Understanding pitch perception through physiological, modeling, and behavioural methods

Abstract

Pitch is a salient perceptual quality that underlies our musical experience, interpretation of speech, and ability to attend to one of multiple speakers. Yet the brain mechanisms that support this key percept remain unclear. We have measured the pitch discrimination of humans, ferrets, and mice on a 2-alternative forced choice task. These experiments show that species differ in their weighting of harmonic and temporal envelope cues for pitch judgments. By applying existing computational models, we demonstrate how cochlear filter properties can explain some of these species differences. We have also used microelectrode recordings in behaving ferrets to understand how individual cortical neurons represent pitch. We find that: (1) cortical activity correlates better with ferrets’ pitch judgements than stimulus f0; and (2) inhibition can shape neural representations of f0 when animals are actively engaged in a pitch discrimination task, compared to when they are passively listening to the same sounds. We are now using 2-photon calcium imaging, during which we can measure the precise spatial position and responses of large numbers of individual neurons simultaneously, to better understand how and where pitch is extracted within the cortical microcircuit.