Comprehension of acoustically degraded speech in Alzheimer’s disease and primary progressive aphasia (preprint)

ABSTRACT Successful communication in daily life frequently depends on accurate decoding of speech signals that are acoustically degraded by challenging listening conditions. This process presents the brain with a demanding computational task that is vulnerable to neurodegenerative pathologies. However, despite recent intense interest in the link between hearing impairment and dementia, daily hearing measures (such as degraded speech comprehension) in these diseases remain poorly defined. Here we addressed this issue in a cohort of 19 patients with typical Alzheimer’s disease (AD) and 31 patients representing canonical syndromes of primary progressive aphasia (PPA), in relation to 25 healthy age-matched controls. As a model paradigm for the acoustically degraded speech signals of daily life, we used noise-vocoding: synthetic division of the speech signal into a variable number of frequency channels constituted from amplitude-modulated white noise, such that fewer channels convey less spectrotemporal detail thereby reducing intelligibility. We investigated the impact of noise-vocoding on recognition of spoken three-digit numbers and used psychometric modelling to ascertain the threshold number of noise-vocoding channels required for 50% intelligibility by each participant. Associations of noise-vocoded speech intelligibility threshold with general demographic, clinical and neuropsychological characteristics and regional grey matter volume (defined by voxel-based morphometry of patients’ brain MR images) were also assessed. Compared with healthy older controls, all patient groups had a significantly higher mean noise-vocoded speech intelligibility threshold, particularly marked in logopenic variant and nonfluent-agrammatic variant PPA and significantly higher in AD than in semantic variant PPA (all p<0.05). Noise-vocoded intelligibility threshold discriminated dementia syndromes (in particular, Alzheimer’s disease) well from healthy controls. Further, this central hearing measure correlated with overall disease severity but not with measures of peripheral hearing or clear speech perception. Neuroanatomically, after correcting for multiple voxel-wise comparisons in pre-defined regions of interest, impaired noise-vocoded speech comprehension across dementia syndromes was significantly associated (p<0.05) with atrophy of left planum temporale, angular gyrus and anterior cingulate gyrus: a cortical network widely implicated in processing degraded speech signals. Taken together, our findings suggest that the comprehension of acoustically altered speech captures a central process relevant to daily hearing and communication in major dementia syndromes, with novel diagnostic and therapeutic implications.

Neuropsychological assessments for dementia research in the COVID-19 era: comparing remote and face-to-face testing (preprint)

Objectives: We explored whether adapting traditional neuropsychological tests for online administration against the backdrop of COVID-19 was feasible for people with diverse forms of dementia and healthy older controls. We compared face-to-face and remote settings to ascertain whether remote administration affected performance. Design: We used a longitudinal design for healthy older controls who completed face-to-face neuropsychological assessments between three and four years before taking part remotely. For patients, we used a cross-sectional design, contrasting a prospective remote cohort with a retrospective face-to-face cohort matched in age, education, and disease duration. Setting: Remote assessments were performed using video-conferencing and online testing platforms, with participants using a personal computer or tablet and situated in a quiet room in their own home. Face-to-face assessments were carried out in dedicated testing rooms in our research centre. Participants: The remote cohort comprised ten healthy older controls (also seen face-to-face 3-4 years previously) and 25 patients (n=8 Alzheimer's disease (AD); n=3 behavioural variant frontotemporal dementia (bvFTD); n=4 semantic dementia (SD); n=5 progressive nonfluent aphasia (PNFA); n=5 logopenic aphasia (LPA)). The face-to-face patient cohort comprised 64 patients (n=25 AD; n=12 bvFTD; n=9 SD; n=12 PNFA; n=6 LPA). Primary and secondary outcome measures: The outcome measures comprised the strength of evidence under a Bayesian analytic framework for differences in performances between face-to-face and remote testing environments on a general neuropsychological (primary outcomes) and neurolingustic battery (secondary outcomes). Results: There was evidence to suggest comparable performance across testing environments for all participant groups, for a range of neuropsychological tasks across both batteries. Conclusions: Our findings suggest that remote delivery of neuropsychological tests for dementia research is feasible.