Nonnumerical stimuli exert surprisingly strong behavioral control in an unconstrained numerical discrimination...

Does number exert greater behavioral control during numerical discrimination learning than do nonnumerical properties of multi-stimulus arrays? Existing evidence has yet to provide a clear answer to this question. Therefore, we devised a new method to simultaneously assess the behavioral effects of item number, total item area, and individual item size during numerical discrimination learning in pigeons and people. Critically, no constraints were placed on which aspects of the stimuli were likely to control discrimination behavior. We surprisingly found that the nonnumerical properties of item size and area came to exert greater behavioral control than did the number of items-for both pigeons and people. The similar response patterns of pigeons and people suggest that common cognitive processes may participate in these two different species.