The effects of attenuation of frequency segments on binaural localization of sound

Perceived location of tonal stimuli d and narrow noise bands presented in two-dimensional space varies in an orderly manner with changes in stimulus frequency. Hence, frequency has a referent in space that is most apparent during monaural listening. The assumption underlying the present study is that maximum sound pressure level measured at the ear canal entrance for the various frequencies serves as a prominent spectral cue for their spatial referents. Even in binaural localization, location judgments in the vertical plane are strongly influenced by spatial referents. We measured sound pressure levels at the left ear canal entrance for 1.0-kHz-wide noise bands, centered from 4.0 kHz through 10.0 kHz, presented at locations from 60 degrees through -45 degrees in the vertical plane; the horizontal plane coordinate was fixed at -90 degrees. On the basis of these measurements, we fabricated three different bandstop stimuli in which differently centered 2.0-kHz-wide frequency segments were filtered from a broadband noise. Unfiltered broadband noise served as the remaining stimulus. Localization accuracy differed significantly among stimulus conditions (p < .01). Where in the vertical plane most errors were made depended on which frequency segment was filtered from the broadband noise.