Development of tactile discrimination capacity in Macaca mulatta. I. Normal infants

Infant macaques between the ages of 7 and 25 weeks of age were trained on a series of manual tactile discrimination tasks. Tactile discrimination capacity, as measured by the most difficult level of size and texture discrimination tasks mastered, was the same for all ages of infants and did not differ from that of adults. Infants as young as 10 weeks of age were found to have a discrimination capacity similar to that of adult macaques, although an adult level of manual motor control had not been achieved by this early age. During the acquisition of size tasks, older animals made fewer errors than did younger animals, suggesting an improved efficiency in size discrimination capacity over the first 6 months of life. By contrast, the efficiency with which the younger animals mastered texture discrimination was superior to that of the older infants. The possible contributions of sensory experience or manual motor control to the maturation of sensory capacity were examined by applying 16 weeks of sensory restriction in one infant and a unilateral motor cortex lesion in another infant, respectively. Only transient impairment was found in either case suggesting that neither tactile experience nor motor control contribute significantly to the maturation of tactile discrimination capacity in infant macaques.