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Charles Leek, Mark Roberts, Irene Reppa, Alan Pegna; What's so special about the N170? Modulation of N170 by geometric shape attributes of three-dimensional (3D) objects. Journal of Vision 2009;9(8):71. doi: 10.1167/9.8.71.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have shown that the N170 component of the event-related potential, although widely associated with face processing, is sensitive to a range of stimulus variables including proficiency of subordinate-level perceptual categorisation (expertise), and, more recently, some measures of variance in low-level image similarity (e.g., ISVP). Here we report results from an ERP study designed to examine the time-course of encoding different geometric shape attributes (edges, surfaces and 3D volumes) during object recognition. A whole-part matching task was used in which Ss were shown a whole novel 3D object followed by a part comparison stimulus containing a sub-set of geometric shape information from the whole object (edges, surfaces or 3D volumes). Ss were instructed to decide whether the part stimuli matched or did not match information in the preceding stimulus. Consistent with earlier published evidence (Leek et al., 2005: JEP: HPP, 31, 668–684) Ss were faster at matching surface and volumetric parts than edges to whole objects indicating a role for surface-based primitives in 3D shape representation. Analyses of the ERP data showed distinct patterns of modulation of the N170 (but not P1) component according to object part-type. Temporal segmentation analyses revealed two distinct scalp topographies within the N170 time period, one for the volumetric part condition and another for the surfaces and edges. The LAURA source localisation algorithm placed the generators of the N170 maps in the ventral occipito-temporal cortex, regions known to support object recognition processes. The N170 modulation cannot be accounted for by either face-selective or expertise-related processes, or in terms of low-level perceptual variance measures such as ISVP. Rather, the data suggest that (1) the N170 responds to relatively high-level and complex geometric attributes of 3D object structure and, (2) different geometric primitives are associated with unique topographical ERP distributions in ventral occipito-temporal cortex.
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