2015 年 65 巻 2 号 p. 63-69
Studies on instrumental learning have rarely been conducted with tailed amphibians. This may be due primarily to difficulties in training newts with food rewards. Most previous studies on instrumental learning by newts have employed runways without a distinct discriminative stimulus associated with food. In this study, we trained newts (Cynops pyrrhogaster) with black rings as the discriminative stimuli at close distance (5 cm ahead). Two newts were trained to pass through one ring with a diameter of 8 cm. One newt failed to show evidence of learning (i.e., decreased response time) with 14 sessions of massed trials (4 trials/session). The second newt, however, learned to pass through rings with diameters of 8, 6, 5, and 4 cm. A 20-trial follow-up probe test was conducted with the second newt, in which the 4-cm black ring and a novel red square were presented side by side. The newt did not choose the black ring over the red square in any of the trials, suggesting that neither the black color nor the circle shape drove the newt’s behavior. In a retention test conducted 185 days later, the newt did not pass through the ring of 4 cm at all, suggesting that this behavior was learned but not retained after 6 months. Presentations of distinctive stimuli in close proximity might enhance appetitive instrumental learning by newts, which is otherwise difficult to accomplish using runway apparatuses with no distinctive cues to elicit instrumental behaviors.