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Nicole D. Anderson, Claudine Habak, Frances Wilkinson, Hugh R. Wilson; Evaluating curvature aftereffects with radial frequency contours. Journal of Vision 2005;5(8):208. doi: 10.1167/5.8.208.
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© ARVO (1962-2015); The Authors (2016-present)
Psychophysical and physiological evidence demonstrates that global shape coding depends on mechanisms located at intermediate levels of visual processing. Evidence also suggests that these mechanisms are vulnerable to adaptation techniques historically used to probe mechanisms underlying performance in lower-level visual tasks. We explored the nature of these global shape aftereffects using radial frequency (RF) patterns, where stimuli are defined in terms of deformations from a circular pattern. On each trial, subjects adapted to a RF pattern with a high (x15 threshold) amplitude for 5 seconds, followed by a brief (53 ms) test RF that was either in-phase or anti-phase to the adapted RF. Subjects identified the phase of the test RF pattern using a 2AFC paradigm. Performance was evaluated by determining the RF amplitude at which subjects equally classified the test stimulus as the in-phase or anti-phase pattern (Point of Subjective Equality (PSE)). With no adaptation, subjects were exquisitely accurate when classifying RF patterns (PSE=1.0arcsec). After adaptation, the PSE shifted towards the pattern that was in-phase with the adapted RF (Peq=52.3arcsec), demonstrating that subjects were more likely to classify the test RF as the anti-phase pattern. This perceived shift is equivalent to a stimulus that is modulated 2–3x above threshold under these conditions. When subjects adapted to a RF pattern with a larger number of cycles, on the other hand, the PSE did not change. Preliminary results suggest that the strength of the shape-specific aftereffect is similar when adapting to either a high (90%) or low (10%) contrast RF pattern. Together, these results suggest that the mechanisms adapted by RF patterns code information that is specific to the geometry of the stimulus, and are located beyond those responsible for contrast gain control.
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