Frequency discrimination of brief tonal steps as a function of frequency in the lesser bulldog bat.
In a two-alternative, forced-choice task lesser bulldog bats were trained to distinguish between a pure tone pulse and a pulse composed of a series of brief tonal steps oscillating between two different frequencies. The tone-step pulse gradually approximates the pure tone pulse as the frequency difference between the steps becomes progressively smaller. Frequency difference limens for the brief tonal frequency steps were determined for a broad range of ultrasonic frequencies. The variation in tone-step difference limens with frequency appears to be correlated to the frequency structure of the bat's short-constant-frequency/frequency-modulated echolocation sound. There was a marked decline in the value of the relative frequency difference limens (Weber ratio) over a fairly narrow range of frequencies above the constant frequency and a sharp increase in threshold above this range. The relative thresholds for frequency discrimination were small and uniform over the frequency range of the frequency-modulated sweep and increased for frequencies below the frequency-modulated sweep. Thus, the most accurate frequency-discrimination abilities occur over a narrow frequency range around the frequency of the constant-frequency component of returning echoes. Frequency discrimination over the range of frequencies of the frequency-modulated component is relatively good.
Roverud
R C
RC
Department of Physiological Science, University of California at Los Angeles 90095-1527, USA. roverud@ucla.edu
D000161:Acoustic Stimulation; D000818:Animals; D002685:Chiroptera / Q000502:physiology*; D004193:Discrimination Learning / Q000502:physiology*; D004455:Echolocation / Q000502:physiology*; D008297:Male