Cues Required for Externalization and Vertical Localization

Abstract

Frequency response measurements of the human pinna for a sound source at a number of different elevation angles in the vertical median plane show surprising 30-dB dips in the 8- to 12-kHz frequency range. For some subjects, these dips or notches tune down in frequency almost linearly as a function of elevation angle. Detailed measurements indicate that there is a systematic frequency difference between the left- and right-ear notches. Psychophysical experiments show that these notches are perceptually significant and can be used to synthetically change the apparent angle of arrival of a sound source. On the basis of these experiments we postulate that vertical median plane localization is achieved by taking the ratio of the left-ear to the right-ear frequency response in certain key frequency bands. By so doing, the brain could deduce the incident angle of signals in the vertical median plane without knowledge of the spectrum of the incoming signal.