Measuring Working Memory Updating with N-Back Task

The n-back task is usually used to investigate the updating of the working memory [37 (link)]. In this task [15 (link)], participants must decide as accurately and quickly as possible whether each letter matches the one presented in the n-trials before in the sequence (n є {1,2,3}). Each participant performed three conditions of the n-back task (1, 2, 3-back) and a control task (0-back), in which they had to decide whether the presented letter was an “X”. Each condition contained 42 stimuli with 14 targets and 28 non-targets and lasted for 150 s. In each condition, the stimuli presentation was controlled by E-Prime^® software 2.0 (Psychology Software Tools, Sharpsburg, PA, USA), which recorded the response times (RT) and response accuracy. Before the appearance of each stimulus, a black cross appeared on the screen for 500 ms. Then, the stimulus was displayed, and the participants had 3000 ms to respond. The participants responded by pressing one of two keys (yes/no) of the Serial Response Box^TM (Psychology Software Tools, Sharpsburg, PA, USA) with their right or left index fingers. We calculated an accuracy score (score A’) using the following formula: 0.5 + ((hit rate − false alarm rate) × (1 + hit rate − false alarm rate))/(4 × hit rate × (1-false alarm rate)) [38 (link)]. The higher the A’ score, the better the cognitive performance.