Twelve young and 11 elderly men (mean ages 21.1
and 70.1) performed a choice-reaction time (RT) task in
which stimulus degradation and stimulus–response
(S-R) compatibility were manipulated. The extant literature
has suggested that the effects of age on RT are usually
augmented (multiplicative) in more difficult task conditions,
but also that the effects of age on the latency of the
P300 component of the event-related brain potential (ERP)
are constant (additive). The results indicated that the
effects of age on RT were enhanced in more difficult conditions,
whether the difficulty consisted of stimulus degradation
or S-R incompatibility. However, the effects of age on
P300 latency were enlarged as the stimuli were degraded,
but not if the S-R mapping was incompatible. Thus, it appears
that task content determines if effects of age on P300
latency are additive or multiplicative. A simple model
is proposed that produces the obtained pattern of effects.