Lateralization of linguistic and melodic processing with age

Neuropsychologia. Vol. 18. pp. 79 to 83. Q Pergamon Press Ltd. 1980. Printed in Great

OOZS-3932/80/0201-0079/502.00/0 Britain.

NOTE LATERALTZATiON

OF LINGUISTIC

AND MELODIC PROCESSING

WITH AGE

JOAN C. B~ROD and HAROLD G~~DGLASS

Aphasia Research Center, Department of Neurology, Boston University School of Medicine, and V. A. Medical Center, Boston, Massachusetts 02130. U.S.A. (Received 26 June 1979) Abstract-This study examined the effect of aging on hemispheric specialization for verbal and melodic materials, using dichotic listening as an index. One hundred and two normal righthanded males between 24 and 79 yr were tested on two occasions, after rigorous audiological screening, with objectivecompensation for smalldifferences in auditory acuity between the ears. While overall scores declined with age, there was no interaction between age and the degree of right ear advantage for verbal material and left ear advantage for melodies. Neither was there any change with age in test-retest stability.

INTRODUCTION THEREhas been little investigation of the developmental course of cerebral dominance at older age levels. Although to date there has been no neuroanatomical evidence of differential degeneration of one hemisphere relative to the other, there is some behavioral data alluding to the possibility that the right hemisphere loses its ability more rapidly than the left [I, 21. Furthermore, there seems to be a decreasing incidence of lefthandedness with age [3-51. BROWN and JAFFE[6] have cited the evidence for increasing differentiation of language representation in the left hemisphere throughout the life span, and suggest that this also implies progressive left cerebral language lateralization with the testable consequence of “an increasing right-ear effect on dichotic listening with age” (p. 109). One study by CLARK and KNOWLES [7] did carry out this test and, in fact, reported a progressive right ear advantage with increasing age. We proposed to re-examine the issue of degree of dominance with age via the dichotic listening technique with additions in rigor, i.e. meticulous audiological screening and objective adjustment for ear discrepancies in hearing. We also broadened the scope of our investigation to include an examination of the dominance of the right hemisphere for melodies and to investigate possible changes in test-retest stability with age.

METHOD Subjects Subjects were 102 male paid volunteers, recruited from various community sources. Out of 342 individuals screened, 122 were accepted for audiological screening bawd on the following criteria: Right-handed by self-report; native English-speaking; neurologically normal; no history of alcohol abuse; no history of learning disabilities; no history of a serious bilateral hearing loss; and no awareness of a significant difference in hearing between the two ears. If a subject met the above criteria, he was scheduled for an audiological examination during which speech reception thresholds (SRT) and speech discrimination scores (SDS) were derived for each ear. Subjects were included in the study if they met all of the following requirements: (1) SDS for each ear was 80% or above; (2) The difference in SDS between the two ears was not greater than 16%; (3) SRT’s for both ears were 44 dB or below; and (4) The difference in SRT between the right and left ears was not greater than 14 dBs. Out of the 122 Ss receiving audiological screening, 16 (1304) did not meet the above criteria and were eliminated from the study. Four more failed to complete the study. Of the 102 subjects who participated finally, there were 20 or 21 in each of the following age groups: 24-39, 40-49, 50-59, 60-69, 70-79; their years of schooling were 15.7, 14.2, 14.6, 13.4, 12.5, respectively. A brief laterality survey of nine activities found 72 % of all subjects to be exclusively right-handed; seventyseven percent of all Ss had no familial history of left-handedness. ANOVAs examining main effects of both Hand Usage and Familial Left-Handedness and their interactions with age were not significant. 79

NOTE

80 Stimuli

The dichotic digit tape consisted of 24 pairs of digit triads randomly generated so that there were always 6 different digits in each trial and so that each triad appeared only once. The digits I-10 (excluding 7) were used. Digit pairs were presented simultaneously at the rate of one digit per 0.75 set; Intertrial Stimulus Intervals were 14 sec. Following the first presentation, headphones were reversed and the 24 pairs played through again yielded 48 trials. The nursery tune tape, developed by PECK [9], consisted of 10. pairs of five familiar children’s nursery jingles hummed by a male singer. Each stimulus was 3.0 set long (i20 msec), consisting of the opening phrase of the nursery tune. The tape was replayed after the 10 dichotic pairs, with headphones reversed, for a total of 20 trials. Equipment

A TEAC Tape Recorder was used to pass the tapes through a Grason Stadler Speech Audiometer Model 162. Ss listened to the tapes through earphones especially calibrated to this particular unit. Threshold deviations and ear discrepancies were compensated with the audiometer to provide equal signals at approximately 40 dB to each ear. For SRTs of less than 4 dB, no correction was made. If SRTs were 4 to 30 dB, the following formula was used for each ear (40 dB + SRT). For five Ss having SRTs slightly greater than 30 dB, the formula (30 dB + SRT) was used to avoid the risk of recruitment effects. Procedure Ss were administered the tapes in random order, i.e. digits first and tunes second or vice versa, on Day 1, and then in the reversed order on Day 2, at least one week later. Test trials on each tape were preceded by a series of practice familiarization trials. Immediately following presentation of each dichotic pair, Ss were tapped in random order on their right or left shoulder by E and asked to report first the materials heard in the ear on the side tapped and then to give the other one. Oral report was used for digits, while to indicate the tunes heard Ss pointed with their right hand to a drawing which corresponded to the theme of the tune. Scoring

Subjects were given credit for each digit or tune given from either ear in any order (Disregarding Order of Report-DOR), and in a second score, for each digit or tune crediting only those reported in the instructed ear order (Correct Order of Report-COR).

RESULTS A series of ANOVAs were carried out examining the effect of Age, Education, and Day of Testing on Ear and Order of Report, as well as on the R - L/R + L index. Since there was no effect of Day of Testing in any of the analyses for either digits or tunes, the results will be presented pooling the data for the Days 1 and 2. Ear advantage for digits und tunes

In all analyses, significant right ear advantages were obtained for tunes. The following ANOVA (a) For Digits, DOR (F = 40.70; df = I, 97; and COR (F = 45.59; df = 1.97; (b) For Tunes, DOR (F = 10.20; dJ= 1,97: and COR (F = 11.64; df= I, 97;

were obtained for digits, and significant left ear advantages results were obtained. P < 0.001) P < 0.001). P = 0.002) P = 0.001).

Effect of’ age

There was a signiticant (P < 0.001) main effect for age, i.e. decreasing scores with increasing age, in analyses for digits and tunes. In none of the analyses for digits, however, was there an interaction between Age and Ear advantage (see Figure I). However, for tunes, there were significant Age by Ear interactions obtained for Day 1 only in one of the analyses done, DOR (f= = 3.59; df = 4, 92; P = 0.01). inspection of ear difference scores revealed that this is not due to any consistent trend across ages but due to an exceptionally large effect in the 60-69 decade, and this significant effect disappeared in Day 2 and when Days 1 and 2 were pooled. R -

L/R

+ L Index

The R - L,‘R + L index was used to compare lateralization across ages because, although this index does not permit the evaluation of individual ear effects or interaction with ear, it does provide a correction

NOTE

81

1OOr 90

Tunes

DOR t;

60

‘0 v

70

e

DOR COR .\ *..___-----cot3

$60 !! 0" 50

-Ri ht Ear -- Le3 t Ear 40..

40

7

*

f

24:39

40-49 50-59 60-69

70-79

Age Groups

: 24-39 40-49 5060

60-69 W?Q

AgaG-

FIG. 1. Per cent of digits and tunes correct by ear for each age group, scored without regard to order of report (DOR) and with credit only for correct order of report (COR).

for differences in base performance either type of material.

[8]. Using the index, there was no main effect of age on either day for

Order of report

Material reported from the first ear was more accurate than second ear report (t0.005 for all analyses), but contrary to anticipations, in no case did we observe an increased ear advantage for second ear report as compared to first ear report. Test-retest

stability

Consistency in direction of ear advantage between the first and second days of testing was examined by decade and for the population as a whole. Overall, 27 % of the population showed a change in the direction of ear advantage for digits and 44% for tunes. x1 tests revealed no significant differences between age groups. Efict

ofeducuarion

In view of the fact that education varied as a function of age (F = 4.19; df = 4,97; P = 0.004), we considered the possibility that the absence of an Age x Ear effect might be due to a compensating and opposing effect of education. An analysis of covariance, correcting for the effect of education, again yielded no significant Age x Ear effect.

DISCUSSION The results of this study failed to confirm our major hypothesis that there is an increasing left hemisphere advantage with age for the processing of dichotic material. In spite of demographic and methodological comparability between this study and the one by CLARK and KNOWLES[7], we failed to replicate their finding that accuracy of recall for digits presented to the left ear declined with age more than for digits presented to the right ear nor our own expectation of an increasing left-ear advantage for melodies with age. We did find, on the other hand, an overall main effect for age for both linguistic and melodic materials showing a decrement in overall accuracy of report. Our findings are compatible with the results of WOODRUFF’S recent survey of the literature [9] which suggests that with age there is more overall error but no “age by [cerebral] hemisphere interaction”. Our data, consistent with her findings, therefore lend more support to ELIASand KINS~OURNE’S model [lo] which “attributes organically based age-related cognitive decline to uniform deterioration of cerebral cortical function” (p. 170) than to BROWN and JAFFE’Shypothesis [6] that left hemisphere specialization increases with age. A possible explanation for the discrepancy between the present findings and those of CLARKand KNOWLES [7] is the greater rigor of the audiological screening in our own study, i.e. objective screening and calibrated compensation for small differences in auditory acuity. Clark and Knowles, on the other hand, used selfreport and a subjective adjustment of loudness in the two earphones. First of all, with our audiom,etric screening, the majority of Ss eliminated were over 50, and within that older group, there were significantly more left-sided hearing deficits relative to right-sided ones (x2 = 7.18; df = 2; P < 0.05). An analysis of the entire group before audiometric screening suggests greater SRT impairment in the left ear with age

82

NOTE

(F = 1.82; df = 4, 114; P = 0.13). Moreover, subjective report cannot be taken as a valid index of ones hearing ability. There were Ss in our study who were unaware of a significant hearing loss in one or both ears or who attributed better hearing to the ear that was, in fact, inferior. Finally, subjective adjustments of hearing level may be confounded by a longstanding compensation for an ear-specific hearing loss, so that inputs of unequal intensity sound the same. Acknowledgemenrrt-This research was supported in part by the Medical Research Service of the Veterans Administration, by USPHS Grants NSO6209 and NSO7615, and by Postdoctoral Fellowships from SSRC and NIH (1 F32AG05007-01). We are grateful to Dr. Edward A. Peck for assistance in generating the tapes, to Dr. Mary Hyde and Errol Baker for assistance with data processing and analysis, and to Mr. Robert Sparks and Mrs. Barbara Barresi for audiological screening.

REFERENCES 1. BEN-YISHAY,Y., DILLER, L., MANDELBERG,J., GORWN, W. and GERSTMANN,L. J. Similarities and differences in Block Design performance between older normal and brain-injured persons: A task analysis. J. abnorm. sot. Psychol. 78, 17-25, 1971. 2. ALBERT, M. and KAPLAN, E. Organic implications of neuropsychological deficits in the elderly. In New Directions in Memory and Aging: Proceedings of the George Talland Memory Conference, L. W. POON, J. L. FOZARD, L. S. CERMAK,D. EHRENBERGand L. W. THOMPSON(Editors). L. Erlbaum, New * Jersey, 1979. 3. BINGLEY,T. Mental symptoms in temporal lobe epilepsy and temporal lobe gliomas with special reference to laterality of lesion and the relationship between handedness and brainedness. Acta Psychiat. Neurol. 33 (Suppl. 120), 1958. 4. SAND, P. L. and TAYLOR,N. Handedness: Evaluation of binominal distribution hypothesis in children and adults. Percept. Mot. Skills 36, 1343-1346, 1973. 5. PORAC. C. and COREN, S. Age trends in manifestation of lateral preference. Paper .presented at the Canadian Psychological As&iation, 1976. 6. BROWN.J. W. and JAFFE.J. Hypothesis on cerebral dominance. Neuroosvcholoaia 13. 107-l 10. 1975. 7. CLARK,- L. E. and KNOWLES,J. B. Age differences in dichotic listen& performance. J. Geiont. 28, 173-178, 1973. 8. KRASHEN,S. An unbiased procedure in comparison of degrees of lateralization of dichotically presented stimuli. In Language and the Left Hemisphere, S. KRASHEN(Editor), Working papers in phonetics, No. 24. U.C.L.A. Press, Los Angeles, 1972. 9. WOODRUFF,D. S. Brain activity and development. In Life-Span Development and Behavior, Vol. 1, P. B. BATES(Editor). Academic Press, New York, 1978. 10. ELIAS. M. F. and KINSBOURNE,M. Age and sex differences in the processing of verbal and nonverbal stimuli. J. Geront. 29, 162-171, 1974.

Cette etude examine les effets de l'age sur la spkialisation hemisphdrique

pour des materiels verbal et melodique en utilisant 1'Bcoute dichotique comme index. 102 hommes droitiers entre 24 et 79

ans Btaient testes a 2 occasions, apres examen audiologique rigoureux et compensation objective de petites differences d'acuite auditive des 2 oreilles. Tandis que les scores globaux diminuent il n'y a pas d'interaction

avec 1'8ge,

entre 1'Sge et le degr6 de l'avantage de

l'oreille droite pour le materiel verbal et l'avantage de l'oreille gauche pour les m6lodies. 11 n'y a pas non plus de modification avec l'age dans la stabilite test-retest.

83

NOTE

Zusammenfassung

In dieser

Untersuchung

Specialisierung

wurde der EinfluQ des Alterns

fur die Verarbeitung

mit Hilfe des dichotischen

H&ens

van verbalem

untersucht.

auf die hemispharische

und melodischem

102 gesunde mannliche

hSnder zwischen

24 und 79 Jahren wurden nach eingehender

Voruntersuchung

unter Ausgleich

zwischen

eventueller

den Ohren in zwei Situationen

mein mit dem Alter

abnahmen,

und Rechtsohreffekt

fUr verbales

Die Test-Retest-Stabilitit

geringer

getestet.

Material

Rechts-

audiologischer

Horschwellendifferenzen

WPhrend die Leistungen

fand sich keine Wechselwirkung oder Linksohreffekt

nahm mit dem Alter

Material

nicht ab.

allge-

zwischen Alter fur Melodien.