Role of broadcast harmonics in echo delay perception by big brown bats |
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Authors: | Sarah A Stamper Mary E Bates Douglas Benedicto James A Simmons |
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Institution: | (1) Department of Psychology, Brown University, Box 1853, Providence, RI 02912, USA;(2) Department of Neuroscience, Brown University, Box GL-N, Providence, RI 02912, USA |
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Abstract: | Big brown bats (Eptesicus fuscus) emit frequency-modulated (FM) echolocation sounds containing two principal down-sweeping harmonics (FM1 ~ 55–25 kHz, FM2 ~ 105–50 kHz). To determine whether each harmonic contributes to perception of echo delay, bats were trained to discriminate
between “split-harmonic” echoes that differed in delay. The bat’s broadcasts were picked up with microphones, and FM1 and FM2 were separated with highpass and lowpass filters at about 55 kHz, where they overlap in frequency. Both harmonics then were
delivered from loudspeakers as positive stimuli in a 2-choice delay discrimination procedure with FM1 delayed 3.16 ms and FM2 delayed 3.46 ms (300 μs delay split). Negative stimuli contained FM1 and FM2 with the same filtering but no delay separation. These were presented at different overall delays from 11 down to 3 ms to
measure the bat’s delay discrimination acuity for each harmonic in the split harmonic echoes. The bats determined the delays
of both FM1 and FM2, but performance was overlaid by a broad pedestal of poor performance that extended for 800 μs. Splitting the harmonics by
300 μs appears to defocus the bat’s representation of delay, revealing the existence of a process for recognizing the normally
simultaneous occurrence of the harmonics. |
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Keywords: | Biosonar Echolocation Echo delay perception FM harmonics Auditory template |
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