title: Investigating local network interactions underlying first- and second-order processing.
abstract: We compared the spatial lateral interactions for first-order cues to those for second-order cues, and investigated spatial interactions between these two types of cues. We measured the apparent modulation depth of a target Gabor at fixation, in the presence and the absence of horizontally flanking Gabors. The Gabors' gratings were either added to (first-order) or multiplied with (second-order) binary 2-D noise. Apparent "contrast" or modulation depth (i.e., the perceived difference between the high and low luminance regions for the first-order stimulus, or between the high and low contrast regions for the second-order stimulus) was measured with a modulation depth-matching paradigm. For each observer, the first- and second-order Gabors were equated for apparent modulation depth without the flankers. Our results indicate that at the smallest inter-element spacing, the perceived reduction in modulation depth is significantly smaller for the second-order than for the first-order stimuli. Further, lateral interactions operate over shorter distances and the spatial frequency and orientation tuning of the suppression effect are broader for second- than first-order stimuli. Finally, first- and second-order information interact in an asymmetrical fashion; second-order flankers do not reduce the apparent modulation depth of the first-order target, whilst first-order flankers reduce the apparent modulation depth of the second-order target.
authors.affiliation: Department of Ophthalmology, McGill Vision Research Unit, McGill University, 687 Pine Ave. West H4-14, Montreal, Que., Canada H3A 1A1. dave.ellemberg@staff.mcgill.ca
authors.forename: Dave
authors.initials: D
authors.lastname: Ellemberg
authors.forename: Harriet A
authors.initials: HA
authors.lastname: Allen
authors.forename: Robert F
authors.initials: RF
authors.lastname: Hess
mesh_terms: D015350:Contrast Sensitivity / Q000502:physiology*; D003463:Cues; D006801:Humans; D009039:Motion Perception / Q000502:physiology*; D009949:Orientation; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D014795:Visual Pathways / Q000502:physiology