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Marc Tibber, Anderson Elaine, Geraint Rees, Michael Morgan; The neural correlates of the 3-dot vernier task: Visuospatial extrapolation examined within the framework of a duplex model of vision. Journal of Vision 2008;8(6):952. doi: 10.1167/8.6.952.
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© ARVO (1962-2015); The Authors (2016-present)
Since the discovery of orientation-specific receptive fields in the occipital cortex some 40 years ago, much progress has been made in elucidating the mechanisms of contour processing. However, many of the studies to date have focused on the role of relatively short-range local interactions between orientation-tuned filters. In contrast, little is known about how information is integrated across spatially disparate regions of the visual field in the absence of explicit local orientation cues. To examine this process, referred to here as visuospatial extrapolation, a block functional magnetic resonance imaging (fMRI) design was employed in which observers performed a version of the three-dot vernier task using Gabor patches. The replacement of the dots with Gabor patches meant that an identical stimulus set could be used to perform a simultaneous orientation discrimination: a suitable control task that involves visuospatial processing without the need for extrapolation across space. The data were consistent with ventral stream activity during the extrapolation task, with task-specific activations being largely restricted to foci within the lateral occipital complex (LOC), an area implicated in the process of form perception and object recognition. In contrast, the orientation discrimination task led to activations in caudal regions of the intraparietal sulcus (IPS), an area characterised by sensitivity to surface orientation and object rotations. Viewed within the framework of the duplex model of vision, these results do not support a simple dissociation of the ventral and dorsal streams for perception and action respectively. Instead, they contribute to a growing body of evidence that suggests a subset of purely perceptual tasks activate a network of cortical foci that incorporate both dorsal and ventral stream regions.
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