The Journal of Neurophysiology Vol. 83 No. 3 March 2000, pp. 1356-1365
Copyright ©2000 by the American Physiological Society
Medical Research Council Institute of Hearing Research, University of Nottingham, Nottingham NG7 2RD, United Kingdom
McAlpine, David,
Dan Jiang,
Trevor M. Shackleton, and
Alan R. Palmer.
Responses of Neurons in the Inferior Colliculus to Dynamic
Interaural Phase Cues: Evidence for a Mechanism of Binaural Adaptation. J. Neurophysiol. 83: 1356-1365, 2000. Responses to sound stimuli that humans perceive as moving were obtained
for 89 neurons in the inferior colliculus (IC) of urethan-anesthetized
guinea pigs. Triangular and sinusoidal interaural phase modulation
(IPM), which produced dynamically varying interaural phase disparities
(IPDs), was used to present stimuli with different depths, directions,
centers, and rates of apparent motion. Many neurons
appeared sensitive to dynamic IPDs, with responses at any given IPD depending strongly on the IPDs the stimulus had just
passed through. However, it was the temporal pattern of the response,
rather than the motion cues in the IPM, that determined sensitivity to
features such as motion depth, direction, and center locus. IPM
restricted only to the center of the IPD responsive area, evoked lower
discharge rates than when the stimulus either moved through the IPD
responsive area from outside, or up and down its flanks. When the
stimulus was moved through the response area first in one direction and
then back in the other, and the same IPDs evoked different responses,
the response to the motion away from the center of the IPD responsive
area was always lower than the response to the motion
toward the center. When the IPD was closer at which the direction of
motion reversed was to the center, the response to the following motion
was lower. In no case did we find any evidence for neurons that under
all conditions preferred one direction of motion to the other. We
conclude that responses of IC neurons to IPM stimuli depend not on the
history of stimulation, per se, but on the history of
their response to stimulation, irrespective of the
specific motion cues that evoke those responses. These data are
consistent with the involvement of an adaptation mechanism that resides
at or above the level of binaural integration. We conclude that our
data provide no evidence for specialized motion
detection involving dynamic IPD cues in the auditory midbrain of the mammal.