Acquisition of discrimination learning of patterns identical in configuration in macaques (Macaca mulatta and M. fuscata).

The acquisition of discrimination of five pairs of pattern cues in a Wisconsin General Testing Apparatus by 223 naive macaque monkeys was compared. The pairs of discriminanda were identical in configuration but varied slightly in either the size of the cue or the size of the background plaque; thus, the degree of separation of the cue from the fringe of the plaque, the response site, was slightly different for each pair of discriminanda. These small differences in cue-response separation had marked effects on the rate of acquisition of the discriminations. Even an increment of separation as small as 0.5 cm resulted in a remarkable retardation of the acquisition. This retardation was due entirely to prolonged performance at the chance level, and not to a slow rate of improvement from the chance to a criterion level. The finding indicates that the difficulty in the acquisition learning on pattern tasks depends largely on the difficulty of attending to the pattern cues at small cue-response separations.