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First published online November 17, 2006
Journal of Experimental Biology 209, 4802-4808 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02574

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Lack of generalization of object discrimination between spatial contexts by a bat

Kai Petra Stich^1,* and York Winter^1,2,*,

¹ Max-Planck Institute for Ornithology, Seewiesen, Germany
² Department of Biology, University of Munich, Germany

Author for correspondence (e-mail: york.winter{at}uni-bielefeld.de)

Accepted 2 October 2006

Discrimination and generalization are important elements of cognition in the daily lives of animals. Nectar-feeding bats detect flowers by olfaction and probably vision, but also use echolocation and echo-perception of flowers in immediate target surroundings. The echo received from an interference-rich flower corolla is a function of a bat's own relative position in space. This raises the question how easily a free-flying bat will generalize an echo stimulus from a learning situation to a new spatial context where differences in relative flight approach trajectories may lead to an unfamiliar spectral composition of the self-generated echoes. We trained free-flying Glossophaga soricina in echoacoustic discrimination in a two-alternative forced-choice (2-AFC) paradigm at location A. We then tested at location B for spontaneous transfer of discrimination ability. Bats did not spontaneously transfer the discrimination ability acquired at A to location B. This lack of spontaneous generalization may have been caused by factors of the underlying learning mechanisms. 2-AFC tasks may not be representative of the natural foraging behaviour of flower-visiting bats. In contrast to insect-eating bats that constantly evaluate the environment to detect unpredictable prey, the spatial stability of flowers may allow flower visitors to rely on spatial memory to guide foraging. The 2-AFC task requires the disregard (learned irrelevance) of salient spatial location cues that are different at each new location. In Glossophaga, a conjunction between spatial context and 2-AFC discrimination learning may have inhibited the transfer of learned irrelevance of spatial location in the 2-AFC task to new spatial locations. Alternatively, the bats may have learnt the second discrimination task completely anew, and were faster only because of an acquired learning set. We suggest a dissociation between 2-AFC task acquisition and novel object discrimination learning to resolve the issue.

Key words: generalization, object discrimination, learning set, cognition, echo location, two-alternative forced-choice, context specific learning, spatial, bat

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