International Journal of Comparative Psychology

Stimulus generalization is a phenomenon in which an animal that is trained to respond to one specific stimulus exhibits a similar but not an identical response when presented with a new similar stimulus. It has been widely demonstrated across a variety of vertebrates. This study investigated stimulus generalization in Western painted turtles (Chrysemys picta), a phenomenon previously rarely studied in turtles. Three turtles were initially trained to criterion in an automated Skinner box on a discrimination task between vertical and horizontal lines. Reward was beef baby food, pumped from a syringe pump. Analysis of the criterion days showed a significant difference between the latencies to the reinforced and unreinforced stimuli, indicating successful discrimination. Following this training, the turtles were tested for stimulus generalization using lines of seven different orientations (from 0 degrees to 90 degrees in 15 degree increments), involving 20 days of testing. The results revealed that response latency varied with the line’s orientation. The fastest latencies were observed for the previously reinforced stimulus and the slowest for the previously unreinforced stimulus, with intermediate response times for the novel intermediate stimuli. This graded pattern formed a generalization gradient, which was best fit by an exponential function (R2 = 0.96). These findings suggest that painted turtles are capable not only of discriminating visual stimuli but also of exhibiting typical stimulus generalization.