Pitch-timbre interactions as measured in discrimination and the frequency-following response

Perceptual interactions between pitch and timbre have been demonstrated repeatedly using discrimination tasks in psychoacoustics. The current study investigates whether the pitch-timbre interaction is reflected in neural signatures of pitch encoding in the brainstem. Listeners discriminated the pitch of harmonic tone complexes with low- or high-spectral centroids (SC) in a yes/no task. Fundamental frequency (F0) varied by one just noticeable difference (JND), while SC could be varied by two- or five- JNDs. Discrimination performance increased when both F0 and SC were higher as opposed to when one was higher, and one was lower. This suggests that higher SCs bias listeners toward “higher pitch” responses, replicating previous studies. Frequency-following responses (FFR) were obtained in response to the same stimuli from the same listeners. The recorded FFR signals were analyzed using autocorrelation functions, to evaluate the coding of periodicity, and the Fourier spectra, as an indicator of the encoded F0. The encoding of pitch-relevant information was similar for all stimuli, regardless of SC. Contrary to bias observed in pitch discrimination performance imposed by SC, the lack of a significant influence of SC in the FFR measurements suggests that the pitch-timbre interaction was not observed at the level of the brainstem.