How are non-retinotopic motion signals integrated? -A high-density EEG study

Objects moving in the visual scene cause retinal displacements that are not the result of motor commands and thus cannot be accounted for by efference copies. Yet, we easily keep track of moving objects even without following them with our gaze. Here, we investigated the neural correlates of non-retinotopic motion integration using high-density EEG. We presented three disks that either flickered at the same location (retinotopic reference frame) or moved left-right in apparent motion, creating a non-retinotopic reference frame in which the features of the disks are integrated across retinal positions. In one disk, a notch was either changing positions across frames in a rotating fashion, or stayed in the same position. The notch then started or stopped rotating after a random number of frames. We found stronger EEG responses for rotating than for static notches. In the novel state (first frame of rotating or static), this effect occurs in the N2 peak and resembles a motion-onset detection signal. Inverse solutions point to the right middle temporal gyrus as the underlying source. Importantly, these results hold for both the retinotopic and the non-retinotopic reference frames, indicating that the rotation encoding is independent of reference frame.