Rhythmic oscillations of visual contrast sensitivity triggered by voluntary action

Abstract

Spontaneous oscillations of brain activity can be synchronized by external stimuli, or by allocation of attention, and this can lead to small synchronous modulation of visual perceptual performance (Landau and Fries, 2012, Thut et al., 2012). Increasing evidence shows that motor processing affects perception in many ways. Here we investigated whether performing an action can generate rhythmic oscillations of visual contrast sensitivity. We measured visual contrast sensitivity for orientation discrimination of briefly (33 ms) displayed Gabors (spatial frequency 1 c/deg; eccentricity 7.5 deg to the left or to the right of fixation) tilted at ± 45 degrees and embedded within dynamic noise (refreshed every frame) that lasted more than 3 s. Participants were asked to execute reaching movements towards the display behind an occluder (which hid the movement: open loop) in the same direction of the position of the right visual target. The visual stimuli were randomly presented at different times with respect to the movement (from ~ 500 ms before to ~ 300 ms after movement onset) and for each subject more than 2000 trials were collected to obtain stable psychometric functions densely sampled over time. Visual contrast sensitivity for both eccentricities varied by about 0.2 log-units, oscillating with periodicity in the theta range (~ 5 Hz). Interestingly, the oscillations in visual performance began before movement onset, suggesting that a motor preparatory signal might be responsible for synchronizing activity in primary visual areas. The present results reinforce growing evidence that sensory and motor functions are strongly interconnected, demonstrating that motor processing can modulate very early sensory function, such as the sensitivity to visual contrast, and suggesting that sensory-motor integration might be, at least partly, mediated by phase modulations of brain rhythmic activity.

Meeting abstract presented at VSS 2014