The Influence of Sensation Level on Speech-Evoked Envelope Following Responses.
Vijayalakshmi Easwar, Jen Birstler, Adrienne Harrison and 2 others
PMID 34260437WHAT IT FOUND
Speech-evoked brain responses at equal audibility are larger for fricatives than vowels, but all grow by about 50% per 10 dB increase in sensation level.
This means response size depends on the sound itself, not just how loud it is relative to threshold.
Key findings
01At 30 dB sensation level, fricatives elicited significantly higher envelope following response amplitudes and phase coherence than all vowel stimuli.
02Growth rates of response amplitude and phase coherence were similar across all speech stimuli, increasing by approximately 50% for every 10 dB increase in sensation level.
03Second formant vowel stimuli produced larger responses than first formant stimuli at equal audibility, likely due to differences in harmonic resolvability.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study included only 21 young adults with normal hearing, so findings may not apply to individuals with hearing loss or other clinical populations. Results are specific to the modified token /susa∫i/ and may not generalise to natural speech or other vowels and fricatives. Between-stimulus differences were reported at 30 dB sensation level; the magnitude of these differences may vary at other levels. The study measured neural encoding of periodic envelopes but did not assess speech perception or functional hearing outcomes.
The easy way to misread this
Do not assume that a smaller envelope following response to a vowel compared to a fricative indicates poorer auditory processing. At equal audibility, fricatives naturally elicit larger responses than vowels, so differences in amplitude reflect stimulus properties rather than neural deficiency.