title: 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.
  
  
  CONCLUSIONS
  Human and nonhuman primates can spot an animal shape in complex natural scenes with striking speed, and this has been taken as evidence that the underlying cortical mechanisms are strictly feedforward. Using a novel paradigm to probe the dynamics of shape perception, we find that two shape stimuli are optimally reinforcing when separated in time by 60 ms, suggesting a fast but recurrent neural circuit. This work (1) introduces a novel method for probing the temporal dynamics of cortical circuits underlying perception, (2) provides direct evidence against the feedforward assumption for rapid shape perception, and (3) yields insight into the role of feedback connections in the object pathway.
authors.affiliation: Centre for Vision Research, York University, Toronto, Ontario, Canada M3J 1P3, Center for Mind/Brain Sciences, University of Trento, I-38068 Rovereto, Italy, mail@jandrewes.de.
authors.forename: Jan
authors.identifier: http://orcid.org/0000-0003-4657-2568
authors.initials: J
authors.lastname: Drewes
authors.affiliation: Centre for Vision Research, York University, Toronto, Ontario, Canada M3J 1P3.
authors.forename: Galina
authors.identifier: http://orcid.org/0000-0003-4416-3250
authors.initials: G
authors.lastname: Goren
authors.affiliation: School of Information Science, Yunnan University, Kunming 650091, China, and Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China.
authors.forename: Weina
authors.identifier: http://orcid.org/0000-0002-9260-1529
authors.initials: W
authors.lastname: Zhu
authors.affiliation: Centre for Vision Research, York University, Toronto, Ontario, Canada M3J 1P3.
authors.forename: James H
authors.identifier: http://orcid.org/0000-0003-3880-4808
authors.initials: JH
authors.lastname: Elder
mesh_terms: D000328:Adult; D025461:Feedback, Physiological / Q000502:physiology*; D005260:Female; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009473:Neuronal Plasticity / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*; D055815:Young Adult
keywords: contour processing; feedback, grouping; perceptual organization; recurrent processing; shape perception; temporal integration