Neurons in the central nucleus of the inferior colliculus (ICC) of decerebr
ate cats show three major response patterns when tones of different frequen
cies and sound-pressure levels (SPLs) are presented to the contralateral ea
r. The frequency response maps of type I units are uniquely defined by a na
rrow excitatory area at best frequency (BF: a unit's most sensitive frequen
cy) and surrounding inhibition at higher and lower frequencies. its a resul
t of this receptive field organization, type I units exhibit strong excitat
ory responses to BF tones but respond only weakly to broadband noise (BBN).
These response characteristics predict that type I units are well suited t
o encode narrowband signals in the presence of background noise. To test th
is hypothesis, the dynamic range properties of ICC unit types were measured
under quiet conditions and in multiple levels of continuous noise. As obse
rved in previous studies of the auditory nerve and cochlear nucleus, type I
units showed upward threshold shifts and discharge rate compression in bac
kground noise that partially degraded the dynamic range properties of neura
l representations at high noise levers. Although the other two unit types i
n the ICC showed similar trends in threshold shift and noise compression, t
heir ability to encode auditory signals was compromised more severely in in
creasing noise levels. When binaural masking effects were simulated, only t
ype 1 units showed an enhanced representation of spatially separated signal
s and maskers that was consistent with human perceptual performance in inde
pendent psychoacoustic observations. These results support the interpretati
on that type 1 units play an important role in the auditory processing of n
arrowband signals in background noise and suggest a physiological basis for
spatial factors that govern signal detection under free-field listening co
nditions.