| Aging has been associated with a decline in executive functions. The ability to switch between tasks is thought to require executive processes. Given that aging has been associated with relative sparing of semantic memory and relative decline in episodic memory, it was hypothesized (a) that older subjects would be slower than their younger counterparts when switching to an episodic task, and (b) that brain activation would be different in both groups. Event Related Potentials (ERP) and Reaction Times (RT) were measured in a cued task-switching paradigm where subjects had to switch between two semantic and two episodic tasks. As expected, episodic tasks were slower than semantic tasks and switch trials were slower than repeat trials in both groups. The absence of group RT differences was probably due to the high functioning status of the elderly participants. Contrary to expectations, episodic switch costs were smaller than semantic switch costs in both groups. As expected, the cue-locked waveform was characterized by a preparatory like negativity. Although the two groups' ERP waves had similar shapes, only the young group had significant condition effects. A significant N400 attenuation to the semantic repeat condition relative to the episodic repeat and switch conditions was interpreted as an index of task-set facilitation. As expected, target-locked activity was characterized by a larger P300 following repeat trials compared to switch trials and was interpreted as more efficient processing of repeat than switch trials. The results are discussed in relation to various task-switching models and in relation to aging and executive processes. |
