Motion nulls for white versus isochromatic gratings in infants and adults

The relative sensitivity of infants and adults to luminance modulations of 2.6-cd/m2, 0.3-cycle/deg broadband isochromatic red, green, or blue test gratings was measured with a motion-nulling technique. Optokinetic nystagmus was used as the response measure. Each test grating was pitted against a standard, 2.6-cd/m2, 50%-contrast white grating, and the contrast of the test grating required for a motion null was determined. The results were similar for both age groups. Both infants and adults required approximately 50% contrast in the red and green gratings, but only about 25% contrast in the blue grating, to produce a motion null. Quantitative analysis of the results suggests that a peripheral photopic luminance mechanism, with or without a small scotopic contribution, controls optokinetic nystagmus responses in all subjects under these conditions.