gms | German Medical Science

The population aged 60 years and older will have increased from 680 million persons in 2009 to 1 billion by 2020, an increase from 11% up to 20% of the world's population (source: United Nations,http://transgenerational.org/). The most widespread sensory impairment in this rapidly growing population is hearing impairment (HI), with an acceleration in prevalence between ages 55 yrs (10%) to 69 yrs (23%).

Epidemiological studies show that HI is correlated with lower levels of health and psychosocial well-being, and that it is also associated with a marked decline of cognitive capacities (e.g., allocation of attentional resources, processing speed...) at older ages. Individuals with HI also show an increased risk of all-cause dementia and they are five times more likely to develop depression. A recent model presented by the Lancet Commission on Dementia Prevention, Intervention and Care shows that HI is the largest potentially modifiable risk factor for dementia among nine health and lifestyle factors (Livingston et al., Lancet, 2017). Strikingly, the model shows that mid-life HI, if eliminated, might reduce the risk of dementia by 9%.

Age-related hearing impairment (presbycusis) slowly emerges over years, as a result of age-related degenerations in the auditory system, hereditary factors, exposure to noise and/or poor health. It is characterized by a bilateral reduction in hearing sensitivity at high frequencies, as measured by pure-tone audiometry (i.e., the gold standard for hearing diagnostics). Importantly, the impact of presbycusis does not only result from reduced audibility, but also from changes in the ability to process the temporal information of speech. Research shows that enhanced sensitivity to speech modulations presumably underlies impaired speech perception. Moreover, both age and HI alter the neural sensitivity to binaural temporal information that is embedded in the temporal fine structure of acoustic stimuli. These HI-related changes are superimposed on age-related changes setting in before middle age.

Moreover, the extent to which speech perception is degraded depends on the type of background noise as well. Informational maskers are considered confusing and therefore more difficult to deal with than energetic maskers. Amplitude modulated energetic maskers show temporary increases in the signal-to-noise ratio (noise dips) that facilitate speech perception, again starting in mid-life. Accurate temporal processing is required to achieve release from masking due to noise dips.

I will discuss several studies, which allowed us to disentangle the complex interplay of aging and peripheral hearing loss with regard to speech perception abilities due to careful participant selection. These use both behavioral and objective measures in young, middle-aged and older persons to gain insight into the temporal processing efficiency of the different subgroups and its relation to speech perception.