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

Abstract

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.