The Journal of Neuroscience, July 1, 2001, 21(13):4844-4851
Tuning to Interaural Time Differences across Frequency
Douglas C.
Fitzpatrick1 and
Shigeyuki
Kuwada2
1 Department of Surgery, University of North Carolina,
Chapel Hill, North Carolina 27599-7070, and 2 Department of
Neuroscience, University of Connecticut Health Center, Farmington,
Connecticut 06030-3405
Interaural time differences (ITDs) are an important cue for
azimuthal sound localization. Sensitivity to this cue depends on
temporal synchrony to the waveform (i.e., phase locking) that begins in
the hair cells and is relayed to the neural comparators. The synchrony
function is low-pass. Therefore, it is expected that neural tuning to
ITDs will become narrower with frequency according to a 1/frequency
function. To test this, we measured ITD tuning across frequency in
neurons from the superior olivary complex, the dorsal nucleus of the
lateral lemniscus, the inferior colliculus, the auditory thalamus, and
the auditory cortex. For some neurons in each nucleus, the ITD tuning
width did become systematically narrower by the expected 1/frequency
relationship. However, in other neurons the ITD tuning width was nearly
constant across frequency. Constant ITD tuning width was infrequently
observed in neurons of the superior olivary complex but was common in
neurons in structures above the superior olivary complex. The nearly
constant ITD tuning was caused both by sharper ITD tuning at low
frequencies and broader tuning at higher frequencies within the
low-frequency band. Neurons with nearly constant tuning to ITDs may be
the mechanism underlying the perception of ITDs in humans in which
just-noticeable differences to changes in ITD decrease by less than the
1/frequency prediction.
Key words:
auditory neurophysiology; auditory pathways; interaural
temporal disparities; sound localization; low-frequency hearing; low-frequency signals
Copyright © 2001 Society for Neuroscience 0270-6474/01/21134844-08$05.00/0