Elaine S. Andersen

Category-Specific Semantic Deficits in Focal and Widespread Brain Damage: A Computational Account

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 Alzheimers disease, in which there is more widespread, patchy damage. We present experiments with a connectionist model that show how ficategory-specificfl impairments can arise in cases of both localized and wide-spread 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 models 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 Alzheimers disease interacts with the structure of semantic memory to yield different patterns of impairment between patients and categories over time.

Double dissociation of semantic categories in Alzheimer's disease

Data that demonstrate distinct patterns of semantic impairment in Alzheimers disease (AD) are presented. Findings suggest that while groups of mild-moderate patients may not display category specific impairments, some individual patients do show selective impairment of either natural kinds or artifacts. We present a model of semantic organization in which category specific impairments arise from damage to distributed features underlying different types of categories. We incorporate the crucial notions of intercorrelations and distinguishing features, allowing us to demonstrate (1) how category specific impairments can result from widespread damage and (2) how selective deficits in AD reflect different points in the progression of impairment. The different patterns of impairment arise from an interaction between the nature of the semantic categories and the progression of damage.

Graded semantic and phonological similarity effects in priming: evidence for a distributed connectionist approach to morphology.

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.

Blind children's language: resolving some differences

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 childs 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.

The impact of input: language acquisition in the visually impaired:

Variation in language development between blind and sighted children may result from a diminution of experience or differences in linguistic input, or it may be a product of other factors. Researchers argue about the relative weighting of these. We examine this argument by reviewing data and findings from our studies of blind childrens language and we evaluate the possible impact of input, both environmental and linguistic. We show that variation cannot be uniquely attributed to either of these, but find evidence that experiential input may influence some areas while linguistic input more strongly affects others. Moreover, there is a complex interaction between these. We also find independent adaptive strategies by the children, pointing to a plasticity in the acquisition process itself.

Sentence Comprehension Deficits in Alzheimer's Disease: A Comparison of Off-Line vs. On-Line Sentence Processing

Two studies explored whether sentence comprehension impairments in Alzheimers disease (AD) are due to deficits in syntactic processing or memory. Study 1 used a picture-pointing sentence comprehension task to measure the final outcome of comprehension in an off-line fashion. It showed the comprehension of 30 patients with AD to be impaired, but suggested that the deficits could not be attributed solely to syntactic impairments. Study 2 investigated the effects of memory on sentence comprehension by comparing off-line (grammaticality judgment) with on-line (cross-modal naming) language processing in 11 AD and 9 control subjects. The results revealed impaired performance in the off-line task but normal performance in the on-line task using the same sentences. Performance on the off-line task correlated with independent measures of verbal working memory. These data are used to argue that sentence comprehension impairments are related to verbal working memory deficits in AD.

Cross-linguistic evidence for the early acquisition of discourse markers as register variables

Abstract Most prior research has focused on the textual uses of discourse markers (DMs): how they (1) create coherence; (2) provide feedback about comprehension; and (3) signal production problems. A less studied function of these forms is their use as markers of the social relationships between interlocutors. This paper compares earlier findings on the acquisition of DMs as register variables in American English and Lyonnais French (Andersen 1990, 1996) with more recent data from a comparable study of Chicano Spanish-speaking children; it demonstrates striking cross-linguistic parallels in the way children learn to use these forms both to convey social meaning and to manipulate the social situation where power relationships are not pre-established. All groups use more lexical DMs and more ‘stacks’ (Well, now then …, Et bon alors …, Y bueno vamos …) to mark higher status roles, with non-lexical variants such as uh, euh, or eh more frequent in the low status roles. In addition to parallel patterns of use, the data also reveal differences that reflect the relative importance of these forms in the different language communities, with French children using more DMs and ‘stacking’ than their American and Spanish-speaking peers.

Naming consistency in Alzheimer's disease

Although lexical semantic deficits are postulated to play a prominent role in the anomia of Alzheimers disease, it is unclear whether the primary disturbance is one of lexical access or one of lexical semantic loss. Response consistency on a naming task is one means of evaluating the underlying source of naming impairment. Access dysfunction usually implies variable word-finding difficulty, while a theory of lexical loss predicts that many word names would be consistently unavailable. Nineteen Alzheimers disease patients were administered a visual confrontation naming task (the Boston Naming Test) on two occasions 6 months apart. Eighty percent of errors occurred consistently at both times; only 20% of errors occurred on only one occasion. Response consistency occurred significantly more often than expected under the assumption of no response consistency. Findings support the hypothesis that anomia in Alzheimers disease is in part due to a loss of lexical semantic information.

Information content versus relational knowledge: Semantic deficits in patients with Alzheimer's disease

Studies of semantic impairment in Alzheimers disease (AD) have yielded conflicting results, some finding evidence of considerable deficits, others finding that semantic knowledge is relatively intact. How do we reconcile findings from picture naming tasks that seem to indicate semantic impairment in AD with results from certain sorting tasks that suggest intact semantics? To investigate the basis of the contradictory results described above, we conducted a study using two types of tasks: (1) picture naming; and (2) board sorting. The board sorting task we used is a simultaneous similarity judgment task, in which participants are asked to place more similar concepts closer together and less similar ones farther apart. We compared the performance of AD patients on these two tasks, using a number of different analyses that yield very different patterns of results. Our results indicate that whether patients show impairment or not depends on both the nature of the task and the subsequent analysis chosen. Specifically, tasks and analyses that focus on relational knowledge (e.g., dog is more related to cat than to camel) lead to different conclusions than those based on specific information about individual items. These findings suggest that the board sorting method, when coupled with multiple analyses, provides a more complete picture of the underlying semantic deficit in AD than previous studies have shown.

Comprehension of long distance number agreement in probable Alzheimer's disease

Two cross-modal naming experiments examined the role of working memory in processing sentences and discourses of various lengths. In Experiment 1, 10 memory impaired patients with probable Alzheimers disease (AD) and 10 healthy elderly control participants showed similar sensitivity to violations of subject-verb number agreement in a short sentence condition and similar degradation to this sensitivity in a long sentence condition. Performance in neither length condition correlated with performance on working memory tasks, suggesting that the processes involved in interpreting a grammatical dependency between adjacent and nonadjacent elements are different from those required in the working memory tasks. In Experiment 2, the same 10 AD patients were less sensitive than the 10 control participants to pronounantecedent number agreement violations in a short discourse condition, but neither group was affected by additional length. In this experiment, performance in both the short and long conditions correlated with working memory performance. These results show that grammatical and discourse dependencies pose different memory and processing demands, and that these differences are not simply due to differences in the amount of intervening material between dependent words. The results also suggest that while the working memory deficits characteristic of AD do not interfere with on-line grammatical processing within sentences, they do compromise on-line discourse processing across sentences. Two cross-modal naming experiments examined the role of working memory in processing sentences and discourses of various lengths. In Experiment 1, 10 memory impaired patients with probable Alzheimers disease (AD) and 10 healthy elderly control participants showed similar sensitivity to violations of subject-verb number agreement in a short sentence condition and similar degradation to this sensitivity in a long sentence condition. Performance in neither length condition correlated with performance on working memory tasks, suggesting that the processes involved in interpreting a grammatical dependency between adjacent and nonadjacent elements are different from those required in the working memory tasks. In Experiment 2, the same 10 AD patients were less sensitive than the 10 control participants to pronounantecedent number agreement violations in a short discourse condition, but neither group was affected by additional length. In this experiment, performance in both the short and long conditions correlated with working memory performance. These results show that grammatical and discourse dependencies pose different memory and processing demands, and that these differences are not simply due to differences in the amount of intervening material between dependent words. The results also suggest that while the working memory deficits characteristic of AD do not interfere with on-line grammatical processing within sentences, they do compromise on-line discourse processing across sentences.