Comparisons of visual search performances cued by the S-cone stimulus value between trichromats and severe anomalous trichromats

Abstract

In this study, we measured visual search performances cued by the S-cone stimulus value for trichromats and severe anomalous trichromats, and compared them. The stimulus consisted of 13 disks on an achromatic background. Twelve disks of them were distractor disks and the rest was a target disk. Two colors whose S-cone stimulus values were different, were assigned to six distractors, respectively. The S-cone stimulus value of the target color was set to the midpoint of two distractor colors. The stimulus duration was varied as a parameter. The observer’s task was to respond which quadrant the target disk which the target color was assigned was on. The correct responses were measured as a function of stimulus duration. We calculated stimulus duration thresholds providing the correct responses of 0.724, and compared those between trichromats and severe anomalous trichromats. The results showed that the stimulus duration thresholds of trichromats became as long as or longer than those of severe anomalous trichromats. This suggests that trichromacy does not always have an advantage over dichromacy.