title: The neural structures expressing perceptual hysteresis in visual letter recognition.
abstract: Perception can change nonlinearly with stimulus contrast, and perceptual threshold may depend on the direction of contrast change. Such hysteresis effects in neurometric functions provide a signature of perceptual awareness. We recorded brain activity with functional neuroimaging in observers exposed to gradual contrast changes of initially hidden visual stimuli. Lateral occipital, frontal, and parietal regions all displayed both transient activations and hysteresis that correlated with change and maintenance of a percept, respectively. Medial temporal activity did not follow perception but increased during hysteresis and showed transient deactivations during perceptual transitions. These findings identify a set of brain regions sensitive to visual awareness and suggest that medial temporal structures may provide backward signals that account for neural and, thereby, perceptual hysteresis.
authors.affiliation: Department of Neurology, Johann Wolfgang Goethe University, Theodor-Stern-Kai 7, D-60590 Frankfurt/M, Germany. akleins@em.uni-frankfurt.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Kleinschmidt
authors.forename: Christian
authors.initials: C
authors.lastname: Büchel
authors.forename: Chloe
authors.initials: C
authors.lastname: Hutton
authors.forename: Karl J
authors.initials: KJ
authors.lastname: Friston
authors.forename: Richard S J
authors.initials: RS
authors.lastname: Frackowiak
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology*; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000502:physiology*; D003071:Cognition / Q000502:physiology; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007088:Illusions / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008297:Male; D009434:Neural Pathways / Q000033:anatomy & histology / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011597:Psychomotor Performance / Q000502:physiology; D011932:Reading; D012683:Sensory Deprivation / Q000502:physiology; D014705:Verbal Behavior / Q000502:physiology*