Michael E. Rudd¹ (), Sean O'Neil¹, Natasha Staneva¹; ¹University of Nevada, Reno

At VSS 2025, we demonstrated an asymmetry in chromatic induction strength along the two half-axes of the LM dimension of MB/DKL color space. Here, we demonstrate a similar asymmetry along the S axis. Two achromatic disks (1.16 deg diam, 30 cd/m2) were presented on opposite sides of a Display++ monitor (Cambridge Research Systems, Kent, UK), each surrounded by an achromatic annulus (60 cd/m2). The annuli had widths 0.19 and 1.78 deg. The display side containing the thinner annulus was randomized across trials. The luminance of the chromatic background was fixed at 45 cd/m2. Across trials, the chromatic contrast of the background was randomly varied from 80% S- to 80% S+ in 17 equal steps. Four participants adjusted the S content of the one of the two disks to match the disks in hue. 50% of the time, the match disk was surrounded by the thin annulus, and 50% of the time it was surrounded by the thick annulus. Changes in the S content of the background induced a contrasting hue change in both the disks and annuli. These hue changes were stronger on the side with the thinner annulus. We wondered if, when changing saturation of the background, the rate of change in the match settings would differ across the background ranges that were either S+ or S- relative to the achromatic point. If so, this might imply the existence of separate underlying half-wave rectified S+ and S- mechanisms characterized by different gains and producing different chromatic induction strengths. This prediction was confirmed, but the direction of the asymmetry varied across observers. In combination with the results or our previous study, these results support a generalization of an edge integration theory of lightness (Rudd, 2010; Rudd & Shareef, 2025) to the chromatic dimensions of color space.

Acknowledgements: Supported by NIGMS P30 GM145646