Abstract
It is known that smooth pursuit eye movement (SPEM) modulates visual contrast sensitivity in an asymmetric manner. For instance, Schütz et al. (2007) reported that contrast sensitivity to a 1 c/deg grating is higher when it drifts in the same direction with the SPEM than in the opposite direction. They interpret this asymmetry in terms of the effect of spatial attention that moves together with, or even leads, the eye. The present study shows that this asymmetry is reversed at high spatial frequency bands. We measured contrast sensitivity for a spatially localized grating (Gabor patch) of 11 c/deg. The spatial window of the grating (s.d. of H0.8 x V0.4 deg) moved in the same velocity with SPEM (1.5 deg/sec), and thereby it was static on the retinal coordinate. The grating within spatial window drifted on the retina either in the same direction or in the opposite direction of SPEM. We found that for a range of retinal temporal frequencies tested (1.4-22.5 Hz), the observer's contrast sensitivity was substantially higher (0.1-0.25 log unit) when the grating drifted in the opposite direction of SPEM than in the same direction. This asymmetry was also observed for the cut-off temporal frequencies for a grating with a contrast of 0.5. For gratings of a low spatial frequency (0.5 c/deg), the cut off frequency was little, or not, higher for gratings in the same same direction than in the opposite direction of SPEM, consistent with the previous study. These results indicate that during smooth pursuit, the visual system becomes more sensitive to high-spatial frequency signals that moves slower than the eye than those that moves faster than the eye. The results cannot be well accounted for neither by spatial attention nor by sensitivity modulations of parvocellular and magnocellular channels.
Meeting abstract presented at VSS 2015