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Lindsay B. Lewis, Ione Fine, Karen R. Dobkins; Effects of context on motion processing: the barber pole illusion in infants. Journal of Vision 2004;4(8):34. doi: 10.1167/4.8.34.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In the barber pole (BP) illusion, perceived direction of a moving grating viewed through a rectangular aperture is biased along the major axis of that aperture, which is thought to reflect integration of one-dimensional (1D) motion signals of the grating interior, which are ambiguous, with two-dimensional (2D) motion signals of the line terminators, which are unambiguous and yield a mean 2D signal dependent on aperture configuration. In this study, we quantified the BP effect in infants. Methods: Using a directional (left vs. right) eye movement technique, we compared infants' ability to track moving gratings (0.8 cpd, 80% contrast, 20 /sec) viewed through multiple horizontal (H) vs. vertical (V) apertures (2 × 4 ). This paradigm relies on the assumption that the more horizontal the perceived direction is, the more salient the horizontal component of the eye movement will be, leading to higher performance. In Exp. 1, the BP effect was quantified as the difference in percent correct performance for an obliquely moving grating (72°) viewed through H vs. V apertures. In Exp. 2, the BP effect was quantified by obtaining the “equivalent direction” (EqDIR), defined as the direction of motion in H apertures that yields the same performance as a 45° grating moving within V apertures. The “effective shift” in perceived direction produced by the aperture configuration was then calculated as the difference between EqDIR and 45°. Results: In Exp. 1, the difference score was ∼10% and did not vary significantly between 1 and 5 months of age (n=50). Preliminary data from Exp. 2 indicate that the effective shift produced by aperture configuration is ∼16° in 3- and 5-month olds (n=8). Interestingly, this value is larger than that of adults (∼4°), measured via perceptual reports of horizontal strength (n=3). Conclusions: The BP illusion appears by 1 month of age, suggesting that infant motion processing is influenced by 2D motion signals afforded by aperture configuration.
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