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Erich W. Graf, Wendy J. Adams, Samira Bouzit; Light priors, learning and feedback. Journal of Vision 2007;7(9):309. doi: https://doi.org/10.1167/7.9.309.
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To interpret ambiguous shading information, observers use the ‘light-from-above’ prior. Previous work has shown that this prior can be modified in response to haptic (touch) feedback indicating that the light position has altered (Adams, Graf and Ernst, 2004). Here, we extend this work to investigate (i) the time-course of this learning, (ii) how long the effects persist, and (iii) whether learning is more efficient when more feedback (binocular depth information) is added.
Before training, observers viewed monocular disks with shading gradients at various orientations. Reported shape (convex or concave) as a function of stimulus orientation was used to recover each observer's assumed light position. During training, observers also ‘touched’ the disks. The haptic (felt) shape of the training stimuli was consistent with a light source shifted by ±30 degrees from the observer's original assumed light position. A second group of observers were given additional stereoscopic depth information during training that was consistent with the haptics (and the new, trained light position). After training, observers again judged the shape of the stimuli based purely on monocular shading information.
Initially, our observers assumed a light position that was roughly overhead. However, the observers who were given only haptic feedback, learned to use a shifted light direction for their prior. Most learning occurred during the first 2 hours of training and the learnt shift persisted at least 10 days. Interestingly, learning was significantly reduced in the group who were given both disparity and haptic feedback.
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