Infant color vision: motion nulls for red/green vs luminance-modulated stimuli in infants and adults

Four-week-olds, 9-week-olds, and adult subjects were tested with low spatial frequency sinusoidal gratings moving at a speed of 25 deg/sec. Luminance-modulated and red/green gratings were presented either separately, or superimposed and moving in opposite directions in a chromatic motion nulling paradigm. An adult observer judged the direction of the slow phase of the subject's eye movements. Luminance-modulated gratings elicited directionally appropriate eye movements in all three age groups, with contrast thresholds decreasing markedly with age. For red/green gratings alone, 4-week-olds responded only marginally, but 9-week-olds and adults produced consistent directionally appropriate eye movements. In the motion nulling condition, 15% contrast luminance-modulated gratings were about equally effective in nulling the motion of the red/green gratings in all three age groups. A formal model of the motion nulling paradigm, separating threshold and equivalent luminance contrast parameters, was developed and applied to the data. Model fits showed that equivalent luminance contrast was constant or nearly constant across age groups. This outcome is consistent with the hypothesis that, with respect to adults, infants show a uniform rather than a differential loss of sensitivity to moving red/green vs luminance-modulated stimuli.