NONUNIFORM SPATIAL INTEGRATION IN MT NEURONS SHAPES MOTION DISCRIMINATION

Visual perception requires integrating noisy dynamic information across time and space to identify relevant stimuli and guide behaviour. In the case of motion perception, neurons in the Middle Temporal area (MT) of macaques have been shown to respond instantaneously to motion within their receptive fields, and studies have analysed how these responses are integrated across time to make decisions. These neurons also exhibit well-documented nonlinear spatial mechanisms, such as surround suppression/facilitation. However, these neural effects have not been mechanistically linked to spatial suppression effects observed in motion perception experiments.Here, we show that the spatial structure of visual stimuli modulates neural responses in visual cortex and impacts perceptual choices, and we propose a model linking these effects.
In a motion discrimination task, we find that macaque choices integrate spatial evidence sublinearly with (i) weaker impact of motion further away from the fovea, and (ii) surround suppression effects causing an attenuation of the responses to motion in the centre of the stimulus. To investigate the neural basis of these effects, we used nonlinear regression models and found evidence for nonuniform spatial integration in MT, with heterogeneous spatial weights across neurons. A decision making model based on pooled responses from a population of MT neurons with these heterogeneous spatial weighting profiles and linear temporal integration, reproduced the spatial effects observed at the behavioural level.
Taken together, our results highlight the impact of nonlinear spatial integration at the level of sensory representations of motion on the perception of spatially distributed motion signals.