Latency of sound localization as a function of azimuth and frequency.

Abstract

Two experiments investigated by means of backward auditory masking the individual localization times of eight loudspeakers arranged equidistantly on a horizontal azimuth around 5. In the first, 5s had to localize a 20-msec. tone of 1,000 Hz., followed by a SOO-msec. mask of white noise at 1 of 10 delay intervals. Localization accuracy improved with increasing delay. The notion of differential processing time was supported by the finding that rate Of improvement depended on speaker position. To meet the argument that these results could have been caused by the tonal quality of individual speakers, the study was repeated with 5s rotated by 90°. Also, frequency of tone was varied so that binaural time differences as well as intensity differences were mediating the localization decision. Despite rotation of 5, the same effects as in the first study were obtained. In addition, localization patterns differed with mediating binaural cues. Using eight loudspeakers installed equidistantly around S's head, Tolkmitt (1970) investigated the perception of bursts of white noise under conditions of rapid sequential presentation. Some of the results suggested that bursts from speakers in the aural axis were localized faster than those generated from median or diagonal positions. It was argued that the reason for this rests with the fact that sound sources along the aural axis are free of front-back ambiguity and consequently require less localization time than sources outside the aural axis. To test this notion, Tolkmitt (1972) investigated the speed of sound localization in a forced-choice reaction time experiment. The same speaker arrangement was used and 5 had to localize white noise coming from one of eight speakers. Controlling for the movement component of reaction time, Tolkmitt (1972) found that the localization time tended to be shortest for the two speakers in the aural axis. As reaction times are rather coarse measurements of mental processes, it was decided to explore localization latencies more fully by means of backward auditory 1 The author wishes to thank A. Heron, G. V. Stanley, K. F. Taylor, and A. J. Wearing for critical reading of the manuscript.