Chromatic tuning of contour-shape mechanisms revealed through the shape-frequency and shape-amplitude after-effects

We investigated whether contour-shape processing mechanisms are selective for color direction using the shape-frequency and shape-amplitude after-effects, or SFAE and SAAE [Gheorghiu, E. & Kingdom, F. A. A. (2006). Luminance-contrast properties of contour-shape processing revealed through the shape-frequency after-effect. Vision Research, 46(21), 3603–3615. Gheorghiu, E. & Kingdom, F. A. A. (2007). The spatial feature underlying the shape-frequency and shape-amplitude after-effects. Vision Research, 47(6), 834–844]. All contours were defined along the ‘red-green’, ‘blue-yellow’ and ‘luminance’ axes of cardinal color space. Adapting and test contours were defined along the same or along opposite polarities within a cardinal axis, and along the same or along different cardinal axes. We found (i) little transfer of the after-effects across different within-axis polarities, for all cardinal axes and for both even-symmetric and odd-symmetric contours; (ii) little transfer between the red–green and blue–yellow cardinal axes; (iii) little transfer between the chromatic and luminance cardinal directions for the SAAE; (iv) large transfer between the chromatic and luminance cardinal directions for the SFAE. We conclude that contour-shape mechanisms are selective for within-cardinal axis polarity and for the chromatic axes within the isoluminant plane. However for certain types of contour-shape processing they are poorly selective along the chromatic versus luminance dimension. Overall our results suggest that contour-shape encoding mechanisms are selective for color direction and that color is important for contour-shape processing.