Improvements in performance on visual tasks due to practice are often specific to a retinal position or stimulus feature. Many researchers suggest that specific perceptual learning alters selective retinotopic representations in early visual analysis. However, transfer is almost always practically advantageous, and it does occur. If perceptual learning alters location-specific representations, how does it transfer to new locations? An integrated reweighting theory explains transfer over retinal locations by incorporating higher level location-independent representations into a multilevel learning system. Location transfer is mediated through locationindependent representations, whereas stimulus feature transfer is determined by stimulus similarity at both location-specific and location-independent levels. Transfer to new locations/positions differs fundamentally from transfer to new stimuli. After substantial initial training on an orientation discrimination task, switches to a new location or position are compared with switches to new orientations in the same position, or switches of both. Position switches led to the highest degree of transfer, whereas orientation switches led to the highest levels of specificity. A computational model of integrated reweighting is developed and tested that incorporates the details of the stimuli and the experiment. Transfer to an identical orientation task in a new position is mediated via more broadly tuned location-invariant representations, whereas changing orientation in the same position invokes interference or independent learning of the new orientations at both levels, reflecting stimulus dissimilarity. Consistent with single-cell recording studies, perceptual learning alters the weighting of both early and midlevel representations of the visual system. reweighting models | Hebbian models A lmost all perceptual tasks exhibit perceptual learning, improving people's ability to detect, discriminate, or identify visual stimuli. These improvements due to practice are the basis of visual expertise. Practice improves the ability to perceive orientation, spatial frequency, patterns and texture, motion direction, and other stimulus features (1-4). Learned perceptual improvements generally show some specificity to the feature and to the retinal location of training. Specificity of trained improvements to retinal location and feature in behavioral studies of texture orientation (5, 6) or simple pattern orientation judgments (7,8) inspired early researchers to posit that practice altered the responses of early visual representations (V1/V2) with small receptive fields, retinotopic structure, and relatively narrow orientation and spatial frequency tuning (6).However, the generalization of learned perceptual skills over retinal locations is almost always practically advantageous, and is sometimes observed (9). Whether perceptual learning reflects changes in retinotopic representations in early visual cortical areas (6) or alternatively-as we have suggested elsewhere-is primarily acco...