A review of auditory processing and cognitive change during normal ageing, and the implications for setting hearing aids for older adults

Abstract

Throughout our adult lives there is a decline in peripheral hearing, auditory processing and elements of cognition that support listening ability. Audiometry provides no information about the status of auditory processing and cognition, and older adults often struggle with complex listening situations, such as speech in noise perception, even if their peripheral hearing appears normal. Hearing aids can address some aspects of peripheral hearing impairment and improve signal-to-noise ratios. However, they cannot directly enhance central processes and may introduce distortion to sound that might act to undermine listening ability. This review paper highlights the need to consider the distortion introduced by hearing aids, specifically when considering normally-ageing older adults. We focus on patients with age-related hearing loss because they represent the vast majority of the population attending audiology clinics. We believe that it is important to recognize that the combination of peripheral and central, auditory and cognitive decline make older adults some of the most complex patients seen in audiology services, so they should not be treated as "standard" despite the high prevalence of age-related hearing loss. We argue that a primary concern should be to avoid hearing aid settings that introduce distortion to speech envelope cues, which is not a new concept. The primary cause of distortion is the speed and range of change to hearing aid amplification (i.e., compression). We argue that slow-acting compression should be considered as a default for some users and that other advanced features should be reconsidered as they may also introduce distortion that some users may not be able to tolerate. We discuss how this can be incorporated into a pragmatic approach to hearing aid fitting that does not require increased loading on audiology services.

Keywords: ageing; auditory processing; cognitive performance; compression ratio; compression speed; hearing aids; noise reduction.

Figure 1

A partial representation of the Cattell-Horn-Carroll (CHC) theory of cognitive abilities showing general intelligence (g) consisting of broad domains of cognitive function, under which there are narrow domains that can be assessed with specific tests. Figure developed from (72, 73). Note that there are a greater number of broad domains and the narrow domains shown are only selected examples of those in each broad domain (24).

Figure 2

The effect of compression speed on speech envelope cues, reproduced with permission from Holube et al. (159). The original speech signal (top left) is processed through a 16-channel system with an exaggerated compression ratio of 8:1 using various release times (τ_rel) from long (1,400 ms, slow-acting compression) to short (15 ms, fast-acting compression).