Biomedical subjects

Chris Westbury

Publications and source records attributed to Chris Westbury.

5 recordsLinked to original sources

PubMed2003

Semantics and semantic errors: implicit access to semantic information from words and nonwords in deep dyslexia.

In this paper we describe dissociations of implicit versus explicit access to semantic information in a patient with deep dyslexia. This acquired reading disorder is characterized by the production of morphological (e.g., SLEEP read as SLEEPING) and semantic errors (e.g., HEART read as BLOOD) and consequently provides a potential window into the operation of both aspects of the language system. The deep dyslexic patient in this study (JO) demonstrated implicit semantic access to items in a number of tasks despite the fact that she was unable to correctly read these items aloud. The findings from this study are consistent with a model of lexical deficits that distinguishes between explicit and implicit access to lexical representations on the basis of inhibitory processes.

Dyslexia↗

PubMed2003

The effect of semantic distance in yes/no and go/no-go semantic categorization tasks.

The effect of semantic distance (Lund & Burgess, 1996) was examined in three semantic categorization experiments. Experiment 1, a yes/no task that required participants to make animal/nonanimal judgments by responding to both sets of stimuli (Forster & Shen, 1996), revealed no effect of semantic distance. Experiment 2, a go/no-go task that required participants to respond to only the experimental (i.e., nonanimal) items, revealed a large effect of semantic distance. In addition, response latencies were longer and error rates were lower to the experimental items in Experiment 2 than to those in Experiment 1. These findings were replicated in Experiment 3, in which semantic distance and task condition were manipulated within subjects. We conclude that these results are consistent with (1) the view that the go/no-go tasks elicited more extensive processing of the experimental items and (2) a connectionist account of semantic activation, whereby processing is facilitated by the presence of semantic neighbors.

Humans↗

PubMed2003

Using genetic programming to discover nonlinear variable interactions.

Psychology has to deal with many interacting variables. The analyses usually used to uncover such relationships have many constraints that limit their utility. We briefly discuss these and describe recent work that uses genetic programming to evolve equations to combine variables in nonlinear ways in a number of different domains. We focus on four studies of interactions from lexical access experiments and psychometric problems. In all cases, genetic programming described nonlinear combinations of items in a manner that was subsequently independently verified. We discuss the general implications of genetic programming and related computational methods for multivariate problems in psychology.

Adult↗

PubMedDate not supplied

The probability of the least likely non-length-controlled bigram affects lexical decision reaction times.

The frequency effect, by which high frequency words are recognized with more ease than low frequency words, is one of the most robust effects in cognitive psychology. Frequency interacts with many word-level variables, to the extent that most effects reported in word recognition literature have an impact only on low frequency words. This has been taken as evidence that high frequency words are accessed in a special way, via either an addressed pathway as in the dual-route model or an assembled pathway as in a PDP model. Under either model, sublexical effects should have no bearing on the ease with which representations for high frequency words are accessed. In this article, however, we describe a series of studies that examine a sublexical effect (namely nonlength controlled minimal bigram frequency) that is only found for high frequency words, suggesting that sublexical processing must play a role in the recognition of even high frequency words.

Cognition↗

PubMedDate not supplied

Distinct neurolinguistic symptom clusters in Alzheimer's-type dementia and primary progressive aphasia.

Mesulam's (1982) report describing six patients with a slowly progressive aphasia without accompanying signs of dementia led to the recognition of a syndrome now known as Primary Progressive Aphasia (PPA). Many more patients have been described since Mesulam's description was published (see Westbury & Bub, 1997, for a review). However, the published literature is both unsystematic and incomplete, making it difficult to place the findings into a coherent theoretical framework. In addition, little previous work (see Mesulam, 1987) has specifically attempted to specify the difference between PPA and dementia of Alzheimer's type (DAT), although the two disorders are easily confused since many language deficits can masquerade on early presentation as memory or cognitive deficits. In this paper, the linguistic deficits of 11 PPA patients are analyzed, and contrasted with the linguistic deficits of a group of 11 DAT patients. Patients in both groups were tested using an extensive battery of language tests, the Psycholinguistic Assessment of Language Battery (Caplan & Bub, 1990; Caplan, 1992). We consider seven linguistic symptom clusters that differentiate the two groups.

Aged↗