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Extraversion and task performance: A fresh look through the workload history lens
Journal of Research in Personality 40 (2006) 432–439 www.elsevier.com/locate/jrp
Extraversion and task performance: A fresh look through the workload history lens 夽 Luz-Eugenia Cox-Fuenzalida ¤, Amanda Angie, Sheri Holloway, Laura Sohl University of Oklahoma, Department of Psychology, 455 West Lindsey Street, Dale Hall Tower 705, Norman, OK 73019, USA Available online 15 February 2006
Abstract This study manipulated workload levels and used a technique examining workload history to test Eysenck’s (1967) theory of extraversion. Participants consisted of 71 undergraduates who had been selected from a larger pool that had completed the Eysenck Personality Inventory. Participants performed an auditory vigilance task while percent correct data were recorded. A repeated measures ANOVA was conducted and results indicated that extraverts and introverts respond diVerently to a sudden decrease in workload level. SpeciWcally, a sudden decrease in workload level resulted in an immediate signiWcant decrement in correct responses for extraverts while the decrement for introverts was minimal. Limitations were discussed and implications for future research were addressed. © 2006 Elsevier Inc. All rights reserved. Keywords: Workload history; Extraversion; Task performance
1. Introduction This study was designed to examine the extent to which manipulating workload levels might be eVective in exploring the theoretical assumptions of extraversion theory. One of the most inXuential theories of extraversion is Hans Eysenck’s. Eysenck (1967) proposed 夽
The authors express their gratitude to the research team from the Personality and Human Performance Lab at the University of Oklahoma for their invaluable assistance in planning the study and assisting with the data collection. * Corresponding author. Fax: +1 405 325 4737. E-mail address: [email protected] (L.-E. Cox-Fuenzalida). 0092-6566/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jrp.2005.02.003
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that behavioral diVerences between introverts and extraverts could be explained in terms of diVerential arousal. According to his theory, extraverts presumably possess lower levels of ascending reticular activating system activity than introverts. Several studies of extraversion have used psychophysiological measures to test Eysenck’s biologically based theory such as: electrodermal activity, electroencephalographic activity (EEG) and evoked potential recordings (see Gale, 1973; Geen, 1976; Stelmack, 1981 for reviews of psychophysiologically based research on extraversion). There has been some inconsistency among the Wndings of the psychophysiological literature because of diVerences in the way many of the studies were conducted (Gale, 1973). The encouraging Wnding, however, is the considerable uniformity in research results in studies that carefully controlled experimental variables, such as task diYculty (Gale, 1973; Stelmack, 1981). Indeed, considerable psychophysiologically based research has generally been supportive of extraversion theory (Amelang, 1991; Eysenck & Eysenck, 1985; Gale, 1973; Matthews & Gilliland, 1999; Stelmack & Wilson, 1982). The hypothesized diVerence in arousal levels between introverts and extraverts is believed to underlie the diVerences observed between these groups in their responses to the environment and on human performance tasks. For example, classical conditioning studies were among the Wrst empirical tests of Extraversion arousal diVerences mediated by responses to environmental stimuli. They established a link between extraversion, arousal, and conditioning, and demonstrated how higher levels of arousal associated with introversion facilitate conditioning (Eysenck, 1981; Franks, 1957; Strelau, 1997; Wilson, 1978). SpeciWcally, the higher arousal of introverts (combined with the understanding that higher arousal facilitates conditioning Franks & Laverty, 1955; Franks & Trouton, 1958; Willett, 1960) enables them to develop conditioned responses faster and better than extraverts (Eysenck, 1981). It is important to note, that the eVects of personality on conditioning may be moderated by situational contexts (e.g., task and/or situational variables). For example, Levey and Martin (1981) reported that the superior conditionability of introverts disappears when stimuli are intense. Eysenck’s theory is applicable to performance tasks that involve more than one level of diYculty (and/or arousal). Past research using performance tasks has enabled researchers to use well-known relationships, such as the inverted-U relationship between stimulus intensity and performance (Broadbent, 1965; Malmo, 1957), to explore the hypothesized diVerences between introverts and extraverts. For example, studies have identiWed signiWcant diVerences between introverts and extraverts in their cognitive performance, particularly memory. Eysenck’s theory predicted that introverts (who are more highly aroused than extraverts) should perform better on long-term memory tasks but poorer on short-term memory tasks, as compared to extraverts (Eysenck & Eysenck, 1985). SpeciWcally, higher arousal levels are believed to result in longer active memory traces enabling greater consolidation and enhanced long-term memory (Walker, 1958). Although, there are factors that can aVect the relationship between personality and memory (task diYculty, distraction, retention intervals) research has been generally supportive of this hypothesized relationship (Furnham & Allass, 1999; HeVernan, 2001; Howarth & Eysenck, 1968; Osborne, 1972; Wilson, 1978). In addition, verbal performance studies have been used in conjunction with drug-induced arousal to investigate diVerences between introverts and extraverts, and the Wndings from these studies have also been supportive of Eysenck’s extraversion arousal-based theory (Gilliland, 1980; Revelle, Amaral, & TurriV, 1976).
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Vigilance studies have proved to be particularly useful for investigating performance diVerences between introverts and extraverts. Although there has been some variability in the types of vigilance tasks used, they all require participants to detect inconspicuous auditory or visual signals over a relatively prolonged period of time. Although there are important variables that can produce diVerent research outcomes (e.g., strength of stimulus, environmental stressors, rate of signals, etc.), Eysenck’s theory would predict superiority of introverts on most vigilance tasks based on introverts heightened arousal state. The theory suggests that introverts’ higher level of arousal enables them to sustain a heightened level of vigilant attention especially when the task is not particularly stimulating. The prediction that introverts characteristically perform better on vigilance tasks than extraverts has been established with some regularity (Davies, Hockey, & Taylor, 1969; Eysenck, 1967, 1981; Eysenck & Eysenck, 1985; Harkins & Geen, 1975; Koelega, 1992; Krupski, Raskin, & Bakan, 1971; Smith & Maben, 1993; Thackray, Jones, & Touchstone, 1974). Important for the purpose of the present study is that the human performance research on workload history suggests that variations in workload, especially sudden shifts to low workload after sustained levels of high workload, might signiWcantly degrade an individual’s performance (Cumming & Croft, 1973; Cox-Fuenzalida, Swickert, & Hittner, 2003; Goldberg & Stewart, 1980; Matthews, 1986). Although the within-subjects manipulation of workload level has not been previously applied to the study of extraversion, sustained vigilance studies that have investigated performance diVerences between introverts and extraverts might indirectly shed light on the viability of the manipulation of workload levels as a method for investigating extraversion. For example, Keister and McLaughlin (1972) conducted a vigilance study investigating signal detection in each of three consecutive 16-min periods. Their data revealed a signiWcant relationship between extraversion and signals detected per period. The signiWcant relationship resulted from the discrepant scores in the third 16-min period. As predicted, there were no diVerences between introverts and extraverts during the Wrst part of the task. However, toward the end of the task, the performance of extraverts declined markedly, resulting in only 42% signal detection, as compared to 58% for the introverts. Keister and McLaughlin (1972) oVered two conceivable explanations that are reXective of hypothesized diVerential levels of cortical arousal and the accretion and dissipation of inhibition characteristic of introverts and extraverts. An important point might be drawn from this study that serves to demonstrate the utility of manipulating workload levels for the study of extraversion. First, performance diVerences between introverts and extraverts on the vigilance task, which extended over a 48-min period, showed that introverts and extraverts responded to their workload environment in unique ways. In addition, there is a series of studies that have examined contextsensitivity, extraversion and performance (Matthews & Deary, 1998). Although arousal was not manipulated by means of within-subject variations in workload levels in these studies, other manipulations believed to inXuence arousal were employed and introverts were found to perform signiWcantly better than extraverts in de-arousing situations (see Matthews, 1992 for a review of these studies). Based on the work of Keister and McLaughlin (1972) and the context-sensitivity Wndings one could predict that changes in workload levels (which often serve to directly manipulate arousal and may be more representative of many real-world work environments than Wxed workload levels) might also result in diVerential responses for introverts and extraverts. Thus, controlled changes in workload history may provide a new, systematic way to manipulate task-evoked arousal, and therefore enable a more exacting
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examination of arousal-related processes that are believed to be responsible for performance diVerences between introverts and extraverts. Furthermore, the examination of workload history has recently been used successfully to test predictions regarding other arousal-based personality traits such as neuroticism (Cox-Fuenzalida et al., 2003), and may prove fruitful in examining Eysenck’s view of extraversion as well. Finally, because extraverts are known to possess lower levels of arousal in comparison to introverts, we predicted that a change in workload level, speciWcally, a decrease in task demand following a period of high workload, would result in a greater performance decrement for extraverts as compared with introverts. Given the moderately stimulating level of the task at high workload, it is proposed that the shift to a lower and less stimulating level may result in a disadvantage for extraverts (possessing lower arousal levels). 2. Method 2.1. Participants Participants were 71 male and female undergraduate students from the University of Oklahoma, selected from a larger pool of students who had completed the Eysenck Personality Inventory (EPI, Form A; Eysenck & Eysenck, 1968). Those who had completed the EPI were screened to identify the upper and lower 27% of the introversion–extraversion distribution. Participants in the upper 27% were classiWed as extraverts and, and participants in the lower 27% were classiWed as introverts (Cox, 1957). In addition, to minimize the potential arousing inXuence of the limbic system (see Eysenck, 1967) all participants were within one standard deviation of the mean EPI neuroticism score for the original sample. The EPI was used to assess the dimensions of extraversion and neuroticism. EPI reliability for the extraversion scale ranges from .80 to .97. For the present study the internal consistency reliability coeYcient for this scale was .96. The scores from this scale can range from 0 to 21 with higher scores indicating higher levels of extraversion. In the current study the mean of extraversion was 13.31 with a standard deviation of 1.4. The selected participants were contacted by phone to participate in the study. Only three of the contacted individuals declined. Participants received extra credit or academic credit for their participation as one option for the requirements of their psychology courses. 2.2. Materials We used a version of the Bakan (1959) vigilance task, an auditory vigilance task consisting of a series of digits that participants must listen to while attempting to detect odd–even–odd combinations (e.g., 7–8–3). This task required the participants to respond by pressing a key on the computer keyboard when they detected a signal. A total of 10 signals were presented in each three-minute period among a string of random digits for the high and low conditions (225 and 90 digits total, respectively).Workload level was manipulated by changing the speed of signal presentation (i.e., 1 digit per every 0.8 s vs. 1 digit every 2 s). The number of signals was held constant (10) for high and low workload levels, but the total number of digits and the diYculty level varied due to the digit rate presentation. The time-out period for participants’ responses was 4.8 s following the presentation of a signal.
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2.3. Procedure Participants were seated at individual workstations and asked to complete informed consent forms. Participants then completed an 18-min practice session. The practice regimen was patterned after that used by Schlegel and Gilliland (1990), who found that thorough instructions followed by Wve to six, 3-min trials were suYcient to produce asymptotic performance on a variety of human performance tasks. The practice session was followed by an 18-min baseline session used for later comparisons. Five-minute breaks were given between the practice and the baseline trials, followed by a 15-min break before the testing session. During the test session, participants engaged in a 9-min trial at high diYculty followed immediately by a 9-min trial at low task diYculty. The test session was designed so that participants would develop a workload history at one level and then be moved immediately to a very diVerent workload level. In other words, the transition from high to low during the test period was perceived as continuous by participants. Participants were tested between the hours of 9:00 a.m. and 4:00 p.m. to control for time of day eVects (Revelle, Humphreys, Simon, & Gilliland, 1980). 3. Results and discussion For purposes of baseline and test data comparisons, median baseline scores were computed on the dependent measure (correct responses) for each participant. In other words, from the low set of baseline trials, the median trial was selected for comparison to performance on the three (3-min) subsequent test trials. Correct responses consisted of the number of responses made within 4.8 s following signal presentation. The results of a repeated-measures ANOVA revealed a signiWcant treatment (FB D (1, 70) D 9.25, p < .05), and treatment by extraversion vs. introversion interaction (FAB D (1, 70) D 10.57, p < .05). Means for pre-test and post-test extraversion were 9.45, SD .91 and 8.28, SD 1.41, respectively. Means for pre-test and post-test introversion were 9.17, SD 1.56, and 8.92, SD 1.61, respectively. These results (see Fig. 1) indicate that, as expected, extraverts and introverts respond diVerently to changes in workload history. The decrement in performance following a sudden shift is clearly more pronounced for extraverts as compared to introverts. These Wndings suggest that at least for this type of task, individuals higher in extraversion may experience more diYculty adapting to sudden changes than
Percent Correct
10
Extraverts Introverts
9.5 d = 0.22 9 d = -0.42
8.5
8
Pre-test
Post-test
Trial Fig. 1. Pre- and post-test performance diVerences of introverts and extraverts.
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those lower in extraversion. It appears that introverts who are higher in arousal are better able to cope with the transition to lower workload levels more eVectively than extraverts. These Wndings appear consistent with Eysenck’s arousal-based theory and previous research suggesting that introverts’ higher level of arousal enables them to sustain heightened vigilant attention when the task is not particularly stimulating (Davies et al., 1969; Eysenck, 1967, 1981; Eysenck & Eysenck, 1985; Koelega, 1992; Krupski et al., 1971; Smith & Maben, 1993; Thackray et al., 1974). In this study, the vigilance task changes from a high to a low workload. The move from a moderately high to a lower task diYculty produces a suddenly less stimulating situation whereby extraverts (because of their lower levels of arousal) may be disadvantaged. These Wndings may have signiWcant implications for situations in which people are required to perform simple vigilance tasks in dynamic environments. The impact of decrements could be particularly important for safety sensitive occupations. Consider for example, a transportation security agent who must screen luggage for potentially threatening content via an X-ray machine. These airport security personnel operate in dynamic environments as larger or smaller groups of people move through the TSA airport security checkpoints. Given the research Wndings of the present study it would seem prudent to further explore the relationship between personality and workload history in real world occupations. Although this study answers important questions regarding the relationship between extraversion and workload history there are some important limitations of the current study. While the Wndings may appear to support the signiWcant inXuence of extraversion and workload history on performance, the degree of inXuence may not be true for other types of tasks. Consequently, before any conclusions can be drawn regarding applicability of these results to real world jobs, future research should examine generalizability of eVects to simulation tasks. Furthermore, the relationship between extraversion, workload history, and performance may be aVected by additional factors (e.g., time on task, breaks, and distractors). It may prove fruitful to systematically manipulate these variables to gain a better understanding of the generalizability of these Wndings. In sum, the results of this study conWrm and extend previous Wndings regarding performance diVerences between extraverts and introverts. This study suggests that the examination of workload history may be useful for testing extraversion theory, as it provides a systematic method for controlling environmental variables that might inXuence the relationship between extraversion and human performance. Furthermore, the present study may have signiWcant implications for applied settings. References Amelang, M. (1991). Results of a (nearly) comprehensive study of Eysenck’s extraversion theory. Psychologische Beitrage, 33(1–2), 23–46. Bakan, P. (1959). Extraversion–introversion and improvement in an auditory vigilance task. British Journal of Psychology, 50, 325–332. Broadbent, D. E. (1965). A reformulation of the Yerkes-Dodson law. British Journal of Mathematical & Statistical Psychology, 18(2), 145–157. Cumming, R. W., & Croft, P. G. (1973). Human information processing under varying task demand. Ergonomics, 16, 581–586. Cox, D. R. (1957). A note on grouping. Journal of the American Statistical Association, 52, 543–547. Cox-Fuenzalida, L. E., Swickert, R. J., & Hittner (2003). EVects of neuroticism and workload history on performance. Personality and Individual DiVerences, 36, 447–456.
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Davies, D., Hockey, J., & Taylor, A. (1969). Varied auditory stimulation, temperature diVerences, and vigilance performance. British Journal of Psychology, 60, 453–457. Eysenck, H. J. (1967). The biological basis of personality. SpringWeld, IL: Thomas. Eysenck, H. J. (Ed.). (1981). A model for personality. New York: Springer. Eysenck, H. J., & Eysenck, S. B. G. (1968). The Eysenck personality inventory. San Diego: Educational and Industrial Testing Services. Eysenck, H. J., & Eysenck, M. (1985). Personality and individual diVerences. New York: Plenum Press. Franks, C. (1957). Personality factors and the rate of conditioning. British Journal of Psychology, 46, 119–126. Franks, C., & Laverty, S. G. (1955). Sodium amytal and eyelid conditioning. Journal of Mental Science, 101, 654– 663. Franks, C., & Trouton, D. (1958). EVects of amobarbital sodium and dexamphetamine sulfate on the conditioning of the eyeblink response. Journal of Comparative Physiological Psychology, 51, 220–222. Furnham, A., & Allass, K. (1999). The inXuence of musical distraction of varying complexity on the cognitive performance of extroverts and introverts. European Journal of Personality, 13(1), 27–38. Gale, A. (1973). The psychophysiology of individual diVerences: Studies of extraversion and the EEG. In P. Kline (Ed.), New approaches in psychological measurement. London: Wiley. Geen, R. G. (1976). Personality, the skein of behavior. St. Louis: Mosby. Gilliland, K. (1980). The interactive eVect of introversion-extraversion with caVeine-induced arousal on verbal performance. Journal of Research in Personality, 14, 482–492. Goldberg, D. R., & Stewart, M. R. (1980). Memory overload or expectancy eVect? ‘Hysteresis’ revisited. Ergonomics, 23, 1173–1178. Harkins, S. G., & Geen, R. G. (1975). Discriminability and criterion diVerences between extraverts and introverts during vigilance. Journal of Research in Personality, 9, 335–340. HeVernan, T. M. (2001). The impact of Eysenck’s extraversion–introversion personality dimension on prospective memory. Scandinavian Journal of Psychology, 42(4), 321–325. Howarth, E., & Eysenck, H. J. (1968). Personality diVerences in serial learning under distraction. Journal of Experimental Research in Personality, 3, 114–116. Keister, M. E., & McLaughlin, R. J. (1972). Vigilance performance related to extraversion–introversion and caVeine. Journal of Experimental Research in Personality, 6, 5–11. Koelega, H. S. (1992). Extraversion and vigilance performance: 30 years of inconsistencies. Psychological Bulletin, 112(2), 239–258. Krupski, A., Raskin, D., & Bakan, P. (1971). Physiological and personality correlates of commission errors in an auditory vigilance task. Psychophysiology, 8, 304–311. Levey, A. B., & Martin, I. (1981). Personality and conditioning. In H. J. Eysenck (Ed.), A model for personality. Berlin: Springer. Malmo, R. B. (1957). Anxiety and behavioral arousal. Psychological Review, 64, 276–287. Matthews, G. (1992). Extraversion. In Handbook of human performance. London: Academic. Matthews, G., & Deary, I. J. (1998). Personality traits. Cambridge: Cambridge University Press. Matthews, M. L. (1986). The inXuence of visual workload history on visual performance. Human Factors, 28(6), 623–632. Matthews, G., & Gilliland, K. (1999). The personality theories of H.J. Eysenck and J.A. Gray: A comparative review. Personality and Individual DiVerences, 26, 583–626. Osborne, J. W. (1972). Short- and long-term memory as a function of individual diVerences in arousal. Perceptual and Motor Skills, 34, 587–593. Revelle, W., Amaral, P., & TurriV, S. (1976). Introversion/extraversion, time stress, and caVeine: EVect on verbal performance. Science, 192, 149–150. Revelle, W., Humphreys, M., Simon, L., & Gilliland, K. (1980). The interactive eVect of personality, time of day, and caVeine: A test of the arousal model. Journal of Experimental Psychology: General, 109, 1–26. Schlegel, R. E., & Gilliland, K. (1990). Evaluation of the Criterion Task Set-Part I CTS Performance and SWAT Data-Baseline Conditions (U) (Tech. Report AAMRL-TR-90-007). Wright Patterson, Norman, Oklahoma. Smith, A. P., & Maben, A. (1993). EVects of sleep deprivation, lunch, and personality on performance, mood, and cardiovascular function. Physiology and Behavior, 54(5), 967–972. Stelmack, R. (1981). The psychophysiology of extraversion and neuroticism. In H. Eysenck (Ed.), A model for personality (pp. 38–60). New York: Springer. Stelmack, R. M., & Wilson, K. G. (1982). Extraversion and the eVects of frequency and intensity on the brainstem evoked response. Personality and Individual DiVerences, 3, 373–380.
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Strelau, J. (1997). The contribution of Pavlov’s typology of CNS properties to personality research. European Psychologist, 2(2), 125–138. Thackray, R., Jones, K., & Touchstone, R. (1974). Personality and physiological correlates of performance decrement on a monotonous task requiring sustained attention. British Journal of Psychology, 65, 351–358. Walker, E. (1958). Action decrement and its relation to learning. Psychological Review, 65, 129–142. Willett, R. A. (1960). The eVect of depressant drugs on learning and conditioning. In H. J. Eysenck (Ed.), Experiments in personality. New York: Praeger. Wilson, G. (1978). Introversion–extroversion. In H. London & J. E. Exner (Eds.), Dimensions of personality (pp. 217–261). New York: Wiley.
Extraversion and task performance: A fresh look through the workload history lens 夽 Luz-Eugenia Cox-Fuenzalida ¤, Amanda Angie, Sheri Holloway, Laura Sohl University of Oklahoma, Department of Psychology, 455 West Lindsey Street, Dale Hall Tower 705, Norman, OK 73019, USA Available online 15 February 2006
Abstract This study manipulated workload levels and used a technique examining workload history to test Eysenck’s (1967) theory of extraversion. Participants consisted of 71 undergraduates who had been selected from a larger pool that had completed the Eysenck Personality Inventory. Participants performed an auditory vigilance task while percent correct data were recorded. A repeated measures ANOVA was conducted and results indicated that extraverts and introverts respond diVerently to a sudden decrease in workload level. SpeciWcally, a sudden decrease in workload level resulted in an immediate signiWcant decrement in correct responses for extraverts while the decrement for introverts was minimal. Limitations were discussed and implications for future research were addressed. © 2006 Elsevier Inc. All rights reserved. Keywords: Workload history; Extraversion; Task performance
1. Introduction This study was designed to examine the extent to which manipulating workload levels might be eVective in exploring the theoretical assumptions of extraversion theory. One of the most inXuential theories of extraversion is Hans Eysenck’s. Eysenck (1967) proposed 夽
The authors express their gratitude to the research team from the Personality and Human Performance Lab at the University of Oklahoma for their invaluable assistance in planning the study and assisting with the data collection. * Corresponding author. Fax: +1 405 325 4737. E-mail address: [email protected] (L.-E. Cox-Fuenzalida). 0092-6566/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jrp.2005.02.003
L.-E. Cox-Fuenzalida et al. / Journal of Research in Personality 40 (2006) 432–439
433
that behavioral diVerences between introverts and extraverts could be explained in terms of diVerential arousal. According to his theory, extraverts presumably possess lower levels of ascending reticular activating system activity than introverts. Several studies of extraversion have used psychophysiological measures to test Eysenck’s biologically based theory such as: electrodermal activity, electroencephalographic activity (EEG) and evoked potential recordings (see Gale, 1973; Geen, 1976; Stelmack, 1981 for reviews of psychophysiologically based research on extraversion). There has been some inconsistency among the Wndings of the psychophysiological literature because of diVerences in the way many of the studies were conducted (Gale, 1973). The encouraging Wnding, however, is the considerable uniformity in research results in studies that carefully controlled experimental variables, such as task diYculty (Gale, 1973; Stelmack, 1981). Indeed, considerable psychophysiologically based research has generally been supportive of extraversion theory (Amelang, 1991; Eysenck & Eysenck, 1985; Gale, 1973; Matthews & Gilliland, 1999; Stelmack & Wilson, 1982). The hypothesized diVerence in arousal levels between introverts and extraverts is believed to underlie the diVerences observed between these groups in their responses to the environment and on human performance tasks. For example, classical conditioning studies were among the Wrst empirical tests of Extraversion arousal diVerences mediated by responses to environmental stimuli. They established a link between extraversion, arousal, and conditioning, and demonstrated how higher levels of arousal associated with introversion facilitate conditioning (Eysenck, 1981; Franks, 1957; Strelau, 1997; Wilson, 1978). SpeciWcally, the higher arousal of introverts (combined with the understanding that higher arousal facilitates conditioning Franks & Laverty, 1955; Franks & Trouton, 1958; Willett, 1960) enables them to develop conditioned responses faster and better than extraverts (Eysenck, 1981). It is important to note, that the eVects of personality on conditioning may be moderated by situational contexts (e.g., task and/or situational variables). For example, Levey and Martin (1981) reported that the superior conditionability of introverts disappears when stimuli are intense. Eysenck’s theory is applicable to performance tasks that involve more than one level of diYculty (and/or arousal). Past research using performance tasks has enabled researchers to use well-known relationships, such as the inverted-U relationship between stimulus intensity and performance (Broadbent, 1965; Malmo, 1957), to explore the hypothesized diVerences between introverts and extraverts. For example, studies have identiWed signiWcant diVerences between introverts and extraverts in their cognitive performance, particularly memory. Eysenck’s theory predicted that introverts (who are more highly aroused than extraverts) should perform better on long-term memory tasks but poorer on short-term memory tasks, as compared to extraverts (Eysenck & Eysenck, 1985). SpeciWcally, higher arousal levels are believed to result in longer active memory traces enabling greater consolidation and enhanced long-term memory (Walker, 1958). Although, there are factors that can aVect the relationship between personality and memory (task diYculty, distraction, retention intervals) research has been generally supportive of this hypothesized relationship (Furnham & Allass, 1999; HeVernan, 2001; Howarth & Eysenck, 1968; Osborne, 1972; Wilson, 1978). In addition, verbal performance studies have been used in conjunction with drug-induced arousal to investigate diVerences between introverts and extraverts, and the Wndings from these studies have also been supportive of Eysenck’s extraversion arousal-based theory (Gilliland, 1980; Revelle, Amaral, & TurriV, 1976).
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Vigilance studies have proved to be particularly useful for investigating performance diVerences between introverts and extraverts. Although there has been some variability in the types of vigilance tasks used, they all require participants to detect inconspicuous auditory or visual signals over a relatively prolonged period of time. Although there are important variables that can produce diVerent research outcomes (e.g., strength of stimulus, environmental stressors, rate of signals, etc.), Eysenck’s theory would predict superiority of introverts on most vigilance tasks based on introverts heightened arousal state. The theory suggests that introverts’ higher level of arousal enables them to sustain a heightened level of vigilant attention especially when the task is not particularly stimulating. The prediction that introverts characteristically perform better on vigilance tasks than extraverts has been established with some regularity (Davies, Hockey, & Taylor, 1969; Eysenck, 1967, 1981; Eysenck & Eysenck, 1985; Harkins & Geen, 1975; Koelega, 1992; Krupski, Raskin, & Bakan, 1971; Smith & Maben, 1993; Thackray, Jones, & Touchstone, 1974). Important for the purpose of the present study is that the human performance research on workload history suggests that variations in workload, especially sudden shifts to low workload after sustained levels of high workload, might signiWcantly degrade an individual’s performance (Cumming & Croft, 1973; Cox-Fuenzalida, Swickert, & Hittner, 2003; Goldberg & Stewart, 1980; Matthews, 1986). Although the within-subjects manipulation of workload level has not been previously applied to the study of extraversion, sustained vigilance studies that have investigated performance diVerences between introverts and extraverts might indirectly shed light on the viability of the manipulation of workload levels as a method for investigating extraversion. For example, Keister and McLaughlin (1972) conducted a vigilance study investigating signal detection in each of three consecutive 16-min periods. Their data revealed a signiWcant relationship between extraversion and signals detected per period. The signiWcant relationship resulted from the discrepant scores in the third 16-min period. As predicted, there were no diVerences between introverts and extraverts during the Wrst part of the task. However, toward the end of the task, the performance of extraverts declined markedly, resulting in only 42% signal detection, as compared to 58% for the introverts. Keister and McLaughlin (1972) oVered two conceivable explanations that are reXective of hypothesized diVerential levels of cortical arousal and the accretion and dissipation of inhibition characteristic of introverts and extraverts. An important point might be drawn from this study that serves to demonstrate the utility of manipulating workload levels for the study of extraversion. First, performance diVerences between introverts and extraverts on the vigilance task, which extended over a 48-min period, showed that introverts and extraverts responded to their workload environment in unique ways. In addition, there is a series of studies that have examined contextsensitivity, extraversion and performance (Matthews & Deary, 1998). Although arousal was not manipulated by means of within-subject variations in workload levels in these studies, other manipulations believed to inXuence arousal were employed and introverts were found to perform signiWcantly better than extraverts in de-arousing situations (see Matthews, 1992 for a review of these studies). Based on the work of Keister and McLaughlin (1972) and the context-sensitivity Wndings one could predict that changes in workload levels (which often serve to directly manipulate arousal and may be more representative of many real-world work environments than Wxed workload levels) might also result in diVerential responses for introverts and extraverts. Thus, controlled changes in workload history may provide a new, systematic way to manipulate task-evoked arousal, and therefore enable a more exacting
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examination of arousal-related processes that are believed to be responsible for performance diVerences between introverts and extraverts. Furthermore, the examination of workload history has recently been used successfully to test predictions regarding other arousal-based personality traits such as neuroticism (Cox-Fuenzalida et al., 2003), and may prove fruitful in examining Eysenck’s view of extraversion as well. Finally, because extraverts are known to possess lower levels of arousal in comparison to introverts, we predicted that a change in workload level, speciWcally, a decrease in task demand following a period of high workload, would result in a greater performance decrement for extraverts as compared with introverts. Given the moderately stimulating level of the task at high workload, it is proposed that the shift to a lower and less stimulating level may result in a disadvantage for extraverts (possessing lower arousal levels). 2. Method 2.1. Participants Participants were 71 male and female undergraduate students from the University of Oklahoma, selected from a larger pool of students who had completed the Eysenck Personality Inventory (EPI, Form A; Eysenck & Eysenck, 1968). Those who had completed the EPI were screened to identify the upper and lower 27% of the introversion–extraversion distribution. Participants in the upper 27% were classiWed as extraverts and, and participants in the lower 27% were classiWed as introverts (Cox, 1957). In addition, to minimize the potential arousing inXuence of the limbic system (see Eysenck, 1967) all participants were within one standard deviation of the mean EPI neuroticism score for the original sample. The EPI was used to assess the dimensions of extraversion and neuroticism. EPI reliability for the extraversion scale ranges from .80 to .97. For the present study the internal consistency reliability coeYcient for this scale was .96. The scores from this scale can range from 0 to 21 with higher scores indicating higher levels of extraversion. In the current study the mean of extraversion was 13.31 with a standard deviation of 1.4. The selected participants were contacted by phone to participate in the study. Only three of the contacted individuals declined. Participants received extra credit or academic credit for their participation as one option for the requirements of their psychology courses. 2.2. Materials We used a version of the Bakan (1959) vigilance task, an auditory vigilance task consisting of a series of digits that participants must listen to while attempting to detect odd–even–odd combinations (e.g., 7–8–3). This task required the participants to respond by pressing a key on the computer keyboard when they detected a signal. A total of 10 signals were presented in each three-minute period among a string of random digits for the high and low conditions (225 and 90 digits total, respectively).Workload level was manipulated by changing the speed of signal presentation (i.e., 1 digit per every 0.8 s vs. 1 digit every 2 s). The number of signals was held constant (10) for high and low workload levels, but the total number of digits and the diYculty level varied due to the digit rate presentation. The time-out period for participants’ responses was 4.8 s following the presentation of a signal.
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2.3. Procedure Participants were seated at individual workstations and asked to complete informed consent forms. Participants then completed an 18-min practice session. The practice regimen was patterned after that used by Schlegel and Gilliland (1990), who found that thorough instructions followed by Wve to six, 3-min trials were suYcient to produce asymptotic performance on a variety of human performance tasks. The practice session was followed by an 18-min baseline session used for later comparisons. Five-minute breaks were given between the practice and the baseline trials, followed by a 15-min break before the testing session. During the test session, participants engaged in a 9-min trial at high diYculty followed immediately by a 9-min trial at low task diYculty. The test session was designed so that participants would develop a workload history at one level and then be moved immediately to a very diVerent workload level. In other words, the transition from high to low during the test period was perceived as continuous by participants. Participants were tested between the hours of 9:00 a.m. and 4:00 p.m. to control for time of day eVects (Revelle, Humphreys, Simon, & Gilliland, 1980). 3. Results and discussion For purposes of baseline and test data comparisons, median baseline scores were computed on the dependent measure (correct responses) for each participant. In other words, from the low set of baseline trials, the median trial was selected for comparison to performance on the three (3-min) subsequent test trials. Correct responses consisted of the number of responses made within 4.8 s following signal presentation. The results of a repeated-measures ANOVA revealed a signiWcant treatment (FB D (1, 70) D 9.25, p < .05), and treatment by extraversion vs. introversion interaction (FAB D (1, 70) D 10.57, p < .05). Means for pre-test and post-test extraversion were 9.45, SD .91 and 8.28, SD 1.41, respectively. Means for pre-test and post-test introversion were 9.17, SD 1.56, and 8.92, SD 1.61, respectively. These results (see Fig. 1) indicate that, as expected, extraverts and introverts respond diVerently to changes in workload history. The decrement in performance following a sudden shift is clearly more pronounced for extraverts as compared to introverts. These Wndings suggest that at least for this type of task, individuals higher in extraversion may experience more diYculty adapting to sudden changes than
Percent Correct
10
Extraverts Introverts
9.5 d = 0.22 9 d = -0.42
8.5
8
Pre-test
Post-test
Trial Fig. 1. Pre- and post-test performance diVerences of introverts and extraverts.
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those lower in extraversion. It appears that introverts who are higher in arousal are better able to cope with the transition to lower workload levels more eVectively than extraverts. These Wndings appear consistent with Eysenck’s arousal-based theory and previous research suggesting that introverts’ higher level of arousal enables them to sustain heightened vigilant attention when the task is not particularly stimulating (Davies et al., 1969; Eysenck, 1967, 1981; Eysenck & Eysenck, 1985; Koelega, 1992; Krupski et al., 1971; Smith & Maben, 1993; Thackray et al., 1974). In this study, the vigilance task changes from a high to a low workload. The move from a moderately high to a lower task diYculty produces a suddenly less stimulating situation whereby extraverts (because of their lower levels of arousal) may be disadvantaged. These Wndings may have signiWcant implications for situations in which people are required to perform simple vigilance tasks in dynamic environments. The impact of decrements could be particularly important for safety sensitive occupations. Consider for example, a transportation security agent who must screen luggage for potentially threatening content via an X-ray machine. These airport security personnel operate in dynamic environments as larger or smaller groups of people move through the TSA airport security checkpoints. Given the research Wndings of the present study it would seem prudent to further explore the relationship between personality and workload history in real world occupations. Although this study answers important questions regarding the relationship between extraversion and workload history there are some important limitations of the current study. While the Wndings may appear to support the signiWcant inXuence of extraversion and workload history on performance, the degree of inXuence may not be true for other types of tasks. Consequently, before any conclusions can be drawn regarding applicability of these results to real world jobs, future research should examine generalizability of eVects to simulation tasks. Furthermore, the relationship between extraversion, workload history, and performance may be aVected by additional factors (e.g., time on task, breaks, and distractors). It may prove fruitful to systematically manipulate these variables to gain a better understanding of the generalizability of these Wndings. In sum, the results of this study conWrm and extend previous Wndings regarding performance diVerences between extraverts and introverts. This study suggests that the examination of workload history may be useful for testing extraversion theory, as it provides a systematic method for controlling environmental variables that might inXuence the relationship between extraversion and human performance. Furthermore, the present study may have signiWcant implications for applied settings. References Amelang, M. (1991). Results of a (nearly) comprehensive study of Eysenck’s extraversion theory. Psychologische Beitrage, 33(1–2), 23–46. Bakan, P. (1959). Extraversion–introversion and improvement in an auditory vigilance task. British Journal of Psychology, 50, 325–332. Broadbent, D. E. (1965). A reformulation of the Yerkes-Dodson law. British Journal of Mathematical & Statistical Psychology, 18(2), 145–157. Cumming, R. W., & Croft, P. G. (1973). Human information processing under varying task demand. Ergonomics, 16, 581–586. Cox, D. R. (1957). A note on grouping. Journal of the American Statistical Association, 52, 543–547. Cox-Fuenzalida, L. E., Swickert, R. J., & Hittner (2003). EVects of neuroticism and workload history on performance. Personality and Individual DiVerences, 36, 447–456.
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