Abstract
What determines individual differences in working memory (WM)? Previous research has suggested that WM performance is largely explained by cognitive abilities such as attentional control. However, it is less clear how strategy use accounts for variation in WM performance. Here we explored factors that underlie individual differences in the optimal encoding strategy. In Experiment 1, two displays alternated repeatedly in a flicker paradigm until participants localized a changing item (target). Importantly, there were two targets (one red and one blue), and participants only had to report one target. The ratio of red to blue items varied on each trial. Therefore, to maximize speed, the optimal encoding strategy is to select/encode items in the smaller colour subset. Although choosing the optimal (small subset) target led to faster performance, there were large individual differences in strategy, with some participants frequently reporting the optimal target, and some reporting this target half of the time. Results further showed no relationship between optimal strategy use and visual WM capacity. Experiment 2 tested whether explicit awareness explains strategy use. We found that providing explicit information on the optimal strategy led to a sudden, large increase in optimal target choice. Open-ended reports also showed that participants who were aware of the optimal strategy were more optimal. Experiment 3 further examined whether increasing task difficulty is sufficient to motivate the optimal strategy. In the “one-shot” variant of our paradigm, the displays were presented only once, thus placing a premium on using the optimal strategy to achieve high accuracy. However, strategy use was still sub-optimal; participants did not always selectively encode the small subset. Taken together, results suggest that strategy and ability produce distinct contributions to task performance. Moreover, explicit knowledge, but not greater task demands, leads to a shift to the optimal encoding strategy.