Low‐frequency ILD elevation cues

It is well known that the binaural ITD (interaural time difference) and ILD (interaural level difference) are the primary cues for azimuth, while monaural spectral features due to pinna diffraction are the primary cues for elevation. Pinna cues appear above 3 kHz, where the wavelength becomes comparable to pinna size. However, it is shown that there are also important low‐frequency ILD elevation cues primarily due to torso diffraction. In the experiments reported, random noise bursts were filtered by individualized head‐related transfer functions, and four subjects were asked to report the elevation angle. Eight conditions were tested, depending on whether the source was in front or in back, in the median plane or on a 45‐deg cone of confusion, and had wide bandwidth or was band limited to 3 kHz. For the band‐limited signal, localization accuracy was at chance level in the median plane, and was poor in front. However, at 45‐deg azimuth in the back, the accuracy was close to that for a wideband source, the average correlation coefficient being approximately 0.75 for the narrow‐band source and 0.85 for the wideband source. A physical explanation for the cues is presented. [Work supported by NSF under Grant No. IRI‐9619339.]