On the human ability to auditorily perceive human speaker´s facing angle

This paper summarizes an empirical study exploring whether or not human listeners can tell the facing direction of a human speaker solely by the auditory sense, and if so, how accurately they are able to do it. The purpose is to find the sound information necessary for ultimately realistic and human-centered telecommunications. The study consists of two parts: listeners´ performance and acoustic analysis. The first part describes the methodologies of assessing human perception and the results obtained. The second part provides the candidates of sound information that convey speaker´s facing angles. Twelve blindfolded listeners were tested on their ability to sense the facing angle of a male who spoke a sentence in an anechoic chamber. The listeners were able to indicate the speaker´s facing angles with a reasonably high confidence. The average response errors were 23.5 degrees for horizontal angles and 12.9 degrees for vertical angles. To estimate acoustic cues that the listeners exploited, the acoustic transfer characteristics from the speaker´s mouth to the listener´s ears were measured for all the facing angles tested. The results suggested that the overall level and spectral tilt were used for the listeners´ judgment along the front-back axis, and the level difference between left and right ears was used for the judgment along the left-right axis.