Temporal dynamics of mirror-symmetry perception

Abstract

Recent studies have suggested that temporal dynamics rather than symmetrical motion-direction contribute to mirror-symmetry perception. Here we investigate temporal aspects of symmetry perception and implicitly, its temporal flexibility and limitations, 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 stimulus presentation) or just two images each presented once (transient stimulus presentation) containing different amounts of symmetry about the vertical axis. We varied the duration of the two images under five temporal-arrangement conditions: (a) whole patterns in which a symmetric pattern alternated with a noise pattern; (b) delayed halves—the halves of the symmetric and noise patterns were presented with temporal delay; (c) matched-pairs—two alternating images each containing equal amounts of symmetrical matched-pairs; (d) delayed matched-pairs—the same as arrangement (c), but with matched-pairs presented with delay; and (e) static—both images presented simultaneously as one. We found increased sensitivity in sustained compared to transient stimulus presentations and with synchronous compared to delayed matched-pairs stimuli. For the delayed conditions, sensitivity decreased gradually with longer image durations (>60 ms), prominently for the transient stimulus presentations. We conclude that spatial correlations across-the-symmetry-midline can be integrated over time (∼120 ms), and symmetry mechanisms can tolerate temporal delays between symmetric dot-pairs of up to ∼60 ms.

Spatiotemporal and Luminance Contrast Properties of Symmetry Perception

“…That is, elements revealed at different times and locations can be assembled into unitary perceived objects [22,23]. The temporal integration of spatial information appears to be constrained to a temporal integration window between 80 ms [24] and 165 ms [21], which is in keeping with findings showing that temporal integration of symmetry occurs within~120 ms [19].…”

“…For both the multiple and two locations conditions we varied elements lifetime durations. There were nine different lifetime durations: 58.8, 117.7, 176.5, 188.2, 200.0, 211.8, 223.5, 235.3, and 294.1 ms (i.e., 5,10,15,16,17,18,19,20 and 25 frames at the 85 Hz refresh rate) corresponding to 17, 8.5, 5.7, 5.3, 5.0, 4.7, 4.5, 4.2 and 3.4 Hz temporal frequency. Starting 'ages' were randomly allocated so that different dot-pairs reached their maximum lifetime and 'died' at different times.…”

“…Although several recent studies have examined the contribution of visual features such as luminance polarity and colour [12][13][14], stereoscopic depth [15][16][17], and motion-direction [18] to symmetry perception, little is known about how spatiotemporal characteristics of dynamic patterns affect symmetry perception. Recent studies have shown that symmetry mechanisms can integrate spatial correlations across the symmetry midline within a~120 ms time window [19] and that limiting the lifetime of pattern elements improves symmetry detection thresholds [18]. Hence, here we investigate how temporal dynamics of spatial relocation and luminance contrast of pattern elements affect symmetry perception in dynamic patterns.…”

“…It has been suggested that these improvements in performance are due to multiple weak or noisy neural responses to symmetry being integrated over time to generate a stronger response. Using dynamic patterns consisting of on-going alternation of symmetric patterns Sharman et al [19] found that the time window for symmetry integration is about 120 ms. On the other hand, Niimi et al [33] varied the stimulus onset asynchrony (SOA) between symmetric stimulus halves and reported a temporal integration window of at least 213.3 ms. Another study measured temporal thresholds for identifying the orientation of the symmetry axis in symmetric textures and found that temporal thresholds varied between 28 to 568 ms as a function of stimulus salience [34]. All together, these studies suggest that the temporal integration window for symmetry might vary with the element lifetime duration and/or temporal frequency of dynamic stimulus presentation.…”

Spatial and Temporal Selectivity of Translational Glass Patterns Assessed With the Tilt After-Effect

“…Other studies investigated temporal integration mechanisms with different types of global structures (Gheorghiu & Erkelens, 2005;Hess & Ledgeway, 2003;Sharman et al, 2018). For example, Sharman et al (2018) investigated the temporal characteristics and limits of symmetry perception. Stimuli were dynamic dot patterns consisting of either an ongoing alternation of two images (sustained presentation) or two images presented once (transient presentation) containing different amount of symmetry along the vertical axis.…”