Role of area MSTd in cue integration for heading discrimination: II. Analysis of correlations between neural responses and perceptual decisions

Abstract

Neurons in area MSTd exhibit spatial tuning in response to optic flow and during inertial motion in darkness. To better understand MSTd's role in heading perception, we studied correlations between single-unit responses and perceptual choices during a fine heading discrimination task. Monkeys reported their heading relative to straight ahead in a Vestibular condition (inertial motion only), a Visual condition (optic flow only), and a Combined condition (congruent inertial motion and optic flow). To assess functional coupling between MSTd responses and perceptual decisions, we computed ‘choice probabilities’ (CPs), which characterize trial-to-trial covariation between neural responses and the animal's choices. Overall, CPs were strongest under the Vestibular condition, in which ∼25% of MSTd neurons showed significant positive effects and the mean CP (0.55) was significantly > 0.5 (p<0.001). Under the Visual condition, ∼16% of neurons showed significant CPs with similar numbers of positive and negative effects. The mean CP (0.51) was not significantly different from chance (p=0.2). Interestingly, ‘congruent’ MSTd neurons with matched visual and vestibular tuning preferences tended to be positively correlated with choices in the Visual condition (mean CP=0.56, p=0.002), whereas neurons with opposite tuning preferences tended to be negatively correlated (mean CP=0.45, p=0.04). Our findings suggest that vestibular signals in area MSTd contribute to heading perception. In addition, the Visual CP data suggest that visual responses of MSTd neurons are read out differently depending on the congruency of visual and vestibular tuning preferences. This highlights the importance of studying multi-sensory integration for understanding heading perception.