Visual working memory declines when more features must be remembered for each object

The article reports three experiments investigating the limits of visual working memory capacity with a single-item probe change detection paradigm. Contrary to previous reports (e.g., Vogel, Woodman, & Luck, Journal of Experimental Psychology. Human Perception and Performance, 27, 92-114, 2001), increasing the number of features to be remembered for each object impaired change detection. The degree of impairment was not modulated by encoding duration, size of change, or the number of different levels on each feature dimension. Therefore, a larger number of features does not merely impair memory precision. The effect is unlikely to be due to encoding limitations, to verbal encoding of features, or to chunk learning of multifeature objects. The robust effect of number of features contradicts the view that the capacity of visual working memory can be described in terms of number of objects regardless of their characteristics. Visual working memory capacity is limited on at least three dimensions: the number of objects, the number of features per object, and the precision of memory for each feature.