One way to organize the results I have presented was adapted by Mike Humphreys
and me from work done by Broadbent (1971), Simon Folkard (1975), Robert Hockey
(1979) and others. In brief, Humphreys and I suggested that increases in both
effort and arousal facilitate the ability to sustain rapid rates of information
transfer but that arousal also inhibits some aspect of short term or working
memory (Humphreys and Revelle, 1984). More recently we have proposed that
although arousal inhibits immediate availability, it facilitates longer term
availability in memory. Furthermore, we suggested that impulsivity interacts
with time of day and time on task to affect arousal, and that achievement
motivation and anxiety interact with rewards and punishments to affect on task
effort.
I like to explain the arousal effects on the rate of information transfer as
well as on memory by analogy to increasing the internal "tick rate" of a
computer. A faster clock speed will lead to more samples of the environment
taken per unit time, which will in turn lead to faster reaction times.
However, increasing the tick rate (taking more samples of the environment) also
will function to change the background context more rapidly. This will lead to
greater difficulties in immediate recall, but will facilitate delayed recall.
What complicates the relationship between stable measures of personality and
performance across situations has been summarized by Rabbit "the human
cognitive system is designed for flexibility, and can carry out any particular
task in many different ways" (Rabbit, 1986, p 155). Indeed, not only do
different people do the same task in different ways, the same people do the
same task in different ways. Motivation can be seen as a control process,
altering the parameters of the cognitive system so as to execute responses most
efficiently. Individual differences reflect higher order rates of change in
these parameter settings (see also Sanders, 1983,1986).
Consider the results from our three reaction time studies. All subjects could
do the task most of the time. Increased incentive or caffeine induced arousal
improved performance. As the task continued, although the fastest responses
remained about the same, some responses were much slower, reflecting an
occasional lapse of attention. High impulsives in the morning and high
neurotics throughout the day were particularly sensitive to this loss of
attention. Incentives were unable to inhibit the decay across time, but
caffeine was able to inhibit the decay. We interpret this result as suggesting
that while effort can improve immediate performance, effort alone is unable to
sustain performance. That is, in a constrained situation, one is unable to
will oneself awake. But at a higher level, effort can increase alertness. As
anyone knows who has struggled to overcome jetlag, drive long distances, or
write an overdue paper by staying up all night, given the proper incentives one
chooses activities that lead to alertness (e.g., stands up, takes brisk walks,
or consumes large doses of caffeine). Thus, we are forced to add a higher
level control process (Figure 5) to the two proposed by Broadbent (1971) or the
hierarchy of resource pools proposed by Mulder (1986) and Sanders (1983, 1986).
5) Broadbent's two levels revisited. Higher order controls adjust the level
of arousal. Although effort can not directly overcome the effect of
inappropriate arousal without the ability to engage in behaviors that modify
arousal, a higher order control process can recognize inappropriate arousal
levels and strategically seek out or avoid arousal inducing behavior. Adapted
from Broadbent, 1971
In 1958 Broadbent organized his discussion of individual differences around
the personality and learning theories of Hans Eysenck and Kenneth Spence.
Extraverts were thought at the time by Eysenck to have stronger reactive
inhibition processes, and anxious individuals were thought to have higher
levels of Hullian drive. Although the dimensions of introversion-extraversion
and stability-neuroticism have remained important, a great deal has changed in
the past 33 years in terms of our theoretical understanding of these
dimensions. A particularly compelling model may be derived by integrating the
neurobiology model of Jeffrey Gray (1972, 1982, 1987) with the multiple
dimensional models of affect of Watson and Tellegen (1985) and Thayer (1989)
(Figure 4). An adequate model needs to integrate differences in affective
reactions to feedback with differences in rates of learning and differences in
performance. Such a model will certainly include the dimensions of
impulsivity-extraversion-surgency and anxiety-emotionality as well as the
behavioral differences observed under different stress manipulations on
different types of tasks. It will also include multiple levels of control
processes and will need to account for individual differences in reactions to
many different kinds of stressors. Although such a model will be more complex
than the ones proposed by Broadbent (1958, 1971), an adequate model will owe a
great deal to the pioneering work of Donald Broadbent. It has been his
willingness to consider individual differences in models of cognitive
performance that has layed the foundation upon which future theories may be
built.
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