An analysis of the monaural displacement of sound in space

Twelve listeners, rendered monaural, were tested on their ability to localize two spectrally different stimuli presented 10° apart in the left hemifield (pretraining session). Both sounds were perceived to be displaced from the midline. Next, listeners were trained to localize one of the sounds (training sessions) and then tested again on both (posttraining sessions). Training temporarily reduced the extent to which listeners displaced the sound from the midline. No transfer of training, however, was observed when listeners localized the other noise band, which differed in its spectral content. It is proposed that no “natural” spectral cues are available for localizing, monaurally, sound originating on or near the midline, but that cues for these positions can be acquired through training. Head-related transfer functions recorded from the pinna and generated by differently centered narrow bands of noise were obtained, along with additional localization data, in an attempt to support the concept of a natural cue for monaurally localizing sound in the horizontal plane. By and large, the results were consonant with this concept.