=+10.14. A matching-to-sample (MTS) task is used by psychologists to understand how other species perceive and use identity relations. A standard MTS task consists of having subjects observe a sample stimulus and then rewarding the subject if it responds to an identical (matching) sample stimulus. Then the psychologist studies the ability of sub- jects to transfer the matching concept to other sample stimuli. Oden, Thompson, and Premack (1988) reported a study in which four infant chimpanzees learned an MTS task with only two training sample stimuli.