Putting the elephant back in the herd: elephant relative quantity judgments match those of other species
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The ability to discriminate between quantities has been observed in many species. Typically, when an animal is given a choice between two sets of food, accurate performance (i.e., choosing the larger amount) decreases as the ratio between two quantities increases. A recent study reported that elephants did not exhibit ratio effects, suggesting that elephants may process quantitative information in a qualitatively different way from all other nonhuman species that have been tested (Irie-Sugimoto et al. in Anim Cogn 12:193–199, 2009). However, the results of this study were confounded by several methodological issues. We tested two African elephants (Loxodonta africana) to more thoroughly investigate relative quantity judgment in this species. In contrast to the previous study, we found evidence of ratio effects for visible and nonvisible sequentially presented sets of food. Thus, elephants appear to represent and compare quantities in much the same way as other species, including humans when they are prevented from counting. Performance supports an accumulator model in which quantities are represented as analog magnitudes. Furthermore, we found no effect of absolute magnitude on performance, providing support against an object-file model explanation of quantity judgment.
KeywordsRelative quantity judgment Ratio effects Elephants Accumulator model Object-file model
We would like to thank the Zoo Atlanta elephant care staff, including Nathan Elgart, Kathryn Hunt, Steve Crews, as well as Rebecca Snyder and Megan Wilson. This work was approved by the Georgia Tech (A10040) and Georgia State University (A11028) IACUC as well as the Zoo Atlanta Scientific Review Committee. This work was supported in part by NICHD Grant P01HD060563 and NSF Grant BCS 0924811.
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