title: Shape perception enhances perceived contrast: evidence for excitatory predictive feedback?
abstract: Predictive coding theory suggests that predictable responses are "explained away" (i.e., reduced) by feedback. Experimental evidence for feedback inhibition, however, is inconsistent: most neuroimaging studies show reduced activity by predictive feedback, while neurophysiology indicates that most inter-areal cortical feedback is excitatory and targets excitatory neurons. In this study, we asked subjects to judge the luminance of two gray disks containing stimulus outlines: one enabling predictive feedback (a 3D-shape) and one impeding it (random-lines). These outlines were comparable to those used in past neuroimaging studies. All 14 subjects consistently perceived the disk with a 3D-shape stimulus brighter; thus, predictive feedback enhanced perceived contrast. Since early visual cortex activity at the population level has been shown to have a monotonic relationship with subjective contrast perception, we speculate that the perceived contrast enhancement could reflect an increase in neuronal activity. In other words, predictive feedback may have had an excitatory influence on neuronal responses. Control experiments ruled out attention bias, local feature differences and response bias as alternate explanations.
authors.affiliation: Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5549, Faculté de Médecine de Purpan, Toulouse Cedex, 31052, France.|Université de Toulouse, Centre de Recherche Cerveau et Cognition, Université Paul Sabatier, Toulouse, 31062, France.
authors.forename: Biao
authors.initials: B
authors.lastname: Han
authors.affiliation: Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5549, Faculté de Médecine de Purpan, Toulouse Cedex, 31052, France.|Université de Toulouse, Centre de Recherche Cerveau et Cognition, Université Paul Sabatier, Toulouse, 31062, France.
authors.forename: Rufin
authors.initials: R
authors.lastname: VanRullen
mesh_terms: D000328:Adult; D056228:Feedback, Sensory / Q000502:physiology*; D005260:Female; D005556:Form Perception / Q000502:physiology; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008959:Models, Neurological; D008960:Models, Psychological; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011594:Psychometrics; D014793:Visual Cortex / Q000502:physiology*; D055815:Young Adult