The perception of target motion during smooth pursuit eye movements in the open-loop condition: characteristics of retinal and extraretinal signals.

During smooth pursuit eye movement, the perception of target motion appears to come from retinal and extraretinal influences. To explore this, two open-loop conditions (experimental stimuli stabilized at the retina) were used: one to look at the combined effect of retinal and extraretinal signals on perception (using sinusoidal target motion); and the other to look at the characteristics of an extraretinal signal alone (using a complex target and square-wave motion). In both conditions subjects tracked target motion in the dark, and subsequently compared it to motion of a similar target in the light. The main findings of the study are that the magnitude of the extraretinal signal decreases with frequency, and that the retinal and extraretinal signals combine additively. This system appears to involve a transport-time, which could be in the form of a time advance. These features of perception have a variety of implications for motor control.