Speech errors in Alzheimer's disease: reevaluating morphosyntactic preservation.

Area of Science:

• Neurolinguistics
• Cognitive Science
• Psycholinguistics

Background:

• Previous research suggested morphosyntax remains intact in probable Alzheimer's disease (PAD), unlike lexical abilities.
• Theoretical debates exist regarding the representation and production of pronouns and closed-class words.
• The dichotomy of speech errors into only morphosyntactic and lexical categories is questioned.

Purpose of the Study:

• To investigate the integrity of morphosyntax in the speech of individuals with probable Alzheimer's disease (PAD).
• To determine if speech errors in PAD are limited to lexical aspects or also affect morphosyntax.
• To challenge the traditional categorization of speech errors in Alzheimer's disease research.

Main Methods:

• Two experiments were conducted comparing speech output of 10 individuals with Alzheimer's disease and 15 healthy controls.
• Experiment 1 analyzed error patterns in spontaneous speech.
• Experiment 2 assessed sentence production using written stimuli (verb and two nouns).

Main Results:

• Individuals with mild PAD showed increased errors across all linguistic domains, similar to healthy older adults, including closed-class and morphosyntactic errors.
• In sentence production, adults with Alzheimer's disease made significantly more closed-class word errors than controls; three participants exhibited near-agrammatic speech.
• Error rates across both tasks were highly correlated within the PAD group.

Conclusions:

• Morphosyntax is vulnerable in probable Alzheimer's disease (PAD), contradicting prior assumptions of its preservation.
• Speech deficits in PAD encompass all language aspects, not solely lexical components.
• Findings support a speech production model where semantic and grammatical features are equally susceptible to activation failures in neurological conditions.