Abstract
We often search targets among heterogeneous and heterochromatic scenes, although previous visual-search studies used uniform and simple stimuli except few experiments. The traditional visual search models cannot be applied to this complex visual search paradigm. To investigate characteristics of heterochromatic visual search we used sets of distractor colors. A set consisted of 13 colors. Each distractor in a set was selected from a spherical range of color difference in the OSA uniform color space to keep color difference conditions constant. A target and a total of 63 distractors (4–5 distractors for each 13 colors) were presented at random positions of an 8×8 grid on the CRT display. The target color was located outside of the spherical distribution of distractors. We used 6 target colors for each distractor distribution. The distance between the target and the center position of distractors was held constant. The position of the set of distractors covered all hues and saturations in the OSA space. We measured the response time to find a target. Categorical color naming for all OSA color stimuli was also performed. The results showed that the response time depended on the categorical color perception, which should be caused in the higher-order color mechanism. When all distractors were included almost in a category (say, green), it was difficult to find a target belonging to the same category (green), even though a target in another category (say, yellow) was easily found. When distractors consisted of several categories, all targets were easily detectable. Here we propose the categorical color search model. In this model, the color visual search process is divided into two stages, the inter-category search and the intra-category search. The model can account for influences of categories of stimulus colors on the visual search. This suggests that the higher-order color mechanism influences the heterochromatic visual search.