce signals equal in quality to the original cumbersome
Fairbanks device (Beasley, Nikam, Riggs, Freeman, and Konkle,

1975).

Intelligibilitylgf Time-Compressed Speech for Normal Listeners

 

 

 

Several investigations of the intelligibility of time—
compressed speech have been carried out. Daniloff, Shriner,
and Zemlin (1968) studied the_effects of time—compression, with
and without frequency distortion, on the perception of vowels
embedded in a /h-d/ context. They electromechanically com-
pressed the stimuli to ratios of 30%, 40%,.50ﬁ, 60%, 70%, and
80%. It was found that vowel confusions under frequency
distortion were related to shifted format frequency positions,
and under time-compression were related to duration. The
major decrease in vowel intelligibility was found to be at a
compression ratio of 70%. It was also found that the female
speaker was more intelligib1e&under all conditions.5

Fairbanks and Kodman (1957) investigated the relationship
between the degree of time-compression and intelligibility.
In their study, a dramatic breakdown in intelligibility occurred
at a time-compression ratio of 80%. Beasley, Schwimmer, and
Rintelmann (1972) time-compressed four lists of the Northwestern
University Auditory Test Number 6 (NUf6) monosyllabic word
test (Tillman and Carhart, 1966) to compression ratios of 30%,
40%, 50%, 60%, and 70%, and presented them at sensation levels
of 8, 16, 24, and 32 dB to 96 normal listeners. The results
of this study indicated that as the amount of time-compression
increased intelligibility decreased, but that the effect was
partially offset by an increase in intensity. Ear differences
were found to be minimal. The subjects in this study were
unaffected by time—compression until a level of 40% was reached,
whereby there was a gradual breakdown in intelligibility up '
through 60% time—compression. At a ratio of 70% time—compression,
there was a dramatic breakdown in intelligibility. At this

18 # 5
level PB Max (the maximum discrimination score for a subject)
was not acheived even at the highest sensation level used in
this study (32 dB). Beasley, Forman, and Bintelmann (1972)
extended the Beasley, Schwimmer, and Bintelmann study to in-
clude a sensation level of 40 dB. Although at 40 dB SL the
drOp at 70% time-compression was not as severe, it was still
dramatic. At compression levels lower than 60% the scores for
32 dB SL and 40 dB SL presentation levels were essentially
the same.

Several possible reasons for the difference between the
results obtained by Fairbanks and Kodman and those obtained
by Beasley, ct al. (1972 a,b) can be noted; 1) Fairbanks and
Kodman used a smaller discard level (10 msec as Opposed to 30
msec) thus making the listening task easier, 2) Fairbanks and
Kodman used trained listeners while Beasley, et al. used naive
subjects, and 3) Fairbanks and Kodman used a maximum sensation
level of 80 dB, as opposed to the maximums of 32 dB and 40 dB
used in the Beasley, et al. studies.

Several studies have used time-compressed speech to assess
intelligibility as a function of subject age. Beasley, Maki,
and Orchik (1973) did a study designed.to obtain time-compression
norms for children. They used the Phonetically Balanced
Kindergarten word test (PB—K SO) and the Word Intelligibility
by Picture Identification test (WIPI) as stimuli. Their results
indicated that children, when compared to adults, were more
adversely affected by time—compression. A dramatic breakdown
in intelligibility scores occurred at a 60% level of time-
eompression and was attributed to the use of different stimuli
and the reduced language processing performance levels of children.

*Calearo and Lazzaroni (1957), deQuiros (1964), and Bocca
and Calearo (1964) found that the length of time needed for
processing accelerated speech increased with age. Sticht and
Gray (1969) studied four groups of listeners; 1) normal hearing_
young adults, 2) normal hearing aged subjects, 3) young adults

with sensorineural hearing impairments, and 4) aged adults

1

with sensorineural impairments. They presented the listeners

\D

with the CID W-22 monosyllabic word lists compressed to ratios
of 36%, 46%, and 59%. They found that both groups of aged
listeners showed a decrease in intelligibility different from
that of the young listeners. Their findings serve to advance '
the theory that age in some way alters the central auditory
pathways. Schon (1970), using time—compression ratios of

30% and 50%, found that normal hearing young and aged subjects
and sensorineurally impaired young and aged subjects eXperi—
enced a decrease in Speech intelligibility as a function of
time—compression. Schon found that subjects also had reduced
intelligibility as a function of time—eXpansion. However,
only time—compression produced a difference in the intelligi-
bility curves of young and aged subjects. Luterman, Welsh,
and Melrose (1966) also used time-compressed speech to study
the perceptual abilities of a geriatric pepulation. They
compressed CID W—22 monosyllabic word lists to ratios of 10%
and 20% and presented them to young and aged listeners with
high frequency hearing losses? They found no differences
between the intelligibility curves of the two groups, however.

Konkle, Beasley, and Bess (1974) studied the intelligi—
bility of time—compressed speech for elderly subjects with
discrimination scores of 90% or better, using the NUﬂ6 mono—
syllabic word lists. They compressed the NUﬂ6 words to ratios
of 0%, 20%, 40%, and 60% and presented them at sensation levels
of 24, 32, and 40 dB. They found that the articulation func—
tion curves of these subjects did not parallel those of younger
subjects. Listener discrimination difficulty occurred at low
time-compression levels, even at higher sensation levels.
These findings point to an impairment of the central auditory
system associated with the aging process.

Thus, several investigators have shown that speech signals
can be altered in such a manner as to reduce the extrinsic re-
dundancy of the signal, thereby making the listening task
more difficult. This increased difficulty, in turn, can be

20 l 5
used to tax the intrinsically redundant Central nervous system
in such a manner as to allow for the delineation of auditory
impairments which may go undetected when using more conven-

tional measuring techniques.

Time—Compressed Speech Intelligihilitr for Impaired Listeners

 

 

 

Investigations have shown that persons with sensorineural
hearing impairments are more_susceptible to various forms of
auditory distortion than normal hearing persons (Harris, 1960;
Tillman, Carhart, and Olsen, 1970; COOper and Cutts, l971;
Gengel, l97l; Nabelek and Pickett, 1974). Foulke (1971) found
that normal listeners required an increase of 10 dB to attain
PB Max when the rate of presentation was increased from 140
words per minute (me) to 250 me, and another 10 dB increase
when the rate was increased to 350 me. He found that persons
with sensorineural hearing losses required more than a 10 dB
increase.in intensity for the same rate increases and.that
subjects with higher central nbrvous system disorders required
even greater increases in intensity.

Kurdziel (1972) presented nine subjects, who had noise
induced sensorineural hearing losses, with time—compressed
monosyllabic words. She found that these persons had reduced
discrimination scores at all levels, but that their intelligi-
bility patterns were similar to those of normal hearing per—
sons. Like normal listeners, intelligibility decreased grade
ually up through 60% time-compression and then decreased dra-
matically at 70% time-compression. Further, as time-compression
increased, a higher sensation level was needed to reach Opti-
mum discrimination. .

Kurdziel and Noffsinger (1973) presented NUf6 monosyllables
time-compressed to ratios of 40% and 60% to subjects with uni—
lateral temporal lobe lesions,.at a level of 40 dB SL. Although
conventional test results were normal for all subjects, at .
40% time—compression no subject acheived a discrimination

.2lLi‘
score of 90% or better. Further, scores for ears ipsilateral
to the lesion showed a moderate decrease in intelligibility,
while scores for ears contralateral to the lesion were sig-
nificantly depressed.

Statement_g£ the Problem

 

It has been shown that monosyllables, as presently used,
are insufficient stimuli for hearing aid evaluations in that
they are incapable of demonstrating physical differences
among aids. Consequently, they are not particularly effec-
tive in assisting the audiologist in hearing aid selection.

It has also been shown that the stimulus materials and tech—
niques suggested to replace them are, to date, clinically im—
practical. These findings led Burney (1972) to state tha

the development of techniques to more thoroughly examine the
differences among hearing aids was an apprOpriate area for
future research. Jerger (1970), Speaking in reference to
traditional speech audiometry: stated that it is still of
limited diagnostic value, that it cannot distinquish among
hearing aids, and that it is not a true representation of Speech
in the real environment. He stated that traditional speech
materials are based on the oversimplified assumption that
distinquishing between phonemes with similar acoustic spectra
iS‘essential to Speech understanding. This is a false assump-
tion according to Jerger. He concluded that it is becoming,
increasingly clear that the key parameter for Speech intelli—
gibility is that of time. Thus, it is not only necessary to
develOpe hearing aid evaluation tools that are effective as
well as efficient, but it is also necessary to develOpe tools
that control for temporal as well as Spectral information.
Further, it is necessary to make these tools difficult enough
to adequately and realistically tax the aided listener in the
hearing aid evaluation situation. One method of increasing'
signal difficulty which has already proven clinically effective
and efficient in diagnostic evaluations and which may subsequently

.22 ' '
prove valuable in hearing aid evaluations, is that of time-

compressed Speech.
The purpose of the present investigation is to evaluate

tine nntmnrtisl 1190 (if fﬁxne—P”V J"F“sed {Twoorﬂi as r1 dir ‘“‘*WJ.T—
J ‘ q, 3 , . }"
hearing 2.‘- ' _ x“ 1 h: ‘ .a. JLuCifiC questions

to be investigated are:
1) What will the effects of aided listening be on the

-intelligibility of time—compressed Speech?
2) Can time—compressed speech be used to objectively

differentiate among hearing aids?

CHAPTER II

EXPERIMENTAL PROCEDURES

This study consisted of 70 subjects randomly assigned to
one of seven echrimental conditions. Each condition was char~
:acterized by three lists of a standardized measure of Speech
(discrimination, presented at three levels of time-compression.
{The lists were heard monaurally in the unaided soundfield or
'through one of the six pre-selected moderate gain ear level
ihearing aids worn monaurally at a gain setting of 30 dB, re:
1000 Hz.

a O
x) 111:) 110 C t S

 

The subjects were 70 normal hearing speakers of General
American English between the ages of 18 and 29, selected from
a university poPulation. Each of the subjects were randomly
assigned to one of seven groups corresponding to one of the
six hearing aids or the unaided condition. Air conduction
and bone cbnduetion thresholds were obtained for both ears of
eaeh subject at the octave intervals between 250 Hz and
4000 Hz. A11 thresholds were 20 dB or better, re: ANSI (1969)
Specificationsy Appendix A shows_the mean air conduction'
and bone conduction thresholds, the ranges, and the standard
deviations for the right and left ears of the 70 subjects.
Right ears were used exclusively in this study since Beasley,
Schwimmer, and Rintelmann (1972) found no ear differences
for time-compressed speech.’ Left ears were covered with a

23

on
Doric” Clark C 1:1nsny Model 117 nrotc etive esrruff thrmnjjhoizt
all Inuit—ttnnssholfl testirn .

A tuned presentation of s CIE U-l word list was presented
thrrmfht loud’nn'ﬂcer (F lectrsvoiec 15 TV. {) in or Fer to ob—
tain a right ear, unaided soundfield sgeech reception threshold.
One of the four toned lists of For-"n A of the NIT/,1"; Auditory
Test was randomly selected and presented at 3? dB 3; (re: SET),
threu h the same loudspeaker in order to obtain a right ear,
unaided soundfield speech discrimination score. All subjects
had 8 er1n1n tion scores of 90? or better. Responses were
\ritten on the answer sheet proviW 3 by the exner mentor
(see inpendix B). These results were obtained innedistely
prior to experimental testing. A sueject rel- ease iorm as

also sirned at this time (sec Append'x C).

Stldnﬂdkﬁ Genrnxrtion

 

The exnerimentsl stimuli used in this study were taken
from Beasley, et al. (19729) and consisted of Lists I, II, and
III of the Fonthwcstern University Auditory Test Number 6 (NU[6)
(Tillman and Carhart, 1966). The lists are shown in Appendix D.
A copy of these lists was made usirw1 an Amnex Model 601 tsne

deck (frequency response 50—1?,000 Vs t 2 d?) and an Annex

H-

Model AG 600-2 tape deck (frequency resoonse F0—13, 000 Hz
’2' dB). Each list was comnressed to “levels of 40” ﬁnd 60,”:
using the Fairbanks electromechanical tine—1o"o1esaior
anpaxu' Ltus (Fairbanks, Everitt, and Jaeger, 1954), as modified
by Zemlin (1971). In order to control for the variable of
possibl: fidelity distortion due to the time—compression1pro—
eedure, each list was also passed through'the time—e o1n1ess1on
apparatus under the 0% time—eonnression condition. In all there
were nine exneiinentsl 113 s, ie, each of th1ec lists at th1ee V
levels of tine—cornnression. Conies of eseh exper'montal list
twang then tunic usirwjtni Axuxxcfﬁodel (7Y1 tans (Rxﬂc and 111.1nnex

Node] AG 600—2 tape deck, monitored by an Annex Nodel AA 690

25 . 0

power amplifier. A Bruel and stcr (Model 1024) Sine Random
Generator was used to generate a 1000 Hz tone which was recorded
at the beginning of each stimulus tape for earphone calibra—
tion. A Grason-Stadler (Model 1701) pure tone audiometer

was used to generate Speech noise, which was also recorded

at the beginning of each tape for soundfield calibration.
Approximstely five seconds of silent interval response time

was allotted between each stimulus item on the experimental

tapes.

- Instrumentation

 

An Allison (Model 22) duel channel audiometer was employed
in this study. .The instrument has an SPL output range of
—10 to 100 dB (re: ANSI, 1969). An Electrovoice 15 TRX
loudSpeaker was used_with the Allison—22 audiometer (frequency
response 300-5000 Hz t 5 dB). Placement of the loudSpeaker
was at a 00 azimuth (re: the listener). The experimental
tspes were presented to the listener via an Ampex Model 600—2
tape deck (frequency re3ponse 40—l0,000 Hz t 3 dB).

All subjects were tested while sitting in a prefabri—
cated double walled chamber (IAC 1200 series). Sound level
measurements, made with a Bruel and Kjaer portable precision
Sound Level Meter (Model 2204/8) showed ambient noise levels
to be within the limits (45 dB-C) Specified as acceptable by
ANSI (1969). The experimenter sat in a single walled control
room (IAC 400 series).

Calibration measurements of the test audiometer were per—
formed every two weeks according to ANSI (1969) Specifications.
Frequency variation, harmonic distortion, sound pressure out—F
put, attenuator linearity, and stimulus rise/decay times were
checked. Sound pressure output levels for Speech noise were-
measured to determine loudspeaker calibration. The output
levels were adjusted to exceed the audiometer attenuator
setting by 12 dB (Dirks, Stream, and Wilson, 1949). The

m

2

calibration noise at the be mginning of each stimulus t9 no we s
designed to peak the VU meter of the audiometer at -2 dB VU.

The hearing aids used in this stucy were the Qualitone
TSP, the Fidelity F—SQ, the Siemens 24 E SL, the De hlberg
HT 1233, the Telex 334, and the Otieon E 11 V. These aids
were selected from clinic stock on the basis of similar
frequency response. They were electromechanieelly measured
according to ANS 3.3 (1969) specifications on a weekly
bss's to ensure eomnlisnee'with manufacturer sneeifice tions.
Roch aid was placed in e Bruel end Kjeer (Hodel 4212) Sound
Ch amber for measuring electroe eoustie characteristics. A
signal was sent to the did by e Pruel end ster (Vedel 1024)
Sine andom Generator, monitored by a Bruel and ster (Model
2607) 1eesur1rs A.'1nlifier. The hearins aid output was moni-
tored by e Bruel and ster (Iodel 2112) Audio Frequency
inectrometer snd grephieslly recorded on s Bruel end Kjwer
(Uodel 2305) Level Recorder. The electroacoustic charac—
teristics of the heering aids esn be found in Tables l~C.
Table 1 shows the gain, saturation, €11eeti‘Je l3: ndxidth,
and harmonic distortion for hearinn aid number 1, the Quali-
tone TSP, measured Recordinﬁ to the ﬁeerinﬁ Aid Indu try Con~
Terence (HAIC) (1061) specifications. Also shown in Te‘le l .
is the gain, seturetion, effective hundwidth, and harmonic

distortion for hearing aid number 1, according to the nrooos ed

Food and Drug Administration (FDA) (1975).‘r1f1c tions.
Tables 2—6 show the results of the same 1e“.urement for

hearing aid numbers 2—6.
Tynerimentsl Procedures

The right es: of each subject (excluding the ten subjec' s
in the unaided group) was fitted with one of the six -xneri-
mentel hearing side, set for a gain of 30 an (re: 1000 He).

Regular Lucite occluding stock eormolds were used. All left

03
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33

ears remained covered with the protective earmuff. A taped
presentation of a CID W-l word list was again presented
through the loudSpeaker, and an aided SRT was obtained. The
subject was then presented with each of the three discrimin—
ation lists under a different level of time—compression, at
a constant level of 32 dB SL (re: the aided SRT). Each sub-
ject was presented with all three lists and all three levels
of time-compression in random order. All subjects were read
standard instructions which appear in Appendix E, and rGSponSGS
were written on the answer sheet shown in Appendix B.

Procedures were identical for the ten subjects in the
unaided group except that they were not fitted with hearing
side. They received all three lists and all three levels of
time-compression at a sensation level of 32 dB (re: the un-
aided SRT). '

Analysis

 

The data were hand scored by the eXperimenter and con-
verted into percentage correct scores. The scores repre—
sented the seven eXperimental conditions corresponding to
the six aided conditions and one unaided condition, at each

of the three levels of time—compression.

CHAPTER III

RESULTS

The results of this study showed certain trends associ-
ated with the intelligibility of monosyllables at varying
levels of time-compression, when heard in the aided and un-
aided conditions. The results revealed decreased intelligi—
bility and greater variability among hearing aids as the
level of time-compression was increased. The discrimination
scores obtained through hearing aids and in the unaided
soundfield condition employed in this study were found to be
lower than those obtained under earphones by Beasley,
Schwimmer, and Rintelmann (1972). Further, Speech reception
thresholds were found to decrease by 2 to 4 dB when obtained
in the aided rather than unaided condition. Finally, a i
change in rank order with increasing time-compression was
seen for four of the six experimental hearing aids. Thus,
the aids which produced the best scores at 0% time—compression
produced the poorest scores at 60% time—compression, whereas,
the aids which produced the poorest scores at 0% time-
compression produced the best scores at 60% time-compression.

Speech Reception Threshold

All Speech reception thresholds obtained for right ears
in the unaided soundfield were within normal limits. Differ—
ences of O to 10 dB were found when Speech thresholds were
remeasured through hearing aids. Forty-six of the 60 sub-
jects showed a decrease in SRT's obtained in the aided condition,.

34

35 .

“two showed improvement, and 12 thresholds remained unchanged.
{Table 7 shows the mean difference between unaided and aided
Speech reception thresholds, the difference ranges, and the
standard deviations for each hearing aid group. On Table 7,
it can be observed that SRT's were poorer by means of 2 to 4
(iB when measured through the six eXperimental hearing aids.
Iiearing aid number 5, the Telex 334, showed the largest de- '
crease and hearing aid number 4, the Dahlberg HT 1233, showed
the smallest decrease. The decrease in aided SRT's found in
this study is 8 to 10 dB less than that reported by Tillman,
Carhart, and Olsen (1970) . "

Aided Discrimination Scores a 0%, 40%, and 60% Time-Compression

 

Intelligibility scores decreased with increasing levels
of time-compression for all hearing aid groups and the unaided
condition. Scores for each subject at each level of time—
compression are shown in Appendix F. Hearing aid number 1,
for example, produced a mean discrimination score of 98.2%
at 0% time-compression, a mean score of 91.0% at 40% time-
compression, anda mean score of 86.4% at 60% time—compression.
Table 8 shows the mean discrimination scores, the ranges,
and the standard deviations for each hearing aid group and
the unaided group at each leveloof time-compression. It can
be seen that the mean score of the unaided group falls below
four of the six hearing aid groups at 0% time—compression
and falls to last place at 60% time-compression. A slight
trend toward increased variability among aids with an increase
in time—compression can also be observed. The seven group
means for 0% time-compression Span a range of only 4.6%,
whereas, at 40% time—compression the means span a range of
7.4%, and at 60% time-compression the means Span a range of
7.0%. Reference to Table 8 shows no general trend toward
greater intersubject variability with each level of time—

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38
compression. Only the unaided group showed increased variability
with each leVel of time—compression. At 0% time—compression
hearing aid number 6 produced its most variable score, at
.40% time-compression hearing aids numbers 2, 3, and 4 pro—
duced their most variable scores, and at 60% time-compression.
hearing aids numbers 2 and 5 produced their most variable
scores. Hearing aid number 2 was equally variable at 40%,
and 60% time-compression.

The Interaction Between Time—Compression and Hearing Aids

 

The trend toward decreased intelligibility with increasing
levels of time-compression was also found by Beasley, Schwimmer,
and Rintelmann (1972) when time—compressed NU#6 monosyllabic
lists were presented to normal hearing subjects under ear—
phones at 32 dB SL. The breakdown reported by Beasley, et al.
was more gradual, however. Table 9 shows the difference
between the mean scores obtained by Beasley, et al. at 0%,
40%, and 60% time-compression, the grand means for all
hearing aid groups, and the means for the unaided group in
this study. It can be seen that at 0% time—compression,
scores obtained under earphones (Beasley, et al.), scores
obtained monaurally in the soundfield, and seoresobtained
through hearing aids were comparable. The decrease in aided
discrimination scores reported by Zink and Alpiner (1968),
Tillman, Carhart, and Olsen (1970), and Zelnick (1970) was
not found in the present study. At 40% time-compression,
however, earphone scores were 1.4% better than aided scores
and 2.2% better than soundfield scores. Aided scores were
.8% better than unaided soundfield scores. (At 60% time-
compression, earphone scores were better than aided scores
'by 4.2% and better than unaided soundfield scores by 9.4%.
Aided scores were 5.2% better than unaided soundfield scores.
The trend toward better earphone than soundfield scores was
also found for children when discrimination scores for the

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tine—c ‘nresscd NIPI, obtained under earphones 3y Thong (197?),
were compare? to tine—compressed WITT scores fore hild rcn of

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f‘

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u‘

Rank Ordering of Hearing dine with TiuC—COWanssion

 

 

A clwunic in.rruﬂ( OFﬁOV‘YTVT obscrwmwi for all.ln3t tvrw of
the six experimental hearing aid ”roups. In other word: the

ﬁn,

aids that produced the best scores at 0, 'll‘—0010T-Sflon

q ' ﬂ ‘ a -. ”d f v a m ' '~ (‘.. r”
produced the pooiest scores at 60% time-COMDIOSulOM, new the
aids that produced the poorest scores at 0% time-compression

produced the bes scores rt 60% time—compression. Table 10

L

shows the rank order for en 31 hearing aid group at each evcl
of time—compression. An attempt was node to correlate the
physical characteristics of the aids with .hc reversal effect.
Factors such as the amount of har rmonic disdaitio present in
each aid, the mnount of interned uletion dis  tortion niesent in
each aid, the effective bandwidth of each aid, the irregularity
of each nid's frequency response, the diffe‘cnce hetween the
energy peaks produced by an aid, and the amount of internal
noise gene rated by each aid were examined.

‘ Hernonic distortion was initially mea surcd according to
HAIC (1961) and FDA (1975) specifications and found to be
non—ex istent for all but t o echrimental aids (see Tables 1—6).
The amount of measurable harmonic distortion for hearing
aids numbers . and 3 was within the limits (10%) specified
as acceptable by UAIC (1961) specifications. Subsequently,
harmonic distortion was remeasurcd wj h a gain setting of
3() dl3 (IT): lINlO Ila), or':is xvoimi h;r tlu3 lixotrniexvo 1dl iﬂiicz
study, rather than with the 5 dB pain setting designated by

HAIC (19(1) "0001f107t103 Again, the amount of harmonic

Table 10.

NO.

NO.

NO.

NO.

NO.

NO.

NO.

at 0%, 40%, and 60% levels of time-compression.

HEARING AID

Qualitone TSP
Fidelity F-59
Siemens 24 E SL
Dahlberg HT 1233
felex 334

Oticon E 11 V

Unaided Condition

0%

TIME-COMPRESSION

40%

4.5'

The rank order of the six experimental hearing aids

60-

4°

distortion associated with each aid was minimal and did not
- appear to influence the rank ordering of aids. Finally, har—
monic distortion was measured a third time in a sweep frequency
mode and again found to be minimal. The harmonic distortion
averages for the frequencies of 500 Hz, 700 Hz, 900 Hz, and
1500 Hz, measured with an input of 75 dB and with a gain
setting of 30 dB (re: 1000 Hz), are diSplayed in Table 11.

Intermodulation distortion was measured with paired input
signals of 75 dB at frequencies of 500 Hz and 1500 Hz, 700 Hz
and 1700 Hz, 900 Hz and 1900 Hz, 1100 Hz and 2000 Hz, 1300 Hz
and 2000 Hz, and 1500 Hz and 2000 Hz. The hearing sids were
oset for 30 dB of gain (re: 1000 Hz). Intermodulation distor—
tion was found to be non-existent for four aids and minimal
for hearing aids numbers 1 and 3. The intermoduletion distor-
tion averages for the above frequencies are also diSplayed in
Table 11.

Differences in effective bandwidth were also minimal and
did not seem to influence rank order. The effective-bandwidth,
as calculated according to HAIC (1961) Specifications, for
each aid can also be found in Table 11. I '

The irregularity of frequency reSponse was calculated
according to the irregularity reSponse index (IRI) preposed
by Jerger and Thelin (1968). Jerger and Thelin described a
method by which the irregularity or jaggedness of the frequency
response is calculated by counting the number of times the
frequency response curve intersects lines drawn in 2.5 dB
steps from a baseline. The baseline is a line drawn to inter-
sect the lowest point of any reversal in the frequency re5p0nse
curve. Jerger and Thelin found a negative correlation between high
IRI and the behavioral performance associated with an did. I
No such trend was seen in this study. The IRI values for each
_aid are shown in Table 11. I

Since time-compression would have a negative effect on
the intelligibility of consonants, which are weaker, shorter,»

43

and of higher frequency, before negatively affecting the more
intense, longer, and lower frequency vowels (Daniloff, Shriner,
and Zemlin, 1968), it was hypothesized that a difference be—
tween the first and second energy peaks of the frequency
response of an aid might be significant. An aid permitting
a greater concentration of energy in the higher frequencies
might be more resistant to distortion under time~compression.
When calculated, however, the peak to peak differences were
found to be minimal and comnsrable for all aids. The peak
to peak differences for each aid are shcwn in Table 11. They
had no apparent influence on rank order. Table 11 also shows
the difference between the average of energy found at 500 Hz
and 1000 Hz and the energy found at 2000 Hz, for each aid.
This difference also had no annarent influence on rank order.

The internal noise generated by each aid was determined
by calculating the difference between the output of an aid
at its maximum gain setting with a 50 dB innut and the outnut
of the aid at its msx'mum gain setting with no input. The
differences between the internal noise values for all aids
were minimal. Subsequently, internal noise was remeasured
with inputs of 50 dB and gain settings of 30 dB (re: 1000 Hz),
or as worn by the listeners in this study. Again, differences
between aids were minimal and did not seem to influence rank
order. Finally, internal noise was calculated using broadband
rendom noise as the input signal. No significant differences
between aids were found. The values found at the 30 db gain

settings, with inputs of 50 dB, are shown in Table ll.

m6 mm mU H mU N NN . Nm ooomlomm we ww.v . > Ha m COUﬂuO m .02

me we me H . me e ea we eewm-eem we we emm xmeme m .02
me ee- me e me we.. we Nm eeem-emm we we mmmw,em mumnwnma e .02
me we me q me we m we eemmuemw we.m wm.e gm m em mamamwm m .02
mo em mo m- mu m e um eeemueem we wm.m emum muwemwem m .02
me we me e mo w eH N: eemmuewm we we.m ems mcouwemso H .02
.z.H mm\mq Nm\am Hag” meonoz<m .Q.2H .Q.m QH¢ Uszdmm

.Uﬂm Hmucmﬁﬂuwmxm 50mm “Om .A.Z.Hv mm coca uwu .mo om mo mcﬂuumm

cﬂmm m um UmHSmmmE mme: Hmcumucﬂ can..Amm\mqv Nm ooom um wmumcm may Ucm Nm oooa
cam um com um wmumcm.wo wmmum>m Gnu cmw3umn wocmummwﬂc msy .Amm\amv mmucmHGMMﬂU
xmmm 0» xmmm mmumcm .AHmHe mmmam> HmH .Ameonozwme mcoﬂumowmwommm .Heeae oHam ou
mcﬂwuooom waywasoamu sucﬂsccmn m>Huomwwm .AD.EHV mv mm mo mamcmﬂm usmcﬁ wmuﬂmm
Ucm.mm oooa ”mu .m© om mo mceuumm cﬂmm m npﬂz vmcﬂmuno mmmmum>m :oHuHoumﬂw coﬂu
ImHJCOEHmuCH .A.Q.mv Nm oooa "mu .mc om mo mewuumm cﬂmm m cam usmcﬂ m6 mu m nuHB

UmHSmmmE Nm ooma Ucw .N: oom .Nm oom .Nm oom Mom mmmmum>m coﬂuuoumﬂo UHCOEHME

.HH GHQMB

CHAPTER IV

DISCUSSION

Time-compressed monosyllabic words were used to devise
a clinically efficient and eXpedient hearing aid evaluation
measure which would constitute a more difficult, and thus more
realistic, listening task. An attempt was made to allow the
procedure to create a wider range of objective scores for
several aids and to produce scores commensurate with the elec-
troacoustic quality of aids.

The results of this study showed that as the level of time-
compression was increased intelligibility decreased. It was
also seen that intelligibility decreased more rapidly for
aided normal listeners than for the normal listeners tested
under earphones by Beasley, Schwimmer, and Rintelmann (1972).
Intelligibility decreased even more rapidly for unaided normal
listeners tested monaurally in the soundfield. Unaided scores
were poorer than aided scores and earphone scores under 40%
and 60% time-compression. Aided Speech reception thresholds
were poorer than unaided speech reception thresholds by 2 to
4 dB. Electroacoustic measurements indicated that there
were no significant physical differences among the six eXperi-
mental aids. Finally, an increase in the level of time-
compression also created a change in rank order for four of
the six aids. ’

The trend toward decreased intelligibility with an increase
in time-compression was eXpected since it had been previously
reported by a number of investigators (Fairbanks and Kodman,
.1957; Luterman, Welsh, and Melrose, 1966; Daniloff, Shriner,

45

46

and Zemlin, 1968; Sticht and Gray, 1959; Schon, 1970; Beasley,
Schwimmer, and Bintelmann, 1972; Beasley, Maki, and Orchik,
1973; and Konkle, Beasley, and Bess, 1974). The fact that
intelligibility decreased more rapidly for normal hearing
subjects tested through hearing aids than for'normal hearing
subjects tested under earphones was also eXpected since Harris
(1960) reported that two types of distortion in combination
serve to more drastically reduce intelligibility. The intro—
duction of a hearing aid_system constitutes a second distor—
tion factor in the form of the non—linear distortion present
in the system itself, and in the form of the more restricted
frequency response of the system which acts as a filter for
Speech. When a normal listener is tested in the aided condi—
tion the amplification of ambient noise also becomes a factor.

The 8.6% decrease in aided, compared to unaided sound—
field, discrimination scores reported by Tillman, et al.
(1970) for-normal hearing subjects was not found in this
study. At 0% time—compression aided scores were decreased by
only .Gﬂ and at 40% and 60% time—compression, aided scores
were better than unaided scores by means of .8% and 5. %,
reapectively. The greater decrease in aided scores obtained
by Tillman, et al. may be attributable to any of several
factors; 1) a 450 azimuth was used by Tillman, et al., whereas,
a 00 azimuth was employed in the present study, 2) additional
signal distortion may have been unavoidably introduced by
the extra transducers employed in the aided conditions of the
Tillman, et al. study,-and/or 3) the aids used in the Tillman,
et al. study may have had electroacoustic characteristics
that were inferior to those of the aids used in the present
study.

‘The increasing decrease in unaided scores, as compared ‘
_to aided scores, that was seen as the level of time—compression
was increased from 0% to 60% may be the result of the inter-
action between intensity and time-compression reported by

47
Beasley, Schwimmer, and Rintelmann (1972). Those investigators
concluded that as time—compression increased an increase in
intensity was reQuired to offset the reduction in intelligi-
bility. The unaided listeners lacked the 30 dB of gain pro-
vided by the hearing aids. At 0% time-compression the addi-
tional intensity provided by the aid apparently was not
required. As the level of difficulty was increased, however,
the advantage of hearing aid amplification was reflected in
improved scores for the aided condition, as compared to the
unaided condition. The amplification advantage was perhaps
great enough to counteract the disadvantage created by the
two factor distortion combination described by Harris (1960).

Unaided soundfield scores that were poorer than earphone
scores, obtained at the same sensation level, were not ex-
pected since Sivian and White (1933), Breakey and Davis (1959),
and Tillman, Johnson, and Olsen (1966) reported soundfield
thresholds that were better than earphone thresholds. Dirks,
Stream, and Wilson (1972) reported that speech reception
thresholds obtained in the soundfield at a 00 azimuth were
better than those obtained under earphones by 3.5 dB. The
decrease in soundfield scores found in the present study
may be attributable to the soundfield listener's lack of pro—
tection from ambient noise, or to the fact that the TDH 39 A/X
earphones used by Beasley, et al. (1972b) had a broader and
more linear frequency reSponse than the loudspeaker used in
the present study. These factors apparently played a more -
prominent role as the difficulty of the task was increased,
since greater decreases in soundfield scores were seen with
increasing levels of time-compression.

The trend toward speech reception thresholds that were
poorer when measured in the aided rather than unaided condition
_ was eXpected. The 2 to 4 dB mean decreases were attributed
to the undesirable effects of aided listening cited previously,.
such as, the amplification of ambient noise, the addition of
distortion by the hearing aid system, and/or the more restricted

48
frequency response of the hearing aid which acts as a filter
for Speech.. The 12.4 dB decrease in aided SRT's found for
normal hearing subjects by Tillman, et al. (1970) is much
larger than the decrease found in this study. Factors cited
previously as possible reasons for the greater decreases in
aided discrimination scores found by Tillman, et al., such

as their use of a 450 azimuth, the extra transducers required
by their eXperimental design, and the possible use of hearing
aids with inferior electroacoustic characteristics, may again
be the basis of the discrepancy between the results,obtained
in that study and those obtained in the present study.

The absence of measurable physical differences among
the CXperimental aids was not eXpeeted since it is commonly
assumed that stock hearing aids are electroacoustically differ—
ent from one another, frequently do not meet their manufacturer
Specifications, and have characteristics that do not remain
stable over time. None of these assumptions were true for
the aids used in this study. These particular aids met their
manufacturer specifications within reasonable limits and their
characteristics remained virtually unczanged ever a period
of twelve weeks. It was also unempected that the differences
among the aids would be so small.

Although all differences among aids were minimal, it was
found.that the two aids with superior electroacoustic qualities,
the Oticon E 11 V and the Telex 334, produced the poorest
scores at 0% time-compression but the best scores at 60% time-
compression. Superior electroacoustic qualities were defined
as the least amount of harmonic distortion, the least amount
of intermodulation distortion, the broadest frequency response,
the smallest IRI, the best peak to peak ratio, and the least
internal noise. The two aids with the poorest electroacoustic
_qualities, the Siemens 24 E SL and the Dahlberg HT 1233,
retained their rank order as the level of time—compression
was increased. In other words, the rank of these aids neither
rose nor fell with an increase in time-compression, but remained

49
in the middle. The aids whose electroacoustic qualities were
judged to be between the most superior and the most inferior,
the Qualitone TSP and the Fidelity F-59, produced the best
scores at 0% time-compression, but the poorest scores at
60% time-compression. This means that the monosyllabic
lists presented under normal conditions, or at 0% time—
compression, did not produce scores reflective of the physi-
cal properties of the aids, but that the monosyllabic lists
presented under more difficult listening conditions, or at
60% time-compression, were reflective of those preperties.
This finding, however, is based upon minimal physical differences.

Clinical Implications

Time-compressed monosyllables may be a promising tool for
hearing aid evaluations. They may provide an alternative to
the use of undistorted monosyllables or monosyllables pre-
sented against noise. As a new hearing aid evaluation tool,
the time-compressed monosyllabic word test met at least
three of the four suggested requirements for hearing aid eval—
uation improvements. First, it was found that compressed
monosyllables did indeed constitute a more difficult listening
task in that scores decreased with an increase in time—compression.
Second, it was found that time—compression improved the
ability of monosyllables to reflect the electroacoustic
quality of aids in that the aids with superior physical char—
acteristics produced the best scores at 60% time‘compression,
but the poorest scores at 0% time—compression. Therefore,
an aid that might be eliminated from selection on the basis
of conventional discrimination test results could actually
provide the best amplification for an individual in more _

_ difficult listening situations. Conversely, the aid selected
for the individual on the basis of conventional discrimination
test results might actually perform the most poorly for him

in more realistic (ie, difficult) listening situations. Again,

50
this finding was based on minimal physical differences among
aids.' Thirdly, the task was found to be clinically eXpedient
and efficient. The use of timeecompression did not permit
a wide spread of scores for the six hearing aids, however.

The Spread of scores at 60% time-compression was only 2.6%
greater than the spread of scores at 0%. This is a differ-
ence of only one to two words. The design of this study did
not permit the use of subjective evaluations on the part of
the listener since each subject were only one aid. Hence, it
is not known whether time-compression improved the ability

of monesyllables to reflect subjective preference. JTherefore,
although time—compressed monosyllables do not fulfill every
requirement suggested for new hearing aid evaluation test
stimuli, they do constitute a potentially valuable tool and
can be added to the limited battery of hearing aid evaluation
techniques.

Time-compressed Speech might be particularly useful in
the determination of hearing aid candidacy and the selection
of amplification for presbycusic clients or hearing impaired
clients with concurrent central nervous system disorders.

Since the perception of time—compressed Speech is related to
central auditory processing (Becca and Calearo, 1964; deQuiros,
1964), it might provide the audielogist with additional insight
into the suitability of amplification for an individual with
a-eentral auditory lesion.

Implications for Future Research

 

The results of this study failed to show a wide Spread
of scores for hearing aids as a function of increased time—
cempressien. This could be due to the fact that the eXperi—
mental aids were much the same electroacoustieally, the possié
'bility that the time-compression levels used were tee small,
or the fact that only normal hearing subjects were employed.
It is recommended, therefore, that the usefulness of time—

51
compressed monosyllables be re-evaluated using hearing aids
with exaggerated electroacoustic differences. Only when
measurable differences exist can they be reflected in objective
scores. Further, Speech at a time-compression level of 70%
should be presented to normal listeners under aided conditions.
This is the time—compression level at which normal listeners ‘
show a marked reduction in intelligibility and it would be
interesting to examine aided performance at this level, as well.
Perhaps a wider range of hearing aid scores would be obtained.
The usefulness of the time—compressed monosyllabic test must
also be re—evaluated with hearing impaired subjects.) The
testing of these subjects would permit an examination of
individual interaction with hearing aids and may permit diff—
erential results among aids. Finally, studies designed to
assess the performance of individuals with nresbycusic hearing
losses and hearing impaired individuals with central nervous
system disorders might provide valuable information about the
ability of these listeners to benefit from amplification.

_ In the future, sentences should be more closely examined
as potential hearing aid evaluation stimuli. The results of
the present study could be construed to support the conclusions
of Jerger, Malmquist, and Speaks (1966), Jerger (1968), and
Jerger and Thelin (1968) who reported that monesyllablee were
not meaningful enough to reflect real differences among
hearing aids. ‘They felt that more complex stimuli such a:
sentences were more apprepriate for hearing aid evaluations..

A sentence test must be used, however, which would sufficiently
tax the aided listener and would not allow him to make use

of the abundant contextual clues inherent in sentences. TEe
use of time-compressed sentences in hearing aid evaluations

is an area apprepriate for future research.

CHAPTER V

S U MM [UR Y

The results of this study indicate that time-compressed
monosyllables constitute a more difficult listening task
which may be used in hearing aid evaluations. Intelligibility
scores were found to decrease with increasing levels of time—
compression. Time-compression did not produce differential
results among hearing aids, however. The spread of hearing
aid group scores was increased by less than 3% when the level
of time—compression was increased from 0% to 60%. This is
a difference of one to two stimulus words.

Electroacoustic differences among the six eXperimental
hearing aids were found to be minimal. The six stock aids
met their manufacturer specifications and their characteris—
tics remained stable over a period of twelve weeks. A change
in rank order was seen with increased levels of time—compression
for four of the six aids, and this change reflected the
electroacoustic quality of the aids. Although physical diff—
erences among aids were minimal, the aids with the superior
electroacoustic characteristics produced the best scores at
60% time—compression, but the poorest scores at 0% time-
compression. 'Superior electroacoustic characteristics were
defined as the least amount of harmonic distortion, the least
amount of intermodulation distortion, the broadest frequency
response, the smallest IRI, the best peak to peak ratio, and
the least internal noise. The aids that produced the best
scores at 0% time-compression also reversed order and produced
‘the poorest scores at 60% time—compression. Hence, time-
compression improved the ability of monosyllables to reflect
the physical quality of hearing aids.

52

53
Intelligibility scores obtained through hearing aids
and in the menaural soundfield condition used in this study
were poorer than those obtained under earphones by Beasley,
et al. (1972a) at 32 dB SL, under both 40% and 60% time—
compression. Speech reception thresholds were poorer by
means of 2 to 4 dB when obtained in the aided rather than

unaided condition.

we .
“l ENDICES

APPENDIX A

Mean air conduction and bone conduction thresholds, ranges,
and standard deviations for the right and left ears
of the 70 subjects.

m6 Cm.h
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APPENDIX B

Subject Answer Sheet

SITTJZWT AT 51".”??? TIBET

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APPENDIX C

Subject Release Form

SUBJF CT RELI'ASE FORT"!

I do hereby authorize Susan Dalebout to measure my
hearing sens itiVity and Speech discrimination ability, both
with and without a hearing aid.

Signature

 

Date

 

APPENDIX D

Three Lists of Form B of the Northwestern University-Auﬂitory
Test No. 6

IIREE LISTS OF FORM E OF THE NOREIHESTERN UNIVERSITY

List I

1. Aburn
2. lot
3. sub
4. home
5. dime
6 o Whi C h
7. keen
8. yes
9. boat
10. sure
11. .hurl
12. door
13. kite
14. sell
15. nag
16. take
17. fall
18. week
19. death
20. love
21. tough
22. gap -
23. moon
24. choice
' 25. king
26. size
'27. pool
28. vine
29. chalk
30. laud
31. goose
32. shout
33.. fat
34. puff
35. jar
36. reach
37. reg
38. mode
39. tip
40. page
41. aid
42. raise
43. bea
44. hash
45. limb
46. third
47. jail
48. knock
49. whin
50. met

NUMBER 6
List II
l.' live
2. voice
3. ton
4. learn
5. match
6. chair
7. deep
8. pike
9. room
10. read.
11. calm
12. book
13. dab
14. loaf
15. gee
l6 . shack
17. far
18. witch
19. rot
20. pick
2 . fail
22. said
3. we;
2.. ass
25. White
26. hush
27. dead
28. pad
29. mill
30. merge
31. juice
3?. ken
33. gin
34. nice
35. numb
36. Chief
37. gaze
38. young
39. keen
40. tool
41. soap
4?. hate
43 . turn
44. rain
45. shawl
46. bought
47. thought
48 bite
49. lore
50. south

AUDITORY TEST

List III

 

‘1. sheep
2. cause
3. rat
4. IV}
5 . mouse
6. talk
7. hire
8. search
9. luck
10. cab
11. rush
12. five
13. team
14. pearl
15. soup
16. half
17. 0119 t

18. reed
19. pole
20. phone

21. life
22. pain
23. base
2‘4. 11109
25. mess

26. qerm
27. thin
28. name
99. ditch

3-. tell
3-. cool
32. seize
:3. 606%“?
34. youth
35. hit
36. late
37. jug
38. wire
39. walk
40. date
41. Iﬂien
4?. ring
43. check
44. note»
45. sun
46. hem
47. void
48. shall
49. lid

50. good

APPENDIX E

Subject Instructions

SUBJECT INSTWUCTIONS‘

You are about-to hear three lists of words. Each word will he
proceeded by the carrier phrase, "you will say". For ex—
ample, you will hear "you will say dog". Your task is to
write the last word you hear on your answer sheet. In the
example, you would write the word "dog". Some of the worns
may sound aster than normal, so listen very carefully.

Feel free to guess if you need to. Are there any questions?

59

APPETTI‘IIX I"

Rew_3cores of the 70 Subjects et 0%,
604 Time-Comnression

Table 13. Raw scores of the 70 subjects at 0%, 40%, and 60%
i . timé—compresSion. Groups are numbered according

to the order of testing.

TIME-COMPRESSION

0% 40% 60%

GROUP NUMBER 1: FIDELITY F-59

Subject I
l « 98% 98% 90%
2 98% 72%. 72%
3 100% 80% 72%
4 100% 92% ' 68%
5 100% 88% 76%
6 96% 94% 88%
7 98% 98% 94%
8 98% 88% 76%
9 92% 86% 92%
10 100% 82% 88%

GROUP NUMBER 2: OTICON E 11 V

Subject _
l 98% 96% 92%
2 86% 88% 80%
3 80% 100% 78%
4 96% 92% 88%
5 100% 92% _ 90%
6 100% 90% 92%
7 98% 94% 84%
8 98% 94% 94%
9 94% 94% 90%
10 98% 92% 88%

GROUP NUMBER 3:. TELEX 334

Subject

1 98% 92% 90%-
2 96% 98% 84%
3 100% 94% 96%
4 98% 94% 80%

. 5 100% 94% 96%
6 98% 94% 82%.
7 94% . 90% 90%
8 80% 92% 72%
9 96% 90% 88%'

10

100% 92% 96%

6O

Table 13 (cont'd):

' 0%

GROUP NUMBER 4: QUALITONE TSP

Subject
98%
100%
100%
98%
96%

'98%
98%
100%
98%

OKOCDQQUlIbWNl-J

'...I

‘ GROUP NUMBER 5: DAHLBERG HT 1233

Subject

100%
98%
96%
92%
98%

100%
96%
98%

100%
98%

OKOQDQCNU'Iub-UJNH

H

GROUP NUMBER 6: SIEMENS 24

Subject
98%

100%
96%

100%
98%
98%
98%
94%
98%
98%

OkOCDQOWUIIwaH

‘..—l

GROUP NUMBER 7: UNAIDED

'Subject
1 100%
2 ' 94%
3 100%
4 98%

96%.

61

SL

TIME-COMPRESSION

40%

98%
96%
80%
96%
94%
86%
84%
90%
90%
96%

98%
90%
86%
94%
90%
86%
90%
86%

_94%
94%

88%
98%
94%
94%
98%
94%
100%
98%
96%
92%

96%
96%
94%
96%

60%

92%
84%
88%
82%
82%
92%
86%
84%
90%
84%

82%
84%
82%
88%
96%
88%
82%
74%
84%
92%

84%
86%
92%
82%
92%
88%
86%
84%
90%
86%

96%
84%
98%
90%

Table 13 (cont'd):

TIME-COMPRESSION

0% - 40% 60%
5 96% 86% 88%,
6 100% 86% 92%
7 100% 92% 90%'
8 98% 86% 100%
9 92% 90% 76%
10 98% 88% 82%

62

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4.

6.

11.

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TY LIBRARIES

3 1293 03070 8394

 

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