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Arthur Shapiro, Alex Rose-Henig; The construction of global shape with the Tusi and Not-Tusi configurations. Journal of Vision 2019;19(10):168. doi: https://doi.org/10.1167/19.10.168.
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© ARVO (1962-2015); The Authors (2016-present)
Hypocycloids -- a geometrical construction in which a circle rolls inside the circumference of a larger outer circle -- have been studied by vision scientists (Rubin, 1919; Dunker, 1929; Johannson, 1950; Wallach, 1985) because the local motion does not always predict the global organization. Shapiro and Rose-Henig (2012, 2013) presented two versions of hypocycloids: in one, local elements oscillate in straight lines through the outer circle’s center (we call this the Tusi configuration, after 13th-century astronomer Nasir al-Din al-Tusi); in another, local elements follow a circular path (the Not-Tusi illusion). The relative phase of the elements determines the global percept (that is, the local elements remain on the same paths, but changing the phases of the elements can lead to the emergence of a hypocycloid or other shapes). We demonstrate that the Tusi and Not-Tusi configurations address fundamental questions concerning interactions between color, motion, attention, and perceptual grouping: 1. Adding noise elements and perturbations to the hypocycloid’s path disrupts static and dynamic configurations equally, suggesting (surprisingly) that motion does not add much to processes that create the global percept; 2. Attending to local elements shifts the percept between translational and rotational hypocycloids; 3. Changing a local element’s luminance changes the perceived direction of motion, thus separating motion perception based on feature analysis from motion perception based on luminance motion energy; 4. Even though the elements follow the same path, identification of global organization can be disrupted by changing elements’ colors and 5. we will discuss methods for translating the configurations into VR environments. Lastly, we will demonstrate other effects based on reverse-phi elements that show that local motion information can be used to create global percepts.
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