Lexical-semantic properties of verbs and nouns used in conversation by people with Alzheimer’s disease

PLOS ONE RESEARCH ARTICLE Lexical-semantic properties of verbs and nouns used in conversation by people with Alzheimer’s disease Eric Williams ID1*, Catherine Theys1,2, Megan McAuliffe1,2 1 School of Psychology, Speech and Hearing, University of Canterbury, Christchurch, New Zealand, 2 New Zealand Institute of Language, Brain and Behaviour, University of Canterbury, Christchurch, New Zealand a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Williams E, Theys C, McAuliffe M (2023) Lexical-semantic properties of verbs and nouns used in conversation by people with Alzheimer’s disease. PLoS ONE 18(8): e0288556. https://doi. org/10.1371/journal.pone.0288556 Editor: Christopher James Hand, University of Glasgow, UNITED KINGDOM Received: February 4, 2023 Accepted: June 29, 2023 Published: August 3, 2023 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal.pone.0288556 Copyright: © 2023 Williams et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: We are unable to make our data publicly accessible, as the data originate from a third-party source and are not owned by us. Our data originate from the Carolina Conversations Collection (CCC), https:// * Abstract Alzheimer’s disease (AD) is accompanied by language impairments and communicative breakdowns. Research into language processing by people with AD (pwAD) has focused largely on production of nouns in isolation. However, impairments are consistently found in verb production at word and sentence levels, and comparatively little is known about word use by pwAD in conversation. This study investigated differences between pwAD and cognitively healthy controls in conversational use of nouns, verbs, and pronouns. Speech samples produced by 12 pwAD and 12 controls for the Carolinas Conversations Collection were analysed for noun, verb and pronoun counts and ratios, lexical diversity overall and among nouns and verbs, copula use, and frequencies and ages of acquisition (AoA) of nouns and verbs produced. pwAD used fewer nouns and a narrower range of words than controls, exhibiting signs of increased reliance on pronouns and decreased noun diversity. Age affected noun frequencies differently within each group—pwAD produced nouns of lower frequencies with age, while controls produced nouns of higher frequencies. pwAD produced nouns of higher AoA than controls. Verb use differed little by group. These findings highlight the need to account for differences between nouns and verbs, including in frequency, AoA, proportion of all words spoken, and context-dependent processing demands, when drawing conclusions on language use by pwAD. They also suggest potential for communicative interventions targeting contextual use of both nouns and verbs. Introduction Alzheimer’s disease (AD) often results in communicative breakdowns that negatively impact the person with AD (pwAD) and caregivers, including by discouraging interactions that could help to preserve dignity and maintain relationships [1–3]. These breakdowns appear at least partially attributable to declining amounts of informative content in speech produced by pwAD. In connected speech, pwAD have been found to produce fewer words than controls, with total output decreasing as the disease progresses [4, 5]. In the speech they do produce, pwAD describe events less accurately, producing fewer information units than controls and PLOS ONE | https://doi.org/10.1371/journal.pone.0288556 August 3, 2023 1 / 21 PLOS ONE carolinaconversations.musc.edu/ccc/about/. This is a digital archive of recorded interviews with American men and women aged 65 and older, many of whom are experiencing cognitive decline or other health issues. Our study involved analysis of speech samples from the CCC, and our data files include all words produced in the speech samples analysed. Even with that information removed from our data files, speech samples can be rebuilt wholly or in part using data relevant to the reported study. Researchers can gain access to the CCC by following the process described here: https:// carolinaconversations.musc.edu/ccc/help/access/ approval. Once researchers have been granted CCC access, reasonable requests for our study-specific data can be directed to any of the study’s authors. Funding: The author(s) received no specific funding for this work. Competing interests: The authors have declared that no competing interests exist. Verb and noun use by people with Alzheimer’s disease thus omitting relevant information [6, 7]. These declines in informative content have resulted in characterizations of spoken discourse by pwAD as vague or empty [6, 8]. Knowledge of how specific lexical-semantic changes affect the informative content of speech produced by pwAD may help improve diagnosis and monitoring of the disease [6, 9]. An improved understanding of the nature of communicative breakdowns can also facilitate interventions that improve communication between pwAD and their caregivers [10, 11]. Consensus findings from studies of single-word tasks suggest impaired production of both verbs and nouns by pwAD compared to controls [7]. Within groups, pwAD tend to be less accurate with verbs than nouns [7]. Impairments in discrete word production reflect effects of connectedness in the semantic network and contributing psycholinguistic properties [7, 12]. Word frequency and age of acquisition (AoA) are believed to influence semantic network development, and pwAD perform less accurately on naming tasks requiring retrieval of words that are less frequent or are acquired later in life [13]. Better performance with nouns has been attributed to stronger relationships within this word class; however, psycholinguistic effects are unclear, as verbs tend to be more frequent than nouns, but are acquired later in life [14]. Lexical-semantic changes are also present in discourse produced by pwAD. Consensus findings indicate that pwAD produce more verbs and fewer nouns than controls in both picture descriptions and spontaneous speech [9, 15–17]. Declines in noun production are accompanied by increased reliance on pronouns, which function as less specific noun substitutes [9, 16, 17]. Findings from picture descriptions suggest that pwAD also use a less diverse range of words than controls in discourse [9, 16]. These changes are accompanied by psycholinguistic differences in the groups’ speech samples. In picture descriptions and story retellings, pwAD rely on simple, generic words including copulas and (...truncated)