The impact of semantic impairment on verbal short-term memory in stroke aphasia and semantic dementia: A comparative study

Abstract

This study presents the first direct comparison of immediate serial recall in semantic dementia (SD) and transcortical sensory aphasia (TSA). Previous studies of the effect of semantic impairment on verbal short-term memory (STM) have led to important theoretical advances. However, different conclusions have been drawn from these two groups. This research aimed to explain these inconsistencies. We observed (a) qualitative differences between SD and TSA in the nature of the verbal STM impairment and (b) considerable variation within the TSA group. The SD and TSA patients all had poor semantic processing and good phonology. Reflecting this, both groups remained sensitive to phonological similarity and showed a reduced effect of lexicality in immediate serial recall. The SD patients showed normal serial position effects; in contrast, the TSA patients had poor recall of the initial list items and exhibited large recency effects on longer lists. The error patterns of the two groups differed: the SD patients made numerous phoneme migration errors whereas the TSA group were more likely to produce entire words in the wrong order, often initiating recall with terminal list items. The SD cases also showed somewhat larger effects of word frequency and imageability. We propose that these contrasting performance patterns are explicable in terms of the nature of the underlying semantic impairment. SD is associated with anterior lobe atrophy and produces degradation of semantic knowledge -this is more striking for less frequent/imageable items, accentuating the effects of these lexical/semantic variables in STM. SD patients frequently recombine the phonemes of different list items due to the reduced semantic constraint upon phonology (semantic binding: Patterson et al., 1994). In contrast, the semantic impairment in TSA follows frontal or temporoparietal lesions and is associated with poor executive control of semantic processing (deregulated semantic cognition: Jefferies and Lambon , explaining why these patients are liable to recall entire words out of serial order.

Dissociable components of phonological and lexical–semantic short-term memory and their relation to impaired word production in aphasia

“…As in the studies of Jefferies et al (2008); Knott et al (2000); Majerus and Van der Linden (2003); R. Martin et al (1999) and Reilly et al (2012), we had assumed that frequency effects on ISR reflect the influence of lexical-semantic language representations on STM. However, according to other authors, the loci of frequency effects are more widespread, and such effects may reflect the influence of both lexical-semantic and phonological levels of language representations (e.g., Ellis & Lambon Ralph, 2000;Hodgson & Ellis, 1998;Kittredge, Dell, Verkuilen, & Schwartz, 2008)-despite the fact that some phonological STM deficit patients do not show frequency effects (see e.g., R. Martin et al, 1994).…”

“…The influence of lexical-semantic knowledge on STM performance was assessed by analyzing lexicality and word frequency effects on ISR (see for example Jefferies et al, 2008;Knott et al, 2000;Majerus & Van der Linden, 2003;Majerus et al, 2004;R. Martin et al, 1999).…”

“…Jones, & Lambon Ralph, 2008;Knott et al, 1997;Majerus, Norris, & Patterson, 2007; R. Martin et al, 1999;Reilly et al, 2012). However, the view that lexical-semantic language representations influence STM capacities has been recently challenged by Papagno, Vernice, and Cecchetto (2013).…”

“…On the other hand, in case of lexical-semantic impairment, given that lexicalsemantic representations cannot boost recall, word frequency and lexicality should not affect recall performance. If phonological representations are intact, there should be a normal phonotactic frequency effect (e.g., Jefferies et al, 2008;Knott et al, 1997;Majerus et al, 2004;R. Martin et al, 1999;Reilly et al, 2012).…”

Selective short-term memory deficits arise from impaired domain-general semantic control mechanisms.

“…Neuropsychological studies have a bearing on this issue, with semantic memory impairments in semantic dementia (SD) and stroke aphasia associated with particular STM deficits (Berthier, 2001;Jefferies, Hoffman, Jones, & Lambon Ralph, 2008;Jefferies, Jones, Bateman, & Lambon Ralph, 2004;Knott, Patterson, & Hodges, 1997Majerus, Norris, & Patterson, 2007;Martin & Ayala, 2004;Martin & Saffran, 1990;McCarthy & Warrington, 1987, 2001Patterson, Graham, & Hodges, 1994). A key feature in both of these groups is a reduction or abolition of the normal effect of "lexicality" -the advantage healthy subjects receive when repeating word lists relative to lists of nonwords as a result of lexical-semantic knowledge (Hulme et al, 1991).…”