Individual differences in motivation and performance

Two dimensions of personality discussed by Broadbent (1958) as important sources of variation in performance were introversion-extraversion and stability-neuroticism. Extraversion was associated with decrements in performance over time and neuroticism was associated with greater decrements following stress. Although it is tempting to propose a single model to account for these effects, what has become clear is that the effects of personality upon performance require multiple levels of explanation. The broad dimensions of personality that are consistently identified from investigator to investigator and shown to be important in different cultures and different times affect behavior in many different ways.

Before reviewing specific effects of personality, it is necessary to consider what are the appropriate dimensions to discuss. Personality researchers can be grouped into those who who study the effect of a single dimension versus those who develop taxonomic models of multiple dimensions. The first approach results in alphabetic organizations of personality traits (ranging from Type A behavior, through Machievelianism to Sensation Seeking) with numerous studies of convergent validity but few studies of discriminant validity. Within the second, multivariate-taxonomic tradition are those most concerned with description and those interested in causal (usually biological) theories. The descriptive taxonomists have agreed that a set of five dimensions can be identified consistently across methods. These "big five" dimensions of self report and peer description have been labeled Surgency, Agreeableness, Emotional Stability, Conscientiousness, and Culture, (Digman, 1990, Fiske, 1949, Goldberg, 1982; McCrae and Costa, 1987; Norman, 1963; and Wiggins, 1979). For the more biologically minded, the theories of Hans Eysenck (1952, 1967, 1981, 1991), Jeffrey Gray (1972, 1981, 1982, 1987), or Jan Strelau (1983, 1985) are appealing descriptions of three fundamental dimensions (Eysenck's Extraversion, Neuroticism, and Psychoticism; Gray's Impulsivity, Anxiety, and Aggression; Strelau's strength of the excitory and inhibitory processes, and balance between these process) that fit within the five factor model [6]. Whether one prefers the three dimensional biological models or the five dimensional semantic descriptions, it is clear that all of these dimensions have substantial genetic loadings and that they are moderately consistent from childhood throughout the life span.[7]

Perhaps because of a greater concern for causal theory among the biologically oriented taxonomists, there has been more research relating introversion-extraversion and stability-neuroticism to performance than there has been for the other dimensions of the "big five". Both of these dimensions may be associated with individual differences in motivational state. Although staying within the two-space defined by Introversion-Extraversion and Neuroticism-Stability, some of the more recent work has examined impulsivity, a component of I/E and anxiety, a component of neuroticism.

Motivational states: Affective valence and intensity

A common assumption when studying human performance is that subjects are alert and optimally motivated. It is also assumed that the experimenter's task at hand is by far the most important thing the subject has to do at that time. Thus, although individual differences in cognitive ability are assumed to exist, differences in motivation are ignored. For compliant college students participating in one of only a few psychology experiments, this assumption might well be true. It is probably less true for psychiatric patients, oil platform workers at the end of their shift, or deep sea divers under several hundred feet of water. Indeed, for almost any subject population of interest it is difficult to believe that the specific experimental task used has an equally powerful motivation effect upon all subjects. In fact, it is possible, even with college students, to show that variations in motivational state are important sources of between subject variation in performance.

Motivational states can be categorized in several different ways. Conventionally, it has been useful to distinguish between the affective direction and the energetic intensity of motivation (Humphreys and Revelle, 1984). More recent work on affective states, however, has suggested that direction may subdivided into positive and negative components (Watson and Tellegen, 1985) and that intensity should be considered in terms of energetic and tense arousal (Thayer, 1989). How these four constructs interrelate is far from clear. Table 1 presents sample adjectives associated with each construct.

Table 1: Adjectives associated with the measurement of affect and arousal

Thayer's dimensions of arousal                  Watson and Tellegen  dimensions of affect       
Energetic Arousal   Tense Arousal       Positive Affect     Negative Affect     
energetic           fearful             alert               nervous             
full-of-pep         jittery             active              jittery             
active              tense               excited             afraid              
wakeful             clutched-up         enthusiastic        scared              
lively              intense             attentive           guilty              
vigorous            (not) quiescent     interested          hostile             
wide-awake          (not) quiet         inspired            distressed          
(not) sleepy        (not) placid        determined          ashamed             
(not) drowsy        (not) still         proud               upset               
(not)  tired        (not) at-rest       strong              irritable           
                    (not) calm                                                  
An alternative four dimensional model of affect and arousal                                                                                 
High Energetic      Low Energy/Tension  High Depression     High Tension        
alert               drowsy              unhappy             nervous             
full-of-pep         dull                gloomy              jittery             
active              placid              blue                afraid              
wakeful             quiet               sad                 tense               
lively              serene              depressed           scared              
aroused             sleepy              angry               guilty              
excited             calm                irritable           surprised           

Affective States

Thayer (1967, 1978, 1989) has discussed four uni-polar dimensions that he groups into two higher order constructs of energetic and tense arousal. He associates energetic arousal with approach behavior and tense arousal with avoidance behavior. Energetic arousal is increased by mild exercise and varies diurnally. Thayer (1989) adopts Gray's hypothesis that approach motivation reflects a sensitivity to cues for reward and that avoidance behavior reflects a sensitivity to cues for punishment. (See also Fowles, 1980).

Matthews, Jones & Chamberlain (1989) report three mood dimensions that are sensitive to external stressors: energetic arousal, tense arousal, and hedonic tone (positive versus negative). They show that energetic arousal is decreased by the administration of Chlorpromazine, Diazepam or sleep deprivation. Tense arousal is increased by pain, or watching TV violence, but is reduced by muscle relaxation.

Watson and Tellegen (1985) have shown that positive and negative affect are independent of each other and can be used in combination to describe many psychopathological conditions. Clark and Watson (1991) recently proposed that differences in positive affect and somatic arousal account for the important distinction between two affective conditions represented by high negative affect, anxiety and depression. They suggest that while depression and anxiety share high negative affect, anxiety also reflects high somatic arousal, and depression represents lack of positive affect.

Energetic arousal

Energetic arousal is a non-directional component of motivation in all of these models of affect. It is also a construct that has been found to be of great heuristic importance in theories of motivation and cognition ever since Broadbent (1958). More importantly, in that individuals seem to differ systematically in their level of energetic arousal, it is a way to link theories of individual differences to theories of behavior.

Even though Corcoran's (1965) definition of arousal as the "inverse probability of falling asleep" is immediately understandable, it is clear that the use of arousal as a construct is problematic. Indeed, some prefer to avoid discussing arousal and use a broader term, energetics, that subsumes many different constructs of motivational intensity and the effects of many environmental stressors (Hockey, Gaillard & Coles, 1986).

Most simply, arousal is a hypothetical construct used to organize the common behavioral effects of exercise, stimulant drugs, sleep deprivation (negatively), time of day, time on task and impulsivity (Anderson, 1990). Each of these separate variables has both a common and specific effect on behavior. Caffeine and amphetamine both make one more alert and able to respond more rapidly and for longer periods of time. Caffeine differs from amphetamine in the locus of its action (post-synaptically versus synaptically) as well as in some peripheral effects (e.g. caffeine induces hand tremor). It is not difficult to demonstrate that different manipulations of arousal have somewhat different effects on the patterning of responses. As an example of a behavioral dissociation, simple reaction time is facilitated by caffeine but is also faster for high impulsives (thought to be less aroused than low impulsives). High impulsives differ from low impulsives in terms of their speed accuracy tradeoff (Dickman and Meyer, 1988) as well as in terms of arousal level.

Sanders (1983) discussed the multiple approaches to the study of stress. One can manipulate the antecedent conditions or examine the physiological consequences. Similarly, there are at least three ways to study the relationship of arousal to performance: 1) by varying the situational demands thought to lead to arousal; 2) by correlating psychophysiological measures to performance; and 3) by correlating self report measures of arousal with performance.

The first approach, manipulations of arousal by the use of stressors such as stimulant drugs, noise, time on task, or time of day, is more commonly used by experimental psychologists. Broadbent's 1971 review suggested that there were common effects for some of these manipulations, but also showed that at least two levels of control processes needed to be invoked to understand all of the effects. A lower level of control associated with executing well learned responses was thought to be sensitive to noise or sleep deprivation and an upper level control process responsible for monitoring the state of the lower level process was thought to be sensitive to alcohol, extraversion, and time on task.

Hockey (1986) has proposed that each manipulation produces its own idiosyncratic state, and that it is a mistake to look for a holy Grail of unified arousal. Several energetics theorists (Gopher, 1986; Mulder, 1986; Sanders, 1983, 1986) have made use of Pribram and McGuinness' (1975) distinction between (phasic) arousal as affecting input processes, (tonic) activation as affecting motor outputs, and effort as an integrative resource allocation mechanism (Figure 2).

2) Levels of control associated with reaction time. Different stages of information processing are affected by different control processes. Modified from Mulder's (1986) revision of Sanders' (1983) model of reaction time.

After reviewing the parallels and differences between physiological measures and psychological manipulations, Broadbent (1971) concluded that "We have therefore no satisfactory physiological reference for the general state which we are discussing, and which we have revealed purely from behavioral studies. In some ways it might have been better therefore to avoid using the term 'arousal' for this behaviorally defined concept, but this would probably do too much violence to the common usage in the literature. The reader should remember however that we are working solely on a psychological level, and that the existence of a physiological concept of arousal is merely an interesting parallel, with no direct contact at present." (p 413). Later he added that "in complicating the theory of arousal we shall need to know more about the functions involved in various tasks; behavioral studies and the physiological attack upon the brain must go hand in hand." (p 447).

The second approach, that of psychophysiological correlates, has proven to be the most difficult. Partly this is due to confusing a within subject concept with between subjects measurement (Venables, 1984). It is also partly due to variations in the time course of different physiological measures. Just as broad motivational constructs affect behavior at different time courses, so do narrow constructs of motivational intensity, (e.g., arousal) have different temporal parameters. EEG measures of arousal have latencies measured in milliseconds while autonomic measures such as Skin Conductance have latencies measured in seconds, and body temperature reflects average levels of metabolic demands during the previous several hours. The disassociations and specific patterning of responses associated with reactions of the hand, the heart and the head (Lacey, 1967) make physiologists particularly cautious whenever they discuss a construct such as generalized arousal.

The third approach is to use self reports of arousal. Thayer (1989) has argued that subjective estimates of energetic arousal are the most likely to be associated with performance. He has also reported that self ratings correlate more with psychophysiological measures than the measures do themselves. This is what would expect if each psychophysiological measure had specific as well as general effects, and if subjective awareness of arousal reflected the general effects.

Matthews (1989) and his colleagues (Matthews, et al., 1989) have done some of the most extensive work examining the relationship between self reported mood and performance. They have found consistent, although complicated, relationships between self reports of energetic arousal and performance on a variety of simple and complex detection tasks. In addition, they have found that state measures of self reported arousal interact with trait measures of individual differences in introversion-extraversion to affect performance on these tasks.

The use of the term arousal to encompass phenomena ranging across many orders of temporal magnitude from the milliseconds of the early stages of the evoked potential (Mulder, 1986) to the effects of 10 minute brisk walks (Thayer, 1989) to the tendency to seek out stimulation throughout a lifetime (Zuckerman, 1991) is thought by many to be a mistake. I disagree. I believe that the concept that changes in resource availability are associated with changes in arousal allows one to integrate the effect on cognitive performance of stable personality traits with those of variety of environmental manipulations. This model has great heuristic value, for it allows an integration of seemingly unrelated phenomena. Such broad lumping together of disparate effects does indeed mask differences, however. Each task and each measure has its own unique variance as well as common variance. What is important is to try to distinguish the unique from the shared variance. But this is the fundamental challenge of any theory. More