EFFECTS OF VARIATIONS OF STIMULUS-RESPONSE SPATIAL CONTIGUITY ON COLOR DISCRIMINATION LEARNING IN SQUIRREL MONKEYS

The effects of presenting color cues in positions that were either spatially-contiguous to or discontiguous from the animals' response sites were observed in squirrel monkeys (Saimiri sciureus boliviensis). Results of previous studies employing Old World primates have shown that differences as little as 2 cm in stimulus-response spatial contiguity have significant effects upon discrimination learning performance. Two adult subjects were trained on a sequence of 20 color discrimination problems. For each problem, both plaques were oriented with either the relevant color stimuli on the near edge (continuous condition) or the far edge (noncontiguous condition) of the stimulus plaques. An analysis of this successive treatment reversal design revealed a significant difference between the mean trials to criterion for contiguous (m = 63) and noncontiguous (m = 261) color problems. These results re-emphasize the important role of S-R spatial contiguity in discrimination learning performance. Moreover, this effect is not trivial, for a change in spatial position of the relevant cues of only a few centimeters produces very large performance deficits.