Long-term memory and the control of attentional control

Abstract

Task-switch costs and in particular the switch-cost asymmetry (i.e., the larger costs of switching to a dominant than a non-dominant task) are usually explained in terms of trial-to-trial carry-over of task-specific control settings. Here we argue that task switches are just one example of situations that trigger a transition from working-memory maintenance to updating, thereby opening working memory to interference from long-term memory. We used a new paradigm that requires selecting a spatial location either on the basis of a central cue (i.e., endogenous control of attention) or a peripheral, sudden onset (i.e., exogenous control of attention). We found a strong cost asymmetry that occurred even after short interruptions of otherwise single-task blocks (Exp. 1-3), but that was much stronger when participants had experienced the competing task under conditions of conflict (Exp. 1-2). Experiment 3 showed that the asymmetric costs were due to interruptions per se, rather than to associative interference tied to specific interruption activities. Experiment 4 generalized the basic pattern across interruptions varying in length or control demands and Experiment 5 across primary tasks with response-selection conflict rather than attentional conflict. Combined, the results support a model in which costs of selecting control settings arise when (a) potentially interfering memory traces have been encoded in long-term memory and (b) working-memory is forced from a maintenance mode into an updating mode (e.g., through task interruptions), thereby allowing unwanted retrieval of the encoded memory traces.

Keywords: Attention; Executive control; Task switching.

Figure 1

Stimulus setup used in the present experiments. Shown is an endogenous-task trial where participants use the center cue to locate the outer circle with the response-relevant information (i.e., L vs. R), while ignoring the sudden-onset stimulus in the periphery (if presented). For exogenous-task trials, subjects would have to locate the sudden-onset stimulus while ignoring the central-cue information (if presented). Stimuli are not drawn to scale; gray was presented as white on black background, black was presented as red.

Figure 2

Example sequence of exogenous-task trials. Both the post-interruption trial and the maintenance trial contain conflict from the endogenous stimulus, whereas the pre-interruption trial contains no conflict.

Figure 3

Mean RTs as a function of trial type (post-interruption vs. maintenance) and presence of conflict as a function of block context in Experiment 1. In the “pure-exo/pure-endo” condition, participants either performed only the endogenous or only the exogenous task throughout the experiment and conflict could occur in either task. In the “exo/endo” condition they performed the endogenous and the exogenous condition in alternating blocks and conflict could occur for either task. In the “exo/endo-noconflict-only” condition participants performed both tasks in alternating blocks, but conflict could occur only for the exogenous task. In the “exo-noconflict-only/endo” condition participants performed both tasks in alternating blocks, but conflict could occur only for the endogenous task.

Figure 4

Mean RTs as a function of trial type (post-interruption vs. maintenance) and presence of conflict as a function of block context in Experiment 2. The “exo/endo-noconflict-only” and the “exo/endo” conditions were identical to the corresponding conditions in Experiment 1. The “exo/endo-conflict-postinterrupt-only” condition was identical to the “exo/endo” condition, however for endogenous trials conflict could occur only on post-interruption trials.

Figure 5

Mean RTs as a function of trial type (post-interruption vs. maintenance) and presence of conflict as a function of mapping between interruption tasks and primary tasks (1:2 mapping versus 2:2 mapping) for Experiment 3.

Figure 6

Mean RTs and errors as a function of task (exogenous vs. endogenous), trial type (post-interruption vs. maintenance), presence of conflict, and control demands of the interruption task for Experiment 4.

Figure 7

Mean RTs and errors as a function of task (spatial Stroop responses to locations vs. words), trial type (post-interruption vs. maintenance), presence of conflict, block half, and control vs. experimental conditions (pure-location/pure-word vs. alternating location/word) for Experiment 5.