The delayed match-to-sample procedure (commonly abbreviated as DMTS) is a modification of the basic match-to-sample procedure (also known as match-from-sample and choice-from-sample), which was first used as early as 1799 (see Weinstein 1941). With the match-to-sample procedure, the subject is presented with a visual sample stimulus and is then also presented with two or more additional comparison stimuli, one of which matches the original stimulus. The subject must then choose the comparison stimulus that matches the original sample stimulus. The subject is usually rewarded for correct matches. With the DMTS procedure, the sample stimulus and comparison stimuli are not presented simultaneously. Instead, there is a delay between the removal of the sample stimulus and the appearance of the comparison stimuli. To begin, the subject is first shown the original sample stimulus for a specified amount of time or until the sample is touched or...