A blind human expert echolocator shows size constancy for objects perceived by echoes

Abstract

Some blind humans make clicking noises with their mouth and use the reflected echoes to perceive objects and surfaces. This technique can operate as a crude substitute for vision, allowing human echolocators to perceive silent, distal objects. Here, we tested if echolocation would, like vision, show size constancy. To investigate this, we asked a blind expert echolocator (EE) to echolocate objects of different physical sizes presented at different distances. The EE consistently identified the true physical size of the objects independent of distance. In contrast, blind and blindfolded sighted controls did not show size constancy, even when encouraged to use mouth clicks, claps, or other signals. These findings suggest that size constancy is not a purely visual phenomenon, but that it can operate via an auditory-based substitute for vision, such as human echolocation.

Keywords:

• blindness
• human echolocation
• size constancy
• vision
• multisensory

Acknowledgments

The authors would like to thank P. Kabirrah for her assistance with auditory testing and C. Byrne for her assistance with data collection. The authors declare no conflict of interest.

Additional information

Funding

This work was supported by funding from the Natural Sciences and Engineering Research Council of Canada to Jennifer Milne and an operating grant to Melvyn Goodale [grant number 6313].