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Jennifer Bittner, Michael Wenger, Rebecca Von Der Heide, Daniel Fitousi; CONUS masking reveals saliency representation in reach-related areas of the posterior parietal cortex. Journal of Vision 2009;9(8):92. doi: 10.1167/9.8.92.
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The parietal reach region (PRR) and Area 5 of the posterior parietal cortex (PPC) have been shown to encode reach plans. However, there have not yet been studies examining the possible effects of attention on visual responses in these parts of the PPC. We used a new masking technique which highlights salient regions of an image, CONUS (Complementary NatUral Scene) masking (Wilimzig et al., 2008), to examine whether PRR and Area 5 represent salient features in natural scenes. Presenting a brief flash of a natural scene (6.2 ms, e. g.) followed by an equally brief flash of the CONUS mask the exact inverse of the natural scene which may simply be obtained by subtracting it from the maximum entry in each respective color channel - to human subjects results in a percept that closely resembles the saliency map of a natural scene by masking non-salient regions of the image while nonlinear temporal integration preserves some information within salient regions of the image. An advantage of this paradigm is that it can produce saliency maps rather automatically and without requiring the subject to perform a behavioral-attention task. A monkey (macaca mulatta) passively viewed natural scenes while PRR and Area 5 spiking activity was recorded from a microelectrode array implant. The activity for non-salient regions of the images decreases due to the presentation of the CONUS mask while activation for salient regions increased consistent with psychophysical results in human subjects. The experimental phenomenon of CONUS masking and finding its neural basis provide important constraints on the current understanding of saliency processing in the brain and on computational approaches to saliency, specifically due to its relationship with temporal integration. In addition, our newly developed paradigm provides an important tool for investigating the neural basis of saliency representation for natural scenes in neurophysiological experiments.
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