title: A visual field dependent architecture for second order motion processing.
abstract: The visual system exploits a cortical hierarchy to process complex inputs such as those defined by modulations of motion and/or texture. One class of visual stimuli, composed of alternate stripes of opposing motion requires at least 2 separate stages of computation within this cortical hierarchy, thought to involve cortical area V1 and extra-striate regions like global motion area MT respectively. Using a psychophysical task, we characterise sensitivity to such stimuli containing periodic spatial modulations of motion gradients as a function of the ratio of the spatial parameters at the two processing levels by manipulating the spatial properties of the carrier and modulator. We find band-passed functions for foveal stimulus presentations showing an optimum sensitivity at ratios in the range of r≤10, informative of the coupling relationship between frequency channels at the carrier and modulator levels. An annulus stimulus (excluding the fovea) with a radius of 15.5° exhibited optima of sensitivity at r>15. This difference in the optimal coupling between filtering stages reflects a processing architecture that changes with eccentricity, consistent with the previously observed smaller differences between mean receptive field sizes in striate and extra-striate filtering stages in the fovea compared to the periphery. This is also important for visual psychophysics when comparing sensitivity for first and second order stimuli across retinal eccentricity.
authors.affiliation: McGill Vision Research, Department of Ophthalmology, McGill University, 687 Pine Avenue West, Rm H4-14, Montreal, QC H3A1A1, Canada. andrew.meso@mcgill.ca
authors.forename: Andrew Isaac
authors.initials: AI
authors.lastname: Meso
authors.forename: Robert F
authors.initials: RF
authors.lastname: Hess
mesh_terms: D000465:Algorithms; D005584:Fovea Centralis / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D009039:Motion Perception / Q000502:physiology*; D010775:Photic Stimulation; D012160:Retina / Q000502:physiology; D012684:Sensory Thresholds; D012984:Software; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology*