The influence of stimulus size on newborns' discrimination of chromatic from achromatic stimuli

We used an habituation procedure to explore newborns' ability to detect successive changes in luminance and based on those data, their ability to discriminate chromatic from achromatic stimuli. Newborns were very insensitive to successive changes in luminance: after habituating to a white square of given luminance, they showed no evidence of dishabituating when the luminance of the square increased or decreased by 0.37 log cd/m2, but dishabituated only to the next larger difference of 0.53 log cd/m2. Moreover, after newborns were habituated to a series of white squares that varied widely in luminance, they did not react when the luminance of the square was increased as much as 0.71 log cd/m2. In the color vision experiments, infants were habituated to a series of white squares of varying luminance and then tested with a chromatic square and with a white square of novel luminance. The size of the squares was also varied. The results showed that newborns discriminated 8 deg red (lambda peak = 650 nm) and 16 deg green (lambda peak = 540 nm) squares from white but required a larger stimulus (16 deg) to demonstrate the discrimination of yellow (lambda peak = 585 nm) from white. In addition, newborns showed no evidence of discriminating a 32 deg blue (lambda peak = 470 nm) square from white. Thus, although the results imply that newborns are at least dichromats, they also show that their color vision mechanisms are immature, particularly those operating in the blue and yellow spectral regions.