Abstract
Hansen, Pracejus, & Gegenfurtner (2009) raised an interesting possibility that non-cardinal mechanisms may be a specialization of the fovea. Cardinal colors are colors that best stimulate the retinal neurons: red, green, violet, chartreuse, black, and white. Non-cardinal colors are all other colors, including ones such as orange and turquoise. Hansen et al. found more circular (not elongated) chromatic discrimination ellipses at 50° than at 5°, suggesting fewer underlying mechanisms and thus the lack of non-cardinal mechanisms peripherally. Here I test this hypothesis by performing visual search with cardinal and non-cardinal stimuli (dot/annulus stimuli of 2.5° diameter, 1.25° central dot; 6 dots total; cardinal stimuli consist of, e.g., red/green target amongst violet/chartreuse distractors) at 0, 10, 20, and 30°, in all three planes of color space. The results so far do not support the hypothesis of foveal specialization of non-cardinal mechanisms. In the isoluminant plane, although performance does drop off in the periphery, it does so equally for cardinal and for non-cardinal stimuli. In the red-green/luminance plane and especially in the violet-chartreuse/luminance plane, performance on the non-cardinal visual search (e.g., intense-red/dim-green target amongst intense-green/dim-red distractors) is difficult even in the fovea. However, as performance drops in the periphery, it does so at similar rates for cardinal and for non-cardinal stimuli.
Meeting abstract presented at VSS 2013