Connected Speech Characteristics of Bengali Speakers With Alzheimer's Disease: Evidence for Language-Specific Diagnostic Markers

Abstract

Background and aim: Speech and language characteristics of connected speech provide a valuable tool for identifying, diagnosing and monitoring progression in Alzheimer's Disease (AD). Our knowledge of linguistic features of connected speech in AD is primarily derived from English speakers; very little is known regarding patterns of linguistic deficits in speakers of other languages, such as Bengali. Bengali is a highly inflected pro-drop language from the Indo-Aryan language family. It is the seventh most spoken language in the world, yet to date, no studies have investigated the profile of linguistic impairments in Bengali speakers with AD. The aim of this study was to characterize connected speech production and identify the linguistic features affected in Bengali speakers with AD.Methods: Participants were six Bengali speaking AD patients and eight matched controls from the urban metropolis, Kolkata, India. Narrative samples were elicited in Bengali using the Frog Story. Samples were analyzed using the Quantitative Production Analysis and the Correct Information Unit analyses to quantify six different aspects of speech production: speech rate, structural and syntactic measures, lexical measures, morphological and inflectional measures, semantic measures and measure of spontaneity and fluency disruptions.Results and conclusions: In line with the extant literature from English speakers, the Bengali AD participants demonstrated decreased speech rate, simplicity of sentence forms and structures, and reduced semantic content. Critically, differences with English speakers' literature emerged in the domains of Bengali specific linguistic features, such as the pro-drop nature of Bengali and its inflectional properties of nominal and verbal systems. Bengali AD participants produced fewer pronouns, which is in direct contrast with the overuse of pronouns by English AD participants. No obvious difficulty in producing nominal and verbal inflections was evident. However, differences in the type of noun inflections were evident; these were characterized by simpler inflectional features used by AD speakers. This study represents the first of its kind to characterize connected speech production in Bengali AD participants and is a significant step forward toward the development of language-specific clinical markers in AD. It also provides a framework for cross-linguistic comparisons across structurally distinct and under-explored languages.

Importance of Task Selection for Connected Speech Analysis in Patients with Alzheimer’s Disease from an Ethnically Diverse Sample

“…For example, in Frog Story, the AD patients produced a lower proportion of pronouns in Bengali, which is in direct contrast with the overuse of pronouns by English-speaking AD patients consistently reported in the literature (e.g., [ 5, 6 ]). Differential performance on the pronoun usage is driven by the pro-drop nature of Bengali, as it allows dropping of the subject nouns [ 3 ]. However, a lower proportion of pronouns was not observed in the picture description in Bengali.…”

“…Sessions were recorded using the digital audio recorder Olympus voice recorder WS-833 for subsequent verbatim orthographic transcription. The Frog Story data have been previously published in Bose et al (2021) to develop language-specific linguistic profile for Bengali speakers [ 3 ].…”

“…To capture the multidimensional nature of connected speech, measures for this study were in keeping with the recommendations from recent reviews for linguistic levels that are essential for characterizing AD speech [ 21, 22 ]. They aimed at quantifying six different linguistic levels of production: 1) speech rate; 2) structural and syntactic measures; 3) lexical measures; 4) morphological and inflectional measures; 5) semantic measures; and 6) measure of spontaneity and fluency disruptions [ 3, 5, 6, 21–24 ]. The Quantitative Production Analysis (QPA) [ 25 ] and the Correct Information Unit (CIU) [ 26 ] analyses were implemented to calculate a set of count and proportional measures for each sample.…”

“…To ensure reliability, transcriptions and coding were reviewed and agreed upon by multiple authors (AB, MD, NSD). Details on transcription, along with definition and description for the full range of variables can be found in Bose et al (2021) [ 3 ].…”

“…Recently, we reported that Bengali-speaking AD patients produced fewer pronouns in novel story telling [ 3 ], in direct contrast with the overuse of pronouns by English-speaking AD patients [ 5, 6 ]. Similarly, Kav & Levy (2003) reported that Hebrew-speaking AD patients produced a similar proportion of inflected words compared to controls in Cookie Theft picture description [ 7 ], a difference that is typically found in English-speaking AD patients [ 5, 8 ].…”