Abstract:
There is much evidence to support an age-related decline in source memory
ability. However, the underlying mechanisms responsible for this decline are not well
understood. The current study was carried out to determine the electrophysiological
correlates of source memory discrimination in younger and older adults.
Event-related potentials (ERPs) and continuous electrocardiographic (ECG) data
were collected from younger (M= 21 years) and older (M= 71 years) adults during a
source memory task. Older adults were more likely to make source memory errors for
recently repeated, non-target words than were younger adults. Moreover, their ERP
records for correct trials showed an increased amplitude in the late positive (LP)
component (400-800 msec) for the most recently presented, non-target stimuli relative to
the LP noted for target items. Younger adults showed an opposite pattern, with a large
LP component for target items, and a much smaller LP component for the recently
repeated non-target items.
Computation of parasympathetic activity in the vagus nerve was performed on the
ECG data (Porges, 1985). The resulting measure, vagal tone, was used as an index of
physiological responsivity. The vagal tone index of physiological responsivity was
negatively related to the LP amplitude for the most recently repeated, non-target words in
both groups, after accounting for age effects.
The ERP data support the hypothesis that the tendency to make source memory
errors on the part of older adults is related to the ability to selectively control attentional
processes during task performance. Furthermore, the relationship between vagal tone and ERP reactivity suggests that there is a physiological basis to the heightened reactivity
measured in the LP response to recently repeated non-target items such that, under
decreased physiological resources, there is an impairment in the ability to selectively
inhibit bottom-up, stimulus based properties in favour of task-related goals in older
adults. The inconsistency of these results with other explanatory models of source
memory deficits is discussed. It is concluded that the data are consistent with a
physiological reactivity model requiring inhibition of reactivity to irrelevant, but
perceptually-fluent, stimuli.
