Object-load and feature-load modulate EEG in a short-term memory task.

Behavioral studies have indicated that multiple features of one object can be stored in working memory without additional costs. In contrast, visual search experiments revealed that search for a multi-featured object takes more time than for a single-featured object. We used EEG to differentiate the effect of object-load and feature-load in a short-term memory task. We independently varied the amount of objects and features that had to be memorized. Object-load modulated P3 amplitude during encoding and induced 10 Hz oscillations during the retention interval. Feature-load modulated the P3 during retrieval. Thus, only object-load seemed to influence encoding and retention while feature-load played a crucial role during retrieval. Our results demonstrate that object-load and feature-load influence short-term memory at different stages.