Sae Kaneko¹, Koharu Sugano¹; ¹Hokkaido University

The perceived color of a target embedded in achromatic or chromatic gratings is affected by the flanking and/or coaxial bar (Munker, 1970; White, 1979). The chromatic and achromatic versions were reported separately, but here we refer to both effects as Munker-White illusion. The exact mechanisms of the effects, or whether the effects share common mechanisms, are unknown. The effects of exposure time on several brightness/lightness illusions have been reported (e.g., Kaneko & Gilchrist, 2020). However, the reported effect on the Munker-White illusion is unclear (Robinson & de Sa, 2008). In this study, we tested the effect of exposure time on achromatic and chromatic Munker-White illusions to explore the temporal dynamics of the illusions and to examine the possibility of shared mechanisms between the two phenomena. Subjects viewed a stimulus made with paper in a custom-made viewing box through a camera shutter, which regulated each exposure time (5 conditions, 15 ms to 907 ms). The task was to report the closest match of two identical targets embedded in a stimulus using a chart with Munsell chips (achromatic or chromatic). In achromatic versions, the neutral gray targets are either on a black bar or on a white bar of a background grating. In a chromatic version, the blue targets are either on a green bar or on a lavender bar. Results from two experiments showed that the achromatic Munker-White illusion was stronger for shorter exposure times. In contrast, we found no effect of exposure time on the chromatic version of the phenomenon. The strength of two illusions within a subject, both collapsed across exposure time conditions and within each condition, showed no significant correlation. The differences in temporal dynamics and the lack of intrasubject correlation suggest that the achromatic and chromatic Munker-White illusion, however similar they appear, may stem from separate mechanisms.

Acknowledgements: This work was supported by JSPS KAKENHI Grant number JP24H0070225.