Shift Costs of Predictable and Unexpected Set Shifting in Young and Older Adults

The main purpose of the present study was to assess the extent to which mixing costs, predictable shift costs, and unexpected shift costs are subject to the effects of aging. To that end, a modified version of traditional task-shifting experiments was developed, which yielded several new findings. Consistent with the task-set reconfiguration view of set shifting, the costs of an unexpected shift were greater than those associated with a predictable task shift. Mixing costs, predictable shift costs, and unexpected shift costs were all observed to increase with age. The effects of age on predictable shift costs could be explained largely in terms of global slowing, whereas age effects on mixing costs and unexpected shift costs were substantially greater than could be expected on the basis of global slowing alone. Thus, when a more representative form of shift cost was studied, the efficiency of the control processes involved in set shifting turned out to be highly sensitive to the effects of age.