Auditory categories for the perception of echo spectra in bats

Abstract

Bats obtain an auditory representation of their environment by sonar. The categories relevant for the perception of echo spectra by Megaderma lyra, a species using multiharmonic sonar calls, were studied in a series of 2-AFC experiments with complex tones. First, the bats classified complex tones on the basis of absolute pitch rather than by their relative pitch. Absolute pitch, combined with a long lasting memory representation of echo spectra, may form the basis of an acoustical library for object identification. Second, evidence was provided for the spontaneous perception of a collective pitch at the fundamental of the complex tones, as well as for the use of a vowellike quality based on the broadband spectral composition of the complex tones. In addition, the bats could be trained to concentrate on the spectral pitch of a single component in complex spectra. Collective pitch, vowel timbre, and spectral pitch perception may all be vital for acoustical orientation in this ground gleaning bat which has to sort out multiple echoes. The collective pitch of the echo allows one to relate each echo to its respective call. The timbre and the spectral pitches of sonar call echoes carry information about object structure. [Work supported by SFB 204.]