The Role of Numerical and Nonnumerical Magnitudes in Pigeons' Conditional Discrimination Behavior

Research on approximate numerical estimation suggests that numerical representations can be influenced by nonnumerical magnitudes. Current theories of numerical cognition differ on the nature of this interaction. The present project evaluated the effect of task requirements on the stimulus control exerted by numerical and nonnumerical magnitudes on pigeons' numerical discrimination behavior. In a series of experiments, we explored the effects of cumulative area and item size on pigeons' numerical discrimination. The effect of cumulative area was assessed by presenting visual displays in which cumulative area and item number were either positively correlated, uncorrelated, or negatively correlated. The effect of item size was evaluated by presenting displays in which the size of individual items was varied across trials. Results confirmed that pigeons' numerical discrimination behavior accorded with Weber's law, a prime indicator of nonsymbolic numerical representation. The results further indicated that pigeons did not use numerical information when nonnumerical magnitudes also provided reliable information to solve the discrimination task. However, task manipulations that rendered the information provided by nonnumerical magnitudes unreliable successfully shifted stimulus control toward numerical magnitudes.