In search of decay in verbal short-term memory

Abstract

Is forgetting in the short term due to decay with the mere passage of time, interference from other memoranda, or both? Past research on short-term memory has revealed some evidence for decay and a plethora of evidence showing that short-term memory is worsened by interference. However, none of these studies has directly contrasted decay and interference in short-term memory in a task that rules out the use of rehearsal processes. In this article the authors present a series of studies using a novel paradigm to address this problem directly, by interrogating the operation of decay and interference in short-term memory without rehearsal confounds. The results of these studies indicate that short-term memories are subject to very small decay effects with the mere passage of time but that interference plays a much larger role in their degradation. The authors discuss the implications of these results for existing models of memory decay and interference.

Figure 1

Interference trial (recent negative; RN) from the recent-probes task. ITI = intertrial interval.

Figure 2

Noninterference trial (nonrecent negative; NRN) from the recent-probes task. ITI = intertrial interval.

Figure 3

Results from Experiment 1 displaying recent negative (RN) and nonrecent negative (NRN) response time (RT) by intertrial interval. The 95% confidence intervals of this plot were based on formulas from Loftus and Masson (1994).

Figure 4

Mean correct response time (RT) results for Experiment 6 in which we either instructed participants to ignore past sets or did not provide any instructions. NRN = nonrecent negative; RN = recent negative. Error bars represent standard error of the mean.

Figure 5

Schematic of two recent negative trials from Experiment 7. Notice that the intertrial interval (ITI) separating the two trials on the left can be a blank 10-s ITI or filled with another trial that lasts for 10 s. In that case, the word golf would be taken from the two-back set. In addition, there were trials when recent negative trials had only a 1-s blank ITI preceding them.

Figure 6

Results from recent-probes task pitting decay against interference. Here we show the results from all the negative trial types. The _1000 or _10000 suffix designates a blank intertrial interval of that length in milliseconds. The two-back designation indicates that the probe word was taken from the two-back set. RT = response time; NRN = nonrecent negative; RN = recent negative. Error bars represent standard error of the mean.

Figure 7

Aggregated data from all experiments. The dashed line with asterisks represents the aggregated data according to delay time across all our studies. The solid line is the linear fit of the effect of delay time on the recent negative–nonrecent negative (RN–NRN) contrast. The dashed line with Xs represents the effect of interference (i.e., taking the two-back probe as the RN probe on the current trial). From the figure one can see the stronger effect of interference compared with time-based decay.