Spatial frequency selectivity during saccadic eye movements revealed by masking

Purpose: Low but not high spatial frequencies are suppressed during saccades (Burr et al., J. Physiol. 1982), probably because of selective suppression of the magnocellular pathway (Burr et al., Nature 1994). Here we investigate further the mechanisms for the suppression, using masking techniques. Methods: Contrast sensitivity for horizontally oriented test grating patches of low spatial frequency (0.07 c/deg) was measured in the presence of continuously displayed, randomly jittering mask gratings of variable contrast and spatial frequency, using a forced-choice procedure. The test gratings were presented briefly (8 ms) during normal vision and during large horizontal saccades. Results: Sensitivity decreased with mask contrast, with a similar (near linear) dependency during normal viewing and during saccades. For both normal and saccadic viewing, maximum reduction in sensitivity occurred when the mask had the same spatial frequency as that of the test (0.07 c/deg), at all levels of mask contrast. Conclusions: That maximum masking occurs at the same spatial frequency of the test implies that mechanisms selective to low spatial frequencies are not totally suppressed during saccades, but continue to operate with reduced sensitivity. This result fits well with the acceleration of the impulse response for luminance but not for chromatic stimuli during saccades (Burr and Morrone, Vision Res. 1996), that may result from gain changes in the magnocellular pathway during saccades.