Behavioral characteristics of rapid visual categorization learning in domestic chicks

The ability to categorize objects and events is a highly adaptive property common among organisms with different nervous systems. Using a bead floor learning paradigm, we systematically analyzed the parameters that enable the rapid formation of a new visual category in young domestic chicks (Gallus gallus domesticus). In one short training session, newborn chicks successfully learned to distinguish food crumbs from the unfamiliar food-like plastic beads and group the latter into a new category of inedible objects. We found that a critical prerequisite for the category acquisition was the occurrence of several non-reinforced exploratory pecks, which served as a behavioral driver of categorization. The presence of food or previous association of the learning context with food reinforcement was not required for the formation of the new "inedible object" category. Chicks were also capable of forming two categories - edible and inedible objects - simultaneously, demonstrating parallel categorization abilities. Analysis of object features showed that changes in the shape or size of beads interfered with their generalization, whereas changes in color did not disrupt assignment of beads of a new color to a previously existing category. Our results provide an ecologically valid model of rapid visual categorization learning in chicks that allows integration of classical avian categorization paradigms with modern neurobiological methods, thus establishing a powerful framework for analysis of dynamics and neural mechanisms of categorical memory formation in avian species.