The effect of processing load on loss of information from short-term memory

We report an experiment in which we varied the nature of the articulatory suppression task being performed during a filled retention interval in serial recall. During the retention interval participants performed one of three computer-paced colour naming tasks designed to prevent subvocal rehearsal: A Stroop color-interference task with items presented at a rate of one every 750 ms, and two color-consistent control tasks at a rate of either 750 ms or 500 ms per item. Memory performance over a 12 s interval declined much more dramatically with the Stroop task and the 500 ms control task than with the 750 ms control. There was no difference between the Stroop condition and the 500 ms control. These results pose problems for models that assume that loss of information from memory is determined entirely by interference, as there are more interfering events in the control 500 ms condition than the 750 ms Stroop. They also pose problems for models relying solely on time-based decay and articulatory rehearsal because all three conditions should block rehearsal and produce equivalent performance. The results illustrate that articulatory suppression tasks are not all equivalent, and suggest that the rate of decay from short-term memory is strongly influenced by the resource demands of concurrent processing.