The perception of relative pitch in the bat M. lyra.

Abstract

As opposed to humans, animals perceive pitch predominantly in terms of absolute categories. In order to establish relative pitch formation in bats, three animals were trained to discriminate falling from rising two-tone sequences in a two-alternative, forced choice behavioral test. Stimuli were six pairs of complex tones, consisting of the first three harmonics. In the first experiment, the spectra of high and low tones fell into different frequency regions (first harmonic of low tone: 9–10.4 kHz; high tone: 34–39.3 kHz). After 2 months, two animals were able to perform the task with an error rate of less than 5%. In the second experiment, 12 tone pairs with overlapping harmonics were presented. The frequency ratio between the two fundamentals of a pair was 2:3, with the fundamental of the lower tone between 13.2 and 18.1 kHz. Only one animal was able to perform this task after 2 weeks of training. Control tasks revealed that the bat utilized absolute pitch clues only to a minor extent. Nevertheless, later experiments showed that the animal was not able to transpose relative pitch categories to frequency ranges beyond the original stimuli. [Work supported by Humboldt Foundation and SFB 204 ‘‘Gehör,’’ München.]