PERCEPTUAL CONSEQUENCES OF OCULAR LENS OVERSHOOT DURING SACCADIC EYE-MOVEMENTS

In a previous paper we compared eye globe records of saccadic eye move ments (recorded with a scleral eye coil) with lens reflection records of the same eye movements (recorded with a dual-Purkinje-image eyetrac ker); we found evidence for considerable dynamic deviations between th e two during and immediately after saccades. We ascribed these deviati ons to the movements of the eye's lens relative to the optical axis of the eye. This paper quantifies a predicted psychophysical effect of l ens displacements during and after saccades. Two small targets, one ab ove the other, were flashed for 2 msec in total darkness, the bottom o ne exactly at the end of the saccade, the top one 30 msec later. The f irst target appears deviated horizontally relative to the other, in a direction opposite to the saccade. Magnitude of the relative mislocali zation can be up to 0.03 deg for each degree of saccadic eye movement. The result shows that the position of the visual image on the retina is affected both by position of the globe and by deviations of the len s from its normal location.