Word retrieval in connected speech in Alzheimer’s disease: a review with meta-analyses

Background: Language assessment in Alzheimer’s disease (AD) demonstrates deficits in single-word production, but rarely includes connected speech. Aims: If Alzheimer’s disease leads to deficits in lexical retrieval, we should find reduced word output in connected speech, limited lexical diversity, an increase in retrieval errors, and an association between scores on tests of single-word production and measures of word retrieval in context. The purpose of this review was to investigate these hypotheses across studies of connected speech in AD. Main Contribution: A search of Medline and PsychNET identified 51 articles (published in 1985–2016) that reported data from 1,114 individuals with AD and 1,280 cognitively healthy individuals. A meta-analysis showed a significant but small reduction in word output in AD. No consistent decrease in the proportion of unique words was documented, but there was indication that individuals with AD produce more frequent words than do controls. An analysis of errors documented a moderate effect size, showing that individuals with AD commit more retrieval errors of all types. A relatively strong association was found between picture-naming scores and measures of word retrieval in connected speech. Conclusions: The review shows that individuals with AD experience significant lexical retrieval difficulties in connected speech.