Dynamics of eye-position signals in the dorsal visual system

Background: Many visual areas of the primate brain contain signals related to the current position of the eyes in the orbit. These cortical eye-position signals are thought to underlie the transformation of retinal input-which changes with every eye movement-into a stable representation of visual space. For this coding scheme to work, such signals would need to be updated fast enough to keep up with the eye during normal exploratory behavior. We examined the dynamics of cortical eye-position signals in four dorsal visual areas of the macaque brain: the lateral and ventral intraparietal areas (LIP; VIP), the middle temporal area (MT), and the medial-superior temporal area (MST). We recorded extracellular activity of single neurons while the animal performed sequences of fixations and saccades in darkness.

Results: The data show that eye-position signals are updated predictively, such that the representation shifts in the direction of a saccade prior to (<100 ms) the actual eye movement. Despite this early start, eye-position signals remain inaccurate until shortly after (10-150 ms) the eye movement. By using simulated behavioral experiments, we show that this brief misrepresentation of eye position provides a neural explanation for the psychophysical phenomenon of perisaccadic mislocalization, in which observers misperceive the positions of visual targets flashed around the time of saccadic eye movements.

Conclusions: Together, these results suggest that eye-position signals in the dorsal visual system are updated rapidly across eye movements and play a direct role in perceptual localization, even when they are erroneous.