Magnified Neural Envelope Coding Predicts Deficits in Speech Perception in Noise

Area of Science:

• Auditory Neuroscience
• Speech Perception
• Hearing Loss Research

Background:

• Understanding speech in fluctuating background noise is difficult for individuals with sensorineural hearing loss (SNHL).
• SNHL alters cochlear processing, potentially exaggerating intensity fluctuations and impacting the neural coding of amplitude-modulated sounds.
• A direct link between magnified neural envelope coding and impaired speech identification in modulated noise has been lacking.

Purpose of the Study:

• To investigate the effects of SNHL on the neural coding of modulated noise in the human auditory cortex.
• To determine if enhanced envelope coding in SNHL listeners is associated with deficits in speech identification in modulated background noise.

Main Methods:

• Magnetoencephalography (MEG) was used to measure neural responses to modulated noise in the auditory cortex.
• Phase locking to the temporal envelope of modulated noise (envelope coding) was quantified in normal-hearing and SNHL listeners.
• Speech identification in modulated background noise was assessed behaviorally.

Main Results:

• SNHL enhanced the amplitude and fidelity of envelope coding in specific auditory cortex regions (posteromedial and posterolateral), with right-hemisphere lateralization observed.
• These enhanced neural responses were not perceptually beneficial.
• Both hearing thresholds and magnified cortical envelope coding in the left hemisphere predicted poorer speech identification in modulated noise.

Conclusions:

• Magnified envelope coding in the auditory cortex, particularly in SNHL, may disrupt the segregation of speech from modulated background noise.
• This disruption leads to deficits in speech perception in challenging auditory environments.
• The findings provide the first direct evidence linking neural processing alterations in SNHL to impaired speech understanding in modulated noise.