Neuropsychologia, Vol. 22. No. 2, pp. 235-240, Prmted ,n Great Br~tam 002x 3932184 $3.00 + 0 00 C’ I984 Pergamx, PTSS Ltd. 1984 zyxwvutsrqpo NOTE CHANGES IN CEREBRAL LATERALIZATION K. OBL.ER LORAINE Department IN AGING? of Neurology, Boston University 150 S. Huntington Avenue, Medical School, Boston VA Medical Boston, MA 02130, U.S.A. Center, STEVEN WOODWARI) Psychology Department, University of Southern Califorma, Los Angeles, CA, U.S.A. and MARTIN L. AI UI’RT Department of Neurology, Boston University 150 S. Huntington Avenue, (Accepted Medical School, Boston VA Medical Centre. Boston, MA 02130, U.S.A. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR 1 0cfohe.p 1983) Abstract-To determine whether there is increasing left hemispheric lateralization for language with age and whether the right hemisphere is selectively impaired with advanced age, we tested 96 nghthanded people aged 25~-80 yr on verbal and non-verbal matching tasks presented tachistoscopically. Task difficulty was equalized by adjusting exposure durations. Exposure duration, error laterality and response latency laterahty were analyzed. Typical field effects as well as age-related slowing and sex by task interactions were observed. However, no systematic age-related changes in lateralization were apparent. INTRODUCTION AKGUMENTShave been made for increasing left hemispheric lateralization for language across the life-span [3] and for selective impairment of the right hemisphere with advanced aging [I]. Dichotic studies of lateralization m aging have produced contradictory results [2,5]. We administered two tachistoscopic tasks to 96 subjects ranging from 25 to 80 yr old. One task requtred a linguistic judgment and the other, a judgment about human faces. We predicted that the task requiring linguistic analysis would demonstrate a right visual field effect (RVFE) while the task requiring a judgment about faces would demonstrate a left visual field effect (LVFE), at least for our young adult male subjects. The question we addressed was whether the direction or degree of visual lateralization would change zyxwvutsrqpo in older adults. M ATERIALS AND M ETHODS Subjects Subjects were right-handed males and females with better than 20/40 corrected visual acuity. For purposes of analyses they were divided into three age groups: young adults (aged 25 39 yr, U = 33), middle-aged adults (aged 50-64 yr, X= 56) and older adults (aged 65-79 yr, X= 70). Each age group consisted of 16 females and 16 males. Stimuli and proredurr For both the verbal and the non-verbal tasks subjects were required to make a same/different judgment on 40 test stimuli presented tachistoscopically in either the left or right visual field. For the linguistic task subjects compared two two-letter syllables written in upper and lower case presented one over the other (e.g. “d”A or &). For the nonverbal tasks subjects saw the upper and lower sections of photographs of informally posed models. In half the items the upper and lower half came from the same photograph. while in the other half they did not [see Fig. 1(a d)]. Two ‘mirror image’ pseudorandomizations of stimulus order, field and trial type were used for each task. Subjects were instructed to fixate on a central point upon hearing a warning stimulus, and then respond accurately and quickly after they judged if the stimuli matched or not. Subjects responded with one palm on a response paddle for same and the other palm on a response paddle for dilfirent ; when the right hand indicated a same response and 235 236 Nolr the left a ~/~//ertwr response. me called this the right-hand-same orientalron Task order. hand orientation. \w~tch orientation and randomization were counterbalanced H Ithin the six age x gender groups. The same procedure was employed for each task. Sub,jects Nere Introduced to each task by meam of 20 pl-actlce tr&, H hich began at 500 msec exposure duration. As subjects mastered the task [he exposure duration wa\ decreased to the point, well beneath the saccadic time preciously measured for their age group [4]. at which subjects performed around 75”,, correctly. Then the 40 stimulw items \bere presented. zyxwvutsrqponmlkjihgfedcbaZYXWVUT RESULT‘S Smce wror rates mere constlamed through exposure duration. subjects‘ exposure duratlonx served as an index of their- performance. .4 three-way analysis of covariance (age x sex x task) was performed on the exposure duration data, covat-ying for total errors on each task. Large main efl&ts for age (P=43.7. d/=2. P~O.001) and task (f‘= 135.4. [I/= I, 89. P<O.OOl ) we!-e observed. the former ~ellecting lengthened exposures for older subjecta (Table 1 ) and the latter. lengthened euposurcs for the facial task (Table 2) There uas no main effect for sex nor for an age K sex Interaction. A large age x task lnteractlon (P = lh.6. C/I- 1. X9. P.zOOOI I derived from a larger age-related Increase In exposure duration for the faces task A sex x task interaction (I; ~: 1.1). c/f: 1, 89. P~O.001) followed from the female suhiccts requiring shorter stimulus exposures than the men In the syllables task hut longer expohurcs than the men in the faces task. Table I. Expohure tlmc (and SO.) required io get X0”,, correct Imsec) Age \- = 70 yr Facial \‘erhal stirnull stimuli Table 9X.3 (30.0) 74.4 (31.0) 2. Exposure 147.7 (34.0) 100.9 (34.5) time (and SD.) required (msec) Men 141.9 (45.1) 107.9 (40.6) Speed:accuracy trade-offwaa assessed within 194.7 (33.8) I 13.4 (47.9) to get 80”,, correct U’omen ____.__ 151.7 (563) X4.6 (39 6 I the eight task x ticld x response type conditions. and error- rates and R(‘pLC ~~ were rebponsc latcncies were found to hc positively correlated m all conditions. Standard phi coefliclents RC+LC calculated for the two tasks and submitted to a four-way (age x sex x task x response type) ANOVA. Only the mam effects for task (F= 15.8, @= 1, 84. P-cO.001 I and hand orientation (F= 15.7, I//= I. 84, P<O.OOl) were sigmficant. Thesyllables task produced a net RVFadvantage (d,=O.O19)and thefaces task a net LVFadvantage (+- mm0.036). The age x sex x task interaction approached significance (P -0.081); however. no conaistent relation between age. sex and laterality was demonstrated. Separate six-wav ANOVAs (age x sex x task x visual field x trial type) were cal-rled out on the erf-or and response latency data (see I’ahles 3 and 4). Aging producing longer response latencies (P (2. X4)== 16.0. P~O.001 J; no main ba NA w GI NA er ER zyxwvutsrqponmlk FIG. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJ 1. 231 239 N07t Table 3. Mean No. of errors 20 right visual field 20 left visual held 5.x 4.4 4.6 4.x 40 facial stimuli 40 verbal stimuli Table 4. Mean response Visual field Facial stimuli Verbal stimuli RVF LVF RVF LVF out of 20 latencies Age .?=33 1067 1039 1166 1184 (and S.D.) (msec) yr (205) (188) (150) (147) Age group Age .?= 56 yr 1171 1163 1744 1389 (191) (234) (219) (273) Age \: = 70 yr 1293 1252 1448 1462 (232) (222) (242) (233) effects were observed for sex. The expected task x visual held interactions were observed m both error (F (1, 84)= 18.2, P<O.OOI)andlatency (F (1, 84)=7.6, P=O.OOX)data. Again, neither age nor sex aloneinteracted with laterality; however, in the error data, as in the phi analysis, the age x sex x task x visual field interaction approached significance (P=O.O79). The same interaction did not approach significance in the latency data. In the latency data a very nearly significant hand orientation x task x visual field interaction (P=O.O51) saw the right-hand-same orientation accentuating the RVFE for syllables and reducing the LVFE for faces. Similarly, the left-hand-same orientation accentuated the LVFE for faces and reduced the RVFE for syllables. This effect, in turn, interacted with age (F (2,84)= 3.72, P-cO.029) such that the affinities between hand orientations and hemispheric advantages were stronger with increased age. Recall that the exposure time measure was significantly greater for the faces task than for the syllable task. By contrast, the response latencies were significantly lower for the faces task than for the syllables task for all three age groups. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA CONCLUSION In sum, although older subjects required longer exposures and took longer to respond, there was no evidence of systematic change in direction or degree of lateralization related to age by any of the three analyses we employed~phi analyses, response latencies and exposure time to criterion. It is worth noting that if we had not performed the laterahty analyses on all three groups we might have been making a very different report. If we had tested only the 25 39-yr-olds and the 54- 64-yr-olds, for example, we would have reported shift towards left dominance for both tasks with increasmg age; if we had tested only the 50-64-yr-olds and the 65-80-yr-olds we would have reported shift towards right dominance for both tasks with increasing age: if we had tested only the 25.39-yr-olds and the 65- 80-yr-olds we would have reported no change for verbal laterality but a tendency tovvards greater right hemisphere responsibility with age for the faces task. Moreover, if we relied on comparison of the two tasks as our measure of laterality we would have suggested opposite results. since there is relatively less prolongation with age of response latency for the face stimuli than for the syllable stimuli. We did not directly analyze the differences between the two tasks for each age group, hownever. because one cannot be sure that these verbal and non-verbal tasks are equivalent in difficulty. Certainly the age x task interactions for exposure duration necessary to achieve criterion also indicate that face judgments become relatively more difficult with age than do syllable judgments and not in a linear manner. This may be due to greater stimulus complexity of pictures or greater practice with reading. In any case, we cannot conclude that subjects show a greater decrement on non-verbal tasks (probably more dependent on right hemisphere activity) with advancing age than on verbal tasks (probably more dependent on left hemisphere activity), although by the exposure time measure our data are consistent with that hypothesis. Even if that were the case, however, the relative contribution of the two hemispheres within each task remains the same across the adult life span, and thus measures of lateral dominance remain the same. A~knor~ledgernr,lr\ This study was supported by grants from the Veterans Admimstratlnn and the National Institutes of Health.We are grateful to MARJORIF NKHOI AS for assistance in testing subjects and data analysis. DI JOAN BOROI) contributed valuable statistical adwce. Anonymous reviewers led us to a suhslantially bettel presentation of our data. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA REFERENCES I zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ALRFRT, M. S. and KAYLA?, E. F. Organic Implications of neuropsychological delicits in the elderlg. In .Ycn Dirrc’/iorls iu ~hlrmor~ and ,4(qiny, I.. W. Poc)\r. J. I_. FOYARI). L. S. CPRII-ZK and D. EHRI:NIII.RG (Editors). Eribaum, Hillsdale, NJ. 1979. 2. BOROI). J. C. and GOOI~;I nss. H. Lateraliratlon of linguistic and rnelociic processing wth age. Neurop.~?c,holo(lia 18, 79-X.3, 19x0. 3. BROU.\, J. and Jktw, J. Hypothesis on cerebral dominance. Nawop,sychologiu 13, I07 I IO, 1975 4. CARTER,J.. OBLER. L.. WOOD~ARD. S. and ALREKT. M. The effect of increasing age on the latency for s:wxd~c eye movements. J. Gcwrlol. 3X, 19X3. 5. CLARK. L. and KNOWI.ES. J Age differences In dxhotic listening performance. .I. Grwrrrvl. 28, I73 17X. 1973.