Human Echolocation: Pitch versus Loudness Information

Blind persons emit sounds to detect objects by echolocation. Both perceived pitch and perceived loudness of the emitted sound change as they fuse with the reflections from nearby objects. Blind persons generally are better than sighted at echolocation, but it is unclear whether this superiority is related to detection of pitch, loudness, or both. We measured the ability of twelve blind and twenty-five sighted listeners to determine which of two sounds, 500 ms noise bursts, that had been recorded in the presence of a reflecting object in a room with reflecting walls using an artificial head. The sound pairs were original recordings differing in both pitch and loudness, or manipulated recordings with either the pitch or the loudness information removed. Observers responded using a 2AFC method with verbal feedback. For both blind and sighted listeners the performance declined more with the pitch information removed than with the loudness information removed. In addition, the blind performed clearly better than the sighted as long as the pitch information was present, but not when it was removed. Taken together, these results show that the ability to detect pitch is a main factor underlying high performance in human echolocation.