This question talked about how a "delayed match-to-sample task" can be used to measure an animal's working memory. What is a delayed match-to-sample task and how can it be used to measure working memory?
This kind of task is generally used when studying short-term memory. Typically, a subject is presented with some stimuli, followed by a probe item after a varying delay; subjects is then asked to recall (information retrieval) if the probe item was presented before (information encoding). A famous example is Sternberg experiment.
Such tasks can rely on non-verbal material, which makes them good candidates for behavioral studies with animals, but see
Paule MG, Bushnell PJ, Maurissen JP, Wenger GR, Buccafusco JJ, Chelonis JJ, Elliott R. Symposium overview: the use of delayed matching-to-sample procedures in studies of short-term memory in animals and humans. Neurotoxicol Teratol. 1998 Sep-Oct;20(5):493-502.
Some on-line demonstration can be found on the CANTAB testing battery: Delayed Matching to Sample (DMS).