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George Sperling, Peng Sun, Charles Chubb; The perceived motion of three varieties of moving barberpole stimuli. Journal of Vision 2013;13(9):767. doi: 10.1167/13.9.767.
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© ARVO (1962-2015); The Authors (2016-present)
In foveal view, the moving barberpole stimulus looks like several barber poles drifting horizontally. It is produced by a diagonal sinusoidal carrier grating with bars drifting up to the right, windowed by a raised, vertical, horizontally-drifting sinusoid. Unlike stationary barber poles, the rigid-motion direction of this stimulus is diagonal, not vertical. Previously, Chubb, Sun & Sperling (2012), demonstrated that pure vertical motion--the barber pole illusion (BPI)--was observed in peripheral but not foveal viewing. Hidden formatting deleted. Delete this text! yes"> Experiments: Peripheral viewing. (1) Decreasing carrier temporal frequency below 10 Hz (enabling higher-order motion systems to participate) caused the perceived motion to deviate from BPI. As carrier speed approached zero, the overall motion (all that could be perceived peripherally) was perceived in the rigid (diagonal) direction . Thus, peripheral BPI in this stimulus requires first-order motion. (2) Flipping the carrier contrast between barber poles removed the global carrier fundamental component but had no effect on the perceived BPI. This shows that the first-order motion component on which BPI depends is local (within a pole) rather than global. (3) Filling the low-contrast regions between barber poles with flickering gratings (lateral masking) failed to abolish the peripheral BPI. In the fovea, the unmasked moving-barber-pole stimulus appears to move in complex patterns. Remarkably, the between-pole masking produced the simple BPI in the fovea. The between-pole masking removed the contrast modulation needed by higher-order motion systems to detect the horizontal pole movement and thereby masking equalized fovea and periphery. Conclusions. The vertical BPI in the moving barberpole stimulus cannot be explained by any Fourier motion components nor any combination thereof, nor by higher-order motion or feature-tracking. Consistent with Chubb et al (2012), the BPI in the moving barberpole stimulus is produced by a higher-order streaming process fed by first-order motion.
Meeting abstract presented at VSS 2013
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