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Ron Dekel, Dov Sagi; Tilt Aftereffect due to Adaptation to Natural Images. Journal of Vision 2015;15(12):764. doi: 10.1167/15.12.764.
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© ARVO (1962-2015); The Authors (2016-present)
Extended exposure to artificial stimuli of limited orientation content is known to result in a shift of perceived orientation away from the mode of the orientation distribution - the tilt aftereffect (TAE). Here we test the generality of this effect using unaltered natural images (N=127) depicting most of their orientation content at a particular orientation (25° clockwise to vertical), selected in a biased half-automatic manner from 10,000,000 images. Nine observers were repeatedly exposed to these images (until response, ~1100 ms, image classification task: animal vs plant), and performed target trials which determined perceived orientation (clockwise vs counter-clockwise of a near-vertical Gabor, duration=30 ms, contrast=0.11, σ=0.25º), randomly interleaved with image trials. Compared to a reference, perceived orientation obtained while being exposed to random natural images, a repeated exposure to images from the biased ensemble produced a steady repulsive TAE of ~1° (p< 0.001). TAE was strongest immediately after image exposure (lag1: 1.44º, ~1.5 sec), minimal on the following trial (lag2: 0.46º, ~3 sec), converging to an intermediate value (0.98º) on later trials. This modulation may reflect repulsive (lag1) and attractive (lag2) short-term TAEs, operating on different timescales. While the larger effect at lag1 clearly resulted from image exposure, it is not ruled out that the reduced effect at lag2 is due to sequential response dependencies. Interestingly, preceding target trials similarly modulated perceived orientation, showing small but significant repulsive TAEs after one trial (p=0.015), and attractive TAEs after two trials (p=0.016). Finally, for comparison, five observers were repeatedly exposed to synthetic adaptors instead of biased images (Gabor, ±25º, duration=1500 ms, contrast=0.27, σ=0.87º), which resulted in a similar repulsive TAE (~1.2º). In conclusion, perceived orientation is modulated by natural images as with synthetic adaptors. Repulsive and attractive TAEs seem to have different timescales.
Meeting abstract presented at VSS 2015
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