Contralateral delay activity does not reflect behavioral feature load in visual working memory

An ongoing debate in visual working memory research is concentrated on whether visual working memory capacity is determined solely by the number of objects to be memorized, or additionally by the number of relevant features contained within objects. Using a novel change detection task that contained multi-feature objects we examined the effect of both object number and feature number on visual working memory capacity, change detection sensitivity, and posterior slow wave event-related brain potential (ERP) activity. Behaviorally, working memory capacity and sensitivity were modulated as a function of both the number of objects and the number of features memorized per object. However, the Contralateral Delay Activity (CDA) was only sensitive to the number of objects, but not to the number of features. This suggests that while both objects and features contribute to limitations in visual working memory capacity, the CDA is an insufficient mechanism to account for feature level representations.