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Michael von Grünau, Samantha Sparapani, Ruben Bastien; Components of the curveball illusion: Independent contributions of carrier and envelope. Journal of Vision 2011;11(11):757. doi: https://doi.org/10.1167/11.11.757.
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Purpose: The curveball illusion (Shapiro et al., 2008) demonstrates a failure of the peripheral visual field to integrate motions without loss of location information. We were interested in examining how the two motion components independently influence the illusion strength across the visual field. Methods: We used a linear version of the illusion, with a starting point 9 deg horizontally to the right of fixation and apparent trajectories in the combinations of up/down and left/right directions. In each case, the speed of the carrier motion or that of the envelope motion was varied. Illusion strength was measured in terms of the perceived angle of the trajectory with respect to vertical. Illusion strength was also measured for the right/up direction for horizontal eccentricities from fixation (0 deg) to 15 deg for both speed variations. Results: Illusion strength was logarithmically related to speed for each component, and this relationship was very similar in all quadrants. Illusion strength also increased logarithmically over the whole range of eccentricities, with no illusion for any speed at fixation. Already at the smallest eccentricity (1 deg) there was a sizable illusion that varied with speed. Illusion strength saturated at around 15 deg eccentricity. Conclusion: The curveball illusion is well-described in terms of the component motion speeds. With constant stimulus size, illusion strength increases sharply and then saturates with increasing eccentricity. Thus, loss of location information occurs across the whole visual field, except in the very center. Shapiro A. et al. (2008). Meeting of Society of Neuroscience.
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