Interactions of motion and form in visual cortex – A neural model

In this work, we present a neural model simulating parts of the motion and the form pathway of the visual cortex. It is shown how the visual features motion, disparity, and form that are represented in a distributed way in areas V1, V2, and MT mutually interact at several levels. Thus, their information is shared without the need of explicit neural representation for each combination of features. In particular, we address the issue of 2D extrinsic motion cues generated at occlusions that have to be treated differently than 2D intrinsic motion features of the same object. We suggest that here information of the form channel, namely the indication of a junction, is necessary to achieve a correct percept in the motion pathway. Furthermore, we investigated the question of how a percept of either pattern or component motion is generated in a scenario of moving bars that only differs in the presence or absence of occlusions, like in the chopstick and the barberpole display. We propose different roles for various kinds of MT cells that are involved in the interactions with the form pathway, simulating purely integrative cells tuned to motion and to motion and stereo, but also contrast cells responding strongly when motion in the surround is in the opposite direction. The model simulations reproduce psychophysical and neurophysiological results of the chopstick as well as of the barberpole illusion. The temporal course of the dominant motion percept generated by the iterative interplay between motion and form pathway is in line with data of ocular following responses in primates and humans.