Hans is clever after all : large number discrimination and intuitive statistics in domestic horses (Equus caballus)
The current study should, first, answer the outstanding question whether domestic horses can discriminate not only small but large discrete quantities as well, using a discrimination task between two different-sized sets of food items. Second, this study examined basic statistical reasoning in horses. Subjects had to choose between two one-item samples drawn from two visible distributions of stones and food items. In both tests horses showed a mean success rate significantly above chance level. A third experiment controlled for use of olfactory cues where mean success rate was at chance level, thus excluding this explanation. Therefore, this study proves large number discrimination in horses and is a first indicator that the ability to make inferences about single-event probabilities is not exclusive to higher primates.
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