Saccades and small-field optokinetic nystagmus in infants.

Developmental studies of infant eye movements may be a useful tool in the early diagnosis of visual abnormalities. We have measured saccades made by infants during the free scanning of stimuli differing in attentional value. When viewing stimuli with high attentional value, infants made saccades that had adult-like peak velocity/amplitude (main sequence) relationships, while for less interesting stimuli, their saccades were slower; saccadic oscillations were also more frequent for these stimuli. In studies of small-field horizontal and vertical optokinetic nystagmus, with binocular viewing, infants' horizontal OKN was of higher frequency and lower amplitude than their vertical OKN. Within vertical OKN, there was a clear asymmetry with reduced responsiveness to downward moving stimuli. This asymmetry declined for older infants; possible interpretations for this change are discussed.