Detection of frequency modulation in the FM-bat Phyllostomus discolor |
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Authors: | K -H Esser R Kiefer |
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Institution: | (1) Abteilung Vergleichende Neurobiologie, Universität Ulm, Albert-Einstein-Allee 11, D-89069 Ulm, Germany |
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Abstract: | In a two-alternative forced-choice procedure lesser spear-nosed bats, Phyllostomus discolor, had to discriminate between a pure tone stimulus and a sinusoidally frequency-modulated signal generated at the same carrier frequency as the tone. Modulation depths of the SFM stimuli were reduced until the animals' performance dropped below the 75%-correct level which was used to determine difference limens for detection of frequency modulation (FMDL). The dependence of FMDLs on modulation and carrier frequency was systematically investigated. For a carrier frequency of 18.5 kHz, average FMDLs increased from 95 Hz at a modulation frequency of 10 Hz to 820 Hz at a modulation frequency of 2000 Hz which corresponds to Weber ratios (2 f/f) of 0.005 and 0.044 respectively. Further, difference limens were found to increase linearly in proportion to carrier frequency throughout a major part (9–74 kHz) of the species' hearing range. In comparison to other mammals, P. discolor has a pronounced capability for frequency discrimination which might be related to the extensive use of individually distinct frequency-modulated communication calls and audio-vocal learning.Abbreviations
FM
frequency modulation
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SFM
sinusoidal frequency modulation
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FMDL
frequency modulation difference limen
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CF
constant frequency
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DLF
difference limen for frequency
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VCO
voltage-controlled oscillator
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SPL
sound pressure level
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WR
Weber ratio |
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Keywords: | Frequency discrimination Hearing Psychoacoustics Operant conditioning Chiroptera |
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