Human echolocation: The relative importance of pitch and loudness

Document type: Conference Papers
Peer reviewed: Yes
Author(s): Bo Schenkman, Mats E. Nilsson
Title: Human echolocation: The relative importance of pitch and loudness
Conference name: The 40th Nordic Ergonomics Society
Year: 2008
ISBN: 978-9979-70-471-3
City: Reykjavik, Iceland
Organization: Blekinge Institute of Technology
Department: School of Management (Sektionen för management)
School of Management S- 371 79 Karlskrona
+46 455 38 50 00
http://www.bth.se/mam/
Authors e-mail: bsc@bth.se, mnn@psychology.su.se
Language: English
Abstract: A sound heard in the presence of a reflected object will be both louder and have a slightly different timbre (“repetition pitch”) than the same sound heard with no reflection. Thus, pitch and loudness are two sources of information that visually handicapped people may use for echolocation. In real life, the two sources of information are confounded, because perceived loudness and repetition pitch both diminishes with distance to the reflecting object. The purpose of the present experiment was to disentangle the influence of each of these sources on human echolocation. Experimental sounds were obtained from binaural recordings with an artificial head in an ordinary room. White noise (500 ms) was emitted from a loudspeaker on the chest of the artificial head. A reflecting aluminum sheet (0.5 m diameter) was located at 1, 2 and 3 m distance to the artificial head. By digital manipulation, the loudness information or the pitch information of the recorded sounds were eliminated, resulting in three kinds of sounds: (1) sounds containing both pitch and loudness information, (2) sounds with only pitch information, and (3) sounds with only loudness information. These three kinds of sounds were presented to 14 sighted students. The psychophysical method of 2-alternative-forced-choice with feedback was used, with 56 trials for each person at each condition. Each trial presented one sound recorded with, and one without, reflecting object. The task was to detect which of the two sounds that was recorded in the presence of the reflecting object. All participants could use echolocation for all three kinds of sounds at the distance of 1m, but performed close to chance with all sounds at 3 m. At the 2 m condition, sounds with only pitch information gave a higher performance compared to sounds with only loudness information, for which the performance was close to random. Thus, pitch alone may provide sufficient information for echolocation at these distances. Audiometric tests were conducted, with focus on the pure tone threshold average and the absolute difference between the ears. The results will have a bearing on the construction of orientation and mobility aids for the visually handicapped.
Subject: Psychology\General
Physical Acoustics\General
Public Health\General
Keywords: blind, echolocation, orientation, perception
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