Delayed matching to sample: the effects of sample-set size on human performance

The discriminative performance of students was assessed on a delayed-matchi ng-to-sample task (DMST) using disks, presented by a computer, as stimuli. The size of the non-matching comparison stimuli was changed, for each parti cipant, until each was 100% correct at 0.05 s delay. Then delays of 0.05, 2 , 4, 8 and 16 s were paired with each of one, four, eight, 16, and 32 sampl e stimuli. Accuracy generally decreased over the one, four and eight sample s, did not change consistently over the largest sample-set sizes and decrea sed as delay increased. Both delay and sample-set size had statistically si gnificant main effects, their interaction was not significant. Fitted expon ential functions gave a measure of discrimination at zero delay, a, and a m easure of the rate of decrement in performance with increasing delay, b. As number of sample stimuli increased there was no systematic change in b, wh ile a decreased most over one to four samples, decreased less with eight sa mples, and decreased least from 16 to 32 samples. These results suggest tha t the effects of varying sample-set size depends on the range of sizes stud ied, thus, they provide a possible explanation for some previous disparate findings. They also suggest that it might be proactive interference that le ads to decreases in accuracy with increasing sample-set size. (C) 2000 Else vier Science B.V. All rights reserved.