Development of audiometric parameters throughout the lifespan. II: Relationships between parameters

Aging is associated with a complex deterioration of hearing functions, which spans from the periphery to central auditory structures. To characterize this process, we measured a wide set of auditory parameters in 290 healthy volunteers aged from 18 to 87 years. In our companion paper, we investigate the age-related progression of individual auditory parameters with the objective of determining average parameters in age decades. The current paper focuses on evaluation of relationships between the variables, which may also change depending on the age and hearing status. We present three types of analyses: 1) clustering of variables, 2) predictions of speech comprehension ability based on the elementary auditory parameters, and 3) mutual correlations between the variables. The analyses are performed in several selected subgroups of subjects, such as those having excellent hearing threshold, or those belonging to a certain age group. The results support the hypothesis that individual auditory functions are interrelated and may be clustered into more general characteristics such as "hearing sensitivity" or "temporal processing". However, grouping of auditory variables is by no means universal and the relationships between variables markedly differ in different subject subgroups. In addition, predictions of speech comprehension ability indicate that speech understanding relies on different mechanisms depending on age and hearing status. We conclude that relationships among auditory functions develop during aging and gradually progress to larger interdependence; eventual classification of phenotypes of hearing abilities must thus consider age of the subject.