Assembling a task space: global determination of local shift costs

Most theorizing on the origin of the costs that are associated with task shifts focuses on local transitions between individual trials. In the present article we argue that this emphasis has resulted in a neglect of more global representational structures, which also determinate shift costs. To substantiate this claim, we employed a set of four tasks that results from a factorial combination of two types of judgment and two judgment-to-response mappings. From previous work it is known that this kind of task combination is associated with a characteristic profile of shift costs as a function of the relation between successive tasks. Previously we have interpreted this profile as an indication of a hierarchically ordered dimensional representation of the two types of judgment and the two judgment-to-response mappings. Such a representation can only be expected to emerge when the two task features, judgment and mapping, vary independently of each other within the same situation. It is shown that the characteristic shift cost profile can indeed only be observed when the performance of any of the four tasks is required in a block of trials. In contrast, with only two tasks occurring in each block of trials, shift costs do not reflect the relation between successive tasks. This finding confirms the importance of global representational structures as a determinant of shift costs beyond local transitions between individual trials.