  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, little is known about the role of this temporal
information for signal processing in the brain. Through psychoacoustic studies
we provide direct evidence that humans employ temporal fine structure to
discriminate between frequencies. To this end we construct 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 test the frequency
discrimination of these phase-changing tones, of control tones without phase
changes, and of short tones that consist of a single wavelets. For carrier
frequencies below a few kilohertz we find that phase changes systematically
worsen frequency discrimination. No such effect appears for higher carrier
frequencies at which temporal information is not available in the central
auditory system.
