Academic journal article Attention, Perception and Psychophysics

Spatiotemporal Form Integration: Sequentially Presented Inducers Can Lead to Representations of Stationary and Rigidly Rotating Objects

Academic journal article Attention, Perception and Psychophysics

Spatiotemporal Form Integration: Sequentially Presented Inducers Can Lead to Representations of Stationary and Rigidly Rotating Objects

Article excerpt

Published online: 13 August 2015

© The Psychonomic Society, Inc. 2015

Abstract Objects in the world often are occluded and in motion. The visible fragments of such objects are revealed at different times and locations in space. To form coherent representations of the surfaces of these objects, the visual system must integrate local form information over space and time. We introduce a new illusion in which a rigidly rotating square is perceived on the basis of sequentially presented Pacman inducers. The illusion highlights two fundamental processes that allow us to perceive objects whose form features are revealed over time: Spatiotemporal Form Integration (STFI) and Position Updating. STFI refers to the spatial integration of persistent representations of local form features across time. Position updating of these persistent form representations allows them to be integrated into a rigid global motion percept. We describe three psychophysical experiments designed to identify spatial and temporal constraints that underlie these two processes and a fourth experiment that extends these findings to more ecologically valid stimuli. Our results indicate that although STFI can occur across relatively long delays between successive inducers (i.e., greater than 500 ms), position updating is limited to a more restricted temporal window (i.e., ~300 ms or less), and to a confined range of spatial (mis)alignment. These findings lend insight into the limits of mechanisms underlying the visual system's capacity to integrate transient, piecemeal form information, and support coherent object representations in the ever-changing environment.

Keywords Form perception . Surface perception . Motion perception . Form-motion interactions . Illusory contours

Introduction

Our ability to see the surfaces of objects relies on mechanisms that integrate form information across the visual field (i.e., spatial integration). Because they so elegantly demonstrate the process of surface formation, Pacman-induced illusory contours (Fig. 1A;Kanizsa,1955, 1979; Kellman & Shipley, 1991)havebeenusedwidelytoinvestigatehowspatial integration processes allow us to perceive unified surfaces of objects even when they are not fully visible. In addition, there is evidence that spatial integration processes also can operate across time (i.e., spatiotemporal integration). For instance, similar surface percepts can be formed through the sequential presentation of Pacman inducers (Fig. 1B; Demonstration Video 1; Kojo, Liinasuo, & Rovamo, 1993).1 This example highlights mechanisms that integrate local form information over both space and time. It also has been demonstrated that these spatiotemporal integration processes can support percepts of translating objects (Kellman & Shipley, 1991). In these cases, however, not only does local form information have to be integrated over space and time, but the position of previously viewed form information has to be updated before the integration (Kellman & Shipley, 1991; Palmer, Kellman, & Shipley, 2006). We used a novel variant of these stimuli to demonstrate that spatiotemporal form integration (STFI) and position updating can support percepts of rigidly rotating surfaces.

As illustrated in the bottom left of Fig. 1C, sequential inducers can be presented such that they are consistent with a rigidly rotating square. Importantly, each inducer itself is static and no changes in configuration occur while they are visible. The stimulus can be conceptualized as a square with the same color as the background that transiently rotates during the inter-inducerinterval and remains stationary when each inducer is present. The inducers can be thought of as filled circles that become partially occluded by the square. Critically, if all four successive inducers were to be presented simultaneously, they would not represent the shape of a square. Instead, because of the rotation that occurs between inducers, they would reveal an irregular, misaligned polygon (Fig. …

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