There is an interaction and codependence between cognitive function and sensory systems in humans. This may not be obvious initially, but when considering how we send stimuli to our brains — through the sensory organs of sight, sound, touch, taste and smell — it seems logical. If we are unable to hear or see external phenomena, how will our brains receive enough information to make sense of the world? Thinking, then, is dependent on the raw material sent to the brain by our senses.
Cognition and hearing also have a compensatory relationship. If cognition deteriorates, say as the result of dementia or physical trauma, hearing becomes more important. Conversely, if hearing deteriorates, cognition becomes more important for daily functioning. Many people with hearing loss, for example, are able to infer what they missed in a conversation because they have sharp cognitive skills. The brain fills in missing pieces of information based on past experience, voice inflection, syntax, and other cues, both verbal and nonverbal. So, if a person hears well and is able to capture all the needed information through hearing, his or her brain doesn’t have to work as hard to fill in the gaps.
A 2013 study by researchers at Johns Hopkins Medicine suggests that elderly people with compromised hearing are at risk of developing problems with memory and thinking sooner than those whose hearing is intact. Led by Dr. Frank Lin, a hearing specialist and epidemiologist, the research team found that annual rates of cognitive decline were 41 percent greater in older adults with hearing problems than in those without.
Another study conducted in 2003 found that higher IQs tend to mitigate the impact of hearing loss. Researchers speculated that this was perhaps due to higher processing speeds in the brain. For patients diagnosed with dementia and already slower processing speeds, hearing loss further compromised their cognitive ability.
Children with hearing loss are less adept at filling in missed information because they have less life experience. Most of what children learn about language and social norms is through passive listening. This makes hearing vital to a child’s ability to do well in school. Audition is so vitally important to education that the entire premise of the U.S. educational system is undermined when a child cannot clearly hear spoken instruction.
The period from birth to 2 years is a critical time for the acquisition of language and cognition for all children, and this period of time is often when deaf and hard of hearing children are deprived of processes that promote healthy language development. Until recently, most experts agreed that these children would be at a severe disadvantage because of their lack of access to auditory input. However, recent studies show that when profoundly deaf children are exposed to a visual language early in life, they develop high levels of language organization. This indicates that signed or visual language may take the place of hearing in the education of deaf children, although much more research must be done to establish this theory.
Treatments to Improve Cognition
Hearing rehabilitation programs can help individuals improve their listening skills, depending on their particular type of impairment. Coupled with hearing aids, other assistive technologies, and visual cues, a person with hearing loss need not also lose cognition abilities. This is a relatively new field of study, and more discoveries are likely forthcoming.