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Object classification by echolocation in nectar feeding bats: size-independent generalization of shape


The nectar-feeding bat Glossophaga can be trained to discriminate two hollow forms, a hollow hemisphere and a paraboloid with the same diameter and depth, in total darkness. During training a saturation level of about 85–90% correct choices or more can be reached within 50–100 visits. To investigate generalization abilities, the bats were tested with pairs of the same shape but of different size. Although no reward was offered, they preferred the hollow sphere (30 mm and 50 mm diameter, but not 18 mm) over the corresponding paraboloids. Thus, the bats were able to generalize some features of the rewarded form and detect them in forms of the same shape but different size. This transposition is remarkable, since the bats could not use absolute spectral characters, but had to pay attention to size-independent features common to hollow hemispheres. Possible cues are the variation of echoes in dependence of different angles of calling direction (constant in spheres, changing with position in paraboloids) and/or the “timbre” of the echoes, i.e. their spectral pattern independent of their absolute pitch

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For intensive and inspiring discussions throughout many years I am grateful to my husband Otto von Helversen. Bernd Ronacher gave valuable help and improved the manuscript. Georg Klump and Wolfgang Wickler gave helpful and critical comments. York Winter, Marc Holderied, Werner Koenigk and Hans Opel gave technical advise and help in all methodological questions. Ralph Simon ran part of the experiments. Maria Bauer prepared the figures. I am grateful to all of them.

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This is the last manuscript that Dagmar von Helversen was able to complete before her death on July 20, 2003. We cherish the memory of a great scientist and a loving and beloved human being. All correspondence relating to this paper should be addressed to: Otto von Helversen, Zoologisches Institut der Universität, Staudtstr. 5, 91058 Erlangen, Germany (e-mail:

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von Helversen, D. Object classification by echolocation in nectar feeding bats: size-independent generalization of shape. J Comp Physiol A 190, 515–521 (2004).

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  • Echo-acoustic object recognition
  • Generalisation
  • Glossophaga
  • Size-independence
  • Spectral structure