THE DEVELOPMENT OF STEREOACUITY IN INFANT RHESUS-MONKEYS

The emergence of stereopsis at 3-4 months postnatal in human infants i s striking and has led to speculation that its rapid onset and subsequ ent development must be due to a dramatic reorganization of the brain. Stereopsis has never been measured in infant monkeys, but previous st udies have demonstrated that many other visual functions develop four times faster in infant monkeys than in humans, We made longitudinal as sessments of stereoacuity in 11 infant rhesus monkeys. A forced-choice preferential-looking technique was used to present random-dot stereog rams during testing, By 8 weeks after birth, all of the monkeys were r esponding to at least coarse levels of disparity (1760 '' [seconds]), and by 13 weeks of age, all were responding to the relatively fine lev el of 88 '' disparity, Age of onset for stereopsis in monkeys was at a bout one-quarter the age when it occurs in humans, as expected, Howeve r, subsequent development proceeded at a similar absolute rate in monk eys and humans, The findings are discussed relative to the neural mech anisms which might be responsible for the differing rates of developme nt, (C) 1997 Elsevier Science Ltd.