Many of us develop problems with understanding and processing speech as we age, particularly in noisy settings like restaurants or bars. This phenomenon, new research at the University of Maryland suggests, is due to changes in the central auditory system that effectively slow or disrupt the way our brains process words.
The study involved 30 adults, young and old, who had normal hearing and no history of neurological disorders. Researchers presented these individuals with a number of speech syllables, progressively altering the frequency of the sounds and measuring their brain activity with small electrodes, and were able to identify substantial differences in how brains of varying ages processed words.
They found that the responses of older adults were significantly delayed compared to the responses of younger adults, particularly with ‘onsets’ and ‘offsets’ of syllables, the beginning and ends of words.
First author, Alessandro Presacco, a doctoral student in the Neuroscience and Cognitive Science program, said:
“Problems in processing complex sounds such as ‘da’ and ‘a’ could help explain their difficulties in understanding speech, particularly in noisy environments."
Trouble Hearing Word Ends
Those difficulties suggest there is more to the challenges than impaired hearing. Principal investigator Samira Anderson, said:
“Although this phenomenon is commonly attributed to hearing loss, it’s often the case that adults with clinically ’normal’ hearing still experience difficulty. I was surprised to see the sudden drop in response size in older adults in the later region of the vowel. It helps me to understand why older adults sometimes have trouble hearing the ends of words."
The team found that there are many possible contributors to the language processing challenges for adults. They range from the brain’s ability to accurately process speech to its inability to sustain neural firing for the duration of the speech.
The study contributes vital information to the goal of understanding exactly why aging minds struggle with words and sounds. By identifying the root cause of language processing difficulties, and mapping how the brain responds to different stimuli, researchers can develop revolutionary therapies and treatments for aging adults.
“There’s a lot we don’t know. These findings are a critical, but incremental contribution to our understanding. Studies like this are helping scientists identify not only the causes of language processing issues, but where the breakdown is occurring specifically,” Anderson said. “Can we draw direct connections between speech processing and perception? Can we train the brain to process language information more efficiently—especially in terms of helping older adults regain lost functionality? These are the types of revolutionary questions we’re trying to answer."
Illustration: Spooky Pooka, Wellcome Images