Ultrasonic binaural echo perception of object's texture by human echolocation

Abstract

Echolocating bats use frequency-modulated (FM) and/or constant-frequency (CF) sound for ultrasonic sensing depending on the situation during flight. We investigated discrimination ability of object’s texture for sighted subjects to understand acoustic clues for texture recognition in human echolocation. FM and CF ultrasonic echoes from six objects with different materials and surface structures were acquired by a 1/7-size miniature dummy head for presentation of 1/7-times pitch converted binaural audible sounds to listeners through headphones. In the results, averaged rate of correct answer in the case of extremely different surface condition (i.e., acrylic board versus artificial grass) was more than 90% while one in the slightly different surface condition (i.e., acrylic board versus foamed polystyrene) was under 40%. Furthermore, the rate of correct answers in the CF sound condition was approximately 13% lower than one in the FM sound condition. The correlation diagram among targets by multidimensional scaling was dispersed more remarkably in the FM sound condition. When the target pair had slightly different surface condition, differences in the notch pattern of amplitude spectra were observed, especially in the FM sound condition. These suggest that FM ultrasonic binaural sound is more effective for slight-different texture perception than CF ultrasonic binaural sound.