The impact of age-related cognitive changes and cognitive decline in speech understanding in noise: a clinical observational study in older adults with normal hearing and mild hearing loss

Introduction and aim: The world population is aging, leading to several challenges. Cognitive decline and Age-Related Hearing Loss (ARHL) occur to many people as they get older, affecting independence, well-being, and quality of life. ARHL can be caused by deficits in either peripheral hearing or Central Auditory Processing (CAP). Difficulties in CAP could interfere with a listener’s ability to understand speech, especially in noisy conditions. However, speech comprehension may depend not only on the status of the auditory system, but also on cognitive functioning. This information can be particularly relevant in aging, which is characterized by a decline in cognitive abilities and a reduction in available mental resources. Potential sources of decline in cognitive functioning are explained by cognitive aging theories through the “fundamental cognitive mechanisms” (i.e., processing speed, inhibitory control, and working memory). The aim of the present study is to shed a light on the relationship between central auditory processes (through a speech understanding in noise test) and cognitive functioning in older adults with mild to moderate cognitive decline and healthy matched controls. The hypothesis is that poorer performance in specific cognitive tasks could be associated with difficulties in understanding sentences in noise, particularly among those experiencing cognitive decline. Materials and methods: A total of 38 older adults with normal hearing and mild hearing loss (mean age 76.95 years old [SD: 5.33], n=25 female) was sorted into two groups: mild to moderate cognitive decline group (n=21) and a control group (n=17). Both the experimental and control group underwent a complete neuropsychological and audiological evaluation. Cognitive functioning was assessed using Mini-Mental State Examination (MMSE), the Brief Neuropsychological Assessment-2 (ENB-2) and the Reaction Times (RT) test from the Vienna Test System; also, cognitive reserve was measured with the Cognitive Reserve Index Questionnaire (CRIq). The audiological assessment included Pure Tone Audiometry (PTA) and the Italian Matrix Sentence Test (IMST). Results: Auditory performance at the IMST showed significant negative correlations with ENB-2 total score (r = -0.488; p = .002), Digit Span (r = -0.378; p = .019), Interference Memory–30” (r = -0.549; p < .001), and Phonemic Fluency test (r = -0.576; p < .001). Positive correlations were found between IMST performance and TMT-A (r = 0.373; p = .021), RT/S1 (r = 0.610; p < .001), and RT/S3 (r = 0.540; p < .001). Multiple regression analysis with stepwise selection was carried out to investigate the relative contribution of selected cognitive variables in predicting IMST performance. The regression model found that performance on the IMST was predicted by RT/S3 (β = 0.519; p < .001), Interference Memory–30” (β = -0.350; p = .003), and Digit Span (β = -0.240; p = .030). The results showed that this model has a significant explanatory power R2 = .619, F(3,34) = 21, p < .001, accounting for approximately 62% of the variance in IMST performance. Conclusions: To the best of our knowledge, this is the first clinical Italian study to analyze this association in older adults by assessing CAP through IMST. In line with previous evidence, this study supports the hypothesis of an interaction between CAP and cognitive functioning. Processing speed, working memory, and short-term memory span were found to be particularly involved in the processing of auditory stimuli, predicting performance on the IMST. This information can be particularly relevant for patients experiencing cognitive decline, as deficits in these functions can impact more their ability to process auditory information. A larger sample study, controlled for the type of cognitive decline, and further research are needed to corroborate these findings and to better investigate the shared mechanisms between auditory and cognitive functioning.