Emergence of the ability to discriminate a blue from gray at one month of age

Two different methods which minimize achromatic cues were used to test the ability of 1-month-olds to discriminate gray from broadband blue (lambda peak = 475-480 nm). Unlike the newborns we tested previously, 1-month-olds demonstrated the discrimination with both methods. In Experiment 1 they showed preferences for each of four blue-and-gray checkerboards over gray squares of the same mean luminance, even though the luminance of the gray checks was varied in small steps over a wide range. In Experiment 2 they looked longer at a blue square than at a gray square, after they had been habituated to five other gray squares of varying luminance. Compared to previous results, these data imply an improvement between birth and 1 month of age in the discrimination of gray from broadband blue. Possible physiological changes underlying this improvement are discussed.