Interference between items stored for distinct tasks in visual working memory

Abstract

The action perspective on working memory suggests that memory representations are coded according to their specific temporal and behavioral task demands. This stands in contrast to theories that assume representations are stored in a task-agnostic format within a "common workspace". Here, we tested whether visual items that are memorized for different tasks are stored separately from one another or show evidence of inter-item interference during concurrent maintenance, indicating a common storage. In two experiments, we combined a framing memory task (memorize a motion direction for continuous direction report) with an embedded memory task (memorize a motion direction for a binary direction discrimination) that was placed within the retention period of the framing task. Even though the temporal and action demands were item specific, we observed two types of interference effects between the items: The embedded motion direction was (1) repulsed away and (2) degraded in precision by the motion direction of the item in the framing task. Repulsion and precision degradation increased with item similarity when both items were concurrently held in working memory. In contrast, perceptual and iconic memory control conditions revealed weaker repulsion overall and no interference effect on precision during the stimulus processing stages prior to working memory consolidation. Thus, additional inter-item interference arose uniquely within working memory. Together, our results present evidence that items that are stored for distinct tasks to be performed at distinct points in time, reside in a common workspace in working memory.

Keywords: Perception and action; Visual working memory.

Fig. 1

Design and results of Experiment 1. a Schematic depiction of an experimental trial of Experiment 1 in the working memory (left) and perceptual (right) condition. In both conditions, subjects first memorized one motion direction (arrows for illustration only) of a random-dot-pattern (RDP) for a continuous report at the end of the trial (framing task). In the embedded task, a second motion direction either had to be memorized for a one second delayed binary discrimination task (working memory condition) or be discriminated directly upon stimulus onset (perception condition). Note that the colors in the trial depiction are for illustrative purposes only. Both RDPs were equally white in the experiment. b Repulsive bias (top) and precision (bottom) of Sample 2 in the embedded task for different levels of similarity (30°, 60°, 90°) and different conditions (working memory, perception). Sample 2 in the embedded task was repulsed by Sample 1 of the framing task in both conditions, as indicated by a shift of the PSE away from the motion direction. This repulsion effect was stronger when Sample 2 was similar to Sample 1 and stored in working memory as compared with when it was dissimilar to Sample 1 and only processed in perception. We also found lower precision (higher SD) for Sample 2 in the working memory compared with the perception condition. This effect, however, was strongly modulated by the motion direction similarity between both samples, indicating that the precision decrease was not due to a general accumulation of noise during the prolonged delay period, but the result of competition between both memory items during concurrent maintenance. Error bars represent within-subject standard errors (Morey, 2008). c Detailed visualization of the repulsive bias including individual subjects’ data. Mean PSE bias was calculated as half the distance between the PSE of trials in which Sample 2 was oriented clockwise relative to Sample 1 (CW) and the PSE of trials in which Sample 2 was oriented counterclockwise relative to Sample 1 (CCW). The figures in c show the mean performance on the direction discrimination task at the level of individual subjects (thin lines). Superimposed is the mean psychometric function (thick line). The dashed line shows the point of subjective equality (PSE) per condition. For CW trials, a shift of the psychometric function to the right indicates repulsion of Sample 2 from Sample 1; for CCW trials, a shift to the left indicates repulsion. (Color figure online)

Fig. 2

Design and results of Experiment 2. a Schematic depiction of an experimental trial of Experiment 2 in the working memory (left) and iconic memory (right) condition. In both conditions, subjects first memorized one motion direction of a random-dot-pattern (Sample 1; arrows only for illustration) for a continuous report at the end of the trial (framing task). For the embedded task, they memorized a second motion direction (Sample 2) for either a one-second delayed (working memory) or an immediate (iconic memory) binary discrimination. Note that the colors in the trial depiction are for illustrative purposes only. Both RDPs were equally white in the experiment. b The results of Experiment 2 replicated the results of Experiment 1 for both repulsive bias (top) and precision (bottom). Specifically, the memory item in the embedded task was repulsed by the memory item of the framing task in both conditions, as indicated by a shift of the PSE away from the motion direction. This repulsion effect was stronger for higher similarity between both samples and for the working memory as compared with the iconic memory condition. The precision of Sample 2 was lower (higher SD) in the working memory than iconic memory condition. This effect, however, was strongly modulated by the motion direction similarity between both samples. Error bars represent within-subject standard errors (Morey, 2008). c Detailed visualization of the repulsive bias including individual subjects’ data. Mean PSE bias was calculated as half the distance between the PSE of trials in which Sample 2 was oriented clockwise relative to Sample 1 (CW) and the PSE of trials in which Sample 2 was oriented counterclockwise relative to Sample 1 (CCW). The figures in c show the mean performance on the direction discrimination task at the level of individual subjects (thin lines) for CW and CCW trials, respectively. Superimposed is the mean psychometric function (thick line). The dashed line shows the point of subjective equality (PSE) per condition. For CW trials, a shift of the psychometric function to the right indicates repulsion of Sample 2 from Sample 1; for CCW trials, a shift to the left indicates repulsion. (Color figure online)