title: Spatial non-homogeneity of the antagonistic surround in motion perception.
abstract: At high contrast, duration thresholds for motion direction discrimination deteriorate with increasing stimulus size. This counterintuitive result has been explained by the center-surround antagonism present in the neurons of visual area MT. Conversely, at very low contrast, direction discrimination improves with increasing size, a result that has been explained by spatial summation. In this investigation, we study the effects of stimulus shape and contrast on center-surround antagonism. Using adaptive Bayesian staircases, we measured duration thresholds of 5 subjects for vertically oriented Gabor patches of 1 cycle/deg with two types of oval Gaussian windows, one vertically elongated (Sx = 0.35, Sy = 2.5 deg) and other horizontally elongated (Sx = 2.5, Sy = 0.35 deg) moving rightward or leftward at a speed of 2 deg/s. We found that at high contrast (92%) duration thresholds were lower for vertically than horizontally elongated windows. However, at low contrast (2.8%), we found that duration thresholds were lower for horizontally than vertically elongated windows. These asymmetric results mirror the spatial non-homogeneity of the antagonistic surround found in MT neurons and suggest that the underlying center-surround antagonism is stronger along the direction of motion.
authors.affiliation: Faculty of Psychology, Departmernt of Basic Psychology I, Complutense University of Madrid, Campusde Somosaguas, Madrid, Spain. iserrano@psi.ucm.es
authors.forename: Ignacio
authors.initials: I
authors.lastname: Serrano-Pedraza
authors.forename: Ellen L
authors.initials: EL
authors.lastname: Hogg
authors.forename: Jenny C A
authors.initials: JC
authors.lastname: Read
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D001499:Bayes Theorem; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008297:Male; D008959:Models, Neurological; D009039:Motion Perception / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D012160:Retina / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology; D055815:Young Adult