Evidence for tilt normalisation may be explained by anisotropic orientation channels K Storrs1, D H Arnold2 |
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1School of Psychology, University of Queensland, Australia |
| Some data have been taken as evidence that prolonged viewing of orientations close to vertical makes them appear more vertical than they had previously – tilt normalisation. After almost a century of research the existence of tilt normalisation remains controversial. Recently it has been suggested that tilt normalisation results in a measurable “perceptual drift” toward vertical, which can be nulled by a slight physical rotation away from vertical [Muller, Schillinger, Do, & Leopold (2009), PLoS One, 4(7)]. We believe these data result from the anisotropic organisation of V1 orientation filters, which are denser and narrower around vertical than oblique orientations. We describe a neurophysiologically plausible model that predicts that, after adaptation, near-vertical stimuli should, if anything, be repelled from, rather than attracted to, vertical. Moreover, the model predicts heightened sensitivity to physical rotations toward vertical compared to rotations away from vertical, for which we present supporting psychophysical data. Given this asymmetry, we suggest that data implying a perceptual drift toward vertical could ensue from taking the average reversal value in a staircase procedure as an estimate of perceptual stasis for near-vertical stimuli. |
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