Generalization of 'same-different' classification abilities in bottlenoseddolphins

Two bottlenosed dolphins taught to classify pairs of three-dimensional obje cts as either same or different were tested with novel stimulus sets to det ermine how well their classification abilities would generalize. Both dolph ins were immediately able to classify novel pairs of planar objects, differ ing only in shape, as same or different. When tested on sets of three objec ts consisting of either all different objects or of two identical objects a nd one different object, both dolphins proved to be able to classify 'all d ifferent' sets as different and 'not all different' sets as same, at levels significantly above chance. These data suggest that dolphins can use knowl edge about similarity-based classification strategies gained from previous training to perform successfully in a variety of novel same-different class ification tasks. Visual classificatory abilities of dolphins appear to be c omparable to those that have been demonstrated in primates. (C) 2000 Elsevi er Science B.V. All rights reserved.