The comprehension of spoken language is a complex skill that requires the listener to map the acoustic input onto the meaningful units of speech (phonemes, syllables, and words). At the sentence level, the listener must detect the syntactic structure of the utterance in order to determine the semantic relationships among the spoken words. Each higher level of analysis is thus dependent on successful processing at the prior level, beginning with perception at the phoneme and word levels. Unlike reading, where one can use eye movements to control the rate of input, speech is a transient signal that moves past the ears at an average rate of 140 to 180 words per minute. Although seemingly automatic in young adults, comprehension of speech can represent a greater challenge for older adults, who often exhibit a combination of reduced working memory resources and slower processing rates across a number of perceptual and cognitive domains. An additional challenge arises from reduced hearing acuity that often occurs in adult aging. A major concern is that, even with only mild hearing loss, the listening effort required for success at the perceptual level may draw resources that would ordinarily be available for encoding what has been heard in memory, or comprehension of syntactically complex speech. On the positive side, older adults have compensatory support from preserved linguistic knowledge, including the procedural rules for its use. Our understanding of speech perception in adult aging thus rests on our understanding of such sensory-cognitive interactions.
Nicole D. Ayasse, Alexis R. Johns, and Arthur Wingfield
Christopher J. Plack and Hannah H. Guest
The psychology of hearing loss brings together many different subdisciplines of psychology, including neurophysiology, perception, cognition, and mental health. Hearing loss is defined clinically in terms of pure-tone audiometric thresholds: the lowest sound pressure levels that an individual can detect when listening for pure tones at various frequencies. Audiometric thresholds can be elevated by damage to the sensitive hair cells of the cochlea (the hearing part of the inner ear) caused by aging, ototoxic drugs, noise exposure, or disease. This damage can also cause reductions in frequency selectivity (the ability of the ear to separate out the different frequency components of sounds) and abnormally rapid growth of loudness with sound level. However, hearing loss is a heterogeneous condition and audiometric thresholds are relatively insensitive to many of the disorders that affect real-world listening ability. Hair cell loss and damage to the auditory nerve can occur before audiometric thresholds are affected. Dysfunction of neurons in the auditory brainstem as a consequence of aging is associated with deficits in processing the rapid temporal fluctuations in sounds, causing difficulties in sound localization and in speech and music perception. The impact of hearing loss on an individual can be profound and includes problems in communication (particularly in noisy environments), social isolation, and depression. Hearing loss may also be an important contributor to age-related cognitive decline and dementia.
Margaret Kathleen Pichora-Fuller
Age-related hearing loss is heterogeneous. Multiple causes can damage the auditory system from periphery to cortex. There can be changes in thresholds for detecting sound and/or in the perception of supra-threshold sounds. Influenced by trends in neuroscience and gerontology, research has shifted from a relatively narrow modality-specific focus to a broader interest in how auditory aging interacts with other domains of aging. The importance of the connection between sensory and cognitive aging was reported based on findings from the Berlin Aging Study in the mid-1990s. Of the age-related sensory and motor declines that become more prevalent with age, hearing loss is the most common, and it is the most promising as an early marker for risk of cognitive decline and as a potentially modifiable mid-life risk factor for dementia. Hearing loss affects more than half of the population by 70 years of age and about 80% of people over 80 years of age. It is more prevalent in people with dementia than in peers with normal cognition. People with hearing loss can be up to five times more likely to develop dementia compared to those with normal hearing. Evidence from cross-sectional studies has confirmed significant correlations between hearing loss and cognitive decline in older adults. Longitudinal studies have demonstrated that hearing loss is associated with incident cognitive decline and dementia. Various biological, psychological, and social mechanisms have been hypothesized to account for these associations, but the causes remain unproven. Nevertheless, it is widely believed that there is a meaningful interface among sensory, motor, and cognitive dysfunctions in aging, with implications for issues spanning brain plasticity to quality of life. Experimental research investigating sensory-motor-cognitive interactions provides insights into how age-related declines in these domains may be exacerbated or compensated. Ongoing research on auditory aging and how it interfaces with cognitive aging is expected to increase knowledge of the neuroscience of aging, provide insights into how to optimize the everyday functioning of older adults, and inspire innovations in clinical practice and social policy.