1) behaviour that occurs in a consistent relation to reinforced behaviour and that, although reinforcers are not explicitly arranged for it, is maintained because it makes reinforcers more likely. For exam le, a stereotyped pattern of drinking is said to mediate spaced responding if, when the pattern is maintained, the next response is more likely to be late enough after the last response that it will be reinforced; or, two different postures held after one or another sample stimulus are said to mediate delayed matching-to-sample if a correct match is more likely when the organism has held the posture since the sample was presented (e.g., it leans to the right after a red but not a green sample and later is more likely to respond to red rather than green if still leaning to the right).

2) On a matching-to-sample task, the comparison stimuli are presented some time after the sample stimuli are turned off. See also matching to sample.