Spatiotemporal and Luminance Contrast Properties of Symmetry Perception

Abstract

Recent studies have shown that limiting the lifetime of pattern elements improves symmetry detection, potentially by increasing the number of element locations. Here, we investigate how spatial relocation, luminance contrast modulation and lifetime duration of elements affect symmetry perception in dynamic stimuli. Stimuli were dynamic dot-patterns containing varying amounts of symmetry about a vertical axis. Symmetrical matched-pairs were: (i) relocated to multiple successive, but random locations (i.e., multiple locations condition); (ii) relocated between the same two locations (i.e., two locations condition); (iii) not, relocated, but their luminance contrast was modulated at different temporal frequencies (i.e., one location condition), and (iv) not relocated, but a single pattern was presented at full contrast (i.e., static condition). In the dynamic conditions, we varied the elements' lifetime duration and temporal frequency of contrast modulation. We measured symmetry detection thresholds using a two-interval forced choice procedure. Our results show improved performance for the multiple locations condition compared to two-location and static conditions, suggesting a cumulative process whereby weak symmetry information is integrated by spatiotemporal filters to increase overall symmetry signal strength. Performance also improved for the static, contrast modulated patterns, but this was explained by a reduction in perceived density. This suggests that different mechanisms mediate symmetry detection in dynamic stimuli and static contrast modulated patterns.

Electrophysiological Evidence of the Amodal Representation of Symmetry in Extrastriate Areas

“…Our results support behavioural [93][94][95][96] and recent neuroscienti c evidence 30,46,51,52 of global processes for symmetry representation. We propose that classic models 6,11,12,[20][21][22][23][24][25] , which emphasise early responses to pairwise correlations in the image, should be updated to consider the exibility of mechanisms for symmetry perception.…”

“…In conclusion, in this study we found evidence of a representation of symmetry generated by the amodal completion of partially occluded symmetrical shapes. This adds to the recent literature showing that the representation of symmetry can exist in the brain at a non-retinotopic global level 30,46,51 (see also behavioural evidence [93][94][95][96] ). The amodal symmetry was indexed by a SPN-like response over extrastriate areas, in line with literature showing amodal completion is achieved at the level of LOC 56,57 .…”

Representation of Natural Contours by a Neural Population in Monkey V4

“…Although a substantial number of natural objects are symmetric and the solid perceptual representation of symmetry has been reported ( Sharman and Gheorghiu, 2018 ; Sakai et al, 2021 ), only a fraction of V4 neurons showed significant tuning to symmetry in the present experiment. The limited spatial extent of the receptive filed might account for this discrepancy.…”