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Veronique Lefebvre, Keith Langley, Peter Bex; Isolating the angular harmonic of the indirect tilt after-effect. Journal of Vision 2009;9(8):974. doi: 10.1167/9.8.974.
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The Angular Harmonic (AH) at which Indirect Tilt After-Effects (TAEs) oscillate provides an important cue in revealing the underlying mechanism(s) responsible for the bias. Assuming that Direct but not Indirect TAEs are tuned for spatial frequency, we estimated the AH for Indirect TAEs using adapt and test gratings whose spatial frequency differed by 25% and whose temporal frequency (TF) was either 0 Hz or 18 Hz. The adapt and test contrasts were 60% and 30% respectively and their relative orientations were varied between 0° and 90°. Subjects reported whether the test grating's perceived orientation was rotated clockwise or anti-clockwise about vertical. At low adapt TFs, the AH of Indirect TAEs was estimated at 4 cycles per full circle, while at the higher adaptor TF, the AH was noisier but nearer to 2. Our results are consistent with the idea that Indirect TAEs arise from the adaptation of mechanisms preferentially selective for orthogonal orientations.
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