Size and shape after-effects: Same or different mechanism?

The shape-frequency and shape-amplitude after-effects, or SFAE and SAAE, are shifts in the perceived shape-frequency and perceived shape-amplitude of a sinusoidal test contour following adaptation to a similar-shaped contour. These shape-effects are the shape analogs of the well-known size after-effect discovered by Blakemore and Sutton (1969), so it is possible that they are mediated by a size-sensitive mechanism. We tested this possibility by comparing the magnitudes of SFAEs/SAAEs elicited by contour/edge adaptors with those from luminance grating and line-grating adaptors. The rationale was that if the shape after-effects using the two classes of adaptors were similar, then they would likely be mediated by the same mechanism. We found that the SFAE and SAAE were greatly reduced when using luminance and line grating adaptors, suggesting that the SFAE and SAAE are not mediated primarily by either first- or second-order size-sensitive mechanisms. Based on previous studies we conclude that SFAEs/SAAEs are mediated by mechanisms primarily sensitive to curvature.