Development of visual acuity in infant chimpanzees

To assess development of visual acuity, a preferential looking procedure was administered to 13 nursery-reared chimpanzee infants ranging in age from 1 to 52 weeks. Chimpanzees exhibited acuity levels poorer than 1 cycle/degree when tested within the first weeks after birth, which is similar to that seen in neonatal humans and monkeys. Acuity improved about tenfold to near 10 cycles/degree during the first year. The time course of chimpanzee acuity development was more similar to that of humans than of monkeys. Tests were conducted at two or three separate viewing distances (38, 76, or 152 cm) in some individuals. This was done because previous observations during neurobehavioral assessments had found optimal focal distance to be longer in chimpanzee than in human infants. The results exhibited a nonsignificant trend for acuity to be better at far (76 or 152 cm) than at near (38 cm) viewing distances. These normative data can be usefully applied to further our understanding of the biological bases of perceptual and motor development and the effects of their coordination on subsequent development of other functions in primates.