Differential human brain activation by vertical and horizontal global visual textures |
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Authors: | Jane E Aspell John Wattam-Bell Janette Atkinson Oliver J Braddick |
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Institution: | 1. Department of Experimental Psychology, University of Oxford, Oxford, UK 3. Brain-Mind Institute, Ecole Polytechnique Fédérale de Lausanne, SV 2805, Station 19, 1015, Lausanne, Switzerland 2. Department of Psychology, University College London, London, UK
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Abstract: | Mid-level visual processes which integrate local orientation information for the detection of global structure can be investigated
using global form stimuli of varying complexity. Several lines of evidence suggest that the identification of concentric and
parallel organisations relies on different underlying neural substrates. The current study measured brain activation by concentric,
horizontal parallel, and vertical parallel arrays of short line segments, compared to arrays of randomly oriented segments.
Six subjects were scanned in a blocked design functional magnetic resonance imaging experiment. We compared percentage BOLD
signal change during the concentric, horizontal and vertical blocks within early retinotopic areas, the fusiform face area
and the lateral occipital complex. Unexpectedly, we found that vertical and horizontal parallel forms differentially activated
visual cortical areas beyond V1, but in general, activations to concentric and parallel forms did not differ. Vertical patterns
produced the highest percentage signal change overall and only area V3A showed a significant difference between concentric
and parallel (horizontal) stimuli, with the former better activating this area. These data suggest that the difference in
brain activation to vertical and horizontal forms arises at intermediate or global levels of visual representation since the
differential activity was found in mid-level retinotopic areas V2 and V3 but not in V1. This may explain why earlier studies—using
methods that emphasised responses to local orientation—did not discover this vertical–horizontal anisotropy. |
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