ON THE NEURAL MECHANISMS UNDERLYING DEVELOPMENTAL AND INDIVIDUAL-DIFFERENCES IN VISUAL FIXATION IN INFANCY - 2 HYPOTHESES

Both developmental and individual differences in fixation duration dur ing the first year of life suggest that the duration of visual fixatio ns is correlated with the rapidity of visual encoding; fixation durati ons decrease significantly over the first year, and individual differe nces in infant fixation duration within ages are reliable characterist ics that correlate with measures of cognitive performance in infancy a nd in later childhood. The mechanism(s) responsible for these apparent individual and developmental differences in fixation duration (and th us, visual encoding) has yet to be determined. This review presents hy potheses concerning two specific CNS systems and how they might contri bute to such individual and developmental differences in infancy. One system is the ''transient'' and ''sustained'' pathways of visual proce ssing within the primary geniculostriate visual system (the magnocellu lar and parvocellular layers of the lateral geniculate). The other sys tem is a ''posterior attentional system'' that has been identified wit h the engagement and disengagement of visuospatial orienting. Evidence is reviewed regarding how each subsystem might account for developmen tal and individual differences in infant visual fixation. (C) 1995 Aca demic Press, Inc.