Resolution of Components of Harmonic Complex Tones by Single Neurons in the Alert Auditory Cortex

Abstract

Humans perceive the pitch of a harmonic complex tone without its fundamental as identical with that of the fundamental presented alone (the phenomenon of the missing fundamental) (cf. de Boer, 1976). In psychophysical experiments, rhesus monkeys were able to match harmonic complex tones with fundamentals to the same without fundamentals (Tomlinson and Schwarz, 1987). It was concluded that rhesus monkeys could perceive the pitch of the missing fundamental. This percept is generally thought to arise within the central nervous system (Houtsma and Goldstein, 1973; Terhardt, 1972). We studied the auditory cortex of alert monkeys to determine how stimulus features relevant to pitch perception might be encoded. Single neurons in auditory cortex of unanesthetized monkeys were isolated, the units’ sensitivity to pure tones and noise stimuli were determined, and sideband inhibition was assessed, typically with two tones. We then applied various complex tones and compared the responses to those obtained using the previous simpler stimuli.