Bioacoustic spatial perception by humans: A controlled laboratory measurement of spatial resolution without distal cues

The angular spatial resolution of a wide-angle air sonar using a continuous transmission frequency-modulated radiation, with the output coupled binaur ally to the auditory system of a user, was measured under restrained contro lled conditions. This was done to determine the effect of adding a narrow c entral field of view of 9 deg to a wide-angle sonar. The target objects wer e three equidistant vertical rods initially spaced apart by 10 deg. This wa s varied down to a spacing of 4 deg. Ten nonvisual subjects achieved an ang ular resolution of 6 deg. Four of these ten subjects continued learning to achieve an unexpected spatial resolution of 4 deg within the 9 deg central field. A mean error of approximately 1 deg in direction accuracy was achiev ed. It is inferred that the unique variations in the octave band ultrasonic echoes within the narrow field, and the invariance of the on-axis echo as one's head is turned, enables this angular resolution and accuracy to be ac hieved within the wide binaural field of view of 50 deg. This ability to re solve specula objects within a narrow angular resolution element of 9 deg i s linked to the bat's ability to seemingly resolve object glints within a d istal resolution element of less than 2 wavelengths. (C) 2001 Acoustical So ciety of America.