Neuropsychologia, 1977, Vol. 15, pp. 517 to. 527 Pergamon Press. Printed in England.

THE EFFECTS OF VISUAL OR AUDITORY CORTICAL LESIONS ON SPEClFIC CROSS-MODAL TRANSFER

IN THE RAT*

EDWARD H. YETERIAN

Department of Psychology, University of Connecticut, Storrs, Connecticut 06268, U.S.A.

(Received 2 October 1976)

Abstract-The effects of discrete visual and auditory cortical lesions on specific cross-modal transfer from vision to audition (V-A), and from audition to vision (A-V), were studied in rats, using a direct vs reversal transfer paradigm. Only sham-operated rats showed significant transfer, in both V-A and A-V. Neither visual nor auditory operates showed significant transfer in either direction. The results demonstrate the importance of visual and auditory cortex to specific transfer between the two modalities.

INTRODUCTION

THE SENSORY environments of animals seldom, if ever, consist of stimuli in only one moda- lity. The ability to associate or exchange information between modalities has been regarded as an underlying factor in the formation of concepts about stimuli in the absence of ver- balization [l], and, indeed, as a necessary precursor to the development of language [2]. While there exists a large body of evidence concerning learning using cues from a single modality, investigations focused on questions of intersensory interaction have been relatively few in number. Perhaps because of the aforementioned emphasis on the relation of inter- sensory interaction to language, the neural bases of such phenomena have been studied almost exclusively in primates, e.g. in monkeys [3], and in bushbabies [4]. Only one lesion study of specific cross-modal transfer (CMT) in a non-primate species has been reported [5].

YETERIAN et al. [5] conducted a partial replication of the procedure of OVER and MACKIN-

TOSH [6], with the introduction of a group of brain-operated subjects. Sham-operated rats and rats with lesions of posterior necortex first learned a visual discrimination involving high and low intensities of white light. Half of the animals in each operated group learned to make a response during the high intensity light, and the other half, during low intensity light. All subjects then received an auditory discrimination task involving a high and a low intensity of white noise. Within each operated group, there were direct transfer animals, which were rewarded for responding during the “same” intensity in both modalities (i.e. to both high, or both low, intensities), and reversal transfer animals, which learned to respond to the high intensity stimulus in one modality and the low intensity in the other. Under this paradigm, specific CMT is indicated by better performance in the transfer modality (here, audition) for direct than for reversal transfer subjects. Yeterian et a2. found significant specific CMT among sham-operated, but not brain-operated, animals, thus demonstrating the importance of posterior necortex for transfer from vision to audition.

*This study is based on a paper presented at the meeting of the Society for Neuroscience, New York, November 1975. Reprint requests should be addressed to Edward H. Yeterian, Harvard Neurological Unit, Beth Israel Hospital, 330 Brookline Ave., Boston, Massachusetts 02215, U.S.A.

517

518 EDWARD H. YETERIAN

In the Yeterian et al. study, the posterior neocortical lesions were designed to include all possible area1 extent of visually responsive neurons. While such lesions did ensure complete removal of visual cortex, a large percentage of auditory cortex was removed as well. Thus, the issue arises as to whether more discrete removals, involving visual or auditory cortex alone, would yield results similar to those of the larger lesions as reported above. One possibility is that both discrete removals would disrupt CMT. An alternative possibility is that the type of discrete lesion might be related specifically to the effect upon the visual to auditory (V-A) specific CMT, i.e. either the visual or the auditory lesion, but not both, would disrupt V-A transfer. Finally, it is conceivable that neither discrete lesion would have an effect on specific CMT from vision to audition, implying that some interaction of the two areas, as reflected in the larger posterior cortical removals, is responsible for the loss of specific CMT.

Additionally, all of the above possibilities regarding the cfTects of discrete visual and auditory removals in the V-A situation merit study in an audition to vision (A-V) transfer situation. By looking at specific CMT in both directions, the uni- or bi-directionality of lesion effects may be revealed.

The present study was designed to investigate the effects of discrete visual and auditory lesions on specific CMT in both the V-A and A-V situations. In order to have the most clear-cut transfer effects by which to determine the presence of lesion deficits, all animals in V-A received a high-intensity Sf in transfer, while those in A-V received a low-intensity transfer S+. In earlier reports [5, 61 it had been observed that direct vs reversal transfer differences were greater for hiV -hiA vs 1oV -hiA animals than for IoV +loA. vs hiV --f 1oA. Also, OVER and MACKINTOSH [6] found that direct vs reversal differences were greater for IoA-tloV vs hiA +loV animals than for hiA +hiV vs 1oA -hiV.

Subjects METHOD

Thirty-six male black-hooded rats (Long-Evans derived), obtained from the breeding colony of the University of Connecticut Department of Psychology, were used. Rats were housed in individual cages in a continuously lit room. Four squads of 9 each were run, with animals that ranged in age from 90 to 130 days at the beginning of training. The first two squads were made up of V-A animals, the second two, A-V animals.

Apparatus A 30 x 25 x 25 cm high chamber, placed in a sound-reducing enclosure and controlled by conventional

relay equipment, was used. A 9 cm lever mounted directly above the food cup served as the manipulandum. The only illumination in the chamber was provided by incandescent light bulbs mounted overhead, diffused through a white Plexiglas roof. The visual discriminative intensities were those used by YETERIAN et al. IS], a high intensity of 14 fc and a low intensity of 0.05 fc, measured 5 cm above the floor of the chamber. During-preliminary training and for the auditory training or transfer, the level of illumination was 0.6 fc. The auditory discriminative stimuli were a high intensity of 95 dB SPL and a low intensity of 66 dB SPL of white noise played through a loudspeaker in the enclosure, The noise was 82 dB during pretraining and visual training or transfer.

Surgery and histology Prior to pretraining, all animals received a surgical procedure: ablation of visual cortex, ablation of

auditory cortex, or a sham operation. Visual cortex was considered to include area 17 and the immediately contiguous portions of 18 and 18a, which receive direct projections from the dorsal lateral geniculate nucleus [7], as well as the remainder of 18 and the dorsomedial aspect of 18a, which receive projections from striate cortex [8]. Auditory cortex included the termination site of medial geniculate nucleus projections as defined by LASHLEY [9], a locus coextensive with areas 41 and 20 of KRIFG [lo] and including also some neocortex immediately rostra1 and caudal to these areas. In a general sense, the intended ablations OT this study were based on a “splitting” of the larger posterior neocortical removals of YETERIAN et al. [51 into a dorsal (visual) and a lateral (auditory) component.

THE EFFECTS OF VISUAL OR AUDITORY CORTICAL LESIONS ON SPECIFIC CROSS-MODAL TRANSFER IN THE RAT 519

Animals were administered 0.1 cm3 atropine sulfate (1 mg/cm3) preoperatively, and 0.1 cm’ Duracillin postoperatively. Pentobarbital sodium was used for surgical anesthesia, at a dosage level of 60 mg/kg. Lesions were produced by suction with the rat placed in a sterotaxic frame equipped with hollow ear bars. The sham-operated subjects were placed in the stereotaxic frame, and the scalp was cut and retracted as in the lesion operation, but no other surgical procedure was carried out.

Following the completion of training and transfer, brain-operated animals were administered a lethal dose of pentobarbital sodium, and were perfused with isotonic saline and 10% formalin. The brains were removed and lesion extents recorded on Lashley diagrams. The brains were embedded in celloidin and sectioned at 30 pm. Every fifth section through the dorsal lateral geniculate and medical geniculate nuclei was mounted, stained with cresyl violet, and examined microscopically for retrograde degeneration.

Preliminary lever-press training Beginning three days after surgery, the rats were reduced gradually to 80% of ad Iibitum body weight.

With the light and the sound at middle intensities, the rats were then trained to press the lever for 45 mg food pellets (Noyes) on a continuous reinforcement schedule, taking from 1 to 5 days to reach a criterion of 50 presses in a single session. Next, over a period of 3 to 7 days, various schedules of intermittent reinforcement were introduced. Just prior to the initiation of training in the first (acquisition) modality, all animals received a VI 24 set schedule for 64 min daily, with a criterion of 300 or more responses in a session.

Visual training ,followed by auditory transfer (V-A) Immediately following the last day of pretraining on the VI 24 set schedule, all animals in the V-A group

received training on a visual intensity discrimination. The experimental sessions were 64 min long, and each consisted of alternating periods of the positive (S+) and negative (S-) stimuli. Within each of eight 8 min blocks, there were two periods of 60 set, and one each of 30 and 90 set, for each stimulus. The sequences were balanced within each 8 min block, and the blocks were balanced across days. During periods of S+, lever-presses were rewarded on a VI 24 set schedule; during S-, no reinforcement could be gained. Within each operated subgroup (visual, auditory or sham), half of the animals received the high intensity (14 fc) as S+ and the low intensity (0.05 fc) as S-. For the other half, opposite stimulus-reinforcement contingencies were used. Training on the visual discrimination problem was continued until a given subject’s response rate during S+ was at least 6 times that during S-for a single session.

After reaching criterion performance in visual training, each animal received auditory transfer sessions, with the high intensity (95 dB) as S+ and the low intensity as S-. Thus, within each operated subgroup, half of the animals underwent direct transfer (St- high in both modalities,) and half underwent reversal transfer (S+ low in vision, but high in audition), in the transfer modality. The lengths and sequencing of St and S- periods within transfer sessions were like those described for visual acquisition.

Training was given 6 days/week, except that the first auditory transfer session always came on the day immediately following the last day of visual training. Animals were run on the auditory transfer discrimina- tion until they had attained a criterion S+/S- ratio of 6.0 or greater in a single session, or until they had heen run for a total of 5 sessions.

Auditory training followed by visual transfer (A-V) The procedure for the animals in this group was analogous to that for V-A animals. Rats in each operated

subgroup were trained first on an auditory discrimination problem to a criterion S+/S- ratio of 6.0 or greater. Half in each operated subgroup received the low intensity as S+, while the other half received the high intensity as Sf. After completing the auditory problem, each animal received the visual discrimination problem with the low intensity as S+, and the high intensity as S-. Thus, as in the V-A situation, each subgroup was composed of direct and reversal transfer subjects.

RESULTS

Histological Figures 1 and 2 show the largest and smallest extents of bilateral removal for animals with

visual and auditory cortical lesions, respectively. All except three of the 12 visual animals sustained total cell loss and atrophy of the dorsal lateral geniculate nucleus. Seven of the auditory animals showed degenerative changes throughout the medial geniculate nucleus, evidenced as varying degrees of neuronal loss, gliosis, and chromatolysis. None of the visual animals showed medial geniculate degeneration, nor did auditory animals show lateral geniculate degeneration.

No systematic relationships were found between lesion extent and number of days to criterion in the acquisition modality. Likewise, there was no systematic relationship between

520 EDWARD H. YETERIAN

extent of lesion and transfer modality performance of individual animals, in terms of mean proportion of responses to S+ in the first half of Day 1 of transfer.

FIG. 1. Largest (above) and smallest (below) bilateral extent of cortical removal for animals with visual lesions.

FIG. 2. Largest (above) and smallest (below) bilateral extent of cortical removal for animals with auditory lesions.

Acquisition performance Mean days to criterion data for the operated subgroups are presented for visual and

auditory acquisition in Table 1. Separate two-factor analyses of variance (Lesion x In- tensity of S+) for each modality yielded no significant main effects or interactions. Neither lesion subgroup on either V-A or A-V took longer to attain criterion than did sham-oper- ated animals. Within the subgroups, high or low S+ subjects were not significantly different in number of days to criterion.

THE EFFECTS OF VISUAL OR AUDITORY CORTICALLESIONS ON SPECIFIC CROSS-MODAL TRANSFER IN THE RAT 521

Table 1. Mean days to criterion for operated subgroups in acquisition

_. Visual lesion Auditory lesion Sham-operated

Acquisition Visual Auditory

High S+ LowS+ High S+ Low Sf

10.33 8.67 7,67 8.00 12.00 1190 8+KI 1033 13.33 14.00 6.33 10.00

Specific cross-modal transfer The mean proportions of responses to S+ on the first day of auditory (V-A) and visual

(A-V) transfer are shown in Figs. 3 and 4, respectively, for the three operated subgroups. In the sham subgroup, specific CMT was shown in that the direct transfer (DT) animals responded more to Sf than did the reversal transfer (RT) animals, in both transfer direc- tions. Among the visual operates, a similar difference was suggested only in V-A. Among auditory operates, there was little or no evidence for the superiority of DT over RT animals in either direction.

090 r 065-

=, 060-

,o 075-

; z 0.70-

: 065- L ;j 060-

2 ‘Z 055-

g 050- 2 a 045-

--‘Sham DT c--Sham RT +Visual DT b -Visual RT

-Auditory DT

D--Auditory RT

0.40);

-r 1 I I I I I I I 2 3 4 5 6 7 8

Blocks of 8 m:n

FIG. 3. Mean proportions of responses to S+ for direct and reversal transfer animals in each operated subgroup on Day 1 of auditory transfer (V-A).

Following OVER and MACKINTOSH [6] and YETERIAN et al. [5], analysis of variance was carried out on the first four 8 min intervals. Overall, specific CMT was demonstrated as a significantly higher proportion of responses to S+ by DT as opposed to RT animals (F= 13.34, df= l/24, P<O*OO5). A significant interaction between Operated Subgroup and DT vs RT indicated that specific CMT was greater for certain subgroups than others (F=4*38, df=2/24, Pt0.05). Separate analyses of variance for each lesion group on each direction of transfer confirmed that sham animals show significant specific CMT in both V-A (F=8*34, df=1/4, Pt0.05) and A-V (F=39*66, df=1/4, Pt0.005). No significant DT vs RT difference was found in either transfer direction for either the visual or the audi- tory subgroups; the DT vs RT difference shown by visual animals on V-A (Fig. 3) was not significant. Thus, while the sham operated subjects showed specific CMT in both directions, neither brain-operated subgroup evidenced this behavior.

522 EDWARD H. YETERIAN

090

t

- Sham DT c-- Sham RT

GJ 085 D- V~sualDT

&- Visual RT

FIG. 4. Mean proportions of responses to Si- for direct and reversal transfer animals in each operated subgroup on Day I of visual transfer (A-V).

The four-factor analysis of variance also yielded a significant Blocks main effect (F-4.08, df=3/72, P<O*Ol), indicative of an overall improvement in performance within the first 32 min of transfer testing. The separate analyses revealed significant improvement only for sham animals in V-A (F-4.81, dJ=:3/12, P<O.O25) and for visual animals in A-V (F-4,07, df=3/12, P (0.05).

Performance across five days of the transfer problem

On the auditory transfer (V-A) problem, three (of the six) sham animals and four visual animals reached criterion performance within five days; none of the auditory animals reached criterion in this time. All animals evidenced improvement over the five sessions, as reflected in increasing S+/S- ratios.

On the visual transfer (A-V) problem, two sham, five visual, and one auditory animal attained criterion within five days. Like the V-A animals, all of the A-V animals showed improved S+/S- ratios over the daily transfer sessions.

In neither V-A nor A-V was there any evidence of an advantage of DT over RT animals in reaching criterion within the five days of training in the transfer modality.

Non-specijc transfer eflects Whether or not rats in a given operated subgroup show specific CMT (as reflected in a

significant DT vs RT difference), it is possible that the discrimination performance of rats in one modality following experience in an alternative modality may differ from that of animals entering the same modality without any prior discrimination experience. Such a crossmodal phenomenon in monkeys has been described by WILSON [ 111. In the left half of Table 2 are given the mean S+/S- ratios for the first visual session of groups having similar visual discrimination experience. The values in the first column are those of V-A animals that had low Sf in acquisition (half of each operatd group); those in the next column are for subjects that had low S+ in visual transfer (all of the A-V rats). Analysis of variance of these data yielded a significant main effect showing transfer performance to be superior to acquisition in the same modality (F= 13.77, df=2/21, P<O*Ol). No other main effect, or

interaction, was significant. Similar values for the first day of auditory acquisition and transfer are presented in the

THE EFFECTSOFVISUALORAUDITORY CORTICAL LESIONS ON SPECIFIC CROSS-MODAL TRANSFER IN THE RAT 523

Table 2. Mean S+/S- ratios for operated subgroups on the first day of acquisition or transfer

Visual lesion Auditory lesion Sham-operated

Low Visual S+ High Auditory S+ Acquisition Transfer Acquisition Transfer

~. ~~~ _. 0.84 209 1.30 1.70 1.10 1.75 1.12 1.15 1.04 1.86 2.61 2.24

right half of Table 2. The third column represents the St/S- ratios of A-V subjects that had high S+ in auditory acquisition; the last column gives data for rats that had high S+ in auditory transfer. Analysis of variance yielded no evidence of an enhancement of auditory discrimination performance by previous visual experience. However, a difference in S+/S- ratios appears among the operated subgroups; in both acquisition and transfer sham ani- mals had the highest mean ratio and auditory animals the lowest. The overall difference was significant (F=8.43, &‘=2/21, PtO.O1); its implications are considered in the section below.

Possible confounding of a failure in speciJc CMT with poor within-modality performance Among A-V animals, the visual and auditory operates performed at a lower level than

did shams on Day 1 of auditory acquisition (see Table 2). However, as seen in the High Auditory S+ column of Table 1, overall acquisition performance (in terms of days to criterion) of all three subgroups was similar. Also, the initial discrimination performance in the transfer modality (vision), as evidenced in the mean S+/S- ratios in the Low Visual S+ Transfer column of Table 2, was not significantly different among the operated sub- groups. Therefore, for A-V animals, little support is provided for the possibility that the lack of specific transfer might be simply the result of poor discrimination performance in either modality alone.

Among V-A animals, this situation is less clear-cut. There are no significant within- modality differences in visual acquisition (see Table 1). However, data from the High Auditory S+ Transfer column of Table 2 suggest that the lack of specific CMT among the visual and auditory operates might reflect their lower (as compared to shams) Day 1 S+/S- ratios. That visual and auditory animals were able to perform a discrimination in the transfer modality was indicated by improved S+/S-- ratios across five days of that modality, as reported above. Such a result, however, cannot preclude the possibility that the failure of those animals to show crossmodal transfer in V-A mirrors an initial, transient decrement in discrimination performance in audition.

DISCUSSION

The data for the sham-operated subgroups in both V-A and A-V demonstrate that speci- fic CMT in the rat, as previously reported in the studies of OVER and MACKINTOSH [6] and YETERIAN et al. [S] is a reproducible phenomenon. The transfer data for the two brain- operated subgroups indicate that, overall, while neither the visual nor the auditory cortical area is critical for intensity discrimination learning in either acquisition modality, both are of equivalent functional importance in the exchange of information between vision and audition. Finally, the data for non-specific transfer effects point to a general facilitation of visual discrimination performance following experience on an auditory discrimination

524 EDWARD H. YETERIAN

(A-V animals), although no performance enhancement was seen following previous visual experience for the animals in V-A. Neither the visual nor the auditory ablation disrupted the non-specific facilitation for the A-V animals; therefore, no insight was gained into the neural substrate of this phenomenon.

That specific CMT effects were limited to the first half of Day 1 of the transfer modality was not unexpected. OVER and MACKINTOSH [6] tested all of their rats on only one session of transfer, and obtained crossmodal effects only in the first half of the session. By the end of the session, all subjects, DT and RT, were performing at about equal levels. YETERIAN rt al. [5] found this same effect to hold for rats in a V-A situation. Interestingly, the presence of crossmodal effects only in the first session of a transfer modality is a consistent (and un- explained) finding across different species: in monkeys [12, 131, in bushbabies [14], and in rabbits [15].

The present finding that visual or auditory cortical removals do not result in a within- modality intensity discrimination deficit in acquisition is consistent with the outcomes of some earlier studies. For example, LASHLEY [16] found that rats that received visual cortex lesions prior to trainir:g in a lightness-darkness discrimination showed no retardation in learning as compared to normal animals. Similar results regarding auditory discrimination have been reported by WILEY [17]. Rats with removals of Fortuyn’s area p learned a noise discrimination as rapidly as normals.

It is important in drawing conclusions about lesion effects on specific CMT that there be no difference among operated subgroups in within-modality learning. The general possi- bility exists that transfer elects are obtained only when the within-modality discrimination can be learned rapidly. For example, a special case of this might be involved if it were found that a lack of specific CMT was correlated with a retardation of learning in the first modality. If this occurred, it would become more difficult to separate the disruption of transfer from a more general disturbance of an animal’s behavior in the early trials of any situation which calls for discriminative responding. Indeed, such a problem was encountered in the YETERIAN et a/. study [5]. In the A-V phase of the present experiment, neither the visual nor the auditory operates showed a within-modality deficit in either acquisition or transfer. This was the case also for the brain-operated animals in V-A with respect to acquisition only. Such results strengthen the conclusion that removal of visual and auditory areas leads to a specific deficit in transfer ability. However, the confounded situation among visual and auditory operates in auditory transfer provides no clear-cut support for this conclusion.

The present findings suggest that both the visual and the auditory areas of rat neocortex have an equivalent functional capacity as “visual-auditory integrators”. One possible basis for such interaction is some degree of convergence of information from the two sensory systems in at least some of the cells of each “modality-specific” area. The neuroanatomical literature on rats has not dealt specifically with the issue of convergence of modality- specific pathways in neocortical areas. However, evidence for auditory input into visual cortex, and for visual input into auditory cortex, has been reported in a study of cortical potentials evoked by peripheral stimulation [lS]. If visual-auditory convergence occurs in both visual and auditory cortex, the possibility exists that each area contains an essential portion of a system concerned with “forming a supramodal principle involving the differen-

tiation of larger and smaller stimuli”, [6] p. 919. DIAMOND and HALL [19] and LENDE [20] have held that the various lines of evolution of mammalian neccortex proceeded from a common ancestor that was characterized by a great overlapping of visual and auditory areas on the posterior pole of the neocortex. It may be that the rat has evolved from this common

T"EEF~E~T~OFVISUALORAUDITORYCORTI~ALLESIONSONSPEC~FICCROSS-MODALTRA~SFERINTHERAT 525

ancestor to the point where it possesses anatomically definable modality-specific areas, within each of which there remains one part of a primordial bi-modal system (once charac- teristic of the entire posterior neocortex). If this were so, then it could be predicted that lesions of either the visual or the auditory neocortex would disrupt specific CMT by deleting an essential portion of a subsystem involved in the crossmodal exchange of information.

Alternatively, the presumed critical region of convergence might be in a separate area of neocortex, or in some subcortical structure [21]. The introduction of animals with lesions of areas other than those involved in vision and audition would be highly desirable in future

studies. The results of some lesion studies in species other than the rat point to the importance of

neocortical association areas, both modality-specific and intersensory, to crossmodal be- haviors: in monkeys [22-241, and in cats [25]. Cortical lesions ina prosimian, the bushbaby, have yielded no deficit in specific CMT [4]. Considering only those species for which some positive lesion effects have been obtained-rat, cat, and monkey-a shift within some phylo- genetic lines in the neural substrates of crossmodal phenomena, from “primary” to “associ- ation” cortex, may be hypothesized. It seems likely that the differential shift in substrates was a result of differential environmental pressures. The rat, in its natural habitat, has remained in an environment in which it is dependent primarily on olfactory information- one in which visual and auditory cues are relatively less critical to survival. While the posterior neocortex of the rat appears to have attained a level of differentiation beyond that of the aformentioned common ancestor, some functional characteristics of the prototypical non-differentiated cortex may remain. For cat and monkey, as compared to rat, acute vision and hearing play major roles in survival; in response to this, their neocortical areas have become differentiated such that primary areas are involved in modality-specific functions, while sensory convergence (and modality-specific) association areas subserve intersensory functions.

Whether or not future findings are consistent with the above schema of cortical function, the present study provides no support for previous hypotheses regarding the neural bases of crossmodal phenomena. WILSON [26] has suggested that crossmodal transfer of stimulus intensity information might be mediated by a neural system non-specific with respect to sensory modality, e.g. reticular formation. More recently, ETTLINGER~~O~OS~~ that “. . . non- primate mammals may possess a lower-order subcortical system . . . which mediates the cross-modal transfer of specific learning” [27], p. 59. While the results here do not preclude the possibility of the involvement of non-specific or subcortical systems in specific CMT in rats, they demonstrate clearly the importance of modality-specific neocortical areas to such

behavior.

Acknowledgements-This research was supported by NIMH Predoctoral Fellowship MH 58160-01. The author expresses his appreciation to Drs. W. A. WILSON, Jr., D. A. YUTZEY, and J. SMITH for their valuable guidance and encouragement.

1.

2.

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THE EFFECTS OF VISUAL OR AUDITORY CORTICAL LESIONS ON SPECIFIC CROSS-MODAL TRANSFER IN THE RAT 527

On a Studi chez des rats les effets de petites lesions

descortex visuel et auditif SW le transfert intermodal spkifique

de la vision B l'audition (V-A) et de l'audition 1 la vision (A-V)

en utilisant un paradigme de transfert direct puis de renversement

de ce transfert. On ne constatait de transfert significatif a la

fois V-A et A-V que chez les rats ayant subi une pseudo OpGration.

Aucun transfert significatif dans une direction ou dans l'autre

n'dtait constat chez les rats opdr&s sur le cortex visuel ou audi-

tif. Ces r&sultats demontrent l'importance du cortex visuel et au-

ditif dans le transfert spdcifique entre les deux modalitbs.

Deutschsprachige Zusammenfassung:

Bei Ratten wurden die Auswirkungen diskreter kortikaler

LBsionen im optischen und auditorischen Bereich auf den

spezifischen gekreuzt-modalen Transfer vom Sehen zum

Haren (V - A) und vom Wren zum Sehen (A - V) untersucht,

indem ein Transfer-Paradigma einmal direkt und einmal

umgekehrt verwandt wurde. lJur scheinoperierte Ratten

zeigten einen signifikanten Transfer in beiden Rich-

tungen (V - A und A - 'J). Wader die im optischen Bereich

noch die im auditorischen Bereich Operierten zeigten ei-

nen signifikanten Transfer in einer der beiden Richtun-

gen. Die Ergebnisse zeigen die Bedeutung des visuellen

und auditorischen Cortex fiir den spezifischen Transfer

zwischen den beiden Modalitsten.