Measuring the lexical semantics of picture description in aphasia

Abstract

BACKGROUND: Individuals with non-fluent aphasia have difficulty producing syntactically laden words, such as function words, whereas individuals with fluent aphasia often have difficulty producing semantically specific words. It is hypothesised that such dissociations arise, at least in part, from a trade-off between syntactic and semantic sources of input to lexical retrieval. AIMS: The aims of this study were (a) to identify quantitative measures of the semantic content of narrative for people with aphasia that are reliable indicators of semantic competence, independent of overall aphasia severity; (b) to determine whether these measures distinguish between fluent and non-fluent aphasia; and (c) to assess whether individuals with fluent and non-fluent aphasia show a trade-off between measures of syntactic and semantic production. METHODS #ENTITYSTARTX00026; PROCEDURES: Connected speech samples were elicited from 16 participants with aphasia, 8 fluent and 8 non-fluent. The semantic sufficiency of the samples was analysed by measuring the proportion of correct information units (CIUs), the type-token ratios (TTRs) of content words, and the proportion of semantically specific ("heavy") to semantically general ("light") verbs produced. These measures were then correlated with syntactic measures from the QPA (Berndt, Wayland, Rochon, Saffran, & Schwartz, 2000) across and within participant groups. OUTCOMES #ENTITYSTARTX00026; RESULTS: CIUs were found to reflect primarily aphasia severity, and not to differentiate between fluent and non-fluent groups. TTRs were also strongly influenced by severity among fluent, but not non-fluent, participants. The ratio of heavy to light verbs reliably distinguished the groups, and showed different patterns of correlation with the syntactic measures. CONCLUSIONS: Results show some evidence for a trade-off between syntactic and semantic inputs to word retrieval, at least among non-fluent participants. The heavy-light verb ratio provides information about semantic specificity, beyond what is provided by the CIU or TTR measures.

Verb use in aphasic and non-aphasic personal discourse: What is normal?

“…Barde and colleagues (2006) compared verb production performance in agrammatic (n = 12) and non-agrammatic (n=11) speakers on the same task, and found that the former showed a light verb production deficit that was not evident in the latter. Gordon (2008) compared the weight of verbs used by non-fluent (n=8) and fluent (n=8) aphasic speakers using a Norman Rockwell picture description task, and found that the former used more heavy verbs than the latter. She further found that linguistic severity (BDAE rating) was not significantly correlated with the heavy-light verb ratio in either aphasic group, although it is uncertain whether this reflects over-reliance on one verb type, or under-use of the other verb type.…”

“…Secondly, findings are based on relatively small samples of aphasic speakers. These include studies with two participants (Armstrong et al, 2011), four and five participants respectively (Armstrong, 2001;2005), eight participants (Breedin et al, 1998), 11 participants , and 16 participants (Gordon, 2008), as well as small sub-groups within aphasic speaker samples (e.g. Breedin et al, 1998).…”

Compound nouns in spoken language production by speakers with aphasia compared to neurologically healthy speakers: An exploratory study

“…Several studies have shown that speakers with non-fluent aphasia have comparatively more difficulties with the production of 'light' verbs (e.g. Breedin, Saffran, and Schwartz, 1998;Barde, Schwartz, and Boronat, 2006), whereas speakers with fluent aphasia have more difficulties with 'heavy' verbs (Gordon, 2008). This dissociation has also been attested in a connectionist modelling experiment (Gordon and Dell, 2003).…”

“…nouns, verbs, adjectives) (Menn, O'Connor, Obler, and Holland, 1995;Edwards, 2005). From a connectionist perspective the different speech production patterns in nonfluent and fluent forms of aphasia have been attributed to a 'division of labour' between syntactic and semantic input cues to speech output (Gordon and Dell, 2003;Gordon, 2008). This division of labour hypothesis is related to the classic account by Roman Jacobson on the relation between different forms of speech output in aphasia and two key processes in language processing: selection of elements (paradigmatic processes) and combination of elements (syntagmatic processes) (Jacobson, 1956).…”

“…For speakers with fluent aphasia the opposite would be the case. Their difficulties with selection of elements (words)a paradigmatic deficitwould lead to a higher reliance on words serving a primarily syntactic purpose at the expense of semantic sufficiency (Gordon, 2008).…”