Category-specific semantic impairments have been explained in terms of preferential damage to different types of features (e.g., perceptual vs. functional). This account is compatible with cases in which the impairments were the result of relatively focal lesions, as in herpes encephalitis. Recently, however, there have been reports of category-specific impairments associated with Alzheimer's disease, in which there is more widespread, patchy damage. We present experiments with a connectionist model that show how "category-specific" impairments can arise in cases of both localized and widespread damage; in this model, types of features are topographically organized, but specific categories are not. These effects mainly depend on differences between categories in the distribution of correlated features. The model's predictions about degree of impairment on natural kinds and artifacts over the course of semantic deterioration are shown to be consistent with existing patient data. The model shows how the probabilistic nature of damage in Alzheimer's disease interacts with the structure of semantic memory to yield different patterns of impairment between patients and categories over time.

A considerable body of empirical and theoretical research suggests that morphological structure governs the representation of words in memory and that many words are decomposed into morphological components in processing. The authors investigated an alternative approach in which morphology arises from the interaction of semantic and phonological codes. A series of cross-modal lexical decision experiments shows that the magnitude of priming reflects the degree of semantic and phonological overlap between words. Crucially, moderately similar items produce intermediate facilitation (e.g., lately-late). This pattern is observed for word pairs exhibiting different types of morphological relationships, including suffixed-stem (e.g., teacher-teach), suffixed-suffixed (e.g., saintly-sainthood), and prefixed-stem pairs (preheat-heat). The results can be understood in terms of connectionist models that use distributed representations rather than discrete morphemes.

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Although the role of visual perception is central to many theories of language development, researchers have disagreed sharply on the effects of blindness on the acquisition process: some claim major differences between blind and sighted children; others find great similarities. With audio-and video-recorded longitudinal data from six children (with varying degrees of vision) aged 0; 9–3; 4, we show that there ARE basic differences in early language, which appear to reflect differences in cognitive development. We focus here on early lexical acquisition and on verbal role-play, demonstrating how previous analyses have failed to observe aspects of the blind child's language system because language was considered out of the context of use. While a comparison of early vocabularies does suggest surface similarities, we found that when sighted peers are actively forming hypotheses about word meanings, totally blind children are acquiring largely unanalysed ‘labels’. They are slow to extend words and rarely overextended any. Similarly, although verbal role-play appears early, attempts to incorporate this kind of language into conversations with others reveal clear problems with reversibility – specifically, the ability to understand the role of shifting perspectives in determining word meaning. Examination of language in context suggests that blind children have difficulties in just those areas of language acquisition where visual information can provide input about the world and be a stimulus for forming hypotheses about pertinent aspects of the linguistic system.