Sound localisation (minimum audible angle test)

Screenshot of the MAA testThe HearCom screening test for sound localisation abilities measures the smallest angle that listeners can distinguish between two sound sources (i.e. the minimum audible angle, MAA). In the MAA test, two broad-band noise stimuli are presented consecutively from different directions, symmetrically spaced on different sides of the straight-ahead direction (as sound localisation acuity is highest there) resulting in the impression of a sound moving either from the left to the right or vice versa. The task for the listener is to indicate the direction of movement of the two sounds. The order, i.e. direction, of the sounds is randomised. Since most people who have a computer have a set of speakers connected to the computer, the test is designed for speakers rather than for headphones. The various positions in space are created using a cross-talk cancellation technique. When the speakers are positioned correctly, listeners should be able to observe sound-presentation angles from 32° the left to 32° to the right. The introductory web pages of the test give advice to the users with ample pictures and examples given on how to position the speakers correctly.

Example stimulus with noise bursts moving from right to left (32° angle):

Person performing the MAA testThe MAA test makes use of an adaptive two-down, one-up procedure with decreasing step sizes. In this way, a threshold value is obtained for 70.7% correct. The MAA value is the average over the last eight reversals. Users are directed to result pages that show their result in one of three categories:

  • “Your performance in this hearing test was well below average” (worst possible result)
  • “Your performance in this hearing test was below average.” (intermediate result)
  • “Your performance in this hearing test was in the normal range.” (best possible result)

Irrespective of the result, the following additional advice is given to the user: “This test does not cover all aspects of hearing, and does not substitute for a medical diagnosis. If you feel that you have a problem with your hearing please visit your GP.”

If the angles across which the averaging for determining the MAA takes place show a high variance, the user is informed that the test score is not very consistent and that a careful repetition of the test may give a better result.

The test requires two computer speakers. It does not work accurately with headphones. It is available via the Internet in several European countries.

To the MAA test page

Literature:
Mills, A.W. (1958) On the minimum audible angle. J. Acoust. Soc. Am. 30, pp. 237-246.