ear dominance for nonsense-syllable recognition … dominance for nonsense-syllable recognition...

J Am Acad Audiol 4 : 319-330 (1993)

Ear Dominance for Nonsense-Syllable Recognition Ability in Sensorineural Hearing-Impaired Children : Monaural versus Binaural Amplification Hiroshi Hattori*

Abstract

The purpose of this investigation was to determine whether an auditory-deprivation/dominant-ear effect associated with nonalternating monaural amplification is present in children . Subjects were 35 children with bilateral symmetric, moderately severe to profound, sensorineural hearing impairment . Seventeen were fitted with nonalternating monaural amplification and 18 were fitted with binaural or alternating monaural amplification . Taped speech stimuli consisted of 20 nonsense syllables. The mean age at which subjects were fitted with amplification was 4.8 years for the monaural group and 4.9 years for the binaural group. The mean period between hearing-aid fitting and the initial test was 4.1 years for the monaural group vs . 3.4 years for the binaural group. The mean interval between the age at retest and the age at which the subject was fitted with amplification was 15.8 years for the monaural group and 13.9 years for the binaural group. Results revealed a significant difference in the mean interaural difference score (IDS) for nonsense-syllable recognition (NSR) at the initial test and at the retest between group A and group B. The results also revealed that the progression from initial test to retest in the IDS for NSR was 10.7 percent for the nonalternating monaurally fitted subjects as compared with -3.3 percent for the binaurally or alternating monaurally fitted subjects. Results are discussed in relation to the theories of auditory deprivation and ear dominance.

Key Words: Auditory deprivation, binaural amplification, ear dominance, hearing disorders, monaural amplification, nonsense-syllable recognition, speech recognition .

L

ong-term monaural but not binaural amplification of adults with bilateral symmetric sensorineural hearing im-

pairment can result in deterioration of suprathreshold speech-recognition ability in the unaided ear as compared with the aided ear. This phenomenon has been reported by several investigators in various countries (Silman et al, 1984; Gelfand et al, 1987; Dieroff and Meibner, 1989; Gatehouse, 1989x, b, 1992 ; Silverman, 1989; Stubblefield and Nye, 1989 ; Emmer,1990 ; Silverman and Silman, 1990 ; Hurley, 1991). This phenomenon has been called auditory dep-

*Department of Otolaryngology, School of Medi-cine, Kobe University, Kobe, Japan

Reprint requests : Hiroshi Hattori, 602 Kamigyo-Ku Itsutsuji-dori, Omiya Higashi-Iru, Kyoto, Japan

rivation (Silman et x1,1984; Gelfand et al, 1987 ; Stubblefield and Nye, 1989 ; Emmer, 1990 ; Silverman and Silman, 1990 ; Hurley, 1991), auditory inactivity (Dieroff and Meibner, 1989 ; Dieroff, 1990), and auditory acclimatization (Gatehouse, 1989a, b) . The term auditory depri-vation refers to restriction, either partially or completely, by monaural amplification of audi-tory speech input into the unaided as compared with the aided ear.

Silman et al (1984) and Gelfand et al (1987) reported that the suprathreshold speech-recog-nition scores of aided ears remained essentially unchanged over time whereas those of unaided ears decreased over time in monaurally fitted adults . In binaurally fitted adults, on the other hand, they found that the suprathreshold speech-recognition scores of both ears remained essen-tially unchanged over time . Consequently, Silman et al (1984) found that the interaural

Journal of the American Academy of Audiology/Volume 4, Number 5, September 1993

suprathreshold speech-recognition difference score (aided minus unaided score in the monaurally fitted group and right minus left score in the binaurally fitted group) was signifi-cantly larger in the monaurally than in the binaurally fitted group at the retest, although it was similar for the two groups at the initial test .

Hattori's (1978) observations of supra-threshold nonsense-syllable recognition scores in some children appear to suggest that audi-tory-deprivation/dominant-ear effects may be present in children as well as adults . These observations arose from longitudinal investiga-tion, which originated in 1965, of primary-school children with bilateral sensorineural hearing impairment of unknown origin who were placed in classes for the hearing impaired (Hattori, 1987, 1988). In the early years of that investiga-tion in Japan, persons with bilateral symmetric sensorineural hearing impairment were fitted either with monaural amplification, which was alternated between ears, or nonalternating monaural amplification rather than binaural amplification. Over the last 15 years, however, the use of binaural rather than monaural (whether alternating or nonalternating) ampli-fication in such cases has become increasingly common in Japan. In Hattori's (1978) report, which presented the results of some case stud-ies, a marked difference was observed in the suprathreshold nonsense-syllable recognition (NSR) score between the aided versus unaided ears of these children despite symmetric pure-tone thresholds .

This investigator also has observed anecdo-tally that some children who initially were fit-ted monaurally rejected binaural amplification later on . This suggests that binaural amplifica-tion cannot be tolerated after monaural ampli-fication causes the aided ear to become domi-nant and the unaided ear to become recessive in suprathreshold speech-recognition ability. Therefore, auditory-deprivation/dominant-ear effects appear to be robust during childhood, as it appears difficult to reverse these effects with binaural amplification.

In summary, the interaural suprathreshold speech-recognition difference score has been reported to be larger in monaurally than binaurally fitted adults (Silman et al, 1984). Also, our own preliminary data suggest the possibility of robust auditory-deprivation/dom-inant-ear effects in children fitted with nonalternating monaural amplification, but not in children fitted with binaural or alternating

monaural amplification. Therefore, the follow-ing was predicted: the auditory-deprivation/ dominant-ear phenomenon is also present in children and can be demonstrated using a suprathreshold NSR test . Therefore, the interaural difference score (IDS) for NSR should increase over time in children fitted with nonalternating monaural amplification, but not in children fitted with binaural amplification or alternating monaural amplification.

We hypothesized that the predicted increase in IDS for NSR in children fitted with nonalternating monaural amplification would reflect improvement in NSR score, which is greater in the aided than unaided ear. Simi-larly, the lack of increase in IDS for NSR in children fitted with binaural amplification or nonalternating monaural amplification would reflect symmetric improvement relating to au-ditory training, maturation, and growth in lin-guistic knowledge.

METHOD

Subjects

Subjects were 35 children with bilateral symmetric sensorineural hearing impairment . Subjects were selected such that the pure-tone audiograms were bilaterally symmetrical. With only a few exceptions, all had congenital hear-ing impairment. All of the subjects had moder-ately severe to profound sensorineural hearing impairment .

The subjects for this investigation, who were in classes for the hearing impaired in primary school, were referred from various centers and clinics to our center . They were referred as part of a long-term follow-up inves-tigation, which began in 1965, on juvenile bilat-eral sensorineural hearing impairment of un-known origin ; the results of this investigation were published by Hattori (1987, 1988).

Subjects were fitted monaurally or bin-aurally at 10 years of age or younger. Group A consisted of 17 children who were fitted with nonalternating monaural amplification. Group B consisted of 18 children who were fitted with binaural or alternating monaural amplifica-tion .

All subjects were fitted with amplification and received hearing-aid orientation with fol-low-up auditory training prior to their referral to our center . During the auditory-training pe-riod immediately following hearing-aid fitting, hearing testing was repeated using behavioral

320

Ear Dominance in Hearing-Impaired Children/Hattori

observation audiometry (BOA), conditioned ori-entation reflex audiometry (COR), or play audi-ometry in the soundfield.

In Japan, between 1957 and 1970, children with bilateral symmetric sensorineural hearing impairment were rarely fitted with binaural amplification. Instead, they were fitted with monaural nonalternating amplification or mon-aural alternating amplification in which ampli-fication was alternated between ears so that each ear received essentially equal amplified stimulation over time . Binaural amplification of children with bilateral symmetric sen-sorineural hearing impairment has become in-creasingly common in Japan during the last 15 years. Therefore, the approach to hearing-aid fitting (binaural, monaural alternating, or mon-aural nonalternating) of the subjects in this investigation reflected both the prevailing ap-proach to hearing-aid fitting at the time and individual clinician preference .

Speech Stimuli

Commercial taped recordings of speech materials, consisting of 6 numbers (2,3,4,5,6,7), and of suprathreshold speech-recognition ma-terials (list 67-S), which were standardized by the Japan Audiological Society, were employed. The suprathreshold speech-recognition test stimuli consisted of 20 nonsense syllables, 3 of which were vowels (e.g ., "a") and 17 of which were consonant-vowel signals (e.g., to, ki, si, etc. ) .

Procedure

Pure-tone, speech-recognition threshold (SRT), and suprathreshold NSR testing were repeated in our center upon subject referral . The SRT and NSR materials were presented through earphones. In suprathreshold NSR test-ing, which was performed following SRT test-ing, the responses were scored as correct if the subject correctly repeated the nonsense sylla-ble. The accuracy of written rather than spoken responses was judged whenever the subject demonstrated speech problems that could inter-fere with determination of the accuracy of spo-ken responses.

To obtain the maximum NSR score, suprathreshold NSR testing was performed first at 20- to 30-dB SL re : SRT, and second at within 5 or 10 dB of the first level, depending on the subject's loudness judgment and the score ob-

tained . The highest NSR score was adopted as the maximum NSR score.

In our center, the pure-tone and speech tests were performed by an experienced audiometrist in a sound-attenuating room three times a year prior to the subject's completing junior high school, one to two times a year afterwards during further educ4tion, and once every 1 to 5 years after they completed their schooling and began their careers.

The initial and retest maximum NSR scores are analyzed in this investigation. The initial NSR score is based on the earliest reliable and valid test and the retest NSR score is based on the most recent hearing test .

Calibration

The accuracy of the sound-pressure levels of the pure-tone and speech stimuli was rou-tinely calibrated using the Briiel & Kjaer Arti-ficial Ear (4152) connected to a Precision Sound Level Meter (2203, 2209) and Octave Filter (1613) . The SPL values for audiometric zero were referenced to ASA-1951 prior to 1982 and to ISO-1964 after 1982 . Therefore, the hearing threshold levels referenced to ASA-1951 were converted to hearing threshold levels referenced to ISO-1964 .

RESULTS

T able 1 summarizes the individual air-conduction audiograms for the aided ver-

sus the unaided ears of each subject who was fitted with nonalternating monaural amplifica-tion (group A). Table 2 illustrates the individual air-conduction audiograms for the left versus right ears of the subjects who were fitted with binaural or alternating monaural amplification (group B) .

The initial-test air-conduction thresholds shown in Tables 1 and 2 are those obtained at the earliest reliable and valid test . In each of these Tables, the subject number(s) associated with a given air-conduction audiogram is shown. Inspection ofTables 1 and 2 reveals very similar pure-tone results across both groups . The audiograms for all of the subjects except S4 and S7 in group B remained essentially unchanged throughout the follow-up period .

The results of t tests revealed a nonsignifi-cant difference (p > .05) in air-conduction thresh-old at the initial test at each frequency between the aided and unaided ears for group A and between the right and left ears for group B.

321


Table 1 Air-Conduction Audiogr Nonalternating Mo

am Results of Subjects Fitted with naural Amplification

Group A Frequency (kHz) Case Name Sex Age Aid Ear 25 5 1 2 4 DS HA Fitting

1 YN F 14 L r 70 80 80 75 70 20 1 .7 I 65 70 80 70 75 70

2 MS F 18 R r 50 75 75 80 65 80 2 I 65 70 75 75 65 25

3 NY M 6 L r 60 65 95 85 75 40 3* I 65 65 95 90 80 30 alternate 6-8

8 R r 55 65 75 90 80 70 I 75 75 80 85 80 40

11 R r 55 75 90 90 80 80 I 65 85 90 90 85 50

14 R r 60 75 100 95 80 70 I 60 80 90 90 80 50

4 YI F 11 R r 60 80 95 105 105 55 3 .5 I 80 80 90 105 105 15

13 R r 65 75 90 110 105 50 I 65 80 85 95 105 20

5 EM M 10 R r 40 70 95 95 90 40 4 I 50 75 90 100 95 30

20 R r 45 70 100 100 105 60 I 55 70 90 100 105 15

6 KH M 6 L r 65 70 70 75 70 75 4 I 65 65 65 70 65 75

17 L r 70 75 75 80 90 65 I 50 60 75 85 70 90

7 H H M 11 R r 45 65 95 1001 - 60 4 I 55 70 95 1001 - 40

15 R r 60 65 100 1001 - 70 I 65 75 95 1001 - 40

22 R r 55 65 95 110 1101 80 I 50 65 95 105 105 60

8 AY F 10 L r 25 60 95 1001 1001 45 4 I 20 60 100 1001 1001 55

21 L r 30 75 100 100 115 40 I 45 75 90 105 110 60

9 MM F 9 R r 60 70 90 1001 1001 35 4 I 60 70 90 1001 1001 35

13 R r 60 75 95 110 1101 50 I 60 65 90 110 1101 40

10 YK F 11 R r 85 85 85 85 75 60 5 I 80 90 80 80 75 50

20 R r 70 80 85 80 75 65 I 75 85 85 80 70 60

29 R r 80 85 85 85 80 70 I 85 85 85 85 75 60

11 IN M 9 L r 45 65 85 95 95 45 5 I 55 70 85 90 90 50

20 L r 45 65 80 85 85 70 I 45 65 80 90 80 75

32 L r 55 70 80 90 85 70 I 75 75 80 85 85 85

12 M H F 16 L r 65 70 95 110 115 20 6 I 55 75 95 110 110 55

20 L r 65 75 95 110 105 0 I 55 75 110 55

13 YS F 8 L r 75 75 85 85 70 55 6 I 65 75 90 85 80 55 alternate 3-4

9 L r 75 75 85 85 65 60 I 55 60 75 75 70 90

16 L r 65 80 85 75 65 65 I 55 65 80 75 60 100

14 IN M 12 R r 55 70 95 1001 1001 50 6 I 55 70 95 1001 1001 25

19 R r 65 75 100 110 - 50 I 65 65 100 110 - 20

322

Table 1 Air N -Conduction onalternating

E

Audiogr Monaur

ar Dominance in Hearing-Impaired

am Results of Subjects Fitted with al Amplification (cont'd)

Child ren/Hattori

Group A Frequency (kHz)

Case Name Sex Age Aid Ear 25 .5 1 2 4 DS HA Fitting

15 KN M 9 R r 50 50 70 70 65 70 6 I 50 55 70 70 70 70

14 R r 40 50 75 75 65 95 I 50 60 75 75 70 100

24 R r 60 65 70 80 65 95 I 65 70 70 65 55 95

32 R r 45 55 70 80 70 90 I 40 50 65 70 70 90

16 KY M 14 R r 40 60 95 85 1001 70 7 .5 I 35 65 85 1001 1001 70

17 R r 45 75 90 105 110 65 I 40 75 90 110 110 55

25 R r 60 75 95 110 120 80 I 50 70 90 105 120 70

17 HY F 10 L r 50 50 60 60 60 25 10 I 60 65 70 65 60 25

24 L r 60 65 70 80 65 95 I 65 70 70 65 55 95

32 L r 65 60 75 85 80 95 I 85 80 65 70 65 95

Aid = aided ear ; DS = discrimination score ; HA Fitting = age at first fitting (years) . F = female ; M = male ; R or r = right ; L or I = left. `Between 3 and 4 years of age, HA use was alternated between ears . 1' Between 6 and 8 years of age, HA use was alternated between ears .

Table 2 Air-Conduction Audiogram Results of Subjects Fitted with Binaural or Alternating Monaural Amplification

Group B Frequency (kHz) Case Name Sex Age Aid Ear 25 5 1 2 4 DS HA Fitting

1 SY M 7 bi r 70 75 95 90 85 85 2.5 I 70 80 80 80 85 80

14 bi r 70 75 90 95 90 70 I 75 75 90 90 85 65

17 bi r 70 75 90 90 85 60 I 75 75 90 90 80 80

2 MI F 7 R r 75 75 75 80 85 70 3 I 55 70 80 80 85 60

12 ma r 70 80 80 80 90 85 I 80 85 85 85 95 85

15 bi r 70 80 85 85 90 70 I 80 85 90 85 100 70

20 bi r 75 90 85 90 95 70 slight I 75 90 90 95 100 70 deterioration

3 NT F 11 ma r 60 70 70 75 70 95 4 4-17 ma I 55 65 80 80 65 80

20 bi r 70 75 75 75 75 90 18-20 bi I 70 75 75 75 75 100

4 FS F 7 bi r 60 55 65 85 1001 95 4 I 55 55 75 85 100 .1. 85 after 13

20 bi r 60 65 90 1101 110 .1. 65 deterioration I 55 70 85 95 1101 70

5 MM M 8 L r 40 50 65 75 65 85 4 4-6 ma I 50 60 70 85 80 80 R 10-12

15 bi r 25 50 70 75 75 90 I 25 55 65 75 65 90

20 bi r 30 60 70 75 75 100 I 25 60 65 75 75 100

27 bi r 30 45 70 75 70 95 1 35 50 60 70 65 95


Table 2 Air-Conduction Audiogram Results of Subjects Fitted with Binaural or Alternating Monaural Amplification (cont'd)

Group B Case Name Sex Age Aid Ear 25

Frequency (kHz) 5 1 2 4 kHz DS HA Fitting

6 OT M 6 ma r 70 80 90 95 90 85 4 I 65 70 80 85 85 75 4-5 .6 ma

12 R r 55 70 85 85 85 85 L 6.10-7 .5 1 50 60 85 85 80 80 L 8.10-10 .5

18 R r 60 65 90 85 95 90 I 60 65 85 85 85 90

7 MN M 6 .8 L r 40 50 80 75 75 90 4 .5 I 45 50 85 80 75 90

17 ma r 65 85 90 90 70 90 8-23 ma 1 65 80 90 85 70 90

23 ma r 85 90 100 100 90 80 progressive I 70 85 95 100 85 80 deterioration

8 SI M 5 ma r 60 60 70 80 65 90 4 .5 I 60 65 85 85 85 80

11 ma r 55 50 65 80 65 100 I 65 70 85 85 85 95

9 TT M 7 ma r 65 70 70 75 50 55 5 I 65 70 65 65 60 60

15 ma r 60 65 75 75 60 70 I 65 70 70 65 65 70

10 KF M 7 bi r 55 65 80 65 65 70 5 I 55 70 80 65 65 70

12 bi r 55 75 80 70 70 100 I 45 70 75 65 60 95

19 bi r 75 80 85 80 70 100 I 70 70 75 70 70 100

11 TY M 6.3 L r 65 70 85 80 80 75 5 1 55 70 85 75 70 85

10 ma r 55 75 90 85 65 85 I 55 75 90 90 75 90

12 SK F 7 ma r 65 75 80 75 60 60 5 .6 I 55 80 85 90 85 55

18 ma r 75 70 80 75 65 85 I 65 80 75 90 85 85

13 MK F 7 .1 ma r 65 55 65 70 75 80 5.6 " I 50 45 65 70 70 90

12 ma r 30 55 65 70 70 90 I 40 50 60 65 70 85

14 TO F 6.6 R r 50 60 75 85 80 85 5 .11 I 45 60 75 80 75 75

10 ma r 40 55 65 75 70 95 I 35 50 65 65 70 95

15 ma r 45 55 70 75 75 95 I 25 50 60 60 60 100

20 ma r 45 40 55 65 65 95 I 25 35 50 60 55 95

15 HO M 12 L r 50 60 70 90 1001 70 6 6-7 ma I 50 55 75 95 1001 65 L 8-12

20 R r 55 60 80 95 1001 85 R 13- 1 55 60 85 95 100 80

28 R r 60 70 85 100 105 75 I 55 60 80 90 100 70

16 UT F 6.3 ma r 55 65 75 65 55 95 6 .1 ma (1w) I 65 75 75 70 60 95

9 ma r 60 70 75 70 55 95 I 75 80 80 70 55 95

12 ma r 60 65 70 70 55 90 I 65 75 75 70 55 90

17 NM F 11 ma r 40 50 75 100 1001 70 6.3 7 ma (6-12m) I 40 60 85 100 1001 70 9 ma (1w)

19 ma r 50 65 95 1101 1101 80 I 35 60 85 110 1101 75

18 HM M 22 ma r 55 60 95 110 1151 75 8 I 45 55 105 110 1151 65

30 ma r 65 70 90 110 1101 80 I 65 65 90 110 1101 85

Aid = aided ear ; DS = discrimination score ; HA Fitting = age at first fitting (years) . F = female ; M = male ; bi = binaural ; ma = monaural alternating ; R or r = right ; L or I = left ; ma (1w) = alternate every 1

week; m = month .

324


The results of t testing also showed a non-significant difference in the pure-tone average (PTA) based on 500, 1000, and 2000 Hz between the 34 ears of group A (the data from both ears were collapsed) and the 36 ears of group B (the data from both ears were collapsed) (p > .05) .

Table 3 shows the maximum NSR scores for the aided versus unaided ear at the initial test and retest (most recent test) for each of the 17 subjects with nonalternating monaural ampli-fication (group A) . Also shown in Table 3 are the ages at which the initial and retest hearing tests were performed, the age at which amplification was fitted, and the interval between the latter and the former . The interval provides a meas-ure of the period of amplification.

Table 4 shows the maximum NSR scores for the right versus left ear at the initial test and retest for each of the 18 subjects with binaural amplification or alternating monaural amplifi-cation (group B) . Also shown in Table 4 are the ages at which the initial test and retest were performed, the age at which amplification was fitted, and the interval between the latter and the former .

The mean age at which subjects were fitted with amplification was 4.8 years (range = 1.7 -

Table 4 Maximum NSR Scores for the Right and Left ears at the Initial Test and Retest in

Subjects fitted with Binaural and Alternating Monaural Amplification

Table 3 Maximum NSR Scores for the Aided and Unaided Ears at the Initial Test and Retest

in Subjects fitted with Nonalternating Monaural Amplification

Group B Case

Maximum NSR Score (%)

Right Left

Age (Years)

HA Test Fitting

Interval (Years)

Test - HA Fitting

Maximum NSR Age Interval 1 80 85 7* 2 .5 4 .5 Score (%) (Years) (Years) 100 95 18* 15.5

Group A HA Test - HA 2 70 60 7 3 4 Case Aid Unaid Test Fitting Fitting 70 70 20* 17

3 . 95 80 11 4 7 1 70 20 14 1 .7 12 .3 90 100 20t 16 2 80 25 18 2 16 4 95 85 7* 4 3 3 40 30 6 3* 3 65 70 20*t 16

70 50 14 11 5 85 80 8 4 4 4 55 15 11 3 .5 7 .5 95 95 27 23

50 20 13 9 .5 6 85 75 6 4 2 5 40 30 10 4 6 90 90 18 14

60 15 2_0 16 7 90 90 6 .8 4 .5 2 .3 6 75 75 6 4 2 80 80 23 $ 18 .5

90 65 17 13 8 90 80 5* 4.5 0 .5 7 60 40 11 4 7 100 95 11* 6.5

80 60 22 18 9 55 60 7 5 2 8 55 45 10 4 6 70 70 15 10

60 40 21 17 10 70 70 7* 5 2 9 35 35 9 4 5 100 100 18* 13

50 40 13 9 11 75 85 6 .3 5 1 .3 10 60 50 11 5 6 85 90 10 5

70 60 29 24 12 60 55 7 5 .6 1 .4 11 50 45 9 5 4 85 85 18 12.4

85 70 32 27 13 80 90 7 .1 5 .6 1 .5 12 55 20 16 6 10 90 85 12 6 .4

55 0 20 14 14 85 75 6 .6 5 .11 0 .7 13 55 55 8 6 t 2 95 95 20 14 .1

100 65 16 10 15 70 65 12 6 6 14 50 25 12 6 6 75 70 28 22

50 20 19 13 16 95 95 6.3 6 .1 0 .2 15 40 40 6.8 6 0.8 90 90 12 5.11

95 95 25 19 17 70 70 11 6.5 4 .5 16 70 70 14 7 .5 6 .5 80 75 19 12 .5

80 70 25 17 .5 18 75 65 22 8 14 17 25 25 10 10 0 80 85 30 22

95 95 32 22

HA Fitting = age at first fitting . *Between .3 and 4 years of age, HA use was alternated between ears . t Between 6 and 8 years of age, HA use was alternated between ears .

HA Fitting = age at first fitting . *Binaural hearing-aid fitting ; all others are alternating

monaural fittings . t Binaural hearing-aid fitting between 18and20years

of age . t Deterioration of hearing threshold levels .

325


10 .1 years) for group A versus 4.9 years (range = 2.5 - 8 years) for group B. Thus, the mean age at which subjects were fitted with amplification was 15.8 years (range = 9 - 27 years) for group A is essentially similar for groups A and B. The mean interval between the age at the retest and the age the subject was fitted with amplification versus 13 .9 years (range = 5 - 23 years) for group B. Thus, the mean period of amplification was also essentially similar for groups A and B.

Table 5 shows the means and standard deviations for the maximum NSR scores at the initial test and retest for the aided and unaided ears of group A and for the right and left ears of group B. Note that the mean maximum NSR score appears to be greater in the aided than unaided ears of group A at both the initial test and retest ; the disparity in maximum NSR score between the aided and unaided ears of group A appears to be greater at the retest than initial test. The mean retest scores appear to be greater than the mean initial-test scores for the aided ears of group A. Statistical analysis re-vealed a significant difference in the mean maxi-mum NSR between the initial test and retest in the aided ears (t = -3.846, df = 14, p < .01) of group A. In the unaided ears, however, nonsig-nificant differences (p > .05) between the initial test and retest scores were obtained . Inspection of Table 5 reveals a trend towards a greater mean retest NSR score than mean initial-test NSR score in the unaided ears of group A.

Inspection of Table 5 also reveals that the mean maximum NSR scores for the right and left ears of group B are similar at both the initial test and retest . The mean retest scores appear to be greater than the mean initial-test scores for both the right and left ears of group B.

Table 5 Means and Standard Deviations of the Maximum NSR Scores for Each Ear at the Initial

Test and Retest for Groups A and B

Table 6 shows the means, standard devia-tions, and ranges for the IDS at the initial test and retest for groups A and B . The results of statistical analysis revealed a significant differ-ence in the mean IDS for NSR at the initial test between group A and group B (t = 2.091, df = 31, p < .05) . That is, the IDS for NSR at the initial test is significantly larger for group A than group B (see Table 6) .

Inspection of Table 5 reveals that this find-ing appears to result from the following: (1) mean maximum NSR scores at the initial test that are greater for the aided than unaided ears of group A, and (2) mean maximum NSR scores at the initial test that are essentially similar for the right and left ears of group B.

The results of statistical analysis on the mean IDSs of groups A and B also revealed a significant difference in the mean IDS for NSR at the retest between group A and group B (t = 5.686, df = 33, p < .0001) . That is, the mean IDS for NSR at the retest for group A is significantly larger than that for group B (see Table 6), although the mean age at hearing-aid fitting and mean period of amplification are similar for the two groups . Inspection of Table 5 reveals that the larger mean retest IDS for group A than group B appears to result from the following: (1) a mean maximum NSR score at the retest that is greater for the aided than unaided ears of group A, and (2) a mean maximum NSR score at the retest that is similar for the right and left ears of group B. These findings support the results of our report on individual cases of children fitted with monaural amplification (Hattori, 1978) .

The difference in IDS for NSR provides a measure of the change or progression in IDS from the initial test to retest . Table 7 shows the IDS (aided minus unaided ear for group A and right minus left ear for group B) for NSR at the initial test and retest, and the difference in IDS

Group Parameter NSR

Initial Test (%)

Retest Table 6 Means, Standard Deviations, and Ranges of the Interaural Difference Scores at the Initial Test and Retest in Groups A and B A

Aided M 52.7 72.3 Interaural Difference Scores (%) SD 14 .1 17 .5 Group Parameter Initial Test Retest

Unaided M 42.7 49 .3 SD 18.6 27 .8 A M 10 .7 26 .5

SD 13 .1 18.0 B Range 0-40 0-55

Right M 79.4 83 .3 SD 12 .0 11 .7 B M 3.3 -1 .7

Left M 76.1 85.0 SD 7.8 5 .9 SD 10 .6 10 .1 Range -10-15 -10-5

326


Table 7 Initial Test, Retest, and the Change between Them in Interaural Difference

Scores in Groups A and B

Subject

Group

Group

Init IDS

Ret IDS

Ret IDS - Init IDS

A 1 50 2 - 55 - 3 10 20 10 4 40 30 -10 5 10 45 35 6 0 25 25 7 20 20 0 8 10 20 10 9 0 10 10

10 10 10 0 11 5 15 10 12 35 55 20 13 0 35 35 14 25 30 5 15 0 0 0 16 0 10 10 17 0 0 0

B 1 5 -20 -25 2 10 0 -10 3 15 -10 -25 4 10 -5 -15 5 5 0 -5 6 10 0 -10 7 0 0 0 8 10 5 -5 9 -5 0 5 10 0 0 0

11 -10 -5 5 12 5 0 -5 13 -10 5 15 14 10 0 -10 15 5 5 0

16 0 0 0 17 0 5 5 18 10 -5 -15

Init = initial ; Ret = retest .

for NSR between the initial test and retest for

each subject in groups A and B . If only a single test was obtained for a subject, then the IDS was

reported as a retest IDS so no difference be-

tween initial test and retest in the IDS for NSR could be calculated . (When only a single test was administered, it was administered long after

the hearing-aid fitting so it was considered as a retest rather than initial test .) Note in Table 7 the absence of the initial-test IDS for NSR and the absence, therefore, of the difference (pro-gression) in IDS for NSR between the initial test and retest for S1 and S2 in group A.

The mean difference in IDS for NSR be-tween the initial test and retest is 10.7 percent (SD = 13.1%, range = -10-35%) for group A versus-5 .3% (SD =10.5%, range= -25-15%) for

group B. The results of statistical analysis re-veals a significant difference between group A and group B in the progression in IDS for NSR between the initial test and retest. That is, the mean difference in IDS for NSR from the initial test to retest is significantly larger for group A than for group B (t = 3.91, df = 31, p < .01) . Inspection of Tables 5 and 6 reveals that the 10.7 percent increase in IDS for NSR between the initial test and retest in group A results from a significant improvement in maximum NSR of 19.3 percent (SD =19.5 %) for the aided ears and a nonsignificant improvement in maximum NSR of 7.3 percent (SD = 21.6%) for the unaided ears from initial test to retest. Inspection of Tables 5 and 6 also reveals that the lack of change (i .e ., the -5.3% change) in IDS for NSR between the initial test and retest in group B results from a mean improvement of 3.9 percent (SD = 15 .0%) for the right ears and 8 .9 percent (SD = 12.0%) for the left ears from initial test to retest in group B .

DISCUSSION

A significant difference in the mean IDS for NSR' between group A and group B was

obtained at the initial test and retest . The mean IDS for NSR increased from 10.7 percent to 26.5 percent from the initial test to retest for group A and remained essentially stable from initial test to retest at near-zero values (i .e ., decreased from 3.3% to -1.7%) for group B. The progres-sion from initial test to retest in IDS for NSR was 15 .8 percent for group Aversus -5.0 percent for group B and was significantly larger for the former than latter group.

As mentioned earlier, the progression in the IDS for NSR for group A reflected a 19.3 percent increase in the maximum NSR score from initial test to retest for the aided ears, which was larger than that (7.3%) for the un-aided ears . Also, the lack of progression in IDS for NSR for group B reflects an improvement of 3.9 percent and 8.9 percent for the right and left ears, respectively, from initial test to retest .

It can be concluded that NSR ability im-proves bilaterally in the children with nonalternating monaural amplification al-though the improvement was markedly larger in the aided than unaided ears; the disparity between the aided and unaided ear increases over time . In the children with binaural or alternating monaural amplification, the im-provement is essentially symmetric and ap-proximates the improvement in the unaided

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ears of the children fitted with nonalternating monaural amplification. The improvement in the aided ears of group A and in the aided right and left ears of group B probably reflects the effects of auditory stimulation from amplifica-tion and auditory training and maturation. The improvement in the unaided ears of group A probably reflects maturation, but not the effects of auditory stimulation from amplification.

These findings suggest that nonalternating monaural amplification of children may be asso-ciated with an inhibition of the improvement in NSR throughout the childhood years in the unaided but not aided ear.

It is likely that the larger increase in the mean NSR score in the aided ears of the children fitted with nonalternating monaural amplifica-tion than the right or left ears of the children fitted with binaural or nonalternating monau-ral amplification is related to the following: at the initial test, the mean maximum NSR scores for the right and left ears of group B were substantially greater than that for the aided ears of group A. Severe-to-profound sensor-ineural hearing impairment probably imposes a limitation on the maximum NSR score that can be obtained . Therefore, ceiling effects in the improvement in maximum NSR were probably reached in group B but not in group A as the former had higher initial-test NSR scores than the latter .

An alternative hypothesis for the larger improvement in NSR score in the aided ears of group A than group B is as follows: it is assumed that the onset of any change in maximum NSR score associated with auditory stimulation from amplification and auditory training for groups A and B occurred at the time of the hearing-aid fitting. Therefore, the maximum NSR score at the initial test may reflect some improvement in NSR score from auditory stimulation in the aided ears of group A and both aided ears of group B. It can be hypothesized that binaural or alternating monaural amplification provides greater auditory input or stimulation to both auditory' nervous system pathways than nonalternating monaural amplification. If it is assumed that groups A and B had similar suprathreshold speech-recognition ability at the time of hearing-aid fitting, auditory stimula-tion, therefore, would be greater in group B than A so the maximum NSR score at the initial test would be greater in the former than latter group. If the auditory-stimulation effects of bin-aural amplification are greatest during the criti-cal period, then it is possible that such effects

were manifested to a greater extent prior to the initial test (post hearing-aid fitting) and to a lesser extent post initial test . The mean period between hearing-aid fitting and the initial test was 4.1 years for group A versus 3 .4 years for group B, but the initial NSR score was greater for group B than group A. It must be assumed that the auditory-stimulation effects accruing from binaural amplification are large, compen-sating for the slightly reduced interval between the hearing-aid fitting and initial test in group B as compared with group A.

The results of this investigation and audi-tory-deprivation studies performed on adults suggest the following differences in the form of auditory deprivation between children and adults . Auditory-deprivation/dominant-ear ef-fects in children with congenital symmetric sensorineural hearing impairment probably begin at birth or prenatally . These effects are imposed by such factors as the magnitude of the hearing impairment, etiology of hearing im-pairment, and so on . These effects probably would be symmetric until the time of nonal-ternating monaural hearing-aid fitting. After nonalternating monaural hearing-aid fitting, speech-recognition ability in the aided ear con-tinuously increases until a maximum limit, which is different for each child, is reached; the limit depending on such factors as the age at first hearing-aid fitting, magnitude and con-figuration of hearing impairment, efficiency of auditory training, linguistic knowledge, matu-ration, and others . In the unaided ear, however, the improvement in speech-recognition ability is continuously inhibited and results primarily from maturation .

These findings support the prediction that the auditory-deprivation/dominant-ear phenom-enon is present in children who are fitted with nonalternating monaural amplification. These findings also support the prediction that the auditory-deprivation/dominant-ear phenom-enon is absent in children who are fitted with binaural or alternating monaural amplifica-tion . Thus, auditory-deprivation/dominant-ear effects appear to be present in children as well as adults .

Auditory-deprivation effects in adults with adult-onset progressive sensorineural hearing impairment (e.g ., presbycusis) probably are evi-denced in speech-recognition ability when the hearing impairment reaches a certain magni-tude . It is likely that these effects are gradual and symmetric. After monaural hearing-aid fit-ting, it appears that the effects of auditory

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deprivation may be halted in the aided ear resulting in maintenance (or possibly improve-ment if there is any reversal of these effects) of the speech-recognition ability in that ear. The effects of auditory deprivation continue in the unaided ear resulting in a deterioration of speech-recognition ability in that ear. The main-tenance (or possibly improvement) of speech-recognition ability in the aided ear together with a deterioration in speech-recognition abil-ity in the unaided ear results in a gradually increasing disparity in speech-recognition score between the aided and unaided ears . Thus, in adults, there is a decrement in speech-recogni-tion ability in the unaided ear post monaural fitting as compared with retarded growth in speech-recognition ability, which essentially reflects maturation, in the unaided ears of chil-dren post monaural fitting. Since the matura-tion factor is not applicable to adults, a decre-ment rather than a limited improvement is seen in the speech-recognition ability of adults .

Because of the small sample sizes, it was not possible to investigate whether there is a critical period for auditory-deprivation/domi-nant-ear effects. That is, the question that must be raised is whether the auditory-deprivation/ dominant-ear phenomenon is more pronounced in children fitted with nonalternating monau-ral amplification during the critical period be-fore 5 years of age than in those fitted after the critical period . By the way, in animals, the early auditory deprivation effects have been studied anatomically (Powell and Erulkan, 1962), electrophysiologically (Batkin et al, 1970), and behaviorally (Wolf, 1943 ; Gauron and Becker, 1959; Tees, 1967 ; Gottleib, 1971). These results indicate the plasticity in the immature brain and the presence of a critical period for the processing of auditory stimuli. If the results of future research validate this hypothesis, then it would appear that auditory-deprivation/domi-nant-ear effects are present throughout the lifespan and the magnitude of such effects are greatest during the critical period, less during childhood after the critical period, and least in adulthood. Longitudinal studies are needed to investigate the nature and magnitude of audi-tory-deprivation effects throughout childhood as well as adulthood.

In the children with alternating monaural amplification, the periodic switching of amplifi-cation from one ear to the other may result in the following situation: first, there may be im-provement in the NSR ability in the aided ear with inhibition of improvement in the NSR


ability in the unaided ear. Second, when ampli-fication is switched, there is inhibition of im-provement in NSR ability in the formerly aided ear with greater improvement in the formerly unaided ear. Large-sample research is needed to investigate whether the development of NSR scores in hinaurally fitted children differ from those in children fitted with alternating monau-ral amplification. In our population, however, amplification was alternated weekly in the chil-dren fitted with alternating monaural amplifi-cation. Research using large samples also is needed to validate the findings ofthis investiga-tion .

The findings reported here suggest that alternating monaural amplification may pre-vent the occurrence of auditory-deprivation or dominant-ear effects in children. Nevertheless, binaural amplification should be preferred over alternating monaural amplification in children in light of the other known advantages associ-ated with binaural amplification even if future studies should reveal that alternating monau-ral amplification prevents the occurrence of auditory-deprivation effects as well as binaural amplification.

Acknowledgment . This investigator gratefully ac-knowledges all of those persons who participated in this long-term study, particularly Mr . Iwai, who performed the hearing tests. This investigator also expresses his appreciation to an anonymous reviewer who provided very constructive comments and suggestions.

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ear dominance for nonsense-syllable recognition … dominance for nonsense-syllable recognition...

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