HAPTIC TO VISUAL CROSS-MODAL ... - Semantic Scholar

A C T A NEUROBIOL.

EXP. 1981, 41: 113-118

Short communication

HAPTIC TO VISUAL CROSS-MODAL RECOGNITION OF OBJECTS IN THE VERVET MONKEY C. RODRfGUEZ ECHENIQUE and M. VALDES SOSA Departamento de Neurofisiologia, Centro ~ a c i o n a i de lnvestigaciones Cientfficas Apartado 6990, Havana, Cuba

Key-words: cross-modal recognition, sensory modality

vervet

monkeys, haptic modality,

visual

Abstract. Five juvenile vervet monkeys (Cercopithecus aethiops) were tested using the Cowey and Weiskrantz technique. The animals had access im the dark to distasteful biscuits of one shape and tasteful biscuits of another shape. Later they were shown a pair of biscuits, one of each shape, and the animal's first selection was scored. A single pair of shapes was used with flavor assigned daily according to a Gellerman schedule. In 6g0/o or trials the monkeys selected the tasteful shape (P < 0.001). The performance in the second half of testing was higher th'an in the beginning which suggests that some kind of learning set develops. Cowey and Weiskrantz (1, 10) described in 1975 a method of ascertaining whether the rhesus monkey (Macaca mulatta) could visually recognize an object which had been previously explored in the haptic mode. Their success in demonstrating this ability closed a period of unsuccesful experimentation (2, 6, 8-10) and cast into doubt conclusions concerning the monkeys' inability to solve complex crossmodal tasks. Theories arising from the above-mentioned work had even pinpointed the lack of a sizeable temporal-parietal-occipital association cortex as the cause of this limitation (8). Cowey and Weiskrantz considered previous failures, not as a demonstration of the monkeys inability, but as an indication that the tasks used were not very relevant to the 8

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animals' motivational st'ate. They created a test where the objects to be discriminated were either edible or very distasteful, and by carrying the task closer to the animals natural feeding behavior demonstrated haptic to visual recognition of objects by the rhesus. Elliot (7), using the same method, replicated the results for the rhesus and presented similar fimd,ings for the c a p u h i n ' m o k e y (Cebus) a\nd the chimpanzee (Pan). These results suggested that haptic-visual cross-modal reoognition exist not only in humans, but also in the great apes, and certain groups of asian and new world monkeys. The vwvet momkey (Cercopithecus aethiops) is part of a wid,ely distributed and abundant genus of the African continent. The species has been adapted to some islands in the Caribbean too. A group of vervets from .Saint Kitts were examined with the Cowey and Weiskrantz method to determine whether they had the ability for hapticvisual cross-modal recognition. Five juvenile vervet monkeys (3 males and 2 females) were used. None had previous experience in the experimental situation. They weighet from 1.5 to 2.5 kg. Since these animals had been captured in the wild, exact determination of age was not possible. One of the monkeys (CR) emitted vocalizatiorls which we have not found in animals of our breeding colony older than 18 mo. As soon as the experiment began the animals were fed daily a t 1 2 m. sufficient food so that no surplus was detected a t 8.00 a.m. next morning. All training was carried out from 8.00 a.m. to 12 m.

Fig. 1. Modified WGTA Box divided into compartments ' A and B by two sliding doors, one opaque and one transparent.

The monkeys normally remained in individual cages. During each daily experimental session they were carried in a transportation cage to a sound attenuating and anechoic chamber. In this room they were

placed in a modified Wllsconsin General Test Apparatrw cage (WGTA) of dimensions 60 X 50 X 30 cm. (Fig. 1). During a preadaption period of several weeks the animals received part of their daily portion of food in this cage. The WGTA cage had two sliding panels, one opaque and one transparent, separating compartments A and B (Fig. 1). The animals' behavior was shaped by placing food in compartment B. The panels were lifted and the animal was allowed to retrieve and eat the food. This was continued with various degrees of darkness until animals were adapted to eat in t h i dark and the experiment began. Duaing 20 days two different shapes of biscuits were presented to the animals in the dark for haptic exploration and were later tested in the light for visual recognition. The shapes used were a ball (approximate of 1 cm diameter) and a cylinder (approximately 2 cm long and 0.25 cm diameter); both weighed 1.0 g. One of the biscuits was tasteful and the other was distasteful. On each day, the flavor of each objecb changed according to a Gellerman Schedule. The biscuits were made out of paste prepared daily from wheatmeal, eggs and butter. The paste was divided into two parts. The one used for the tasteful biscuits received sugar and the other part received a solution of 5O/o quinine sulphate common salt and white sand. Each half of the paste was divided in pieces and given one of the two shapes described above, which were cooked (200°C) until they had a light brown color. An experimental session was carried out as follows. Each monkey was placed in compartment A of the WGTA box and the lights of the chamber were turned off after closing the rear door. The darkness in the chamber was tested by human observers, who reported no vision after 30 min of dark-adaptation. A sample of 10 tasteful object of one shape and 10 distasteful objects of the other shape had been placl?d in the compartment B and covered with a light shield. The sliding panels were removed and the experimenter retired to another dark room. The animals were allowed to explore, taste and eat the biscuits placed in compartment B. Thirty minutes later the experimenter returned, lowered the sliding panels and lifted the rear door. The monkeys always abandoned the WGTA cage and moved into the transport cage immediately and were examined carefuly to see if pieces of food had been carried out. This never happened. The WGTA cage was cleaned to eliminate any biscuits left. The biscuits of each kind eaten or nibbled were counted. It was observed that the good biscuits were eaten almost alway whereas the distasteful ones were reject. The animals were replaced in compartment A again. A single test

pair of one tasteful and one distasteful object, identical to those explored haptically in the dark, were placed in compartment B of the WGTA cage. The lights were turned on and the opaque sliding panel was raised, and 20 s later the transparent sliding panel was also raiskd. The animals' first selection of a biscuit was taken as it's response. If the monkey took first the tasteful object it's response was scored as a success, if a distasteful object was the first selection a failure was scored. The position of the tasteful object in the light was shifted from left-to right following a pseudo-random schedule, with the condition that it appeared 50°/o of the time in each side. A control series of five trials was presented on the last day of the' experiment. In the light two biscuits of the same shape were presented to the animal, one tasteful and one distasteful. The side on which the tasteful biscuit was presented was shifted from left to right in a pseudorandom fashion. If the animal selected the tasteful object, a success was scored. The scores were tested by the binomial test against the null hypothesis that they were responding at chance level (50°/o). As shown in Table I the pooled results of the group for the 20 sessions permit the rejection of the null hypothesis. Comparison of the TABLE I Number of correct choices. Monkeys CA

AL

GU

--

IN 1-10 TRIALS IN 11-20 TRIALS I N 1-20 TRIALS

CR

AN

-

-

8* 9* 17*

7 8* 15*

8* 7 15*

4 9* 13

Total of correct trials

4 5 9

31 - 50 38**- 50 69**-100

Statistically significant by binomial test (P < 0.05); Statistically significant by Z according to the normal approximation in binomial test (P< 0.001).

**

first 10 days and the second 10 days shows a higher percentage of success during the latter period. Clearcut individual difference were evident. In the control series out of 25 trials, 42O/o were successes, i.e., selection was not significantly different from chance. The animals showed no tendency to prefer one side or the other.

The CR who showed the lowest performance in the test (50°/o), was the only monkey with a preference (statistically significant, P < 0.02) for one of the shapes. This was also the youngest monkey. Our main finding is that after haptic experience in the dark with biscuits of two different shapes, each with a distinctive taste, the vervets selected the edible stimuli at above chance level (70°/o). The failure to select the tasteful object when the positive and negative stimuli had the same shape, excludes cues due to the material of the biscuits themselves such as color, smell and others. Since the significance of each shape changed from day to day, the only strategy which could lead to success would be the cross-modal transfer of information. The fact that the proportion of correct selections is higher for the second half of the experiments suggests that some sort of learning set is being acquired. This increment is most dramatic for monkey AN. Though this monkey's global performance did not reach statistical significance, the proportion of correct trial is significant in the second half of the experiment due to the great increase of correct responses. The only animal whose performance was systematically at chance was CR. This was also the youngest animal. It is not possible to decide, with the evidence available, if his failure is due to the lack of maturity of the neural mechanisms responsible for cross modal recognition, or if attention factors (favoring vicarious preferences) are to blame. Our results are comparable to those described in the literature lor other species of primates (7, 11) and thus suggest that cross-modal recognition (in the haptic-visual direction) exists in the green monkey. We thank Prof. Frank Ervin for giving us monkeys used in this work and for his suggestions and helpful comments. Thanks a r e also due to Prof. B. Zernicki and K Zieliliski for their kindness in reading and correcting the manuscript.

1. COWEY, A. and WEISKRANTZ, L. 1975. Demonstration of cross-modal matching in rhesus monkeys, Macaca mulatta. Neuropsychologia 13: 117-120. 2. DAVENPORT, R. K. 1976. Cross modal perception in apes. Ann. N. Y. Acad. Sci. 280: 143-149. 3. DAVENPORT, R. K. and ROGERS, C. M. 1971. Perception of photographs by apes. Science 168: 279-280. 4. DAVENPORT, R. K. and ROGERS, C. M. 1971. Perception of photographs b y apes. Behavior 39: 2-4. 5. DAVENPORT, R. K., ROGERS, C. M. and RUSSELL, I. S. 1973. Cross-modal perception in apes. Neuropsychologia 11: 21-28.

6. DAVENPORT, R K.,ROGERS, C. M. and RUSSELL, I. S. 1975. Cross-modal perception in apes: altered visual cues and delay. Neuropsychologia 13: 229-235. 7. ELLIOT, R. C. 1977. Cross-modal recognition in three primates. Neuropsychologia 15: 183-186. 8. ETTLINGER, G. a n d BLAKEMARE, C. B. 1967. Cross-modal matching in the monkey. Neuropsychologia 5: 147-154. 9. FREIDES,D. 1974. Human informaticm processing and sensory modality: crossmodal functions, information complexity, memory and deficit. Physiol. Psychol. 4: 281-284. 10. WEGENER, J. G. 1965. Cross-modal transfer in monkey. J. Comp. Physiol. Psychol. 59: 450-452. 11. WEISKRANTZ, L. and COWEY, A. 1975. Cross-modal matching in the rhesus monkey using a single pair of stimuli. Neuropsychologia 13: 257-261. Accepted 16 October 1980