A quick method for determining the relative minimum audible distance using sound images

Auditory localization plays an essential role in various tasks, including spatial orientation, locomotion, attention and memory. Optimization of experimental routine is important for preliminary assessment of the subject's sound localization ability. In the present study, a new quick technique for estimating the relative minimum audible distance (RMAD) using sound images is introduced. Twenty adults with normal hearing took part in six RMAD measurements in free field. The reference RMAD values were obtained using a method of constant stimuli by physically positioning a real sound source. The same method was used with stationary sound images created by superposition of signals emitted by two loudspeakers. To optimize the measurements, the RMADs were determined for the sound images using two adaptive psychoacoustic procedures known as one-down, one-up and two-down, one-up staircases. The group-average RMADs obtained by the method of constant stimuli for both types of stimuli and by two adaptive procedures were similar, 7% (SD = 2%). The effect of whether subjects were sighted or blindfolded was not significant for measurements of RMAD to sound images. The average measurement times were 373 s (SD = 20 s) for the method of constant stimuli, 85 s (SD = 9 s) for the one-down, one-up, and 124 s (SD = 14 s) for the two-down, one-up procedure. The results are consistent with the previous studies and confirm the validity of the measurements of RMAD using adaptive procedures with stationary sound images as a quick method.