On the Neural Mechanisms Underlying Developmental and Individual Differences in Visual Fixation in Infancy: Two Hypotheses

Abstract

Both developmental and individual differences in fixation duration during the first year of life suggest that the duration of visual fixations is correlated with the rapidity of visual encoding: fixation durations decrease significantly over the first year, and individual differences in infant fixation duration within ages are reliable characteristics that correlate with measures of cognitive performance in infancy and in later childhood. The mechanism(s) responsible for these apparent individual and developmental differences in fixation (and thus, visual encoding) has yet to be determined. This review presents hypotheses concerning two specific CNS systems and how they might contribute to such individual and developmental differences in infancy. One system is the "transient" and "sustained" pathways of visual processing within the primary geniculostriate visual system (the magnocellular and parvocellular layers of the lateral geneculate). The other system is a "posterior attentional system" that has been identified with the engagement and disengagement of visuospatial orienting. Evidence is reviewed regarding how each subsystem might account for developmental and individual differences in infant visual fixation.