Human echolocation: Detection of objects by visually handicapped people
Bo Schenkman, Gästforskare från Blekinge Tekniska Högskola
Human Communication seminar series
An ongoing project aimed at understanding how visually handicapped people detect objects by reflected sounds, often called echolocation or biosonar, will be described. This ability was tested in a number of separate studies. Noise bursts with different durations were binaurally recorded in an ordinary room and in an anechoic chamber using a manikin. As a reflecting object, a 1.5 mm thick aluminum disk with a diameter of 0.5 m was placed at distances 0.5 m to 5 m. The recorded sounds were subsequently presented to blind and sighted participants in listening experiments using a 2-alternative-forced choice paradigm. The task of the persons was to detect which of two sounds that contained a reflecting object. Feedback was provided. In general, the blind participants were better than the sighted, but a few blind people were superior within their own group. Another experiment was conducted on two of the high performing blind persons, confirming their superior performance. In addition, a special one-case study, using the same methodology as earlier, was conducted on a blind man with exceptional performance. Echolocation was generally better in the ordinary room than in the anechoic one. In another study the separate influences of pitch and loudness were disentangled. Blind people relied more on both pitch and loudness, but could utilize both sources. Audiometric measures hint that auditory room perception could be of importance for echolocation. Size perception has also been studied, but so far only on sighted persons. The explanation of how blind persons can detect faint echo signals will require an explanation based on perception, acoustics, individual characteristics and physiology.