Neural signs of flexible categorization: evidence from the flexibility of inclusion of humans in animal/non-animal categorization.

The temporal course of the human brain dealing with flexible categorization was analyzed by using an event-related potential (ERP) technique in an animal/non-animal categorization task in two parallel experiments. Participants shown animal, person, mixed and non-animal images were asked if they saw 'animals' after being instructed to exclude humans in the category of 'animals' in Experiment 1, while they were told to define humans as animals in Experiment 2. The ERP data analysis showed that targets elicited larger P150 amplitudes than non-targets, which may reflect early perceptual detection and selection. Images including humans (person and mixed images) elicited larger anterior N2 amplitudes than animal images, regardless of the polysemy of the animal category, which may reflect an extra load on attention and monitoring processes in flexible categorization. Compared to non-targets, targets elicited larger P3 amplitudes, which may be associated with the categorical decision process.