Human Echolocators Have Better Localization Off Axis

Abstract

Here, we report novel empirical results from a psychophysical experiment in which we tested the echolocation abilities of nine blind adult human experts in click-based echolocation. We found that they had better acuity in localizing a target and used lower intensity emissions (i.e., mouth clicks) when a target was placed 45° off to the side compared with when it was placed at 0° (straight ahead). We provide a possible explanation of the behavioral result in terms of binaural-intensity signals, which appear to change more rapidly around 45°. The finding that echolocators have better echo-localization off axis is surprising, because for human source localization (i.e., regular spatial hearing), it is well known that performance is best when targets are straight ahead (0°) and decreases as targets move farther to the side. This may suggest that human echolocation and source hearing rely on different acoustic cues and that human spatial hearing has more facets than previously thought.

Head movement and its relation to hearing

“…Even though the highest binaural cue resolution occurs at the midline, the point in azimuth where two side-by-side locations have the greatest difference in naturally occurring binaural cues is at that intermediate-lateral position (35° to 55°). Taken together, the findings of Milne et al (2014) and Thaler et al (2022) strongly suggest that given freedom of head movement, the echolocators used head position in the yaw domain to maximize the binaural information contrasted between successive repetitions of self-emissions.…”

“…In the Milne et al (2014) study, specific head movements were characterized as anecdotal speculation that “echo saccades”, like eye saccades, provide additional “sound” snapshots to aid perception. In a follow-up study by Thaler et al (2022) that tested blind echolocators’ ability to discriminate the position of a 7.5 mm wooden disk, results showed better localization for intermediate-lateral positions (45°) compared to midline (0°) or extreme lateral (90°) positions ( Thaler et al, 2022 ). Further analysis of the binaural level and timing information reaching the two ears, revealed that the greatest rate of change in binaural intensity and timing differences as a function of azimuthal angle occurred for objects located at 35° to 55° relative to 0° midline.…”