A summary of research investigating echolocation abilities of blind and sighted humans

Abstract

There is currently considerable interest in the consequences of loss in one sensory modality on the remaining senses. Much of this work has focused on the development of enhanced auditory abilities among blind individuals, who are often able to use sound to navigate through space. It has now been established that many blind individuals produce sound emissions and use the returning echoes to provide them with information about objects in their surroundings, in a similar manner to bats navigating in the dark. In this review, we summarize current knowledge regarding human echolocation. Some blind individuals develop remarkable echolocation abilities, and are able to assess the position, size, distance, shape, and material of objects using reflected sound waves. After training, normally sighted people are also able to use echolocation to perceive objects, and can develop abilities comparable to, but typically somewhat poorer than, those of blind people. The underlying cues and mechanisms, operable range, spatial acuity and neurological underpinnings of echolocation are described. Echolocation can result in functional real life benefits. It is possible that these benefits can be optimized via suitable training, especially among those with recently acquired blindness, but this requires further study. Areas for further research are identified.

Human echolocation - spatial resolution and signal properties

“…In terms of the spectral content of these oral clicks, there is energy at multiple parts of the audible range, with peak frequencies typically between 2 and 8 kHz (Schörnich et al, 2012;Thaler & Castillo-Serrano, 2016), which is low compared to echolocating bats, who can produce emissions in the ultrasonic range (i.e. frequencies higher than 20 kHz; Kolarik et al, 2014).…”

“…Although it had been thought by some that such additional factors would impair the ability to detect and discriminate objects, in a manner similar to the effect of background noise on sound localisation (Kolarik et al, 2014), Schenkman & Nilsson (2010) in fact showed that a reflecting object could be detected up to a distance of 100 cm in an anechoic chamber, but up to 200 cm in a conference room. Furthermore, in a study by Tonelli and colleagues (2016), in which the reverberation time was as long as 1.4 s (Tonelli et al, 2016), participants' ability to echolocate (both in the precision and accuracy of depth judgment) was still better in a reverberating room compared to an anechoic one.…”

“…The typical pattern of activity at the ear of an echolocator consists of the following successive sounds: the emission only, the superimposition of the emission and echo and, finally, the echo only (Kolarik et al, 2014), and for echoes returning from distant objects there may be a period of silence. One application of active echolocation is in the detection of an object in front of the echolocator and inferring its distance from the temporal delay between the emission and echo.…”

“…This variability was partially predicted by the age of blindness-onset -with those who lost their vision at an earlier age having better performance in this task. This level of acuity has been compared to that of sound source localisation in the frontomedial plane (Kolarik et al, 2014) and corresponds approximately to monocular visual acuity in the same task at a retinal eccentricity of 35° (Teng et al, 2012). In comparison, Wallmeier, Geßele and Wiegrebe (2013) tested sighted participants' ability to discriminate the azimuth of an object in virtual acoustic space.…”

Human echolocation: waveform analysis of tongue clicks

“…Participants showed accurate spatial localization and discrimination of objects with the same surface area but different shapes. These days more research has accumulated to suggest that echolocation may also give information about an object's distance and azimuth, shape, material, size and motion [5,6,9]. It has been suggested that the spectral composition of echoes may provide a vital source of environmental information [5,7,8].…”