December 2022
Volume 22, Issue 14
Open Access
Vision Sciences Society Annual Meeting Abstract  |   December 2022
Seeing mixed percepts in apparent motion quartets during passive and volitional perception
Author Affiliations
  • Nathan H. Heller
    Dartmouth College
  • Ananya Alleyne
    Dartmouth College
  • Patrick Cavanagh
    Dartmouth College
    Glendon College
  • Peter U. Tse
    Dartmouth College
Journal of Vision December 2022, Vol.22, 3987. doi:
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      Nathan H. Heller, Ananya Alleyne, Patrick Cavanagh, Peter U. Tse; Seeing mixed percepts in apparent motion quartets during passive and volitional perception. Journal of Vision 2022;22(14):3987.

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      © ARVO (1962-2015); The Authors (2016-present)

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The apparent motion quartet is an ambiguous stimulus where motion is typically seen either vertically or horizontally. Previous studies have claimed that only one direction can be seen at a time. Here we report that it is possible to perceive both vertical and horizontal motion simultaneously (i.e., a mixed percept). In Experiment 1, participants passively viewed a single presentation of two frames of the quartet motion sequence, then reported whether they experienced vertical motion, horizontal motion, or “both”. We identified the aspect ratio where each participant was equally likely to report vertical or horizontal motion – the point of subjective equality (PSE). Across all aspect ratios, participants reported “both” on an average of 11% of trials. The mean aspect ratio across all “both” trials did not differ significantly from the PSE. Experiment 2 examined volitional perception, the ability to will to see one or the other direction. When the stimulus was set to their PSE from Experiment 1, participants had 75% success in willing horizontal motion (better than chance) but failed to will vertical motion better than chance rates. Interestingly, these vertical trials produced more “both” percepts, though fewer than in passive viewing (5.4%). Our results show that it is possible to simultaneously see horizontal and vertical motion in apparent motion quartets as a split in both directions away from the two initial corners. During passive viewing, these split percepts were most common near the PSE. During volitional perception, the split percepts were reduced in frequency and more frequent when willing vertical than horizontal motion.


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