Binaural reproduction aims at recreating a realistic audio scene at the ears of the listener using headphones. In the real acoustic world, sound sources tend to be externalized (that is perceived to be emanating from a source out in the world) rather than internalized (that is perceived to be emanating from inside the head). Unfortunately, several studies report a collapse of externalization, especially with frontal and rear virtual sources, when listening to binaural content using non-individualized Head-Related Transfer Functions (HRTFs). The present study examines whether or not head movements coupled with a head tracking device can compensate for this collapse. For each presentation, a speech stimulus was presented over headphones at different azimuths, using several intermixed sets of non-individualized HRTFs for the binaural rendering. The head tracker could either be active or inactive, and the subjects could either be asked to rotate their heads or to keep them as stationary as possible. After each presentation, subjects reported to what extent the stimulus had been externalized. In contrast to several previous studies, results showed that head movements can substantially enhance externalization, especially for frontal and rear sources, and that externalization can persist once the subject has stopped moving his/her head.

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SummaryThe loudness related to a sound may vary according to the localization of its source. This phenomenon is described as directional loudness and has been mainly observed for high-frequency sounds and for sources located in the horizontal plane. Because of the acoustic shadow of the head, the left and right ear pressures are modied depending on the source azimuth and the global loudness resulting from a summation process may vary accordingly. But directional loudness has also been reported to occur at 400 Hz, where shadowing eects are usually rather small. It might therefore be suspected that directional loudness eects could be inuenced by other parameters involved in the localization process. In a previous study, a small but signicant increase of loudness with increasing interaural time dierence (ITD) was shown for low-frequency pure tones (200 and 400 Hz) at a low loudness level (40 phon). The present study aimed at getting insight into the potential cause and extent of this eect by assessing the loudness of similar pure tones lateralized with headphones by applying an interaural level dierence (ILD) in addition to an ITD and by measuring the eect of ITD at the hearing threshold. It showed signicant eects of both ILD and ITD on loudness, and no interaction between these factors. As the eects added even when the factors were contradictory, it supports the hypothesis that the eect is caused by the ITD itself and is not related to the localization process. However, the ITD eect was not signicant at the hearing threshold.

When presented with a spatially discordant auditory-visual stimulus, subjects sometimes perceive the sound and the visual stimuli as coming from the same location. Such a phenomenon is often referred to as perceptual fusion or ventriloquism, as it evokes the illusion created by a ventriloquist when his voice seems to emanate from his puppet rather than from his mouth. While this effect has been extensively examined in the horizontal plane and to a lesser extent in distance, few psychoacoustic studies have focused on elevation. In the present experiment, sequences of a man talking were presented to subjects. His voice could be reproduced on different loudspeakers, which created disparities in both azimuth and elevation between the sound and the visual stimuli. For each presentation, subjects had to indicate whether the voice seemed to emanate from the mouth of the actor or not. Results showed that ventriloquism could be observed with larger audiovisual disparities in elevation than in azimuth.