The electrophysiological response to visual symmetry: beyond the retinal image

Karakashevska, Elena (2025) The electrophysiological response to visual symmetry: beyond the retinal image PhD thesis, University of Liverpool.

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Abstract

This thesis investigates the conditions under which the extrastriate cortex constructs object- level representations of planar symmetry. We used EEG to measure an Event Related Po- tential (ERP) called the Sustained Posterior Negativity (SPN). Both symmetrical and asym- metrical stimuli create ERPs at posterior electrodes. After the P1 and N1 component of the visual evoked potential, amplitude is lower for symmetry. More salient visual symmetries produce a larger (more negative) SPNs. Previous research has found that the brain always responds to symmetry in the frontoparallel plane. However, the response to symmetry in perspective is sometimes reduced. This reduction is called SPN perspective cost. In three empirical studies, we investigated visual manipulations that could hypothetically modulate SPN perspective cost. In Chapter 4, we found substantial SPN perspective cost with dots, and a reduction in SPN perspective cost with polygons (published). In Chapter 5, we found that SPN perspective cost was not reduced by monocular viewing, prior presentation of static frames, or prior presentation of moving frames (published). In Chapter 6, we found thatimmersivevirtualrealityeliminatedSPNperspectivecost(acceptedRegisteredReport). We conclude that the extrastriate cortex can readily construct object level (allocentric, post constancy) representations of planar symmetry when sufficient cues are available to support 3D interpretation.

Item Type:	Thesis (PhD)
Divisions:	Faculty of Health & Life Sciences Faculty of Health & Life Sciences > Inst. Population Health
Depositing User:	Symplectic Admin
Date Deposited:	14 Aug 2025 08:48
Last Modified:	14 Aug 2025 12:21
DOI:	10.17638/03193430
Supervisors:	Makin, Alexis Bertamini, Marco Poliakoff, Ellen
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3193430
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