Identification of early visual evoked potential generators by retinotopic and topographic analyses

Abstract

4AbstrackThis study investigated the cortical sources of the early (5&250 ms) components of the pattern-onset visual evoked potential (VEP). VEPs were recorded in response to a small circular checkerboard stimulus that was flashed over a range of visual field positions. Temporally and spatially overlapping VEP components were distinguished by differences in retinotopic sensitivity and scalp topography, and by inverse dipole modeling. The C1 component (5Cr80 ms) was found to change its polarity and topography systematically as a function of stimulus position in a manner consistent with the retinotopic organization of the striate cortex. The P1 component (comprised of the P75 and PlO0 subcomponents) had a time course that overlapped the C1 but could be distinguished from the C1 by its differing topography and reduced sensitivity to stimulus position. The P1 generators were localized to the lateral extrastriate cortex. Inverse dipole models were consistent with these striate and extrastriate source locations for the C1 and P1, respectively. The N1 component (120-180 ms) was found to originate from several spatially distinct generators that differed in their retinotopic organization.

Neurophysiological evidence for two processing times for visual object identification

“…Rather we propose that these components reflect object selection processes. 3 The timing of this function fits well with known visual processing times: (a) the earliest (125-175 ms) effects of perceptual categorization occur ∼100 ms after striate cortex activation (50-80 ms) [10], and (b) this visual categorization (i.e. discriminating faces from other objects) is easier and less specific than the basic level naming that overtly reveals identification success in the present study.…”

A brief introduction to the use of event-related potentials in studies of perception and attention

“…First, we see the C1 component which flips polarity based in whether the eliciting stimulus appears in the upper or lower visual field and is believed to be generated by activity in primary visual cortex (Clark, Fan, & Hillyard, 1995; Clark & Hillyard, 1996; Estevez & Spekreijse, 1974; Jeffreys & Axford, 1972). This initial deflection is followed by the P1 and N1 components as information propagates through the visual system and perceptual analysis is performed (Heinze et al, 1994; Heinze, Mangun, & Hillyard, 1990; Luck, 1995; Vogel & Luck, 2000).…”

Retinotopic mapping of visual event-related potentials

“…The interest in the retinotopic variations of the visual ERPs has been almost exclusively focused on the C1 component (Ales et al, 2010b(Ales et al, , 2013Clark et al, 1995;Kelly et al, 2013aKelly et al, , 2013b. However, we still lack a detailed retinotopic map of later components, which are more commonly studied in the ERP literature, such as P1 and N1 (Di Russo et al, 2012;Klimesch, 2011;Mangun et al, 1998).…”

“…The second line of research has employed stimulation and recording protocols typically used in ERP studies (e.g. SOAs > 200 ms and multichannel scalp recordings; Clark et al, 1995;Di Russo et al, 2002. However, these studies have not exhaustively covered the visual field.…”

“…As in mfVEP studies, we stimulated the visual field from the fovea to the periphery (up to 22° eccentricity radius) at different polar angles (in 30°-45° steps). However, in line with previous ERP studies (Clark et al, 1995;Di Russo et al, 2002, we employed multichannel EEG recordings and larger SOAs (200-400 ms) with a twofold aim: to reduce neural adaptation and to strengthen the contribution of extrastriate cortex. In addition, we used beamforming analysis (Gross et al, 2001;Van Veen et al, 1997) to localize the neural origin of the visual ERP components.…”