The transition from scotopic to photopic vision in 3-month-old infants andadults: an evaluation of the rod dominance hypothesis

The scotopic to photopic transition was tested in adults and 12-week-old in fants using a large field motion nulling technique at a series of luminance s between - 3.57 and 2.76 log cd m(-2). The stimuli were composed of 0.25 e ye deg(-1), 5.6 Hz blue/black and yellow/black sinusoidal grating component s, superimposed and moving in opposite directions. The contrasts of the two components were traded off to determine motion nulls at each luminance lev el. An eye movement based response measure was used for infant subjects, wh ereas self-report was used in adults. In both age groups, the motion null v alues approached a scotopic asymptote consistent with V'(lambda) at the low est luminance levels, and a photopic asymptote consistent with V-10(lambda) at the highest luminance levels. The scotopic to photopic transition was g radual and occurred over about 3 log units between about -2 and 1 log cd m( -2) in both groups. The null values for infants and adults were highly simi lar at each luminance level, and the shapes of the transition curves were v irtually identical at the two ages. These data suggest that at each differe nt luminance level, the balance between rod-initiated and cone-initiated si gnals in the extrafoveal luminance channel is similar or identical in 12-we ek-old infants and adults. (C) 2000 Elsevier Science Ltd. All rights reserv ed.