The Influence of Temporal Phase Differences on Texture Segmentation

Abstract

Scene segmentation and perceptual grouping are important operations in visual processing. Pattern elements constituting individual perceptual objects need to be segregated from those of other objects and the background and have to be bound together for further joint evaluation. Both textural (spatial) and temporal cues are exploited for this grouping operation. Thus, pattern elements might get bound that share certain textural features and/or appear in close spatial or temporal contiguity. However, results on the involvement of temporal cues in perceptual grouping are contradictory [Kiper et al. (1991). Society for Neuroscience Abstracts, 17, 1209; Fahle (1993). Proceedings of the Royal Society of London B, 254, 199-203]. We therefore reinvestigated the relative contributions of temporal and spatial cues and their interactions in a texture-segmentation paradigm. Our data show that the visual system can segregate figures solely on the basis of temporal cues if the temporal offset between figure and ground elements exceeds 10 msec. Moreover, segregation of figures defined by orientation differences among pattern elements is facilitated by additional temporal cues if these define the same figure. If temporal and textural cues define different figures, the two cues compete and only the more salient pattern is perceived. By contrast, the detection of a figure defined by orientation is not impaired by conflicting temporal cues if these do not define a figure themselves and do not exceed offset intervals of 100 msec. These results indicate the existence of a flexible binding mechanism that exploits both temporal and textural cues either alone or in combination if they serve perceptual grouping but can exclude either of the two cues if they are in conflict or do not define a figure. It is proposed that this flexibility is achieved by the implementation of two segmentation mechanisms which differ in their sensitivity for spatial and temporal cues and interact in a facultative way.

Pop-out from abrupt visual onsets

“…In contrast to previous studies (e.g. Leonards, Singer, & Fahle, 1996;Fahle & Koch, 1995;Kiper, Gegenfurtner, & Movshon, 1996), they imply that perceptual organization can depend more upon temporal than upon non-temporal cues, possibly because, in our paradigm, the timing of the relevant neural activity is closely locked to external stimulus events. Thus, though we assume that other interpretations are possible 3 , we see our results as providing strong prima facie support for the synchronization hypothesis.…”

“…If onset time is just another variable on which features may differ then synchrony of onset should not prevent pop-out due to other contrasts. Fourth, when temporal stimulus cues to grouping or segregation have been put in conflict with non-temporal cues the non-temporal cues have been found to be dominant (Leonards, Singer, & Fahle, 1996;Fahle & Koch, 1995;Kiper, Gegenfurtner, & Movshon, 1996). Grouping by synchrony in our paradigm should therefore not prevent pop-out due to non-temporal contrasts.…”

“…There have been many psychophysical tests of this synchronization hypothesis (Fahle, 1993;Alais et al, 1998;Usher & Donnelly, 1998;Lee & Blake, 1999;Leonards et al, 1996;Leonards & Singer, 1998;Lee & Blake, 2001). Most show some role for timing in perceptual grouping, but some show that temporal cues have little effect when in competition with non-temporal cues (Leonards et al, 1996;Fahle & Koch, 1995;Kiper et al, 1996). These psychophysical studies therefore show that stimulus timing can be a cue to grouping, but they do not show any special status for timing amongst the many other cues that are also effective.…”

Spatial and temporal coherence in perceptual binding

“…This finding, too, makes sense in terms of a temporal binding mechanism that operates to collate features of a given object over space, including viewing conditions where central portions of the object are occluded (21). Results from experiment 2 also complement a recent study demonstrating that texture features defining a figure are more easily segregated from their background when those figural features appear and disappear in synchrony (14). Evidently, temporal synchrony is not absolutely necessary for figural binding, however, because disruptions in the temporal synchrony of figural elements does not inevitably impair perceptual grouping (12, 13).…”

“…Results from those experiments, however, have led to contradictory conclusions (12)(13)(14). To pursue this question of figural binding from a complementary perspective, we tested for enhanced detectability of temporal synchrony among spatial features that define a visual object.…”