Discrimination of Mirror-Image Patterns by Rhesus Monkeys

Abstract
Twelve rhesus monkeys were trained to discriminate between (a) lateral mirror-image problem, (b) vertical mirror-image problem, (c) problems in which one stimuli was rotated 90°, and (d) nonidentical problems. Type (a) problems were most readily discriminated whereas type (c) problems were least readily discriminated. The other problems were of intermediate difficulty. Stimuli placed one above the other were less discriminable than those placed side by side. No interaction existed between type of stimulus placement and direction of the comparison. The results are explained by the fact that the monkeys tend to inspect the bottom edges of the stimuli, which differ in discriminability as a function of the direction of the mirror-image reflection.

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