Abstract
During natural vision, visual input arrives to the brain in the context of ongoing oculomotor behavior. Saccadic eye movements, in particular, occur 3–5 times a second and have profound perceptual consequences, not limited to saccadic suppression and spatiotemporal warping, but also attention-like enhancements preceding eye movements. While previous studies have identified signatures of saccadic suppression in early visual cortex, none have identified pre-saccadic enhancements. Here, we studied the representation of visual information in V1 immediately preceding and following saccadic eye movements. Unlike previous studies that used repetitive planned saccades, we used a full-field foraging paradigm that enabled very high saccade counts under more realistic viewing conditions. Awake, head-fixed marmosets freely viewed full-field sinewave gratings to identify small targets embedded in the scene while we recorded from populations of V1 neurons using linear electrode arrays. The spatial frequency and orientation of the full-field gratings were updated randomly on each frame to support subspace reverse correlation (Ringach et al., 1997). Saccades produced substantial pre- and- post-saccadic firing rate modulations in almost all neurons. Post-saccadic modulations followed a biphasic form with suppressive firing rate changes preceding enhancements whereas pre-saccadic modulations were largely explained by gradual decreases in firing rate starting 100ms before saccade onset. Using a linear-nonlinear-Poisson model fit to spiking data, we decomposed these firing rate modulations into a stimulus-driven linear component and a monotonic nonlinearity that maps the output of the linear stage into spike rate. Although firing rates decreased preceding saccades, the slope of the spiking nonlinearity became steeper, enhancing selectivity for preferred stimuli immediately preceding the saccade onset. This enhancement occurred most frequently in neurons with high preferred spatial frequencies in agreement with the human psychophysical phenomena. These results show that pre-saccadic activity is enhanced for V1 neurons carrying higher spatial frequency information during free-viewing.
Acknowledgement: NIH U01-NS094330, U of R SPIN grant to JFM T32EY007125 to SHC JLY is an Open Philanthropy Fellow of the Life Sciences Research Foundation