Relational responding by eastern box turtles (Terrapene carolina) in a series of color discrimination tasks

Prior work with chelonians has demonstrated their capacity for successful performance in cognitive tasks, including those requiring color discrimination. Here, we sought to expand on historical research and determine whether eastern box turtles (Terrapene carolina) are capable of not only making simple color discriminations but also whether they can demonstrate abstract concept formation evidenced by using a relational response rule in their discrimination performance. Two eastern box turtles were rapidly and successfully trained on a black-and-white two-choice discrimination task using painted paddles and food reinforcement. After mastery, a medium gray paddle was added as a choice stimulus and turtle "Flippy" was reinforced for selecting the darker of the 2 stimuli presented in each trial, and turtle "Mario" was reinforced for selecting the lighter of the paddles presented. Nonreinforced probe trials incorporating light and dark gray stimuli paired with all other color options were then added to each session to test the turtles' ability to use the relationship between choice stimuli to guide responding. The turtles successfully selected the paddles corresponding to their assigned relational response rule of "darker" or "lighter" at a level significantly above that predicted by chance. The turtles then demonstrated immediate generalization of their relational rule in testing with a novel array of blue paddles. Finally, the turtles continued to use their relational rule when presented with a novel array of green paddles in a traditional transposition task. Together, these findings support the capacity for higher order cognitive functioning in chelonians beyond that previously described.