Abstract
Spatiotemporal boundary formation (SBF) is the perception of illusory boundaries, global form, and global motion from spatially and temporally sparse transformations of texture elements (Shipley and Kellman, 1993a, 1994; Erlikhman and Kellman, 2015). It has been theorized that the visual system uses positions and times of element transformations to extract local oriented edge fragments, which then connect by known interpolation processes to produce larger contours and shapes in SBF. To test this theory, we created a novel display consisting of a sawtooth arrangement of elements that disappeared and reappeared sequentially. Although apparent motion along the sawtooth would be expected, with appropriate spacing and timing, the resulting percept was of a larger, moving, illusory bar. This display approximates the minimal conditions for visual perception of an oriented edge fragment from spatiotemporal information and confirms that such events may be initiating conditions in SBF. Using converging objective and subjective methods, experiments showed that edge formation in these displays was subject to a temporal integration constraint of ~80 ms between element disappearances. The experiments provide clear support for models of SBF that begin with extraction of local edge fragments, and they identify minimal conditions required for this process. We conjecture that these results reveal a link between spatiotemporal object perception and basic visual filtering. Motion energy filters have usually been studied with orientation given spatially by luminance contrast. When orientation is not given in static frames, these same motion energy filters serve as spatiotemporal edge filters, yielding local orientation from discrete element transformations over time. As numerous filters of different characteristic orientations and scales may respond to any simple SBF stimulus, we discuss the aperture and ambiguity problems that accompany this conjecture and how they might be resolved by the visual system.
Highlights
Spatiotemporal boundary formation (SBF) is the perception of continuous contours, global form, and global motion from the sequential transformation of sparse texture elements (Shipley and Kellman, 1993a, 1994; Erlikhman and Kellman, 2015)
Based on both the objective performance and subjective rating tasks, SBF was seen for virtual bars moving at 13.2◦/s, but not bars moving at 2.6◦/s in this study
This “virtual velocity” difference affected temporal properties in the displays: element offset duration (EOD) and ISI were both shorter for the faster displays. The results of this experiment indicate that establishing oriented edge fragments in SBF depends on temporal parameters, but the data permit a variety of hypotheses about which temporal properties, such as EOD or ISI, matter and what their limits might be
Summary
Spatiotemporal boundary formation (SBF) is the perception of continuous contours, global form, and global motion from the sequential transformation of sparse texture elements (Shipley and Kellman, 1993a, 1994; Erlikhman and Kellman, 2015) An example of this process is shown, and the effect can be seen in Movie 1. Upon entering or exiting the boundary, the elements change in some property, such as shape, orientation, or, as in this case color—from black to white when inside the boundary and vice versa when falling outside. This produces a pattern of element transformations along the boundary of the object as it moves across the display. Accretion and deletion of texture (Gibson et al, 1969; Kaplan, 1969; Andersen and Cortese, 1989) is an example of transformations that produce SBF, but the class of possible element transformations that produce perception of continuous contours, shape and motion is much broader (Shipley and Kellman, 1994)
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