Volume 17, Number 5,
Issue of March 1, 1997
pp. 1720-1733
Copyright ©1997 Society for Neuroscience
Spatially Selective Auditory Responses in the Superior Colliculus
of the Echolocating Bat
Received March 25, 1996; revised Nov. 26, 1996; accepted Dec. 2, 1996.
Doreen E. Valentine and
Cynthia F. Moss
Program in Neuroscience, and Department of Psychology, Harvard
University, Cambridge, Massachusetts 02138
When a bat approaches a target, it continuously modifies its
echolocation sounds and relies on incoming echo information to shape
the characteristics of its subsequent sonar cries. In addition, acoustic information about the azimuth and elevation of a sonar target
elicits orienting movements of the head and pinnae toward the sound
source. This requires a common sensorimotor interface, where echo
information is used to guide motor behaviors.
Using single-unit neurophysiological methods and free-field auditory
stimulation, we present data on biologically relevant specializations
in the superior colliculus (SC) of the bat for orientation by sonar. In
the bat's SC, two classes of spatially tuned neurons are distinguished
by their sensitivity to echoes. One population shows facilitated,
delay-tuned responses to pairs of sounds, simulating sonar emissions
and echoes. Delay tuning, related to encoding target range, may play a
role in guiding motor responses in echolocation, because the bat
adjusts its emissions with changes in target distance. The
delay-facilitated response depends on the direction of stimulation and
on the temporal relationship between the simulated emission and echo in
the sound pair, suggesting that this class of neurons represents the
location of a target in three dimensions. A second population encodes
the target in two dimensions, azimuth and elevation, and does not show
a facilitated response to echoes delivered from any locus. Encoding of
azimuth and elevation may be important for directing head aim, and this class may function in transforming auditory spatial information into
signals used to guide acoustic orientation.
Key words:
superior colliculus;
echolocation;
bats;
acoustic
orientation;
spatial perception;
sensorimotor integration