Using eye movements to explore switch costs in working memory.

Updating object locations in working memory (WM) is faster when the same object is updated twice in a row compared to updating another object. In analogy to repetition priming effects in perceptual attention, this object-switch cost in WM is thought of as being due to the necessity to shift attention internally from one object to another. However, evidence for this hypothesis is only indirect. Here, we used eye tracking and a classic model of perceptual attention to get a more direct handle on the different processes underlying switch costs in spatial WM. Eye-movement data revealed three different contributors to switch costs. First, overt attention was attracted initially towards locations of the previously updated object. Second, longer fixation periods preceded eye movements between locations of different objects as compared to (previous and new) locations of the same object, most likely due to disengaging and reorienting focal attention between objects. Third, longer dwell times at the to-be-updated location preceded manual responses for switch updates as compared to repeats, probably indicating increased uncertainty between competing sources of activity after the actual attention shift. Results can easily be interpreted with existing (perceptual) attention models that propose competitive activation in an attention map for target objects.