Frequency discrimination of brief tonal steps as a function of frequency in the lesser bulldog bat |
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Authors: | R C Roverud |
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Institution: | (1) Department of Physiological Science, Box 951527, University of California at Los Angeles, Los Angeles, CA 90095-1527, USA e-mail: roverud@ucla.edu Fax: +1-310-206-9184, US |
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Abstract: | 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.
Accepted: 20 March 1999 |
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Keywords: | Frequency discrimination Hearing Bat Frequency analysis Psychoacoustics |
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