Abstract
The color-motion asynchrony was originally discovered in a visual stimulus that changes color (e.g., red and green) and direction of motion (e.g., upward and downward) rapidly and repeatedly. In order for a human to perceive those changes taking place simultaneously, direction change must precede color change by about 80 ms (Moutoussis & Zeki, 1997). This color-motion asynchrony was recently shown by the correspondence task with stimuli that change color and motion just once, but not by the temporal order judgment task (Linares & López-Moliner, 2006; Self et al., 2010). The purposes of this study are 1) to see whether the temporal order judgment task can also show the color-motion asynchrony by eliminating the artifact in the earlier studies and 2) to examine whether the luminance change alone can show the similar effect. We employed the method of constant stimuli. Tasks were either the correspondence task or the temporal order judgment task. The color/luminance of the stimuli were 1) equiluminant (28 cd/m2) colors varied along the L/(L + M) axis, 2) equiluminant (28 cd/m2) colors varied along the S/(L + M) axis, or 3) equal energy white at 8 cd/m2 and 40 cd/m2. The results from five observers showed that the color-motion asynchrony was observed in both tasks. The mean asynchrony for the correspondence task was 97 ms (SEM = 15) and that for the temporal judgment task was 66 ms (SEM = 13). A two-way ANOVA (task x color/luminance) with repeated measures showed that this difference between the tasks was significant, F(1, 4) = 7.905, p = 0.048. Further, the results revealed that the luminance change also showed the color-motion asynchrony. Therefore, the color-motion asynchrony is not strictly limited to the color change in an equiluminant plane. Rather, the phenomenon needs to be investigated in a broader context including the achromatic system.