A common cortical detection mechanism for perception and movement
26.3017, Saturday, 16-May, 2:45 pm - 6:45 pm, Banyan Breezeway
Alex White1, Martin Rolfs1; 1Bernstein Center for Computational Neuroscience & Department of Psychology, Humboldt University Berlin
Visual input is shared by many perceptual, cognitive, and motor functions. We can study the architecture of the brain by determining when these streams of sensory processing diverge. We took this approach to investigate two fundamental perceptual and motor functions: visual detection and microsaccadic inhibition. Microsaccades are small, spontaneous eye movements that occur during attempted fixation. They are briefly and reflexively inhibited following the onset of a visual stimulus. Does microsaccadic inhibition rely on the same detection mechanisms as conscious perception, or an independent, possibly subcortical processing stream? Observers fixated a small point and detected a Gabor stimulus flashed briefly on a random half of trials. We measured perceptual sensitivity (d’), and oculomotor sensitivity for the same stimulus, derived from the drop in microsaccade rates following stimulus onset. In a first experiment, we found that foveal contrast thresholds for perceptual and oculomotor responses were very similar. In fact, microsaccades were inhibited if and only if the observer reported seeing a stimulus, even when no stimulus was present. This finding suggests a strong link between perception and oculomotor control: they share a source of internal noise. We then used orientation-specific adaptation to determine whether the signal triggering microsaccadic inhibition goes through visual cortex. In two experiments using foveal and peripheral targets, respectively, each trial began with several seconds of adaptation to a flickering grating. The target Gabor, flashed after the adaptor on 50% of trials, either had the same (adapted) or the orthogonal (unadapted) orientation. Consistent with classic phenomena known to rely on orientation-selective cortical neurons, perceptual sensitivity was reduced for the adapted orientation. Oculomotor sensitivity followed the same pattern: microsaccadic inhibition was less pronounced for the adapted than the orthogonal orientation. We conclude that even the most reflexive oculomotor responses rely on the same cortical detection mechanisms as perception.