Orienting attention to locations in mental representations

Abstract

Many cognitive processes depend on our ability to hold information in mind, often well beyond the offset of the original sensory input. The capacity of this visual short-term memory (VSTM) is limited to around three to four items. Recent research has demonstrated that the content of VSTM can be modulated by top-down attentional biases. This has been demonstrated using retrodictive spatial cues, termed "retro-cues," which orient subjects' attention to spatial locations within VSTM. In the present article, we tested whether the use of these cues is modulated by memory load and cue delay. There are a number of important conclusions: (1) Top-down biases can operate on very brief iconic traces as well as on older VSTM representations (Exp. 1). (2) When operating within capacity, subjects use the cue to prioritise where they initiate their memory search, rather than to discard uncued items (Exps. 2 and 3). (3) When capacity is exceeded, there is little benefit to top-down biasing relative to a neutral condition; however, unattended items are lost, with there being a substantial cost of invalid spatial cueing (Exp. 3). (4) These costs and benefits of orienting spatial attention differ across iconic memory and VSTM representations when VSTM capacity is exceeded (Exp. 4).

Figure 1

A trial order schematic (Experiment 1), for two trials with informative spatial retro-cues and one neutral trial. The upper two trial schematics show probe present trials, the lower schematic shows a probe absent trial.

Figure 2

Results from Experiment 1: the upper panel shows d prime scores for valid and neutral trials across the SOAs. The lower panel shows reaction times (RT) for the same comparison. In all cases the error bars show the standard error of the mean.

Figure 3

Results from Experiment 2: the upper panel shows d prime scores for valid, neutral and invalid trials across the SOAs. The lower panel shows RT for the same comparison. In both cases the error bars show the standard error of the mean.

Figure 4

A trial order schematic (Experiment 3), showing trials across three levels of load and three levels of cue-validity. The upper two schematics are probe present trials, the lower schematic is a probe absent trial.

Figure 5

Results from Experiment 3: the upper-left panel shows d prime across load, for the three levels of cue validity; the upper-right panel shows K estimates (proportion of hits minus proportion of false alarms, multiplied by load), for the same comparison; the lower panel shoes RT for the same comparison. In all cases the error bars show the standard error of the mean.

Figure 6

Results from Experiment 4: the upper two panels show d prime across the two levels of load, for iconic memory (left) and VSTM (right) SOAs, with the three levels of cue validity; the middle two panels show the same comparison for K estimates (the proportion of hits minus proportion of false alarms, multiplied by load); the lower two panels show the same comparison for mean RT. In all cases the error bars show the standard error of the mean.