Abstract
It has been suggested that information-integration (two-dimensional) category boundaries can be learned with immediate but not delayed feedback because of the time course of the dopamine function in the brain (Maddox, Ashby & Bohil, 2003). Here we examined the role of feedback delay in visual perceptual learning in an orientation identification task. Contrast thresholds were measured in a 2AFC orientation task tracking 65% correct at 5.4 degree in the periphery (e.g.,five-sessions of training with -55 ± 8 deg in top left and bottom right, then switching to five-sessions of training with 35 ± 8 deg in top right and bottom left locations). Training at 65% accuracy of this task has been shown to yield learning with feedback but no learning without feedback (Liu, et al., 2010, 2012), while transfer to an orthogonal reference angle training with feedback yielded independent learning in the two training phases (Dosher & Lu, 2007). We found that five sessions of training with 3-sec delayed feedback led to limited learning, while more robust learning resumed in the subsequent five transfer sessions with immediate feedback: the effective learning rate with immediate feedback during transfer was close to twice of that during training with delayed feedback, with essentially the same starting threshold. The results were well fit by the integrated reweighting theory (IRT, Dosher et al 2013) in which the delayed feedback reduced its effectiveness, with the feedback weight decreased from 1.0 in immediate feedback to 0.1 in delayed feedback. Perceptual learning in the orientation task differs from category learning tasks in that the decision rule is one dimensional and explicitly instructed; yet similar susceptibility to feedback delay suggests potentially common neural substrates in perceptual learning and information integration category learning.