Non-retinotopic adaptive center-surround modulation in motion processing

The early visual system is organized retinotopically. However, under ecological viewing conditions, motion perception occurs in non-retinotopic coordinates. Even though many studies revealed the central role of nonretinotopic processes, very little is known about their mechanisms and neural correlates. Tadin and colleagues found that increasing the spatial size of a high-contrast drifting-Gabor deteriorates motion-direction discrimination, whereas the opposite occurs with a low-contrast stimulus. The results were proposed to reflect an adaptive center-surround antagonism, whereby at low-contrast the excitatory center dominates whereas at high-contrast suppressive-surround mechanisms become more effective. Because ecological vision is non-retinotopic, we tested the hypothesis that the non-retinotopic system also processes motion information by means of an adaptive center-surround mechanism. We used the Ternus-Pikler display designed to provide either a retinotopic or a non-retinotopic reference-frame. Our results suggest that the non-retinotopic processes underlying motion perception are also mediated by an adaptive center-surround mechanism.