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Signal integration for perceptual decision about motion and depth in cortical area V5/MT
Neuroscience should tell us how activity in the brain gives rise to our experience of the world. Visual experience is fundamentally dependent on combining information from different visual and contextual cues to guide behaviour. An important challenge is to identify brain sites for which we can demonstrate a direct link between activation of a neuronal circuit and the behavioral report of a specific percept, action or decision. My laboratory has identified cortical circuitry in visual area V5/MT in the primate that is specialised for processing cue combinations of binocular depth and direction of motion. These visual cues are combined in a columnar structure, which allowed us to employ electrical microstimulation in the awake behaving primate as a causal intervention that can alter the reported perceptual appearance of a visual stimulus. These experiments show that V5/MT contributes directly to conjoint encoding of depth and direction in visual stimuli. Furthermore, manipulation of the available reward size in the task changes the effectiveness of the electrical microstimulation. By using computational modeling, we show that these experimental results lead to the conclusion that change in reward affects the sensory processing of the visual information. Converging evidence from electrical stimulation, neurophysiology and computational approaches in both monkeys and humans suggest that sensory and reward information are already combined in visual cortex. Reward may therefore influence behaviour both by biasing decisions but also through changing how we perceive the world.
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