Perceptual learning in visual category acquisition

Conceptual distinctiveness supports detailed visual long-term memory for real-world objects

Humans have a massive capacity to store detailed information in visual long-term memory. The present studies explored the fidelity of these visual long-term memory representations and examined how conceptual and perceptual features of object categories support this capacity. Observers viewed 2,800 object images with a different number of exemplars presented from each category. At test, observers indicated which of 2 exemplars they had previously studied. Memory performance was high and remained quite high (82% accuracy) with 16 exemplars from a category in memory, demonstrating a large memory capacity for object exemplars. However, memory performance decreased as more exemplars were held in memory, implying systematic categorical interference. Object categories with conceptually distinctive exemplars showed less interference in memory as the number of exemplars increased. Interference in memory was not predicted by the perceptual distinctiveness of exemplars from an object category, though these perceptual measures predicted visual search rates for an object target among exemplars. These data provide evidence that observers' capacity to remember visual information in long-term memory depends more on conceptual structure than perceptual distinctiveness.

Perceptual learning

Perceptual learning involves relatively long-lasting changes to an organism's perceptual system that improve its ability to respond to its environment. Four mechanisms of perceptual learning are discussed: attention weighting, imprinting, differentiation, and unitization. By attention weighting, perception becomes adapted to tasks and environments by increasing the attention paid to important dimensions and features. By imprinting, receptors are developed that are specialized for stimuli or parts of stimuli. By differentiation, stimuli that were once indistinguishable become psychologically separated. By unitization, tasks that originally required detection of several parts are accomplished by detecting a single constructed unit representing a complex configuration. Research from cognitive psychology, psychophysics, neuroscience, expert/novice differences, development, computer science, and cross-cultural differences is described that relates to these mechanisms. The locus, limits, and applications of perceptual learning are also discussed.

On the relationship between category intensions and extensions in children

We contrasted four theories of natural language category acquisition by investigating the relation between category intensions and extensions in children (kindergarteners, second graders, fifth graders) and in college students. Everyone was asked to define a category term, to make category membership judgments of possible exemplars, and to judge whether the possible exemplars possessed features generated by them and by previous adult subjects. Adult judges were also asked to judge whether the possible exemplars possessed the features generated by the subjects. Children's intensions and extensions were very consistent. In addition, children's extensions were reliably smaller than adults', and the features which children generated were more specific than those generated by adults. None of the existing theories discussed can explain this pattern of results. An exemplar-based model is proposed to do so.