Head-related transfer functions for differently centered narrow noise bands were obtained on 6 subjects. Derived from these measurements were covert peak areas (CPAs), defined as the spatial constellation of loudspeakers that generates maximal sound pressure at the entrance of the ear canal for specific bands offrequency. On the basis of previous data, we proposed that different frequency bands served as important spectral cues for monaural localization of sounds from different loci and that location judgments were directed toward the CPAs associated with the different bands. In the first study, the stimuli were bandpass filtered so that they contained only those frequencies whose associated CPAs occupied either the monaural listener's "upper" or "lower" spatial regions. Loudspeakers, separated by 15 0 , were stationed in the left hemifield, ranging from 0 0 to 180 0 azimuth and -45 0 to 60 0 elevation. Subjects reported the loudspeaker from which the sound appeared to originate. Judgments of the sound's elevation were in general accord with the CPAs associated with the different frequency segments. In the second study, monaural localization tests were administered in which different 2.0-kHz·wide frequency bands linked with specific CPAs were notch filtered from a 3.5-kHz highpass noise band. For the control condition, the highpass noise was unfiltered. The data demonstrated that filtering a frequency segment linked with specific CPAs resulted in significantly fewer location responses directed toward that particular spatial region. These results demonstrate in greater detail the relation between the directional filtering properties of the pinna and monaural localization of sound.Although binaural localization of sound in space is consistently more accurate than monaural localization, listeners are able to localize sounds in the lateral regions of the hemifield with a fair degree of accuracy when using only one ear. A reasonable explanation of this observation is that people simply learn what an acoustic stimulus sounds like when it comes from a particular region in space. Durlach and Colburn (1978) were more specific. They proposed that we learn the acoustic receptivity pattern of our own pinnae and that we also become familiar with the spectra of everyday sounds. The sound's spectrum at the entrance of the ear canal is the result of the external sound's spectrum being modified by the directional filtering properties of the pinna. Note, however, that according to Durlach and Colburn, proficient monaural localization requires prior knowledge of the spectrum of the sound source. This idea, although attrac-

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