Intrinsic contrast noise and infant visual contrast discrimination.

In these experiments, the amounts of intrinsic contrast noise and contrast-dependent noise were independently estimated from optokinetic nystagmus (OKN) contrast discrimination thresholds in 7-week-old human infants and adults. This report shows that the poor contrast sensitivity of infants occurs mostly because there is about 106 times more intrinsic contrast noise in the infant visual system than in the adult visual system. The intrinsic contrast noise is combined nearly linearly with the visual signal in infancy, whereas noise and visual signal are combined in a highly non-linear way for adults. The standard deviation of the visual signal differs between infants and adults by a factor of about 2 for OKN data and a factor of 13 for behavioral data. The large amount of intrinsic contrast noise found by this analysis is quantitatively consistent with data obtained by forced-choice preferential looking (FPL), and visually evoked potential (VEP) contrast sensitivity is correctly predicted to be near adult values in infancy.