The electrophysiological correlate of contour integration is modulated by task demands

Neural representation of feature synergy

“…A contour defined by aligned luminance or color elements in a surround of randomly oriented elements produces a negative deflection starting at 220 ms across occipital electrodes (Mathes and Fahle, 2007;Mathes et al, 2006). This contour-specific negative deflection resembles a negative shift observed at occipital electrodes for both single-and double-feature target GRF stimuli in experiments 2 and 3 of the present study, regarding latency, spatial distribution, and experimental conditions where these were elicited.…”

The neural origins of visual crowding as revealed by event-related potentials and oscillatory dynamics

“…This result is consistent with the evidence of Chicherov et al (2014) that, though with a different behavioral paradigm, equally demonstrated that the earliest signature of visual crowding was a suppression of the N1 component. Previous studies on texture segmentation (Bach & Meigen, 1992Caputo & Casco, 1999;Fahle, Quenzer, Braun, & Spang, 2003) and contour detection Mathes, Trenner, & Fahle, 2006;Shpaner, Molholm, Forde, & Foxe, 2013) typically found N1 suppression to be associated with the inability to segment a stimulus target from the background. Conversely, N1 amplitude is enhanced when a structure emerges (Kanizsa figures, Murray et al, 2002;Glass patterns, Pei, Pettet, Vildavski, & Norcia, 2005).…”

The construction of perceptual grouping displays using GERT

“…Traditionally, the most common approach is to place background elements according to an underlying grid and then add positional noise (e.g., Altmann, Deubelius, & Kourtzi, 2004;Bex, Simmers, & Dakin, 2001;Dumoulin & Hess, 2006;Field et al, 1993;Kourtzi, Tolias, Altmann, Augath, & Logothetis, 2003;Kuai & Yu, 2006;Li & Gilbert, 2002;Mathes & Fahle, 2007a, b;Mathes, Trenner, & Fahle, 2006;May & Hess, 2007;Mullen, Beaudot, & McIlhagga, 2000;Nygård, Sassi, & Wagemans, 2011;Tanskanen, Saarinen, Parkkonen, & Hari, 2008). In a similar fashion, Hadad, Maurer, and Lewis (2010) placed background elements on imaginary concentric circles around the embedded closed contour.…”

“…Braun (1999) pointed out that a grid method often results in a different density profile for contour and background elements and suggested an iterative correction algorithm to reduce positional cues. Some researchers (e.g., Mathes & Fahle, 2007a, b;Mathes et al, 2006;May & Hess, 2007) have heeded this warning and have attempted to approximate an equal average distance from contour and background elements to their neighbors, across all generated displays. Other authors have described how they have randomly drawn contour and background elements from a common positional distribution (Nygård et al, 2009(Nygård et al, , 2011Watt et al, 2008), applied boundary conditions to an iterative element positioning algorithm (Braun, 1999;Schinkel et al, 2005), or selected stimulus displays on the basis of a subjective screening (Geisler et al, 2001).…”