The effect of experience on the development of tactual-visual transfer in pigtailed macaque monkeys

The study described here is the first to experimentally demonstrate the effects of experience on the development of tactual-visual transfer. Infant pigtailed macaque monkeys (Macaca nemestrina) were reared from birth to 2 months of age in special cages that allowed the separation of tactual and visual experience. When assessed on a battery of measures at the end of the 2-month period, animals reared without the opportunity to integrate information across the two sensory modalities performed at chance levels on a paired-comparison measure of tactual-visual transfer and performed worse than controls in a visually guided reaching task. After living in the standard laboratory environment for 2 additional months, they were reassessed. While their visually guided reaching now no longer differed from that of controls, they continued to perform at chance on the tactual-visual transfer assessment and their performance on this task was significantly worse than the control groups. Performance on visual acuity and visual recognition memory measures did not differ between groups at either age, suggesting that the deficit was limited to tactual-visual functioning. The results are discussed in terms of a possible sensitive period during which specific environmental input is required for the development of normal tactual-visual cross-modal processing.