Categorical similarity may affect colour pop-out in infants after all

Gerhardstein, Renner, and Rovee-Collier (1999) reported an investigation of pop-out in infant visual search with targets differing in colour from the distractors. They varied the perceptual distance between target and distractors and their categorical relationship. Targets were either in the same category as distractors or in a different category. They reported that at 3 months, infants showed increased pop-out as perceptual distance increased, but there was no categorical effect. Here, we argue that their stimuli were not adequate to address these issues. Use of incandescent light rather than the normal illuminant C differentially affected the perceptual differences among their stimuli, and there may have been an unintended category boundary present in an intended within category pair. We argue that these faults in the stimuli can account for their pattern of results. They were aware of the possible consequences of using incandescent light and ran a preliminary study on adults comparing category membership and perceived similarity among their stimuli under incandescent light and illuminant C. They report that the illuminant had no effect. We replicated and extended their adult study and found that there were effects of the illuminant as well as evidence consistent with the unintended boundary. Reasons for the discrepant results are discussed, and the requirements for a valid investigation outlined