Electrophysiological evidence of the amodal representation of symmetry in extrastriate areas

Abstract

Extrastriate visual areas are strongly activated by image symmetry. Less is known about symmetry representation at object-level rather than image-level. Here we investigated electrophysiological responses to symmetry, generated by amodal completion of partially-occluded polygon shapes. We used a similar paradigm in four experiments (N = 112). A fully-visible abstract shape (either symmetric or asymmetric) was presented for 250 ms (t0). A large rectangle covered it entirely for 250 ms (t1) and then moved to one side to reveal one half of the shape hidden behind (t2, 1000 ms). Note that at t2 no symmetry could be extracted from retinal image information. In half of the trials the shape was the same as previously presented, in the other trials it was replaced by a novel shape. Participants matched shapes similarity (Exp. 1 and Exp. 2), or their colour (Exp. 3) or the orientation of a triangle superimposed to the shapes (Exp. 4). The fully-visible shapes (t0–t1) elicited automatic symmetry-specific ERP responses in all experiments. Importantly, there was an exposure-dependent symmetry-response to the occluded shapes that were recognised as previously seen (t2). Exp. 2 and Exp.4 confirmed this second ERP (t2) did not reflect a reinforcement of a residual carry-over response from t0. We conclude that the extrastriate symmetry-network can achieve amodal representation of symmetry from occluded objects that have been previously experienced as wholes.

Amodal completion across the brain: The impact of structure and knowledge

“…The absence of a distinct amodal completion signature in EVC resonates with prior studies that also did not detect activity in response to partially occluded objects within this region ( Lerner et al., 2002 ; Lerner et al., 2004 ; Olson et al., 2004 ; Weigelt et al., 2007 ; Rampone, Adam, Makin, Tyson-Carr, & Bertamini, 2022 ). Nonetheless, other investigations did report EVC involvement ( Rauschenberger et al., 2006 ; Hulme & Zeki, 2007 ; Ban et al., 2013 ; Erlikhman & Caplovitz, 2017 ; de Haas & Schwarzkopf, 2018 ).…”

Symmetry Perception and Psychedelic Experience

“…This SPN could have been caused by the recall of a polygon stored in visu term memory. This memory reactivation SPN was still generated when participan attending to color in Experiment 3 of Rampone et al [170]. This is perhaps a rare e Rampone et al [170] conducted further comparable experiments.…”

“…This memory reactivation SPN was still generated when participan attending to color in Experiment 3 of Rampone et al [170]. This is perhaps a rare e Rampone et al [170] conducted further comparable experiments. Revealing onehalf of a previously seen symmetrical or asymmetrical polygon was enough to generate an SPN.…”

“…These shifting o experiments again show extraretinal symmetry representations are only generate they are task-relevant. Rampone et al [170] conducted further comparable experiments. Revealing of a previously seen symmetrical or asymmetrical polygon was enough to gen SPN.…”