Radial orientation and direction biases in the response of human visual cortex to kinetic contours

Abstract

Event Abstract Back to Event Radial orientation and direction biases in the response of human visual cortex to kinetic contours It has recently been observed using fMRI that radial orientations produce higher activity in retinotopic regions of visual cortex (Sasaki, Y. et al. (2006) Neuron 51, 661-670). Here, we report analogous biases for: (1) the axis of motion (horizontal or vertical) of unoriented textures; (2) the orientation of ‘kinetic’ contours defined solely by the borders between strips of texture moving in opposite directions. fMRI at 3T was used to measure the BOLD signal (1.5mm cubic voxels; TR = 3s.) in the visual cortex of six human subjects viewing kinetic contour stimuli presented in 15-second blocks. Stimuli were composed of 0.6° strips of spatial white noise texture presented in an annulus 1-6° in radius. The texture in alternate strips moved in opposite directions (left-right or up-down) at 3°. The strips themselves were static and tilted 45°either left or right from vertical. A systematic pattern of bias across the cortical surface was evident in response to the axis of motion of the textures when data were pooled across the orientation of the kinetic contours. Comparison with flat maps of the visual field representation obtained from phase-encoded retinotopic analysis revealed that representations of the vertical (horizontal) meridian tended to respond more strongly to vertical (horizontal) motion. Specifically, a bias for horizontal motion was evident within V1 and along the borders between V2 and V3; a bias for vertical motion was apparent along the borders between V1 and V2 and at the extremes of V3. Pooling data across the axis of motion of the textures revealed a different pattern of bias: the response to a given orientation was stronger in the quadrants of the visual field for which contour orientation was predominantly radial. Specifically, the response to leftward (rightward) tilted gratings tended to be stronger in the dorsal part of the left (right) visual cortex and the ventral part of the right (left) visual cortex. Quantitative analysis of the variation in the proportion of voxels preferring a particular axis of motion as a function of the meridian angle of the visual field representation (in 10° bins) revealed a radial direction bias significant across subjects at p < 0.05 or better in each of areas V1, V2 and V3. Similar analysis showed a radial bias for the orientation of kinetic contours at p < 0.01 in each of these areas. Radial orientation bias likely results from a disproportionate number of neurons being tuned to radial orientations. The existence of radial biases for the orientation of kinetic (‘non-Fourier’) as well as luminance-defined (‘Fourier’) contours could reflect processing by cue-invariant orientation mechanisms or by distinct neuronal populations subject to similar anisotropies in orientation tuning. The radial bias for motion might be related to the phenomenon of ‘motion streaks’ whereby temporal integration by the visual system introduces oriented blur along the axis of motion. We speculate that all the observed forms of radial bias reflect a single underlying anisotropy in the way (Fourier and non-Fourier) stimulus energy is processed across the visual field. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). Radial orientation and direction biases in the response of human visual cortex to kinetic contours. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.016 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 29 Jan 2009; Published Online: 29 Jan 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.