Stimulus similarity and retroactive interference and facilitation in monkey short-term memory

Four experiments examined the effects of similarity between the sample and an interpolated stimulus in a modified delayed-matching-to-sample (DMTS) paradigm. Ss were 4 pigtail, 1 cynomolgus, and 2 rhesus monkeys. The basic trial sequence was as follows: (a) A sample was presented, and the response to it was either rewarded or nonrewarded; (b) an interpolated stimulus was presented, and the response to it was either rewarded or nonrewarded; and (c) after a delay interval a choice test was given between the initial sample and a new stimulus, with the sample being correct if it had been initially rewarded and incorrect if it had been initially nonrewarded. When the sample and the interpolated stimulus were associated with opposite outcomes, retroactive interference increased as the similarity of the 2 stimuli increased. When the 2 stimuli were either both rewarded or both nonrewarded, retroactive facilitation was observed so long as the sample and interpolated stimuli were similar along either the relevant or an irrelevent dimension. Test probes involving the interpolated stimulus and a new stimulus revealed asymmetrical interactions such that the interpolated stimulus influenced performance on the initial stimulus more than the initial stimulus altered performance on the interpolated stimulus. (28 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).