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Learning to See and Conceive

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L19 Human concept learning depends upon perception. Our concept of “car” is built out of perceptual features such as “engine,” “tire,” and “bumper.” However, recent research indicates that the dependency works both ways. We see bumpers and engines in part because we have acquired “car” concepts and detected examples of them. Perception both influences and is influenced by the concepts that we learn. We have been exploring the psychological mechanisms by which concepts and perception mutually influence one another, and building computational models to show that the circle of influences is benign rather than vicious.Perceptual Learning Is “Early” Neurologically, Functionally, and DevelopmentallyAn initial suggestion that concept learning influences perception comes from a considera-tion of the differences between novices and experts. Experts in many domains, including radiologists, wine tasters, and Olympic judges, develop specialized perceptual tools for analyzing the objects in their domains of expertise. Much of training and expertise involves not only developing a database of cases or explicit strategies for dealing with the world but also tailoring perceptual processes to more efficiently represent the world (Gibson 1991). Tuning one’s perceptual representation to the environment is a risky proposition. Once a perceptual representation has been altered, it affects all “downstream” processes that act as consumers of this altered representation. It makes sense to adapt perceptual systems slowly and conservatively. However, the payoffs for perceptual flexibility are also too enticing to forego. They allow an organism to respond quickly, efficiently, and effec-tively to stimuli without dedicating on-line attentional resources. Instead of strategically determining how to use an unbiased perceptual representation to fit one’s needs, it is often easier to rig up a perceptual system to give task-relevant representations, and then simply leave this rigging in place without strategic control. Perceptual learning is early in several senses: neurological, functional, and developmental.Learning to See and ConceiveRobert L. Goldstone, Alexander Gerganov, David Landy, and Michael E. RobertsTommasi_09_Ch09.indd 163 10/28/2008 2:25:37 PML1164 Robert L. Goldstone and colleagusNeurological EvidenceSeveral sources of evidence point to expertise influencing perceptual processing at a rela-tively early stage of processing. First, electrophysiological recordings show enhanced electrical activity at about 164 milliseconds after the presentation of dog or bird pictures to dog and bird experts, but only when they categorized objects within their domain of expertise (Tanaka and Curran 2001). A similar early electrophysiological signature of expertise is found with fingerprint experts when they are shown upright fingerprints, but is delayed when the fingerprints are inverted (Busey and Vanderkolk 2005). Interestingly, the timing and form of this expertise-related activity is similar to the pattern found when people are presented with faces, a stimulus domain in which, arguably, almost all people are experts (Gauthier et al. 2003).Second, prolonged practice with a subtle visual categorization results in much improved discrimination, but the improvements are highly specific to the trained orientation (Notman et al. 2005). This profile of high specificity of training is usually associated with changes to early visual cortex (Fahle and Poggio 2002). Practice in discriminating small motions in different directions significantly alters electrical brain potentials that occur within 100 milliseconds of the stimulus onset (Fahle 1994). These electrical changes are centered over the primary visual cortex, suggesting plasticity in early visual processing. Karni and Sagi (1993) find evidence, based on the specificity of training to eye (interocular transfer does not occur) and retinal location, that is consistent with early, primary visual cortex adapta-tion in simple discrimination tasks. In the auditory modality, training in a selective atten-tion task produces differential responses as early in the sensory processing stream as the cochlea (Puel et al. 1988). This amazing degree of top-down modulation of a peripheral neural system is mediated by descending pathways of neurons that project from the audi-tory cortex all the way back to olivocochlear neurons, which in turn project to outer hair cells within the cochlea (Suga and Ma 2003).Third, expertise can lead to improvements in the discrimination of low-level simple features, as with the documented sensitivity advantage that radiologists have over novices in detecting low-contrast dots in X-rays (Sowden et al. 2000). Fourth, imaging techniques have succeeded in identifying brain regions associated with the acquisition of expertise. Expertise for visual stimuli as eclectic as butterflies, cars, chess positions, dogs, and birds has been associated with an area of the temporal lobe known as the fusiform face area (Bukach et al. 2006). The identification of a common brain area implicated in many domains of visual expertise suggests the promise of developing general theories and models of perceptual learning. This is the main purpose of our work.Several other pieces of auxiliary evidence point to experience having early effects on perception, where “early” is operationalized neurologically in terms of a relatively small number of intervening synapses connecting a critical brain region to the external world. Experience making fine tactile discriminations influences primary somatosensory cortices. Monkeys trained to make discriminations between slightly different sound frequencies Tommasi_09_Ch09.indd 164 10/28/2008 2:25:37 PML1Learning to See and Conceive 165develop somatosensory cortex representations for the presented frequencies than control monkeys (Recanzone et al. 1993). Similarly, monkeys learning to make a tactile discrimi-nation with one hand develop a larger cortical representation for that hand than for the other hand (Recanzone et al. 1992). Elbert and colleagues (1995) measured brain activity in the somatosensory cortex of violinists as their fingers were lightly touched. There was greater activity in the sensory cortex for the left hand than the right hand, consistent with the observation


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