QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online August 30, 2006
Journal of Experimental Biology 209, 3599-3609 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02398

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Simon, R. Articles by von Helversen, O. Search for Related Content PubMed PubMed Citation Articles by Simon, R. Articles by von Helversen, O.

Size discrimination of hollow hemispheres by echolocation in a nectar feeding bat

Ralph Simon, Marc W. Holderied and Otto von Helversen^*

University of Erlangen, Institute of Zoology II, Staudtstrasse 5, 91058 Erlangen, Germany

View larger version (54K): [in a new window]   Fig. 1. The apparatus we used for the training experiments. To avoid position learning the central column with 16 spokes and feeders was randomly turning left and right. Only two of the feeders displaying the positive size of hollow hemisphere provided a reward. Two others of the same size and 12 further hemispheres of six different sizes did not provide any reward. Visits to all 16 feeders were logged automatically.

View larger version (23K): [in a new window]   Fig. 2. The size range of hemispheres we used in the experiments and measurements. The marks on the ruler indicate the radius of the respective hemisphere.

View larger version (21K): [in a new window]   Fig. 3. Size discrimination in the training experiments. (A) Relative frequency of unrewarded visits to hollow hemispheres of different sizes, for training experiments with five different positive sizes (r=9, 19, 29, 38.5 and 48.5 mm) and a total of nine bats. The frequencies were calculated and averaged for groups of 100 consecutive unrewarded visits each. The frequency of visits to the unrewarded positive size was set to 100%. Values are means ± s.e.m. The broken line marks the 75% level. Data for up to four individuals were pooled (filled circles: one bat, n=2000; filled squares: two bats; n=1300, 2000; filled triangles: four bats, n=300, 800, 2300, 3100; filled diamonds: one bat, n=2900; open squares: one bat, n=1100). (B) r for 75% discrimination as a function of the radius r. r was measured between the training r and the intercept with the 75% discrimination level, and is always plotted over the smaller value of r. The solid black line gives the linear regression (F1,16=19.65, R2=0.55, P=0.0004), the broken black line gives the linear regression when passing through the origin (F1,17=181.62, R2=0.91, P<0.0001). The 95% confidence intervals are indicated by black dotted lines.

View larger version (29K): [in a new window]   Fig. 4. Echo features of a hollow hemisphere (r=25 mm) for 90 directions (-90° to 90°, in 2° increments) measured at a distance of 20 cm. (A) Relative amplitude. (B) Directional pattern of the impulse response function (white: positive amplitudes; black: negative amplitudes) Edges, 1st, 2nd reflections, see text and Fig. 5D. (C) Spectral directional pattern between 20 and 140 kHz.

View larger version (23K): [in a new window]   Fig. 5. (A) Impulse response of a hollow hemisphere (r=38.5 mm) for an angle of sound incidence of 10° (edges, 1st, 2nd to nth reflections, see text and D). The time gap between first and second reflection (gap1-2) is marked with a grey bar. (B) Duration of the gap between first and second reflection plotted over the radius of the hollow hemispheres. The gaps were measured (black triangles) from the impulse response functions, and calculated (open squares) from Eqn 2 in the text. (C) Relative amplitude of the echoes of hollow hemispheres of different sizes measured from an angle of 10° in a distance of 40 cm (D) Sound reflections within a hollow hemisphere, for a sound source at infinite distance such that incoming and outgoing rays are parallel and assuming that wavelength is small in comparison to the radius.

View larger version (48K): [in a new window]   Fig. 6. Prominent frequency notches in the echo spectrum (20-140 kHz) of different sized hollow hemispheres. (G) Notch frequencies displayed as a function of the reciprocal value of the radius. The shaded area indicates the frequency range of the echolocation call of Glossophaga soricina. (A-F) Spectral directional patterns and spectra (averaged over 13 single spectra from -60° to +60°) of six hollow hemispheres of different sizes. Note that the frequency scale is logarithmic. The arrows indicate the frequency notches. For tone gradation key in steps of 6 dB, see Fig. 4C.

View larger version (15K): [in a new window]   Fig. 7. The 75% discrimination threshold for hemisphere sizes plotted for different echo parameters. (A) Just-noticeable difference in sound pressure level, (B) just-noticeable difference in duration of the time gap between first and second reflection (gap1-2) of the impulse response of the echo and (C) just-noticeable change of the spectrum. Arrowheads indicate the position of the mean (). The black circles mark values derived from Schmidt (Schmidt, 1992).