Abstract
Color vision declines in the periphery (20–40° eccentricity) and has been thought to be less functioning. Therefore there have been relatively few studies on color vision in the extreme-periphery (>40°). This area, however, is subject to greatest ambiguity, thus the most heavily modulated by attention and other sensory modalities. In a series of psychophysics, we tested our “compensation hypothesis” which proposes that the brain compensates for the sparse, ambiguous visual input in the extreme-periphery, by unambiguous signals from the fovea or another sensory modality. Here, we examine the effect of eccentricity and foveal color on color perception in the extreme-periphery. In Experiment1, a brief central fixation (white, 50ms) was presented twice with 450ms interval. After the interval, a target (red/green, 50ms) was presented at one of the 16 locations between 65° to 95° (on left/right). The observers named target’s color (red/green/not-seen) and then reported its confidence by 5-point scale (5:very sure~1:very unsure). In Experiment2, observers performed the same task except fixation’s color (red/green/white). Target was presented in the extreme-periphery (left/right) where the average confidence for the correct naming in Experiment1 met 2. Colors used in both experiments were individually adjusted so as to have perceptually-equal brightness. Fixation’s and target’s color, and location of the target were randomized. In Experiment1, as expected, correct naming responses (e.g., “red” to red target) decreased, and wrong naming responses (e.g., “green” to red target) increased with increasing eccentricity of target location. Surprisingly, however, confidence for the wrong naming was increased and reached to plateau at around 85° eccentricity. Experiment2 showed that incongruent fixation’s color induced wrong naming (e.g., green fixation induced “green” response to red target) with high confidence. Thus, observers actually perceived illusory color, implying that ambiguous input in the extreme-periphery is compensated by unambiguous foveal color signal.
Acknowledgement: JSPS KAKENHI (No.18KK0280)