title: Directional anisotropy of motion responses in retinotopic cortex.
abstract: Recently, evidence has emerged for a radial orientation bias in early visual cortex. These results predict that in early visual cortex a tangential bias should be present for motion direction. We tested this prediction in a human imaging study, using a translating random dot pattern that slowly rotated its motion direction 360 degrees in cycles of 54 s. In addition, polar angle and eccentricity mapping were performed. This allowed the measurement of the BOLD response across the visual representations of the different retinotopic areas. We found that, in V1, V2, and V3, BOLD responses were consistently enhanced for centrifugal and centripetal motion, relative to tangential motion. The relative magnitude of the centrifugal and centripetal response biases changed with visual eccentricity. We found no motion direction biases in MT+. These results are in line with previously observed anisotropies in motion sensitivity across the visual field. However, the observation of radial motion biases in early visual cortex is surprising considering the evidence for a radial orientation bias. An additional experiment was performed to resolve this apparent conflict in results. The additional experiment revealed that the observed motion direction biases most likely originate from anisotropies in long range horizontal connections within visual cortex.
authors.affiliation: Functional Neurobiology, Helmholtz Institute, Utrecht University, Utrecht, The Netherlands. m.a.h.l.l.raemaekers@uu.nl
authors.forename: Mathijs
authors.initials: M
authors.lastname: Raemaekers
authors.forename: Martin J M
authors.initials: MJ
authors.lastname: Lankheet
authors.forename: Sanne
authors.initials: S
authors.lastname: Moorman
authors.forename: Zoe
authors.initials: Z
authors.lastname: Kourtzi
authors.forename: Richard J A
authors.initials: RJ
authors.lastname: van Wezel
mesh_terms: D016880:Anisotropy; D001931:Brain Mapping; D006801:Humans; D008279:Magnetic Resonance Imaging; D009039:Motion Perception / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*