September 2011
Volume 11, Issue 11
Free
Vision Sciences Society Annual Meeting Abstract  |   September 2011
The modulation of illusion susceptibility by TMS in right SPL demonstrates its role in the processing of global, but not local, contextual information
Author Affiliations
  • Paul Dassonville
    Department of Psychology and Institute of Neuroscience, University of Oregon, USA
  • Benjamin D. Lester
    Department of Psychology and Institute of Neuroscience, University of Oregon, USA
Journal of Vision September 2011, Vol.11, 1037. doi:10.1167/11.11.1037
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      Paul Dassonville, Benjamin D. Lester; The modulation of illusion susceptibility by TMS in right SPL demonstrates its role in the processing of global, but not local, contextual information. Journal of Vision 2011;11(11):1037. doi: 10.1167/11.11.1037.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Previous work (Walter & Dassonville, 2008) has shown that predominantly right-lateralized regions of superior parietal lobule (SPL) are more active when participants make location judgments in the presence of an illusion-inducing visual context (the induced Roelofs effect), compared to when the same judgments are made in isolation. However, the specific role played by these parietal regions in encoding contextual information remains unclear. We assessed the effects of suppressing the neural activation within these parietal regions by applying slow (1 Hz) repetitive TMS. Participants (n = 13) performed an orientation judgment in the context of the Rod-and-Frame illusion (RFI, in which the perceived orientation of a target line is biased by the global context provided by a large tilted frame) or the Simultaneous Tilt illusion (STI, in which the perceived orientation of a target line is biased by local interactions between the target line and a surrounding array of tilted lines). Accuracies in these judgments were assessed before and after 10 minutes of rTMS applied, in separate sessions, to the right SPL, left SPL, or a control site at the vertex. If right SPL is an active processor of visual context, suppressing it should lead to a drop in illusion magnitude. Alternatively, if right SPL is involved in an active inhibition of the effects of context, an increase in illusion magnitude is expected. Participants' susceptibility to the illusion-inducing effects of the RFI decreased after TMS over right SPL, compared to left SPL and vertex. In contrast, susceptibility to the STI was unaffected by TMS, regardless of the stimulated region. In no region did TMS cause a decrease in the precision of the participants' perceptual reports for either illusion. These findings indicate that right SPL is involved in the active processing of global, but not local, contextual information in the visual image.

NIH/Institute of Neuroscience: Systems Physiology Training Program #5 T32 GM007257-33, and a Summer Research Award from the Office of the Vice President for Research, University of Oregon. 
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