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Abstract
The present review focuses on the utility of the amplitude of P3 of as a measure of
processing capacity and mental workload. The paper starts with a brief outline of
the conceptual framework underlying the relationship between P3 amplitude and task
demands, and the cognitive task manipulations that determine demands on capacity.
P3 amplitude results are then discussed on the basis of an extensive review of the
relevant literature. It is concluded that although it has often been assumed that
P3 amplitude depends on the capacity for processing task relevant stimuli, the utility
of P3 amplitude as a sensitive and diagnostic measure of processing capacity remains
limited. The major factor that prompts this conclusion is that the two principal task
variables that have been used to manipulate capacity allocation, namely task difficulty
and task emphasis, have opposite effects on the amplitude of P3. I suggest that this
is because, in many tasks, an increase in difficulty transforms the structure or actual
content of the flow of information in the processing systems, thereby interfering
with the very processes that underlie P3 generation. Finally, in an attempt to theoretically
integrate the results of the reviewed studies, it is proposed that P3 amplitude reflects
activation of elements in a event-categorization network that is controlled by the
joint operation of attention and working memory.