The brain can be trained to hear better, study finds
[Feb. 11, 2023: Rachael Grahame, University of Maryland]
The way in which we experience music and speech differs from what has until now been believed. (CREDIT: Creative Commons)
Those who struggle to understand someone giving an excited, rapid-fire account of an adventure, or who lose the thread of a conversation during a noisy cocktail party might be dealing with problems detecting rapid changes in sound—and new University of Maryland research could help.
In a recent study published in the Journal of the Association for Research in Otolaryngology (JARO), researchers in the Department of Hearing and Speech Sciences found that people aged 18-30 and 65-85 with normal hearing—as well as participants from the older age group with hearing impairment—could all be trained to boost their ability to differentiate subtle changes in the speed, or “rate,” of sounds. Such changes can make it difficult to understand speech in challenging situations, such as in noisy or reverberant environments, or when listening to people who talk fast.
“We've seen some evidence that these temporal processing deficits might be improved in animal models, but this is the first time we've shown it in humans,” said Associate Professor Samira Anderson, the publication’s lead author. Her co-authors include Professors Matthew Goupell and Sandra Gordon-Salant.
For the training, participants in the 40-person experimental group compared multiple series of rapid tones (think beeps or clicks) in nine sessions over three weeks. Compared to members of the 37-person control group, who were asked to detect a single tone in , those in the experimental group showed overall improvement.
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Most significantly, older normal-hearing people who undergo training can essentially restore their ability to discriminate fast changes in the timing of sounds to levels similar to those observed for young adults.
This rate discrimination study is one of three UMD projects funded by the $8.2 million Neuroplasticity and Auditory Aging program project grant awarded in 2017 to Gordon-Salant, director of the UMD Hearing Research Lab and principal investigator for the projects. Each seeks to examine how the aging brain contributes to auditory and speech perception difficulties, and ultimately whether targeted auditory and cognitive training can help restore effective auditory processing—with distinctly different approaches.
We recruited 301 listeners for a double-blind randomized controlled clinical trial and determined if they met the following age and audiometric criteria for these groups: young normal hearing (YNH, age 18–30 years), older normal hearing (ONH, age 65–85 years), and older hearing impaired (OHI, age 68–85 years).
Normal hearing was defined as pure-tone thresholds ≤ 25 dB HL (re: ANSI 2018) from 125 to 4000 Hz in the right ear. Impaired hearing was defined by a high-frequency pure-tone average (average thresholds at 1, 2, and 4 kHz) > 30 dB HL and thresholds at 2 and 4 kHz < 70 dB HL (to ensure signal audibility).
Hearing thresholds were required to be symmetrical (no interaural differences > 10 dB at any frequency) for all listeners, and there were no air-bone gaps > 10 dB at any frequency. Word recognition scores were > 70% for a single 25-word lists of the NU-6 test (Tillman and Carhart 1966) presented bilaterally at 75 dB HL in quiet.
Middle ear function was normal bilaterally based on average values for tympanometric peak pressure, peak admittance, tympanometric width, and equivalent volume. Acoustic reflexes were present from 500 to 2000 Hz, elicited ipsilaterally and contralaterally. Finally, auditory brainstem responses (ABRs) were recorded, and Wave V latencies were < 6.8 ms with no interaural asymmetries > 0.2 ms.
Additional criteria included the following: A passing score of ≥ 26 on the Montreal Cognitive Assessment (MoCA; Nasreddine et al. 2005), a negative history of neurological disease, a passing score on the Snellen vision screening chart ≤ 20/50 (Hetherington 1954), being a native English speaker, and earning a high school diploma.
All procedures were reviewed and approved by the Institutional Review Board (IRB) at the University of Maryland, College Park. Listeners provided informed consent and were monetarily compensated for their time.
The 125 listeners who met the study criteria were randomly assigned to one of two training groups: experimental and active control. Of these, 48 listeners did not complete the study. Seventeen listeners were dismissed due to: non-compliance with training (3), poor quality data (7), an adverse event (1), and excessive time delay associated with COVID-19 (6).
Twenty-six listeners withdrew from the study due to medical or transportation issues. Eleven listeners were lost to follow-up. The final numbers of listeners in each training group were 40 experimental (14 YNH, 16 ONH, and 10 OHI; 30 females) and 37 active control (15 YNH, 14 ONH, and 8 OHI; 28 females).
Note that 1% of listener data (31 of 2618 measurements) are missing because of isolated issues during data collection or because of anomalous data that did not converge.
Pre- and post-training phase-locking factor (PLF) for 100- and 300-Hz rates is displayed in the time–frequency domain for young normal-hearing (YNH), older normal-hearing (ONH), and older hearing-impaired (OHI) listeners in the experimental (top three panels) and active control (bottom three panels) groups. (CREDIT: Journal of the Association for Research in Otolaryngology)
The rate discrimination study is the first to show that “auditory training promotes neural changes in the brain, known as neuroplasticity,” Gordon-Salant said. “The results offer great hope in developing clinically feasible auditory training programs that can improve older listeners’ ability to communicate in difficult situations.”
Gordon-Salant and colleagues are actively recruiting individuals who have normal hearing or mild-to-moderate hearing loss to participate in the next phase of this rate discrimination study, as well as the other neuroplasticity grant-funded study on whether memory demands impact the effectiveness of humans’ training program.
The grant’s third project, which focuses on aging animals’ ability to hear sounds amid noise, is led by Shihab Shamma of the Department of Electrical and Computer Engineering and Institute for Systems Research.
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Note: Materials provided above by the University of Maryland. Content may be edited for style and length.
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