Abstract
The capacity of visual short-term memory (VSTM) is severely limited to about four or fewer items. Because of this limitation, it is important to understand whether we can accurately control the contents of VSTM through top-down and/or bottom-up control processes. To test this, subjects were presented with displays containing targets, marked by a distinctive cue, and distractors. If subjects are poor at controlling the contents of VSTM, distractors should intrude into memory, causing a high false-alarm rate.
When to-be-remembered items were presented sequentially, distractors were encoded into VSTM, suggesting that control processes fail to limit or purge VSTM of distractors. Distractors were encoded at both easy and hard setsizes, suggesting that memory load theory does not modulate distractor processing. Confidence ratings showed that subjects were similarly confident about their memories for targets and distractors. However, distractor memory traces were relatively short-lived, as assessed by a surprise recognition memory test at the end of the experiment. In contrast to these findings, distractors were not encoded into VSTM when to-be-remembered items were presented simultaneously. We speculate that control processes fail in sequential VSTM because visual transients cause unselective and automatic encoding of stimuli. Once stimuli are encoded, control processes have only limited success in managing the contents of VSTM.