In this study, 36 middle-aged, healthy subjects (33 males and 3 females) were required to maintain linguistic information (letters) online. The letters called upon different cognitive operations (orthographic; orthographic and phonetic; or orthographic, phonetic and semantic). It was found that online maintenance capacity depends on the cognitive operations associated with the letters and on their serial position. Additionally, the cognitive operation effect on online maintenance was modulated by the serial position.
These data favor a model for WM consisting of a simple holding place where verbal information maintenance depends on what the information is used for. We will discuss an integrated model for online information maintenance that accounts for the serial position effects.