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
Age-related hearing loss affects over half of the elderly population, yet it remains poorly understood. Natural aging can cause the input to the brain from the cochlea to be progressively compromised in most individuals, but in many cases the cochlea has relatively normal sensitivity and yet people have an increasingly difficult time processing complex auditory stimuli. The two main deficits are in sound localization and temporal processing, which lead to poor speech perception. Animal models have shown that there are multiple changes in the brainstem, midbrain, and thalamic auditory areas as a function of age, giving rise to an alteration in the excitatory/inhibitory balance of these neurons. This alteration is manifest in the cerebral cortex as higher spontaneous and driven firing rates, as well as broader spatial and temporal tuning. These alterations in cortical responses could underlie the hearing and speech processing deficits that are common in the aged population.
Hearing loss is common, with approximately 17% of the population reporting some degree of a hearing deficit. Hearing loss has profound impacts on health literacy, health information accessibility, and learning. Much of existing health information is inaccessible. This is largely due to the lack of focus on tailoring the messages to the needs of deaf and hard of hearing (DHH) individuals with hearing loss. DHH individuals struggle with a variety of health knowledge gaps and health disparities. This demonstrates the importance of providing tailored and accessible health information for this population. While hearing loss is heterogeneous, there are still overlapping principles that can benefit everyone. Through adaptation, DHH individuals become visual learners, thus increasing the demand for appropriate visual medical aids. The development of health information and materials suitable for visual learners will likely impact not only DHH individuals, but will also be applicable for the general population. The principles of social justice and universal design behoove health message designers to ensure that their health information is not only accessible, but also equitable. Wise application of technology, health literacy, and information learning principles, along with creative use of social media, peer exchanges, and community health workers, can help mitigate much of the health information gaps that exist among DHH individuals.
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.
Clinical linguistics is the branch of linguistics that applies linguistic concepts and theories to the study of language disorders. As the name suggests, clinical linguistics is a dual-facing discipline. Although the conceptual roots of this field are in linguistics, its domain of application is the vast array of clinical disorders that may compromise the use and understanding of language. Both dimensions of clinical linguistics can be addressed through an examination of specific linguistic deficits in individuals with neurodevelopmental disorders, craniofacial anomalies, adult-onset neurological impairments, psychiatric disorders, and neurodegenerative disorders. Clinical linguists are interested in the full range of linguistic deficits in these conditions, including phonetic deficits of children with cleft lip and palate, morphosyntactic errors in children with specific language impairment, and pragmatic language impairments in adults with schizophrenia. Like many applied disciplines in linguistics, clinical linguistics sits at the intersection of a number of areas. The relationship of clinical linguistics to the study of communication disorders and to speech-language pathology (speech and language therapy in the United Kingdom) are two particularly important points of intersection. Speech-language pathology is the area of clinical practice that assesses and treats children and adults with communication disorders. All language disorders restrict an individual’s ability to communicate freely with others in a range of contexts and settings. So language disorders are first and foremost communication disorders. To understand language disorders, it is useful to think of them in terms of points of breakdown on a communication cycle that tracks the progress of a linguistic utterance from its conception in the mind of a speaker to its comprehension by a hearer. This cycle permits the introduction of a number of important distinctions in language pathology, such as the distinction between a receptive and an expressive language disorder, and between a developmental and an acquired language disorder. The cycle is also a useful model with which to conceptualize a range of communication disorders other than language disorders. These other disorders, which include hearing, voice, and fluency disorders, are also relevant to clinical linguistics. Clinical linguistics draws on the conceptual resources of the full range of linguistic disciplines to describe and explain language disorders. These disciplines include phonetics, phonology, morphology, syntax, semantics, pragmatics, and discourse. Each of these linguistic disciplines contributes concepts and theories that can shed light on the nature of language disorder. A wide range of tools and approaches are used by clinical linguists and speech-language pathologists to assess, diagnose, and treat language disorders. They include the use of standardized and norm-referenced tests, communication checklists and profiles (some administered by clinicians, others by parents, teachers, and caregivers), and qualitative methods such as conversation analysis and discourse analysis. Finally, clinical linguists can contribute to debates about the nosology of language disorders. In order to do so, however, they must have an understanding of the place of language disorders in internationally recognized classification systems such as the 2013 Diagnostic and Statistical Manual of Mental Disorders (DSM-5) of the American Psychiatric Association.
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.