Change Detection Task

The change detection task (Luck & Vogel, 1997) is the standard laboratory measure of visual working memory (VWM) capacity. On each trial participants view a brief memory array of colored squares (the memory display), followed by a blank retention interval. A test display then appears with the squares in the same positions — either identical or with one square changed to a different color. Participants respond S (same) or D (different).

Performance is summarized as Cowan's K (Cowan, 2001): K = N × (H + CR − 1), where N is set size, H is the hit rate (correct 'different' responses on change trials), and CR is the correct-rejection rate (correct 'same' responses on no-change trials). K estimates how many items are held in VWM at a given set size. Averaging or fitting K across set sizes 2, 4, 6, and 8 gives a reliable estimate of individual VWM capacity, which typically plateaus at 3–4 items in young adults and declines with age, fatigue, and cognitive load.

VWM capacity is robustly correlated with fluid intelligence, reading comprehension, and attentional control (Cowan et al., 2005; Vogel & Machizawa, 2004), making this task widely used in cognitive and clinical research. The task demands no speed — accuracy is the sole measure — which reduces performance variability from motor speed differences and makes the task suitable for clinical populations, older adults, and online testing.