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Abstract:
Abstract: Behavioral studies have shown increased reaction
times to the first instance of a new task immediately following a
switch from another task. This "switch cost" has been found to be
relatively greater for elderly than for young subjects. We sought
to investigate the physiological correlate of this task-switching
cost by recording high-density (64 channel) event-related
potentials (ERPs). Stimuli were letter-number pairs (e.g. 4G, B7,
3E...) presented centrally. Subjects were required to perform a
letter discrimination task (vowel vs. consonant) for a series of
three stimulus presentations before switching to a number
discrimination task (odd vs. even) for the next three stimulus
presentations. This alternation (AAA BBB AAA...) was then continued
for the duration of the run. This design allowed us to examine the
ERPs to the first stimulus (post-switch), the second stimulus
(nested) and the third stimulus (pre-switch) and to compare
responses to identical stimuli in these different positions. For
stimuli in the second and third positions, a long slow processing
negativity was evident for both young and elderly. However, in the
first position where the switch-cost effect is found behaviorally,
this processing negativity was of lesser amplitude in both age
populations but was relatively more depressed in elderly than young
subjects.
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