What we talk about when we talk about access deficits

Abstract

Semantic impairments have been divided into storage deficits, in which the semantic representations themselves are damaged, and access deficits, in which the representations are intact but access to them is impaired. The behavioural phenomena that have been associated with access deficits include sensitivity to cueing, sensitivity to presentation rate, performance inconsistency, negative serial position effects, sensitivity to number and strength of competitors, semantic blocking effects, disordered selection between strong and weak competitors, correlation between semantic deficits and executive function deficits and reduced word frequency effects. Four general accounts have been proposed for different subsets of these phenomena: abnormal refractoriness, too much activation, impaired competitive selection and deficits of semantic control. A combination of abnormal refractoriness and impaired competitive selection can account for most of the behavioural phenomena, but there remain several open questions. In particular, it remains unclear whether access deficits represent a single syndrome, a syndrome with multiple subtypes or a variable collection of phenomena, whether the underlying deficit is domain-general or domain-specific, whether it is owing to disorders of inhibition, activation or selection, and the nature of the connection (if any) between access phenomena in aphasia and in neurologically intact controls. Computational models offer a promising approach to answering these questions.

When words fail us: insights into language processing from developmental and acquired disorders

“…An outstanding question is whether problems with computational complexity are confined to the syntactic domain, as argued by Van der Lely [21], or whether they form part of a more general deficit that extends to affect other systems. In a similar vein, Mirman & Britt [22] describe a range of phenomena in acquired aphasia that are not readily explained in terms of impaired language representations. Some patients appear to have difficulty accessing lexical information, yet their performance on specific items is inconsistent from trial to trial, and/or influenced by factors such as presentation rate or provision of cueing.…”

“…First, we now have several implemented models for processing of written and spoken language that have been applied to acquired disorders [22,35,[42][43][44]. Some of these model the learning process as well as the stable state, yet applications to developmental disorders are rare (but see Ziegler et al [33]).…”

Verb Production in Aphasia: Testing the Division of Labor between Syntax and Semantics

“…Such a pattern would result from impairment to the semantic system with the syntactic system remaining intact. This impairment of semantics with the relative sparing of syntax is analogous to the impairment seen in certain individuals with aphasia, who show difficulties in accessing and using lexical-semantic representations during word production, resulting in problems of word-finding and semantic errors (Papathanasiou, Coppens, & Potagas, 2013;Mirman & Britt, 2014). Impairment specifically to the semantic system with the sparing of syntactic ability also occurs in Alzheimer's disease (Kim & Thompson, 2004).…”

“…However, the impact of frequency on lexical retrieval in aphasia is not straightforward. While some people with aphasia demonstrate the standard facilitative effects of frequency seen in neurologically healthy individuals (i.e., increased speed and ease of access to more frequent words), others show no frequency effect, or show increased speed and accuracy for less frequent words, and the mechanisms underlying these different frequency effects are unclear (see Mirman & Britt, 2014, for a review of frequency effect findings).…”

“…In this case, semantic diversity refers to the variability of a word's meaning across different contexts, which tends to increase with word frequency. Aphasic individuals with semantic access deficits have been shown to have more difficulty retrieving these highly variable words, possibly due to reduced cognitive control processes during lexical selection or the reduced ability to select among competing lexical items, which accounts for the lack of facilitative frequency effects found in these individuals (Marshall, Pring, Chiat, & Robson, 2001;Hoffman, Rogers, & Ralph, 2011;Mirman & Britt, 2014). In this account for word retrieval deficits, individuals with semantic access deficits should demonstrate increased difficulty retrieving light verbs, as these verbs are highly semantically diverse (i.e., highly variable in meaning depending on context).…”