1 Complexity and Working Memory Resources : Task Characteristics Necessitating

The executive functions of human working memory have recently become a common target of investigation, mainly in neuroimaging and patient studies. Those studies have indicated that executive functions are (a) strongly related to the functions of the prefrontal structures, and (b) are required whenever the task reaches a certain level of complexity. However, numerous attempts to operationally define that level of task complexity have resulted in different, and sometimes contradictory hypotheses as to what specific task characteristics necessitate executive control over attentional resources. The experiment reported here attempts to address that issue from a behavioural perspective. A dual task was used and task characteristics which have previously been shown to be of importance in defining task complexity, were varied independently of each other. Several previous neuroimaging and patient studies were used to predict a specific pattern of interference between the two tasks, depending on whether the activation of overlapping brain regions should be expected. Two points are relevant in discussing the results. First, methodologically, they show that neuroimaging results can be successfully used to generate behavioural predictions. Second, conceptually, the results show that one of the previously proposed task complexity features the need to carry out multiple processing operations simultaneously is not sufficient by itself to necessitate executive processes. It is suggested that a task characteristic predictive of executive resources involvement, is the need for alternating between different processes (or schemas) during behaviour a mechanism which was originally proposed to underlie the executive control over attentional resources (Norman and Shallice, 1986).