Perceptual integration and attention in human extrastriate cortex

Abstract

Visual crowding is a perceptual phenomenon with far-reaching implications in both perceptual (e.g., object recognition and reading) and clinical (e.g., developmental dyslexia and visual agnosia) domains. Here, we combined event-related fMRI measurements and wide-field brain mapping methods to investigate whether the BOLD response evoked by visual crowding is modulated by different attentional conditions. Participants underwent two sessions of psychophysical training outside the scanner, and then fMRI BOLD activity was measured simultaneously in early visual areas (including the visual word form area, VWFA), while they viewed strongly-crowded and weakly-crowded Gabor patches in attended and unattended conditions. We found that crowding increased BOLD activity in a network of areas including V1, V2, V3A, V4/V8, and VWFA. In V4/V8 and VWFA we found an increased activity related to attention. The effect of crowding in V1 was recorded only when attention was fully devoted to the target location. Our results provide evidence that some area beyond V1 might be the likely candidate for the site of crowding, thus supporting the view of visual crowding as a mid-level visual phenomenon.

Detailed spatiotemporal brain mapping of chromatic vision combining high‐resolution VEP with fMRI and retinotopy

“…Functional individual data from both two‐condition experiment and phase‐encoded retinotopy were analyzed using a customized version (retinotopy capable) of FreeSurfer (csurf, M. Sereno, http://www.cogsci.ucsd.edu/~sereno/.tmp/dist/csurf) based on standard procedures described in many previous studies (e.g., Sereno et al, ; Sereno, Pitzalis, & Martínez, ; Hagler, Riecke, & Sereno, ; Pitzalis et al, ; Pitzalis, Strappini, et al, ; Pitzalis, Bozzacchi, et al, ; Pitzalis, Sdoia, et al, ; Strappini et al, ). Briefly, pre‐processing included motion correction, averaging across the two scans for each stimulus type to increase the signal to noise ratio, and aligning to the structural images.…”

“…We mapped polar angle (measured from the contralateral horizontal meridian around the center of gaze) and eccentricity (distance from the center of gaze) using phase‐encoded stimuli, as described elsewhere (e.g., Pitzalis et al, ; Pitzalis, Fattori, et al, ; Pitzalis, Bozzacchi, et al, ; Pitzalis, Sereno, et al, ; Pitzalis, Sdoia, et al, ; Sereno et al, ; Strappini et al, ; Strappini, Galati, Martelli, Di Pace, & Pitzalis, ). High‐contrast light and dark colored checks counterphase flickered in either a ray‐ or a ring‐shaped configuration (polar angle and eccentricity, respectively).…”

“…After reconstruction, each hemisphere was then completely flattened using five relaxation cuts: one cut along the Calcarine fissure, three equally spaced radial cuts on the medial surface, and one sagittal cut around the temporal lobe. ucsd.edu/~sereno/.tmp/dist/csurf) based on standard procedures described in many previous studies (e.g., Sereno et al, 1995;Sereno, Pitzalis, & Martínez, 2001;Hagler, Riecke, & Sereno, 2007;Pitzalis et al, 2006Pitzalis et al, , 2010Pitzalis, Strappini, et al, 2012;Pitzalis, Bozzacchi, et al, 2013;Pitzalis, Sdoia, et al, 2013;Strappini et al, 2015Strappini et al, , 2016Strappini et al, , 2017. Briefly, pre-processing included motion correction, averaging across the two scans for each stimulus type to increase the signal to noise ratio, and aligning to the structural images.…”

Empirical Evidence for Intraspecific Multiple Realization?

“…Others have pointed to V3 (Tyler and Likova, 2007;Bi et al, 2009), V4 (Motter, 2006), or higher visual areas (Chung et al, 2007;. Although the existence of a "crowding area" is still debated, the modulation of the neural activity from early to higher visual areas, like the visual word form area (VWFA), is consistent with the increase in the receptive field size Pelli and Rosen, 2015;Strappini et al, 2017a) and with the occurrence of visual crowding at multiple levels in the visual hierarchy (Whitney and Levi, 2011).…”

“…Some psychophysical and neuroimaging studies have suggested that V1 can be the earliest area showing neural activity modulated by crowding (Anderson et al, 2012;Millin et al, 2013;Chen et al, 2014;Kwon et al, 2014). However, crowding related activation in V1 is absent when attention is diverted away from the stimulus, indicating that V1 involvement in crowding may be the result of feedback suppression coming from higher-order areas (Strappini et al, 2017a).…”