Abstract
In a series of physiological and psychophysical experiments, our lab has previously shown that there are significant differences in brain representations and visual perception between natural vision and vision in laboratory experiments. Complex natural scenes and saccadic eye movements alter vision relative to experiments with simple stimuli flashed during prolonged fixation. Here we show that natural vision has significant effects on contrast sensitivity and that these effects are predictable from patterns of activation in macaque V1. Animals were trained to perform a 2AFC contrast discrimination task while recordings from V1 were made with 96 electrode Utah arrays. Conditions in which saccades brought stimuli into receptive fields were compared with other conditions that required fixation before stimuli were flashed. In both conditions the Gabor target stimuli were positioned on a complex natural scene background. We find, with similar visual input, that saccades across a complex scene alter contrast sensitivity relative to sensitivity with flashed stimuli. Specifically, contrast sensitivity is worse at lower spatial frequencies (1-4 cy/deg) but similar at higher spatial frequencies when a saccade brings the Gabor target into view. This effect is comparable to the reduced contrast sensitivity our lab has reported in similar human psychophysics experiments. The differences between "saccade" and "flash" contrast sensitivity functions is consistent with the effects of saccades across complex scenes on V1 spiking and LFP activity and the spatial frequency dependence of neural changes. Importantly, the spatial frequency dependence of the effects appears related to the statistics of natural scenes rather than magno/parvo processing differences. These findings are important for the characterization of V1 responses and perception in natural vision and for the clinical assessment of contrast sensitivity.
Meeting abstract presented at VSS 2014