 A matched to sample procedure is the topic. Matching to sample, matched to sample, just depends on how you talk to. Really matched to sample is a procedure for studying conditional relations and stimulus equivalents. So, can you match to a sample? So it's a procedure for investigating conditional relations or stimulus equivalents. A matching sample trial begins with presenting the organism, the person, the animal, the dog, the cat, the fish, any other animals? You could say pigeon. Pigeon oftentimes. So a matched to sample procedure that you would often see in the lab is presenting a pigeon with a triangle and then the triangle goes dark and then they present multiple stimuli, one of which would be a triangle, maybe another which is a square, and the pigeon needs to choose the triangle in order to earn the reinforcer. That's a traditional matched to sample. You could also teach the pigeon not to match the sample, so you could teach it to choose the one that was not the triangle, but that's irrelevant. The fun things you can do with this is to detect how an organism sees different objects in their environment and what they see other objects as. So, what's the stimulus equivalence and how can we explore that stimulus equivalence?