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Clara Casco, Gianluca Campana; Distinct neural correlates of texture segmentation and grouping by collinearity in humans. Journal of Vision 2007;7(9):973. doi: 10.1167/7.9.973.
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© ARVO (1962-2015); The Authors (2016-present)
We investigated whether facilitation by collinearity in segmentation and grouping of texture elements arises through the same or different neural mechanisms. The texture stimuli consisted of 9×9 matrices of Gabor-elements all oriented at 45° except for three central Gabors oriented at either 90° or 180° to form horizontal or vertical 3-Gabor groups. Within a block, the Gabors in the groups were either collinear and iso-oriented with group orientation, or else non-collinear and ortho-oriented. Both psychophysical and event-related potentials (ERP) responses were obtained under identical stimulus conditions and two different tasks, each performed with attention either fully engaged or partially withdrawn by a digit categorization in eccentric RSVP. The local task involved segmentation based on local orientation contrast, and consisted in discriminating the orientation (horizontal or vertical) of the central Gabor in the 3-Gabor group. The global task, involving both segmentation and grouping, consisted in discriminating the orientation of the 3-Gabor group.
Psychophysical data showed lower accuracy and larger effect of attention in the local task, but similar collinear facilitation in the two tasks. Texture-specific potentials reflected a collinear facilitation in the local task, indexed by a larger negativity peaking at N75 and N200 for electrodes in the occipital region (Oz, O1 and O2). In the global task, collinear facilitation was indexed by a larger positivity peaking at P60, and a reduced negativity peaking at N75 and at N150 for Oz, O1 and O2 electrodes. Consistently with our previous work (Casco et al., 2005), disengagement of attention affected the ERPs amplitude more for collinear stimuli, specifically for the N75 component (in both tasks) and for the P60 (in the global task). The novel findings are a different neural correlate of facilitation by collinearity in segmentation and grouping, and a different neural correlate of attentional modulation for segmentation and grouping.
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