title: BOLD activation varies parametrically with corner angle throughout human retinotopic cortex.
abstract: The Alternating Brightness Star (ABS) is an illusion that provides insight into the relationship between brightness perception and corner angle. Recent psychophysical studies of this illusion have shown that corner salience varies parametrically with corner angle, with sharp angles leading to strong illusory percepts and shallow angles leading to weak percepts. It is hypothesized that the illusory effects arise because of an interaction between surface corners and the shape of visual receptive fields: sharp surface corners may create hotspots of high local contrast due to processing by center-surround and other early receptive fields. If this hypothesis is correct, early visual neurons should respond powerfully to sharp corners and curved portions of surface edges. Indeed, the primary role of early visual neurons may be to localize the discontinuities along the edges of surfaces. If so, all early visual areas should show greater BOLD responses to sharp corners than to shallow corners. On the other hand, if corner processing is exclusively constrained to certain areas of the brain, only those specific areas will show greater responses to sharp vs shallow corners. To address this we explored the BOLD correlates of the ABS illusion in the human visual cortex using fMRI. We found that BOLD signal varies parametrically with corner angle throughout the visual cortex, offering the first neurophysiological correlates of the ABS illusion. This finding provides a neurophysiological basis for the previously reported psychophysical data that showed that corner salience varied parametrically with corner angle. We propose that all early visual areas localize discontinuities along the edges of surfaces, and that specific cortical corner-processing circuits further establish the specific nature of those discontinuities, such as their orientation.
authors: Department of Neurobiology, Barrow Neurological Institute, 350 West Thomas Road, Phoenix, AZ 85013, USA. smart@neuralcorrelate.com
authors: Xoana G
authors: XG
authors: Troncoso
authors: Peter U
authors: PU
authors: Tse
authors: Stephen L
authors: SL
authors: Macknik
authors: Gideon P
authors: GP
authors: Caplovitz
authors: Po-Jang
authors: PJ
authors: Hsieh
authors: Alexander A
authors: AA
authors: Schlegel
authors: Jorge
authors: J
authors: Otero-Millan
authors: Susana
authors: S
authors: Martinez-Conde
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping / Q000379:methods; D015350:Contrast Sensitivity / Q000502:physiology; D005260:Female; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009903:Optical Illusions; D010364:Pattern Recognition, Visual / Q000502:physiology; D010775:Photic Stimulation; D011601:Psychophysics; D012160:Retina / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*