Fundamental frequency-dependent changes in vowel-evoked envelope following responses

Scalp-recorded envelope following responses (EFRs) provide a non-invasive method to assess the encoding of the fundamental frequency (f₀) of voice that is important for speech understanding. It is well-known that EFRs are influenced by voice f₀. However, this effect of f₀ has not been examined independent of concomitant changes in spectra or neural generators. We evaluated the effect of voice f₀ on EFRs while controlling for vowel formant characteristics and potentially avoiding significant changes in dominant neural generators using a small f₀ range. EFRs were elicited by a male-spoken vowel /u/ (average f₀ = 100.4 Hz) and its lowered f₀ version (average f₀ = 91.9 Hz) with closely matched formant characteristics. Vowels were presented to each ear of 17 young adults with normal hearing. EFRs were simultaneously recorded between the vertex and the nape, and the vertex and the ipsilateral mastoid—the two most common electrode montages used for EFRs. Our results indicate that when vowel formant characteristics are matched, an increase in f₀ by 8.5 Hz reduces EFR amplitude by 25 nV, phase coherence by 0.05 and signal-to-noise ratio by 3.5 dB, on average. The reduction in EFR characteristics was similar across ears of stimulation and the two montages used. These findings will help parse the influence of f₀ or stimulus spectra on EFRs when both co-vary.