The Frequency Following Response (FFR) May Reflect Pitch-Bearing Information But is Not a Direct Representation of Pitch

Abstract

The frequency following response (FFR), a scalp-recorded measure of phase-locked brainstem activity, is often assumed to reflect the pitch of sounds as perceived by humans. In two experiments, we investigated the characteristics of the FFR evoked by complex tones. FFR waveforms to alternating-polarity stimuli were averaged for each polarity and added, to enhance envelope, or subtracted, to enhance temporal fine structure information. In experiment 1, frequency-shifted complex tones, with all harmonics shifted by the same amount in Hertz, were presented diotically. Only the autocorrelation functions (ACFs) of the subtraction-FFR waveforms showed a peak at a delay shifted in the direction of the expected pitch shifts. This expected pitch shift was also present in the ACFs of the output of an auditory nerve model. In experiment 2, the components of a harmonic complex with harmonic numbers 2, 3, and 4 were presented either to the same ear (“mono”) or the third harmonic was presented contralaterally to the ear receiving the even harmonics (“dichotic”). In the latter case, a pitch corresponding to the missing fundamental was still perceived. Monaural control conditions presenting only the even harmonics (“2 + 4”) or only the third harmonic (“3”) were also tested. Both the subtraction and the addition waveforms showed that (1) the FFR magnitude spectra for “dichotic” were similar to the sum of the spectra for the two monaural control conditions and lacked peaks at the fundamental frequency and other distortion products visible for “mono” and (2) ACFs for “dichotic” were similar to those for “2 + 4” and dissimilar to those for “mono.” The results indicate that the neural responses reflected in the FFR preserve monaural temporal information that may be important for pitch, but provide no evidence for any additional processing over and above that already present in the auditory periphery, and do not directly represent the pitch of dichotic stimuli.

Speech-evoked ABR: Effects of age and simulated neural temporal jitter

“…In addition, while scalp-recorded evoked potentials have limitations in terms of determining specific response generators, parametric adjustment of the spectral content of the stimulus presented to the listener would provide informative data in terms of understanding what nerve fibers are dominating the recorded response. While the body of sABR literature related to the aging auditory system has increased rapidly in recent years, there are relative few studies that have investigated complex tonal stimuli in the aging brainstem and parametrically adjusted, for example, the harmonic structure of the complex (Marmel et al, 2013; Gockel et al, 2011). In this study, we focused on the response from the sustained portion of the stimulus in order to relate our findings generated with a complex stimulus to other findings generated by on-going tonal stimuli; this focus precluded consideration of how earlier segments of the stimulus (e.g., noise burst, formant transition) may have affected the later sustained response.…”

Subcortical representation of musical dyads: Individual differences and neural generators

“…Electrodes were positioned at the high forehead hairline (active), the seventh cervical vertebra (reference), and at Fpz (ground; Bidelman and Krishnan, 2009;Bones et al, 2014;Gockel et al, 2011;Gockel et al, 2012;Krishnan and Plack, 2011;Krishnan et al, 2005). This electrode configuration allowed for direct comparison with Bones et al (2014), and also ensured that contamination by the cochlear microphonic cannot occur (e.g.…”

Sensitivity of envelope following responses to vowel polarity

“…Averaging responses to opposite polarities has also been used to enhance Envelope Following Responses (EFR) by reducing contamination by the Frequency Following Response (FFR) and cochlear microphonic (Aiken and Picton, 2008). The EFR is a response phase-locked to the stimulus envelope which is minimally affected by an inversion of stimulus polarity and hence preserved when responses to opposite polarities are added (Aiken and Picton, 2008;Gockel et al, 2011;Greenberg et al, 1987;Small and Stapells, 2005). The FFR is a neural response phase-locked to the stimulus fine structure/spectral characteristics.…”