Temporal contrast sensitivity during smooth pursuit eye movements

Abstract

During smooth pursuit eye movements, stimuli other than the pursuit target typically move across the retina, and this might have an effect on their detectability. We used a 2AFC paradigm to measure detection thresholds for 1 cpd vertical Gabor stimuli of temporal frequencies between 1 deg/s and 24 deg/s, which moved horizontally within a Gaussian window. Observers had to indicate whether the Gabor targets were displayed 4 deg above or below the center of the screen. Observers kept fixation on a small target spot that was either stationary or moved at a speed of 8 deg/s in the same or opposite direction as the Gabor. We found that temporal contrast sensitivity was mainly limited by the temporal frequency on the retina. The high temporal frequency cutoff was shifted from 21 Hz under fixation to 15 Hz when the eyes and target moved in opposite directions and to 27 Hz when eyes and target moved in the same direction. However, there were significant sensitivity differences at the peak temporal frequency. Sensitivity was greatest for the fixation condition, reduced by 8% for the condition when eyes and Gabor target moved in the same direction, and reduced by 16% when they moved in opposite directions. The loss in sensitivity for peripheral targets during pursuit could be due to the attentional demands of pursuit or the jitter of the target on the retina caused by small fluctuations in the speed of eye movements.