Biomedical subjects

Chris Westbury

Publications and source records attributed to Chris Westbury.

10 recordsLinked to original sources

PubMed2006

NUANCE: Naturalistic University of Alberta Nonlinear Correlation Explorer.

In this article, we describe the Naturalistic University of Alberta Nonlinear Correlation Explorer (NUANCE), a computer program for data exploration and analysis. NUANCE is specialized for finding nonlinear relations between any number of predictors and a dependent value to be predicted. It searches the space of possible relations between the predictors and the dependent value by using natural selection to evolve equations that maximize the correlation between their output and the dependent value. In this article, we introduce the program, describe how to use it, and provide illustrative examples. NUANCE is written in Java, which runs on most computer platforms. We have contributed NUANCE to the archival Web site of the Psychonomic Society (www.psychonomic.org/archive), from which it may be freely downloaded.

Behavioral Research↗

PubMed2006

Word frequency effects in high-dimensional co-occurrence models: A new approach.

The HAL (hyperspace analog to language) model of lexical semantics uses'global word co-occurrence from a large corpus of text to calculate the distance between words in co-occurrence space. We have implemented a system called HiDEx (High Dimensional Explorer) that extends HAL in two ways: It removes unwanted influence of orthographic frequency from the measures of distance, and it finds the number of words within a certain distance of the word of interest (NCount, the number of neighbors). These two changes to the HAL model produce measures of word neighborhood density that are reliably predictive of human lexical decision reaction times.

Humans↗

PubMed2005

Implicit sound symbolism in lexical access: evidence from an interference task.

Köhler (1929) reported anecdotally that, when asked to choose, subjects were much more likely to attach the name 'takete' to a spiky abstract object, and the name 'baluma' (or, by 1947, 'maluma') to a curvy abstract object. Follow-up work has suffered from the same three weaknesses as Köhler's original anecdotal study: a reliance on small number of stimuli carefully selected by the experimenter; the use of manipulations that were transparent to the subject; and the use of overtly semantic tasks. This paper reports two experiments that replicate and extend Köhler's claims using an implicit interference task that allows for multiple measures per subject, and does not require subjects to make explicit decisions about the relation between visual form and meaning. Subjects undertook a lexical or letter decision task with the stimuli presented inside spiky or curvy frames. Reaction times show interference patterns consistent with Köhler's claims. This demonstrates that the effect is pre-semantic. Neurological reasons for these word/shape and character/shape interference phenomena are discussed.

Auditory Perception↗

PubMed2004

Deep dyslexia and semantic errors: a test of the failure of inhibition hypothesis using a semantic blocking paradigm.

Deep dyslexia is an acquired reading disorder that involves the production of semantic errors and the inability to read aloud nonwords successfully. Several explanations for this reading impairment posit multiple loci of damage to account for the various error types produced in deep dyslexia. In contrast, the failure of inhibition hypothesis suggests that damage in the phonological output lexicon alone can explain these errors. Specifically, this hypothesis proposes normal processing via orthographic and phonological reading routes, as well as an intact semantic system. However, slowed or reduced inhibitory connections result in the failure to suppress spuriously activated neighbours in the phonological output lexicon, where neighbourhood can be defined in terms of phonology, orthography, or semantics. Given a failure to inhibit semantically related candidates, semantic reading errors occur. Important to the test of this hypothesis is that it evolves several predictions that are contrary to performance observed in the normal population. In particular, semantic errors are predicted to be greater in conditions where words are blocked according to semantic category than in random presentations. In addition, a semantic interference effect is expected. The results of semantic blocking were consistent with these predictions and lend support to the failure of inhibition hypothesis.

Attention↗

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

Word associations in deep dyslexia.

Deep dyslexia is an acquired reading disorder resulting in the production of semantic errors during oral reading and an inability to read aloud nonwords. Several researchers have postulated that patients with deep dyslexia have both phonological and semantic access impairments but the data supporting these claims are not convincing. In fact, the hallmark feature of deep dyslexia--the semantic errors--strongly implies that these patients can access semantic information from printed words. We test the integrity of the semantic system in two such patients through auditory and visual word association tasks. The data support the notion that semantics remains intact and that the disorder and associated errors arise through a selection impairment related to failure of inhibitory connections in the phonological lexicon.

Association↗

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↗