Temporal fine structure sensitivity measured with pulse-spreading harmonic complexes.

Two experiments investigated sensitivity to temporal fine structure (TFS) in a group of normal hearing participants. The stimuli were bandpass filtered pulse-spreading harmonic complexes (PSHCs) with a regular envelope repetition rate and a phase adjusted so that the TFS peaks were progressively shifted across envelope periods. For up-PSHCs, the TFS peaks were advanced, yielding a rising pitch percept, while for down-PSHCs, the peaks were delayed, yielding a falling pitch percept. Experiment 1 showed that in a fixed frequency region, there was a range of rates for which the direction of the pitch change could be identified. Cochlear model simulations suggested that participants may use either place-of-excitation and/or temporal cues to perform this task. Experiment 2 showed that there was an envelope rate below which down-PSHCs and up-PSHCs could not be discriminated. This lower envelope rate limit of TFS sensitivity significantly increased with increases in frequency region and was similar to the lower rate limit of melodic pitch. The results in high frequency regions suggest that TFS cues are available up to 10 kHz when the rank of the lowest component present in the passband is 18, and all harmonics are presumably unresolved.