The effects of performance feedback and their implications for the time course and stabilization of perceptual learning
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Visual perceptual learning (VPL) is defined as a long-term performance improvement on a visual task due to repeated exposure or training. Behavioral factors such as feedback (knowledge of performance accuracy) can strongly influence VPL, but remain sparsely studied. Here a series of experiments is presented in which subjects were trained to detect two coherent motion directions over 7 days. One of the two directions was consistently paired with feedback and the other was not. Results show that feedback can augment the performance benefits accrued for its paired stimuli while simultaneously inhibiting VPL of unpaired stimuli. The psychophysical data strongly suggest that feedback may exert its benefits by facilitating the long-term consolidation and stabilization of VPL, thus making VPL robust against interference from the presentation of new, novel stimuli. These results highlight an "inferential gap" intrinsic to these types of investigations: traditional measures of performance accuracy are coarse, and the gulf between an observer's percept and the chosen performance metric makes it difficult to determine the underlying causes of observed effects. New computational techniques such as "classification images" (stimulus-based templates of the criteria observers employ while performing tasks) offer an opportunity to narrow this gap. Another series of experiments demonstrates that classification images can be adapted to accurately characterize VPL in detail. Observers were trained to detect oriented gratings, similar to classical VPL studies, or coherent motion stimuli, replicating the previous experiments. Images computed from oriented gratings parallel the psychophysical data and present a more complete view of stimulus sensitivity. Images computed from coherent motion stimuli show clear beneficiary effects of feedback that are strikingly consistent with the aforementioned results. Furthermore, the images reveal a temporal"blink" effect, suggesting that observers preferentially process later frames of the stimuli, as well as a spatial bias indicating that observer focus shifts to spatial locations congruent with direction of motion. These effects would have remained hidden without the sensitivity provided by classification images. The results of these experiments show that feedback exerts powerful effects on the stabilization of VPL, and that classification images can reveal such perceptual dynamics in great detail.
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