Different patterns of harmonics in frequency-following responses

Area of Science:

• Auditory Neuroscience
• Bioacoustics
• Human Physiology

Background:

• Preliminary research highlighted significant individual variations in harmonic distortion within frequency-following responses (FFRs).
• These differences were observed in response to high-intensity, low-frequency auditory stimuli recorded using surface electrodes in humans.

Purpose of the Study:

• To investigate and categorize the intersubject differences in harmonic distortion patterns of FFRs.
• To explore potential correlations between psychoacoustical measures of harmonic distortion and FFR patterns.

Main Methods:

• Spectral analysis was used to measure the relative amplitudes of the fundamental and second harmonic components of FFRs from 10 subjects.
• Subjects' responses were classified into three distinct patterns (Type I, II, and III) based on harmonic ratios.
• A tone-on-tone octave masking (TOM) technique was employed for psychoacoustical evaluation of second harmonic distortion.

Main Results:

• FFRs from 10 subjects were categorized into three distinct patterns based on the ratio of fundamental to second harmonic components.
• Type I responses (>10 dB ratio) were observed in 3 subjects, Type II (0-10 dB) in 5 subjects, and Type III (second harmonic ≥ fundamental) in 2 subjects.
• No correlation was found between the psychoacoustical TOM results and the FFR patterns observed in the subjects.

Conclusions:

• Human FFRs exhibit significant interindividual variability in harmonic distortion patterns.
• The underlying causes for these distinct FFR patterns remain unclear.
• Psychoacoustical perception of harmonic distortion does not directly correlate with the measured FFR harmonic distortion patterns.