Interocular transfer of mirror image discriminations by chiasm-sectioned monkeys.

Abstract

Abstract Chiasm-sectioned monkeys, trained monocularly, learned to discriminate left-right (L-R) mirror images faster than up-down (U-D) in contrast to normal monkeys Unlike those of an earlier report, the chiasm-sectioned monkeys in our experiment consistently failed to choose the mirror image stimulus when tested for interocular transfer of discriminations of L-R mirror images under a variety of conditions. Compared to normal monkeys or to their own performance on U-D mirror images, however, they did show a deficit in interocular transfer of the L-R discriminations, performing near chance when first tested with the untrained eye. We attribute the chance performance to a conflict between two response tendencies: verdical performance based on unreversed sensory information transferred by the callosum, and reversed performance based on masking by the bitemporal hemianopia. Reversal occurs because one half of an asymmetric stimulus, seen by the testing eye, resembles the opposite half of its mirror image, seen by the training eye. Related asymmetries in attention may play a significant role in the difficulty that normal animals often show in discriminating L-R mirror images.