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The Z-Box illusion: dominance of motion perception among multiple 3D objects


In the present article, we examine a novel illusion of motion—the Z-Box illusion—in which the presence of a bounding object influences the perception of motion of an ambiguous stimulus that appears within. Specifically, the stimuli are a structure-from-motion (SFM) particle orb and a wireframe cube. The orb could be perceived as rotating clockwise or counterclockwise while the cube could only be perceived as moving in one direction. Both stimuli were presented on a two-dimensional (2D) display with inferred three-dimensional (3D) properties. In a single experiment, we examine motion perception of a particle orb, both in isolation and when it appears within a rotating cube. Participants indicated the orb’s direction of motion and whether the direction changed at any point during the trial. Accuracy was the critical measure while motion direction, the number of particles in the orb and presence of the wireframe cube were all manipulated. The results suggest that participants could perceive the orb’s true rotation in the absence of the cube so long as it was made up of at least ten particles. The presence of the cube dominated perception as participants consistently perceived congruent motion of the orb and cube, even when they moved in objectively different directions. These findings are considered as they relate to prior research on motion perception, computational modelling of motion perception, structure from motion and 3D object perception.

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Availability of data and material

The datasets generated during and/or analyzed during the current study are available from the corresponding author upon request.

Code availability

Experimental and data processing code are available from the corresponding author upon request.


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This project was supported by National Science Foundation OIA 1632849 to MDD and colleagues. The authors would like to thank our research assistant Joshua Warren, who provided invaluable assistance in data collection and presentation of findings.


This project was supported by NSF OIA 1632849 (RII Track-2 FEC: Neural networks underlying the integration of knowledge and perception) to MDD and colleagues.

Author information




Both authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by JEZ. The first draft of the manuscript was written by JEZ and both authors commented on previous versions of the manuscript. Both authors read and approved the final manuscript.

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Correspondence to Joshua E. Zosky.

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The authors have no relevant financial or non-financial interests to disclose.

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The approval was obtained from the ethics committee of University of Nebraska – Lincoln. The procedures used in this study adhere to the tenets of the Declaration of Helsinki.

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Zosky, J.E., Dodd, M.D. The Z-Box illusion: dominance of motion perception among multiple 3D objects. Psychological Research (2021).

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