Pigeons show same-different conceptualization after training with complex visual stimuli.

Eight pigeons were first trained to peck 1 button in the presence of 16 distinct 4?×?4 arrays of identical pictures and to peck a 2nd button in the presence of 16 distinct 4?×?4 arrays of nonidentical pictures. Later, they were tested with 16 other same and 16 other different stimulus arrays involving untrained pictures. Performance to the testing arrays greatly exceeded chance levels, thus suggesting same-different conceptualization by pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)