Theoretical organization of results

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.

Motivation as a control process.

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

Theories of individual differences

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.