Sustained and transient properties of mirror-symmetry perception

Abstract

Recent studies suggest that temporal dynamics rather than symmetrical motion-direction contribute to mirror-symmetry perception. Here we investigate temporal aspects of symmetry perception by examining how symmetrical pattern elements are combined over time. Stimuli were dynamic dot patterns consisting of either an on-going alternation of two images (sustained condition) or just two images each presented once (transient condition) containing different amounts of symmetry about the vertical axis. We varied the presentation duration of the two images between 23.5ms and 294ms under five temporal-arrangement conditions: (1) ‘whole pattern’ in which a symmetric pattern alternated with a noise pattern; (2) ‘delayed halves’ – the halves of the symmetric and noise patterns were presented with temporal delay; (3) ‘matched-pairs’ – each image contained 50% of the symmetric and 50% of the noise dots; (4) ‘delayed matched-pairs’ – the same as arrangement 3, but with matched-pairs presented with temporal delay; (5) ‘static’ – both images presented simultaneously as one. Performance was poorer for transient vs sustained presentation and the effect of temporal delay between symmetrical pairs and halves was more pronounced in the transient conditions. In summary, cross-correlation across the symmetry axis can be integrated over time and symmetry detection mechanisms can tolerate delays of up to about 60ms. Dedicated UnZip software is recommended for accessing the dataset, for example, IZArc.