Measurement of trace strength in memory for pictures

Four experiments using a yes-no recognition task with snapshots examined (1) the effect of presenting not one but two items simultaneously, either both targets or both distractors, for a single judgment at a retention test trial; (2) the rate of forgetting; (3) the interaction between retention interval and the exposure duration at acquisition; (4) acquisition as a function of the number of times a picture was presented. In each case performance was assessed by calculating the discriminability index d'. The results supported the hypotheses that trace strength is lognormally distributed, that forgetting is exponential, and that in acquisition trace strength is a linear function of the number of presentations.