title: A cortical locus for anisotropic overlay suppression of stimuli presented at fixation.
abstract: Human contrast sensitivity for narrowband Gabor targets is suppressed when superimposed on narrowband masks of the same spatial frequency and orientation (referred to as overlay suppression), with suppression being broadly tuned to orientation and spatial frequency. Numerous behavioral and neurophysiological experiments have suggested that overlay suppression originates from the initial lateral geniculate nucleus (LGN) inputs to V1, which is consistent with the broad tuning typically reported for overlay suppression. However, recent reports have shown narrowly tuned anisotropic overlay suppression when narrowband targets are masked by broadband noise. Consequently, researchers have argued for an additional form of overlay suppression that involves cortical contrast gain control processes. The current study sought to further explore this notion behaviorally using narrowband and broadband masks, along with a computational neural simulation of the hypothesized underlying gain control processes in cortex. Additionally, we employed transcranial direct current stimulation (tDCS) in order to test whether cortical processes are involved in driving narrowly tuned anisotropic suppression. The behavioral results yielded anisotropic overlay suppression for both broadband and narrowband masks and could be replicated with our computational neural simulation of anisotropic gain control. Further, the anisotropic form of overlay suppression could be directly modulated by tDCS, which would not be expected if the suppression was primarily subcortical in origin. Altogether, the results of the current study provide further evidence in support of an additional overlay suppression process that originates in cortex and show that this form of suppression is also observable with narrowband masks.
authors.affiliation: Department of Psychology and Neuroscience Program,Colgate University,Hamilton,New York.
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Hansen
authors.affiliation: Department of Psychology,Concordia University,Montréal,Québec,Canada.
authors.forename: Bruno
authors.initials: B
authors.lastname: Richard
authors.affiliation: Department of Psychology and Neuroscience Program,Colgate University,Hamilton,New York.
authors.forename: Kristin
authors.initials: K
authors.lastname: Andres
authors.affiliation: Department of Psychology,Concordia University,Montréal,Québec,Canada.
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Johnson
authors.affiliation: School of Optometry and Vision Science,University of Waterloo,Waterloo,Ontario,Canada.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Thompson
authors.affiliation: Department of Psychological & Brain Sciences,University of Louisville,Louisville,Kentucky.
authors.forename: Edward A
authors.initials: EA
authors.lastname: Essock
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016880:Anisotropy; D005260:Female; D005829:Geniculate Bodies / Q000502:physiology; D006801:Humans; D008297:Male; D008959:Models, Neurological; D009433:Neural Inhibition / Q000502:physiology*; D010470:Perceptual Masking; D010775:Photic Stimulation; D011601:Psychophysics; D065908:Transcranial Direct Current Stimulation; D014793:Visual Cortex / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: Broadband noise; Contrast sensitivity; Horizontal effect; Overlay suppression; tDCS