Direct evidence for encoding of motion streaks in human visual cortex

Author:

Apthorp Deborah1,Schwarzkopf D. Samuel23,Kaul Christian23,Bahrami Bahador2345,Alais David6,Rees Geraint23

Affiliation:

1. School of Psychology, University of Wollongong, Wollongong, New South Wales 2522, Australia

2. Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK

3. Wellcome Trust Centre for Neuroimaging, University College London, 12 Queen Square, London WC1N 3BG 10003, UK

4. Interacting Minds Project, Institute of Anthropology, Archaeology and Linguistics, Aarhus University, Aarhus University Hospital, Norrebrogade 44, Building 10 G, 8000 Aarhus C, Denmark

5. Centre of Functionally Integrative Neuroscience, Aarhus University Hospital, Norrebrogade 44, Building 10 G, 8000 Aarhus C, Denmark

6. School of Psychology, University of Sydney, Sydney, New South Wales 2006, Australia

Abstract

Temporal integration in the visual system causes fast-moving objects to generate static, oriented traces (‘motion streaks’), which could be used to help judge direction of motion. While human psychophysics and single-unit studies in non-human primates are consistent with this hypothesis, direct neural evidence from the human cortex is still lacking. First, we provide psychophysical evidence that faster and slower motions are processed by distinct neural mechanisms: faster motion raised human perceptual thresholds for static orientations parallel to the direction of motion, whereas slower motion raised thresholds for orthogonal orientations. We then used functional magnetic resonance imaging to measure brain activity while human observers viewed either fast (‘streaky’) or slow random dot stimuli moving in different directions, or corresponding static-oriented stimuli. We found that local spatial patterns of brain activity in early retinotopic visual cortex reliably distinguished between static orientations. Critically, a multivariate pattern classifier trained on brain activity evoked by these static stimuli could then successfully distinguish the direction of fast (‘streaky’) but not slow motion. Thus, signals encoding static-oriented streak information are present in human early visual cortex when viewing fast motion. These experiments show that motion streaks are present in the human visual system for faster motion.

Publisher

The Royal Society

Subject

General Agricultural and Biological Sciences,General Environmental Science,General Immunology and Microbiology,General Biochemistry, Genetics and Molecular Biology,General Medicine

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