title: Electrophysiological responses to symmetry presented in the left or in the right visual hemifield.
abstract: Symmetry is a highly salient feature in the visual world, abundant in both man-made and natural objects. In particular, humans find reflectional symmetry most salient. Electrophysiological work on symmetry perception has identified a difference wave known as the Sustained Posterior Negativity (SPN) originating from extrastriate areas. Amplitude is more negative for symmetrical than random patterns, from around 200 msec after stimulus onset. For the first time, we report responses to patterns presented exclusively in one hemifield. Participants were presented with reflection or random dot patterns to the left and right of fixation (3.2°). They judged whether the patterns were light red or dark red in colour. In Experiment 1, the pair always included one symmetrical and one random pattern. In Experiments 2 and 3 we varied the information presented contralaterally. The SPN was generated separately in each hemisphere in response to what was presented in the contralateral visual hemifield (a lateralised SPN). We conclude that a symmetry-sensitive network of extrastriate areas can be activated independently in each cerebral hemisphere.
authors.affiliation: Department of Psychological Sciences, University of Liverpool, United Kingdom. Electronic address: damien.wright@liverpool.ac.uk.
authors.forename: Damien
authors.initials: D
authors.lastname: Wright
authors.affiliation: Department of Psychological Sciences, University of Liverpool, United Kingdom.
authors.forename: Alexis D J
authors.initials: ADJ
authors.lastname: Makin
authors.affiliation: Department of Psychological Sciences, University of Liverpool, United Kingdom.
authors.forename: Marco
authors.initials: M
authors.lastname: Bertamini
mesh_terms: D000293:Adolescent; D000328:Adult; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology; D010775:Photic Stimulation; D014794:Visual Fields / Q000502:physiology*; D055815:Young Adult
keywords: Bilateral symmetry; Callosal hypothesis; ERPs; Interhemispheric connections; Sustained posterior negativity