Radial Bias for Motion – Centrifugal or Centripetal?
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1
University of Sydney, School of Psychology, Australia
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2
Australian Research Council Centre of Excellence in Vision Science, Australia
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3
The University of Western Sydney,, School of Social Sciences and Psychology, Australia
Background: As an animal moves through the environment complex patterns of image motion stimulate the eyes. These patterns provide important cues in the coordination of navigation and locomotion in humans and other animals. Recent reports indicate that human early visual cortex responds preferentially to motion radial to the point of fixation. Here, we sought to investigate the determinants of this radial bias for motion.
Method: In 2 experiments, functional magnetic resonance imaging (fMRI; n = 6 human subjects) at 3T was used to measure blood-oxygenation level-dependent (BOLD) activity in functionally-defined regions of visual cortex to band-pass filtered random dot fields moving along 16 different complex motion trajectories (contracting, expanding, rotating and spiralling fields) centred at the fovea. In the first experiment these were “full-field” dot patterns that simulated optic flow. In the second experiment stimuli were restricted either to an annulus close to the fovea (0.75-1.87 deg) or further in the periphery (4.81-6.28 deg). Eye position and attention were controlled by requiring subjects to monitor a sporadic dimming of the fixation spot. Eye position was also recorded in some subjects using the MR-compatible EyeLink1000 gaze tracking system.
Results: Anisotropies were observed in the pattern of BOLD activity dominated by a greater response for contracting or expanding fields. The pattern of these anisotropies changed systematically with eccentricity in visual areas V1-V3, V3A/B and hV4 (but not V5/MT+), evolving from a preference for expanding over contracting patterns close to the fovea, to the exact opposite at the most peripheral region stimulated. This effect was most robust in V2 and V3. In the second experiment, there was again a general preference for radial motions (contracting/expanding), though this did not differ with eccentricity.
Discussion: Characteristic processing anisotropies for complex motions exist in human early visual cortex, but their strength and direction depend upon eccentricity when presented full-field. The results suggest that the visual cortex dynamically adjusts its activity in response to moving stimuli depending on the trajectory they are describing on the retina. This may reflect the predictability of the stimulus motion, which is known to have a significant influence on both perceptual variables and visual cortical activity.
Acknowledgements
Funding: This work was supported by a National Health and Medical Research Council
grant (C.W.G.C.; grant number APP1027258), an Australian Research Council (ARC) Future
Fellowship (C.W.G.C.; grant number FT110100150), an ARC Post-doctoral Fellowship
(T.L.W.; grant number DP11010217) and the ARC Centre of Excellence in Vision Science.
The authors thank Dr Isabelle Mareschal and Dr Sam Solomon for helpful discussions and
Kirsten Moffatt and the MRI radiography team at St. Vincent's hospital.
Keywords:
Complex motion perception,
Early Visual Cortex,
fMRI,
Optic Flow,
radial bias
Conference:
ACNS-2013 Australasian Cognitive Neuroscience Society Conference, Clayton, Melbourne, Australia, 28 Nov - 1 Dec, 2013.
Presentation Type:
Poster
Topic:
Sensation and Perception
Citation:
Maloney
RT,
Watson
TL and
Clifford
CW
(2013). Radial Bias for Motion – Centrifugal or Centripetal?.
Conference Abstract:
ACNS-2013 Australasian Cognitive Neuroscience Society Conference.
doi: 10.3389/conf.fnhum.2013.212.00039
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Received:
15 Oct 2013;
Published Online:
25 Nov 2013.
*
Correspondence:
Dr. Ryan T Maloney, University of Sydney, School of Psychology, Sydney, Australia, ryan.maloney@sydney.edu.au