ReviewA review of causal mechanisms underlying the link between age-related hearing loss and cognitive decline
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A consideration of causal mechanisms underlying the link between age-related hearing loss and cognitive decline
Age-related changes in sensory sensitivity and acuity, and in cognitive processing, are among the most robust findings in psychology. Such declines will become more common as the world’s population shifts towards a greater number of older adults (Mathers et al., 2000, World Health Organization, 2012). Declines in hearing and cognition are functionally interdependent, since there is no sharp division between sensation and perception, and cognition. A growing body of research highlights the role
Operational definitions of hearing loss and cognitive function, and their limitations
The ways in which hearing and cognition are operationally defined and assessed will influence the nature of the apparent relationship between them. Hearing loss in studies that have evaluated links with cognitive function has almost exclusively been measured using pure-tone audiometry (PTA), in which detection thresholds for pure tones across a range of frequencies are measured monaurally, yielding indices of hearing sensitivity (e.g., Anstey et al., 2001a, Anstey et al., 2001b, Gennis et al.,
Is there a link between hearing loss and cognitive decline?
Early research reported that hearing loss was more common in those with dementia than without after controlling for age (Herbst and Humphrey, 1980, Hodkinson, 1973, Peters et al., 1988, Uhlmann et al., 1989; see also, Kay et al., 1964, Weinstein and Amsel, 1986, who did not control for age). Work by Gates et al., (1996) showed that central auditory dysfunction (as measured by a closed-set synthetic sentence identification task with an ipsilateral competing talker) significantly increased
Hypothesized relationships between age-related hearing loss and cognitive decline
The work reviewed in the previous section suggests a small link between hearing loss and cognitive function, but does not speak to the nature of the link – does hearing loss cause cognitive decline, or does cognitive decline result in hearing loss, or does some other factor cause both types of decline? Several possible relationships have been postulated (see Figure 1). Cognitive decline may reduce the cognitive resources that are available for auditory perception, manifesting as hearing loss
Cognitive load on perception hypothesis
According to this view, declining cognitive capacity places a cognitive load on perception, which is then poorer (CHABA, 1988, Lindenberger and Baltes, 1994; Fig. 1A). There is little evidence for the idea that cognitive decline precedes hearing loss, either from behavioral studies, or from structural-equation modeling work (e.g., Humes et al., 2013a, Lindenberger and Baltes, 1994). In a longitudinal study, Kiely et al. (2012) found that probable cognitive impairment predicted faster rates of
Information-degradation hypothesis
According to the information-degradation hypothesis (CHABA, 1988, Lindenberger and Baltes, 1994, Pichora-Fuller, 2003, Schneider and Pichora-Fuller, 2000; Fig. 1B), declines in older adults’ cognitive performance manifest as a consequence of compensating for impaired auditory input (owing either to normal aging or to pathology; Pichora-Fuller, 2003, Schneider and Pichora-Fuller, 2000, see also Schneider et al., 2005). Evidence for the information-degradation hypothesis has been extensively
Sensory-deprivation hypothesis
The sensory-deprivation hypothesis posits that perceptual declines cause more permanent cognitive declines (CHABA, 1988, Lindenberger and Baltes, 1994, Humes et al., 2013a, Lin et al., 2013, Pichora-Fuller, 2003, Schneider and Pichora-Fuller, 2000, Sekuler and Blake, 1987, Uhlmann et al., 1989), possibly through neuroplastic changes that disadvantage general cognition in favor of processes supporting speech perception (Lin et al., 2013; Fig. 1C). Whereas the information-degradation hypothesis
Common-cause hypothesis
The common-cause hypothesis (Baltes and Lindenberger, 1997, CHABA, 1988, Lindenberger and Baltes, 1994; Fig. 1D), proposes that a common mechanism underlies both age-related changes in cognition and hearing (and other sense modalities) through widespread neural degeneration. In evaluating the common-cause hypothesis, we refer both to the cognitive aging literature and to literature evaluating age-related declines in other sensory modalities.
Not only do older adults experience greater perceptual
Summary of hypotheses
In reviewing the four hypothesized relationships between hearing loss and cognitive decline, the information-degradation and common-cause hypotheses emerge as strong contenders. The information-degradation hypothesis is well-supported by the cognitive literature, and accounts for documented independent contributions of sensory or perceptual deficits to cognitive decline (e.g., Lin et al., 2013, Lin et al., 2011b). The common-cause hypothesis accounts for the fact that multiple sensory
Working framework
The framework presented in Fig. 2 attempts to capture the explanatory power of multiple empirically supported directional relationships between hearing loss and cognitive decline. This framework highlights the multiple, cumulative, deleterious processes to which the auditory/cognitive system is vulnerable (Jagust, 2013). Sensation/perception and cognitive function are interdependent, and deficits at one point in the system will have multiple, cascading, effects at other points.
Neurodegenerative
Directions for future research
Research linking age-related hearing loss to cognitive decline has largely relied on PTA, a behavioral index of hearing sensitivity, which may underestimate the link (Humes et al., 2013a). As deficits in hearing acuity may precede elevations in PTAs (e.g., Frisina and Frisina, 1997; He et al., 1998; Kujawa and Lieberman, 2009), it would be useful to explore the degree to which the relationship between hearing loss and cognitive decline, as observed through audiometry, extends to aspects of
Conclusion
Causal inferences about the nature of the relationship between hearing loss and cognitive decline are difficult to make, due to the correlational nature of much of the research. The nature of the link is also obscured by variability in the way that cognition is assessed, and by the limited way in which hearing loss is typically assessed. Changes in frequency selectivity have arguably the greatest impact on everyday communication, and yet have seldom addressed, although the recent interest in
Acknowledgements
We would like to thank Julia Huyck, Agnès Alsius-Rance, Michael Akeroyd, and Jean-Pierre Gagné for their helpful comments on earlier drafts of this paper.
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