Phase delays between tone pairs reveal interactions in scalp-recorded envelope following responses. (5th February 2018)

• Record Type: Journal Article
• Authors: Easwar, Vijayalakshmi; Banyard, Ashlee; Aiken, Steven; Purcell, David
• Is Part Of: Neuroscience letters. Volume 665(2018)
• Page Start: 257
• Page End: 262
• Publication Date: 2018-02-05
• Subjects: Vowel simulation -- Auditory steady-state response; Neurology -- Periodicals; Neurology -- Periodicals; Research -- Periodicals; Neurologie -- Périodiques; Neuroanatomie -- Périodiques; Neuropharmacologie -- Périodiques; Neurophysiologie -- Périodiques; Neurology; Periodicals; Electronic journals; 617.48
• DOI: 10.1016/j.neulet.2017.12.014
• Languages: English
• ISSNs: 0304-3940

Abstract

Highlights: Multiple frequencies in broadband periodic sounds can evoke independent responses. Envelope following responses to broadband sounds interact across frequencies. Variable relative phase between stimulus frequencies can unveil these interactions. The nature of phase interactions among responses is linear. Delayed high frequency stimulus components could maximize scalp-recorded amplitude. Abstract: Evoked potentials to envelope periodicity in sounds, such as vowels, are dependent on the stimulus spectrum. We hypothesize that phase differences between responses elicited by multiple frequencies spread tonotopically across the cochlear partition may contribute to variation in scalp-recorded amplitude. The present study evaluated this hypothesis by measuring envelope following responses (EFRs) to two concurrent tone pairs, p1 and p2, that approximated the first and second formant frequencies of a vowel, while controlling their relative envelope phase. We found that the scalp-recorded amplitude of EFRs changed significantly in phase and amplitude when the envelope phase of p2, the higher frequency tone pair, was delayed. The maximum EFR amplitude occurred at the p2 envelope phase delay of 90°, likely because the stimulus delay compensated for the average phase lead of 73.57° exhibited by p2-contributed EFRs relative to p1-contributed EFRs, owing to earlier cochlear processing of higher frequencies. Findings suggest a linear superimposition of independently generated EFRs from tonotopically separated pathways. This suggests that introducing frequency-specific delays may help to optimize EFRs to broadband stimuli like vowels.