Description
- Abstract:
- Echolocating bats form an acoustic image of their world derived from echoes of their emitted sounds. In their natural environment, bats must avoid interfering clutter echoes from vegetation and potential jamming from other bats' sound-echo pairs. This dissertation investigates how big brown bats (Eptesicus fuscus) deal with two major perceptual difficulties, clutter rejection and jamming avoidance. In the first experiment, analysis of the sounds of bats flying in the field and in a laboratory flight room supported a jamming avoidance response (frequency shift) in bats flying in close proximity to other bats emitting sounds of similar frequency. Next, bats were flown in a flight room to examine how they cope with the broadcast-echo ambiguity that results from dense, range-extended clutter. Bats made small changes in frequency which appeared to segregate the echo streams from successive broadcasts. The final three experiments used a psychophysical paradigm in which the bats were trained to discriminate the delays of echoes. In the third experiment, the time-frequency structure of returning echoes was manipulated in several ways to examine the effect on echo delay acuity. Next, the smallest misalignment of the two main harmonics in echoes that would result in a disruption of acuity, or a defocused delay image, was determined. In the last experiment, a masking paradigm was used to show that defocused echoes of the type used in the previous experiment do not cause masking interference. This dissertation illustrates how small frequency shifts might help bats match echoes to a broadcast and reject background clutter and mismatched echoes. The bat's method for suppressing interference is to disrupt the acuity of delay perception for its images of undesired echoes so that the target of interest is rendered very obvious by the much greater degree of sharpness in its images. This perceptual mechanism can turn small differences in frequency between sounds into a means of "turning off" the salience of other bats' sound-echo pairs, as well as defocusing lowpass filtered clutter echoes.
- Notes:
- Thesis (Ph.D. -- Brown University (2011)
Access Conditions
- Rights
- In Copyright
- Restrictions on Use
- Collection is open for research.
Citation
Bates, Mary E.,
"Perceptual Challenges in Bat Echolocation: Jamming Avoidance and Clutter Rejection"
(2011).
Psychology Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.7301/Z0QZ287F
