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Charles C.-F. Or, Michel Thabet, Hugh R. Wilson, Frances Wilkinson; Detection of radial frequency motion trajectories. Journal of Vision 2010;10(7):825. doi: 10.1167/10.7.825.
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© ARVO (1962-2015); The Authors (2016-present)
Humans are extremely sensitive to radial deformations of static circular contours (Wilkinson, Wilson, & Habak, 1998, Vision Research). Here we investigate the detection of motion trajectories defined by these radial frequency (RF) patterns over a range of radial frequencies, using the method of constant stimuli combined with a two-interval forced-choice (2IFC) paradigm. The stimulus was a radially symmetric difference-of-Gaussians blob (peak spatial frequency: 2.74 cpd, bandwidth: 1.79 octaves at half amplitude) moving around the trajectory defined by an invisible RF pattern (motion RF), or by a circle of equivalent mean radius, for one complete revolution. The observer's task was to identify the interval containing the motion RF as a function of deformation amplitude; threshold was defined as 75% correct performance. Radial frequencies of 2 – 5 cycles were tested at a mean radius of 1.0 arc deg and a mean rotation speed of 3.14 arc deg/s (2.0 s for a complete revolution). Detection thresholds ranged from 0.8 – 4.6 arc min and followed a power function with an average exponent of −1.48 as a function of radial frequency. This decreasing trend was consistent with that found in static RFs, although detection thresholds for motion RFs were significantly higher (0.2 – 0.5 arc min for static RFs). Whether the sensitivity to motion RFs is dependent on local cues or global shape is currently under investigation. Importantly, we showed that these novel stimuli should be a useful tool to investigate trajectory learning and discrimination.
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