Abstract
To test infant chromatic discrimination, researchers have used diverse means, of varying effectiveness to control luminance artifacts that would invalidate such demonstrations. In an elegant analysis of several studies using a range of protocols and methods for stimulus control, Brown and Lindsey (Vis. Neurosci.2013) found that infant responses could be explained solely on the basis of chromatic differences, as if, in effect, they ignored luminance differences. Given infant contrast luminance sensitivity, it seems unlikely that luminance would not influence performance. We examined this issue by testing how infants integrate chroma and lightness differences using Maximum Likelihood Conjoint Measurement (Knoblauch and Maloney, 2012). Twenty-one 6 month olds were tested using a set of stimuli in which chroma and lightness covaried independently, with 3 levels defined along each dimension. All 36 pairings of stimuli were randomly presented, with the the direction of the first eye-movement used as a measure of preference or choice of which stimulus was more salient. About one quarter of the infants completed 2 sets of presentations (72 trials). All infant data were analyzed, however, within a mixed-effects model. Results were compared with adult data in which observers were instructed specifically to judge chroma or lightness and adult data based on first eye movement to most salient stimulus. In brief, infants preferred stimuli of higher chroma but higher lightness reduced preference, indicating a veiling effect qualitatively similar to adult chroma judgments. Thus, infant preferences integrate chroma and lightness similarly to how adults judge chroma differences.