Many people find it difficult to understand a multitude of converging voices in a crowded room. Commonly referred to as the “cocktail effect”, people with hearing loss find it particularly difficult to understand speech in a noisy environment.
New research suggests that for some listeners it may have less to do with actually discerning sounds. Instead, it may be a processing issue in which two ears mix different sounds together – a condition known as binaural pitch merging.
The research, co-authored by scientists at Oregon Health & Science University and the VA Portland Health Care System, was published today in the Journal of the Association for Otorhinolaryngology Research.
The lead author of the study attributes these difficulties to an abnormally large binaural fusion in people with hearing loss. The new study suggests that, for people with hearing loss, the merging of different sounds from both ears leads to a mixture of sounds in an often unintelligible way.
“It differs from what people with normal hearing experience in what is known as the ‘cocktail effect’,” said Lina Reiss, Ph.D., associate professor of otolaryngology / surgery. head and neck at OHSU School of Medicine. “People with normal hearing can separate and understand multiple voices, but they don’t know which voice is saying what.”
Reiss, who herself has a hearing loss and is part of the Oregon Hearing Research Center at OHSU, previously co-authored research in 2018 that first demonstrated a fusion of wide binaural height in hearing loss. . With another study showing the mixing of merged pitches, the research suggested the possibility that similar merging and mixing could occur with sounds in speech.
The new study put the theory to the test.
Researchers from OHSU and VA’s National Center for Rehabilitation Auditory Research recruited 11 people with normal hearing and 10 with hearing loss. Participants were fitted with headphones in a soundproof double-walled booth at the Hatfield Research Center at OHSU.
Two vowel sounds were played simultaneously in the headphones, with a different vowel sound played in each ear, and with pitch varying between male and female voices. Participants were then asked to respond on a touchscreen to identify specific vowel sounds.
Using statistical analysis, the researchers definitively revealed that hearing impaired people had an abnormal fusion of speech in both ears, even for different pitches of voice.
When different vowel sounds were merged, participants heard an entirely new vowel sound. For example, the vowel “ah” (as in “hot”) pronounced by a female speaker would merge with the vowel “ee” (as in “attention”) pronounced by a male speaker, and would be heard as “eh” (as in “head”).
“An abnormal binaural merge may provide a new explanation for the difficulties hearing listeners have in understanding speech in multi-speaker environments,” the authors concluded.
Reiss called it a breakthrough, suggesting the possibility of new therapies to improve speech perception among the millions of people with hearing loss around the world.
“This suggests more targeted rehabilitation strategies to improve the perception of speech in noise,” she said.
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Material provided by Oregon University of Health and Sciences. Original written by Erik Robinson. Note: Content can be changed for style and length.