Academic journal article Attention, Perception and Psychophysics

Structure-from-Motion: Dissociating Perception, Neural Persistence, and Sensory Memory of Illusory Depth and Illusory Rotation

Academic journal article Attention, Perception and Psychophysics

Structure-from-Motion: Dissociating Perception, Neural Persistence, and Sensory Memory of Illusory Depth and Illusory Rotation

Article excerpt

Published online: 13 November 2012

© Psychonomic Society, Inc. 2012

Abstract In the structure-from-motion paradigm, physical motion on a screen produces the vivid illusion of an object rotating in depth. Here, we show how to dissociate illusory depth and illusory rotation in a structure-from-motion stimulus using a rotationally asymmetric shape and reversals of physical motion. Reversals of physical motion create a conflict between the original illusory states and the new physical motion: Either illusory depth remains constant and illusory rotation reverses, or illusory rotation stays the same and illusory depth reverses. When physical motion reverses after the interruption in presentation, we find that illusory rotation tends to remain constant for long blank durations (Tblank ≥ 0.5 s), but illusory depth is stabilized if interruptions are short (Tblank ≤ 0.1 s). The stability of illusory depth over brief interruptions is consistent with the effect of neural persistence. When this is curtailed using a mask, stability of ambiguous vision (for either illusory depth or illusory rotation) is disrupted. We also examined the selectivity of the neural persistence of illusory depth. We found that it relies on a static representation of an interpolated illusory object, since changes to low-level display properties had little detrimental effect. We discuss our findings with respect to other types of history dependence in multistable displays (sensory stabilization memory, neural fatigue, etc.). Our results suggest that when brief interruptions are used during the presentation of multistable displays, switches in perception are likely to rely on the same neural mechanisms as spontaneous switches, rather than switches due to the initial percept choice at the stimulus onset.

Keywords 3D perception . Depth and shape from motion . Motion in depth . Rivalry/bistable perception . Multi-stable displays

Introduction

When the sensory system faces ambiguous input that is consistent with several equally plausible interpretations, it does not settle on a single percept. Instead, an observer perceives semistochastic switches between all possible alternatives, a phenomenon called multistable perception (Blake & Logothetis, 2002; Leopold & Logothetis, 1999). In the present study, we employed a structure-from-motion (SFM) stimulus (also known as the kinetic depth effect or depth from motion) to examine the interaction of the two features in conflict: illusory rotation and illusory depth. In an SFM display, dots move back and forth across the screen in a certain pattern to produce a vivid impression of a 3-D object rotating in depth (Sperling & Dosher, 1994; Wallach & O'Connell, 1953) (see Movie 1). Although competition occurs for both illusory rotation and illusory depth, most prior work concentrated on the ambiguity of illusory rotation alone.

One reason for this is an intrinsic link between the two, since both illusory depth and illusory rotation are constrained by the same physical motion. This is illustrated in Fig. 1a: If the illusory sphere rotates clockwise, the green dot appears closer to the observer than the red one. A spontaneous reversal of illusory rotation necessarily implies that the illusory depth order of the dots must reverse accordingly (the green dot must then appear further away from the observer than the red one). This association effectively conceals illusory depth and reduces the two observables to a single variable.

The second reason is that the question about the illusory depth of the interpolated object is meaningless when the object is depth symmetric. In this case, individual dots interpolate to the same illusory object for both alternative states of their own illusory depth. In Fig. 1a, it is impossible to know whether the illusory sphere (depicted as a gray circle) follows the example dots and reverses its depth, although current evidence strongly suggests that it remains constant (Brouwer & van Ee, 2006; Li & Kingdom, 1999; Pastukhov, Vonau, & Braun, 2012; Petersik, 1979; Stonkute, Braun, & Pastukhov, 2012; Treder & Meulenbroek, 2010; Zivotofsky & Goldstein, 2007). …

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