Recurrent processing in the formation of shape percepts

Abstract

The human visual system must extract reliable object information from cluttered visual scenes several times per second, and this temporal constraint has been taken as evidence that the underlying cortical processing must be strictly feedforward. Here we use a novel rapid reinforcement paradigm to probe the temporal dynamics of the neural circuit underlying rapid object shape perception and thus test this feedforward assumption. Our results show that two shape stimuli are optimally reinforcing when separated in time by ~60 ms, suggesting an underlying recurrent circuit with a time constant (feedforward+feedback) of 60 ms. A control experiment demonstrates that this is not an attentional cueing effect. Instead, it appears to reflect the time course of feedback processing underlying the rapid perceptual organization of shape.