Minimum Audible Movement Angle as a Function of the Azimuth and Elevation of the Source

Abstract

In the future auditory directional cues may enhance situational awareness in cockpits with head-coupled displays. This benefit would depend, however, on the pilot's ability to detect the direction of moving sounds at different locations in space. The present investigation examined this ability. Auditory motion acuity was measured by the minimum audible movement angle (MAMA): the minimum angle of travel required for detection of the direction of sound movement. Five experienced listeners were instructed to indicate the direction of travel of a sound source (broadband noise at 50 dBA) that moved at a velocity of 20 deg/s. Nine azimuth positions were tested at 0 deg elevation. Five elevations were then tested at 0 deg azimuth. Finally two azimuth positions were tested at an elevation of 80 deg. The position of the source did not significantly affect the MAMA for azimuth locations between +40 and -40 deg and elevations below 80 deg. Within this area the MAMA ranged between 1 and 2 deg. Outside this area the MAMA increased to 3 to 10 deg.

Auditory Spatial Perception: Auditory Localization

“…The size of the error increases with greater vertical deviations from the horizontal plane as well as for locations behind the listener. Strybel et al (1992a) found LE in the vertical plane to be largest at 80° of elevation. In addition, Davis and Stephens (1974) observed that the vertical mean absolute error (MUE) decreased monotonically as sound intensity increased from a 10-dB sensation level (SL) to a 70-dB SL reaching a plateau at about 3.5° at a ~50-60 dB SL.…”

The audible facing angle

“…Also of interest is the effect of dynamic change in facing angle. In the localization literature, differences have been found between the minimum audible angle (MAA) and the minimum audible movement angle (MAMA) (Chandler and Grantham, 1992;Harris and Sergeant, 1970;Mills, 1958;Perrott and Musicant, 1981;Perrott and Saberi, 1990;Strybel et al, 1992). It may be that differences between static and dynamic audible facing angles also exist.…”

Nonspeech Auditory Output

“…The minimum auditory angle (MAA) is the smallest separation between two sources that can be reliably detected. Strybel, Manligas and Perrott (1992) report that in the median plane sound sources only 1° apart can be detected. At 90° azimuth (directly opposite one ear) sources must be around 40° apart.…”