The discrimination of low-frequency tones employs temporal fine structure
An auditory neuron can preserve the temporal fine structure of a low-frequency tone by phase-locking its response to the stimulus. Apart from sound localization, however, much about the role of this temporal information for signal processing in the brain remains unknown. Through psychoacoustic studies we provided direct evidence that humans employ temporal fine structure to discriminate between frequencies. We constructed tones that are based on a single frequency but in which—through the concatenation of wavelets—the phase changes randomly every few cycles. We then tested the frequency discrimination of these phase-changing tones, of control tones without phase changes, and of short tones that consist of a single wavelet. For carrier frequencies below a few kilohertz we found that phase changes systematically worsen frequency discrimination. No such effect appeared for higher carrier frequencies at which temporal information is not available in the central auditory system.
The stimulus for psychophysical testing comprised four concatenated wavelets, each with a distinct, random phase.