MIB As Noisy Excitable System

Perceptual disappearance of a salient target induced by a moving texture mask (MIB: Motion Induced Blindness) is a striking effect poorly understood. Here we ask whether the mechanisms underlying MIB represent an excitable system. Excitable systems exhibit fast switches from one state to another (e.g., visible/invisible) induced by an above threshold perturbation, and a stimulus independent dynamics followed by a refractory period. In the experiments disappearance was induced by masks consisting of slowly rotating radial bars placed at different eccentricity relative to the target leading to periodic perturbation of the visual field around the target (a bright parafoveal spot or Gaussian blob, surrounded by a protection zone where bars were not shown). The bars passing around the target location induced an abrupt target disappearance within a range of rotation speed (up to 95%, depending on condition, ~0% without bars), pointing to locality. As expected from excitable systems, disappearance time was not affected by additional bars crossing the target during invisibility. Also, adding a second set of rotating bars, with a displaced center, increased invisibility time only slightly, but significantly. After the target reappeared, it stayed for at least 0.5-2 sec (refractory period). Overall, slowly moving bars are very good inducers of perceptual disappearance when targets are visible, while hardly affecting an invisible target. Invisibility periods (0.5-2sec on average) show little dependence on mask configuration. Therefore, the mechanisms governing MIB represent an example of an excitable system where transition to the invisible state is induced by the mask, with the following dynamics determined mostly by internal network properties. The implementation of such systems requires two components with substantially different time scales, such as adaptation and inhibition. Additionally, variability in invisibility periods and less than perfect efficiency in invisibility induction by the mask, point to the presence of noise in the dynamics. Meeting abstract presented at VSS 2016