06.01.2016: Dora Angelaki

A Bayesian Journey through our sixth sense: From sensors to cortex and beyond

Navigation and spatial orientation are vital functions in our lives. Sensory information arises from the balance (vestibular) organs in the inner ear. However, the brain must correct for a sensory ambiguity inherent in otolith vestibular afferents, as they cannot distinguish inertial accelerations (experienced during navigation) from changes in spatial orientation relative to gravity. A neural correlate of the brain’s ability to resolve this ambiguity is found in the simple spike activities of Purkinje cells in the caudal cerebellar vermis. In the absence of robust sensory information, perception of our movement through space becomes illusionary, as predicted by Bayesian priors that signal we are stationary in space. In addition, a fundamental aspect of our sensory experience is that information from different modalities is often seamlessly integrated into a unified percept. Recent computational and behavioral studies have shown that humans combine sensory cues according to a statically optimal scheme derived from Bayesian probability theory; they perform better when two sensory cues are combined. We have explored multisensory cue integration for self‐motion (heading) perception using both visual (optic flow) and vestibular (linear acceleration) signals. A neural correlate of this interaction during a heading direction discrimination task is found in the activity of single neurons in the macaque visual cortex. Neurons with congruent heading preferences for visual and vestibular stimuli show improved sensitivity and lower neuronal thresholds under cue combination. Indeed, Fisher information analysis of the population activity predicts the main properties of behavior.