63. The neural correlates of a three-element alignment task: visuospatial interpolation in the absence of explicit local orientation cues

M.S. Tibber1 mtibber@yahoo.com E.J. Anderson2,3 e.anderson@fil.ion.ucl.ac.uk D.R. Melmoth1 G. Rees2,3 g.rees@fil.ion.ucl.ac.uk M.J. Morgan1,2 m.j.morgan@city.ac.uk

1Department of optometry and Visual Science, City University, London, UK.
2Institute of Cognitive Neuroscience, UCL, London, UK.
3Wellcome Trust Centre for Neuroimaging, UCL, London, UK.

There is a wealth of literature on the role of relatively short-range interactions between low-level orientation-tuned filters in the perception of discontinuous contours. However, little is known about how spatial information is integrated across more distant regions of the visual field in the absence of explicit local orientation cues, a process referred to here as visuospatial interpolation. One possibility is that the relative position of stimulus elements is encoded in the form of covert oculomotor plans in the eye movement control networks. To examine this hypothesis we used high field functional magnetic resonance imaging to study brain activity while observers either judged the alignment of three Gabor patches by a process of visual interpolation, or discriminated the orientation of the individual patches. Compared to the orientation discrimination, the interpolation task did not evoke activity in areas associated with eye movement control; instead, activity was restricted to a region that coincides with previous reports of the lateral occipital complex, an area implicated in the perception of form and illusory contours. In contrast, the orientation task, which involves visuospatial processing but no interpolation across space, evoked activations that included caudal regions of the intraparietal sulcus, an area characterised by sensitivity to surface orientation and object rotations. These results do not support a role for a covert oculomotor strategy during spatial interpolation, but instead, hint at a possible commonality between the processing of discontinuous contours and the encoding of relative position during an interpolation task.