The relative contribution of interaural time and magnitude cues to dynamic sound localization

Abstract

This paper presents preliminary data from a study examining the relative contribution of interaural time differences (ITDs) and interaural level differences (ILDs) to the lcxalization of virtual sound sources both with and without head motion. The listeners' task was to estimate the apparent direction and distance of virtual sources presented over headphones. Stimuli were synthesized from minimum phase representations of nonindividualized directional transfer functions. During dynamic conditions, listeners were encouraged to move their heads; the position of the listener's head was tracked and the stimuli were synthesized in real time using a Convolvotron to simulate a stationary external sound source. ILDs and lTDs were either correctly or incorrectly correlated with head motion: (1) both ILDs and ITDs correctly correlated, (2) ILDs correct, ITD fixed at 0" azimuth and 0 ' elevation, (3) IT& correct, ILDs fixed at 0 ' . 0". Similar conditions were run for static conditions except that none of the cues changed with head motion. The data indicated that, compared to static conditions, head movements helped listeners to resolve confusions primariIy when ILDs were correctly correlated, although a smaller effect was also seen for correct ITDs. Together with the results for static conditions, the data suggest that localization tends to be dominated by the cue that is most reliable or consistent, when reliability is defined by consistency over time as well as across frequency.

Influence of head tracking on the externalization of speech stimuli for non-individualized binaural synthesis

“…As expected, many subjects reported that stimuli were sometimes externalized while moving their heads, then internalized once they stopped moving their heads. It can therefore be hypothesized that the improvement brought by head movements and head tracking would have been even higher compared to previous studies if subjects had been asked to report externalization while moving their heads, as they were in Begault et al (2001), Wenzel (1995) and Brimijoin et al (2013).…”

“…In contrast to Begault et al (2001) and Wenzel (1995), subjects in the experiment of Brimijoin et al (2013) were not asked to estimate distance after each presentation, but simply to report a binary choice of whether the stimulus emanated from either inside or outside the head.…”

“…However, these studies were either informal or lacked sufficient subjects (only three subjects in Kawaura et al) and quantitative data. Other studies suggest that the effect of head movements coupled with head tracking on externalization is small (Wenzel, 1995) or even null (Begault et al, 2001).…”

“…In Wenzel (1995), six subjects listened to a 3 s broadband Gaussian noise presented from 40 different locations: eight azimuths every 45°for five different elevations (−36°to +36°), using non-individualized HRTFs. Two different conditions were evaluated: (1) neither head tracking nor head movement versus (2) with head tracking and head movements (though subjects were requested not to lean their heads far forward or to the side).…”

“…In Wenzel (1995), who also used non-individualized HRTFs, subjects were asked to provide numerical estimates of distance in inches (the distance scale was anchored by 0 inches for a sound at the center of the head and 4 inches for a sound located at the perimeter of the head). Results were then converted into externalization rate (defined as the percentage of time a stimulus was perceived outside the head, i.e.…”