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Marwan Daar, Charles C.-F. Or, Hugh Wilson; Increment threshold functions for radial frequency motion trajectories exhibit a dipper function above threshold. Journal of Vision 2012;12(9):644. doi: 10.1167/12.9.644.
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© ARVO (1962-2015); The Authors (2016-present)
Radial frequency (RF) trajectories are a new class of stimuli that have been developed to study the visual perception of periodic motion (Or, Thabet, Wilkinson, and Wilson, 2011). These stimuli are described by a moving dot that traverses a circular path through space with periodic radial deformations whose frequency, amplitude, and phase can be independently specified. Here, we show how the discrimination of RF amplitude varies across different reference amplitudes in a 2 alternative forced choice task. Using an RF3 trajectory (a pattern with three cycles of deformation along its trajectory), increment thresholds for seven observers were measured at four different reference amplitudes: Detection (discriminating a circular motion from RF3), 1X (discriminating a pair of RF3 patterns, with the amplitude of one member of this pair set to (1X) threshold obtained from the detection condition), 2.5X, and 5X. Data show that thresholds for detecting changes in amplitude show an approximately two-fold decrease at 1X and 2.5X, relative to detection threshold, and then recover to detection threshold levels at 5X. Mean thresholds (± standard errors) for detection, 1X, 2.5X, and 5X (in minutes of arc): 2.30 ± 0.31, 1.21 ± 0.18, 1.06 ± 0.12, 2.31 ± 0.42, respectively. A repeated measures ANOVA showed a main effect of base increment: F(1,6) = 95.80, p<0.0001 ); paired sample t-tests showed a significant difference between detection and 1X, T(6) = 3.59 (p<0.05); detection and 2.5X, T(6) = 4.28 (p<0.01); and no difference between detection and 5X, T(6) = -0.03 (p = 0.98). Observers were also tested using an RF5 trajectory, and the same pattern was found. As a control, this effect was measured using different angular speeds of the RF trajectory. We conclude that the discrimination of RF trajectories along different base amplitudes points to a sigmoidal neural response function for deviations from circular trajectories.
Meeting abstract presented at VSS 2012
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