Journal of Experimental Psychology: General

Transcription

1 Joural of Experimetal Psychology: Geeral VOL. 109, No. 1 ARCH 1980 The Iteractive Effect of Persoality, Time of Day, ad Caffeie: A Test of the Arousal odel William Revelle, ichael S. Humphreys, Lisa Simo, ad Kirby Gillilad Northwester Uiversity SUARY The persoality dimesio of itroversio/extraversio is oe of the few persoality dimesios that ca be reliably idetified from study to study ad ivest^ gator to ivestigator. The importace of this dimesio withi persoality theory is due both to the stability of the trait ad the ifluetial theory of H. J. Eyseck. The basic assumptio i Eyseck's theory of itroversio/extraversio is that the persoality differeces betwee itroverts ad extraverts reflect some basic differece i the restig level of cortical arousal or activatio. Assumig that there is a curviliear relatioship (a iverted U) betwee levels of stress ad performace leads to a test of this arousal theory. That is, moderate icreases i stress should hider the performace of itroverts who are presumably already highly aroused. However, the same moderate icrease i stress might help the performace of the presumably uderaroused extraverts. Revelle, Amaral, ad Turriff.reported that the admiistratio of moderate doses of caffeie hidered the performace of itroverts ad helped the performace of extraverts o a cogitive task-similar to the verbal test of the Graduate Record Examiatio. Assumig that caffeie icreases arousal, this iteractio betwee itroversio/extraversio ad drug coditio supports Eyseck's theory. This iteractio was explored i a series of experimets desiged to replicate, exted, ad test the geerality of the origial fidig. The iteractio betwee persoality ad drug coditio was replicated ad exteded to additioal cogitive performace tasks. However, these iteractios were affected by time of day ad stage of practice, ad the subscales of itroversio/extraversio, impulsivity, ad sociability, were differetially affected. I the morig of the first day, low impulsives were hidered ad high impulsives helped by caffeie. This patter reversed i the eveig of the first day, ad it reversed agai i the eveig of Day 2. We cocluded that the results from the first day of testig require a revisio of Eyseck's theory. Istead of a stable differece i arousal betwee low ad high impulsives, it appeared that these groups differed i the phase of their diural arousal rhythms. The result is that low impulsives are more aroused i the morig ad less aroused i the eveig tha are the high impulsives. A variety of peripheral or strategic explaatios (differeces i caffeie cosumptio, guessig strategies, distractio, etc.) for the observed performace icremets ad decremets were proposed ad tetatively rejected. It seems probable that some fudametal chage i the efficiecy with which iformatio is processed is resposible for these performace chages. Copyright 1980 by the America Psychological Associatio, Ic /80/ $

2 REVELLE, HUPHREYS, SION, AND GILLILAND Oe of the few persoality dimesios that most persoality theorists agree is robust eough to idetify from study to study ad ivestigator to ivestigator is that of itroversio/extraversio. It has bee show that this persoality dimesio ca be idetified i such varied item sets as behavioral measures (Eyseck, 1947), peer ratigs, ad self-report ivetories (Cat-tell, 1957, 1973; Howarth, 1976; Norma, 1969). Itroversio/extraversio has also bee idetified as a promiet factor i a set of items sampled from all major persoality ivetories (Browe & Howarth, 1977). H. J. Eyseck (1947, 1967), more tha ayoe else, has popularized this trait ad cotributed to its theoretical developmet ad measuremet. Eyseck's theory of itroversio/extraversio has received eough support for him to claim (1976) that it represets a paradigm of persoality measuremet. It has bee reported that differeces i itroversio/extraversio are related to differeces i physiology, vigilace performace, social iteractio, sexual behavior, creativity, effectiveess of cogitive processig, susceptibility to stress, ad may other diverse experimetal ad observatioal fidigs. I this article we will show that some of these fidigs, specifically the differetial susceptibility to stress of itroverts, are quite reliable but that they may ot be related to the overall cocept of itroversio/extraversio. Specifically, we shall report o a series of studies attemptig to replicate, defie the boudary coditios, ad exted the basic fidigs of Revelle, Amaral, ad Turriff This research was supported i part by Grat H from the Natioal Istitute of etal Health. We would like to thak R. Brooks, W. Brow, K. Budzeika,. Kohl, S. Lawso, R. iller, J. itrega, ad A. Tepp for help i coductig this research. We also would like to thak C. Duca, W. Hill, ad B, Uderwood for extesive commets o a earlier draft. Kirby Gillilad is ow at the Uiversity of Oklahoma. Requests for reprits should be set to William Revelle, Departmet of Psychology, Northwester Uiversity, Evasto, Illiois 601. (1976), who showed that o a cogitive task, time pressure ad caffeie iteracted with itroversio/extraversio. The cogitive task employed was a 60-item multiplechoice test of verbal ability similar to the Graduate Record Examiatio. Each subject served i each of three testig coditios. I oe coditio, the subjects had as much time as they eeded to complete the test. Durig the remaiig two testig coditios, subjects were allowed a limited amout of time to complete the test. I oe of the two timed coditios, subjects were give a placebo, ad i the other coditio they were give 0 mg of caffeie. Whe the umber of items aswered correctly was corrected for guessig ad stadardized withi time coditios, the performace of itroverts was foud to fall by.63 SD whe they were goig from the relaxed coditio to the timed plus caffeie coditio. The performace of the extraverts, o the other had, icreased by.43 SD whe they were goig from the relaxed to the timed plus caffeie coditio. The curret article is a report o six studies, five of which are reported for the first time here, that have followed that iitial fidig. Before describig this research, however, it is ecessary to cosider some issues relevat to the performace of itroverts ad extraverts i arousig or stressful coditios. Arousal Theory of Itroversio/Extraversio H. J. Eyseck's basic theory of itroversio/extraversio ca be summarized as the logical derivatio from three hypotheses. 1. The first hypothesis is that idividual differeces i itroversio/extraversio are related to differeces i the restig (basal) level of cortical arousal or activatio. It has bee reported that compared to extraverts, itroverts are more sesitive to auditory stimulatio (Smith, 1968) ad to pai (Haslam, 1967); have higher sedatio thresholds (Sloae, Davidso, & Paye, 1965); higher levels of ski coductace (Revelle, 1974) ; ad have more spotaeous galvaic ski resposes (Coles, Gale, & Klie, 1971). Itroverts have also bee

3 PERSONALITY AND AROUSAL reported to be more resistat to the decremet i vigilace performace that is associated with low levels of arousal (Carr, 1971; Keister & claughli, 1972; Krupski, Raski & Baka, 1971). Similarly, Crider ad Lu (1971) reported that the orietig respose habituates more quickly amog extraverts tha amog itroverts. 2. The secod hypothesis is that there is a optimal level of arousal for ay particular task. I other words, there is a curviliear relatioship (a iverted U) betwee levels of arousal ad performace (Broadhurst, 1959; Duffy, 1962, 1972; Yerkes & Dodso, 1908). It is further assumed that this optimal level of arousal varies as a fuctio of task parameters such that this peak level is higher for easier rather tha for harder tasks. 3. A third hypothesis is that there is a curviliear relatioship betwee arousal ad hedoic toe. That is, there is a preferred or ideal level of arousal, ad amouts of arousal either above or below that are ot as pleasat as those at the optimal level. With these three hypotheses it is possible to derive predictios about the performace of itroverts ad extraverts i arousig ad oarousig situatios. That is, i a borig situatio (e.g., a vigilace task with a low probability of sigal occurrece), itroverts should perform better tha extraverts. This is predicted o the basis of the higher arousal of itroverts tha extraverts ad the low arousal properties of the task. As the task becomes more arousig, however, itroverts should quickly attai their optimum level of arousal (if they were ot there already). As itroverts pass through the descedig side of the iverted-u curve, extraverts would most probably be ascedig. Thus, for moderately arousig tasks, the performace of itroverts ad extraverts should ot differ. As the task becomes eve more arousig, the itroverts should become overaroused ad their performace should deteriorate. Extraverts, with iitially low levels of arousal, o the other had, should ot attai their optimum level util well after the itroverts are past theirs. Thus, with low levels of arousal itroverts are expected to perform better tha extraverts, ad with high levels of arousal extraverts are expected to be superior to itroverts. The fidigs of Revelle et al. (1976) support this predictio, assumig that time pressure is more arousig tha o time pressure ad that caffeie is more arousig tha a placebo. Additioal support for the iverted-u predictio may be foud i the work of Davies ad Hockey (1966), who foud that i a visual cacellatio task, sigal frequecy ad oise level iteracted with itroversio/ extraversio. By assumig oisy coditios to be more arousig tha quiet coditios, a high sigal frequecy to be more arousig tha a low sigal frequecy, ad itroverts to be more aroused tha extraverts, Davies ad Hockey (1966) foud it possible to order the visual cacellatio scores of their subjects i a curviliear order. The performace of extraverts improved with icreases i either sigal frequecy or oise level, whereas the performace of itroverts deteriorated whe both oise ad sigal frequecy were icreased. Further evidece for the iverted-u hypothesis of itroversio/extraversio was reported by Corcora (1972). Assumig that sleep deprivatio leads to a lower arousal level, Corcora foud that although icreasig sleep deprivatio produced decremets i performace for extraverts, sleep deprivatio actually led to improvemets i the performace of itroverts. The task was presumed to be quite arousig: Subjects were required to follow with a stylus a highly complex path aroud may holes i a drum revolvig at high speed. To iduce high arousal, errors were puished with 100-dB white oise. O this task, it was assumed that itroverts were iitially overaroused ad extraverts were optimally aroused. Sleep deprivatio was thought to brig the itroverts dow to more optimal arousal levels but to take the extraverts below their optimal poit. Aother relatioship that ca be predicted from the arousal preferece hypothesis is that extraverts should be stimulatio seekers ad itroverts stimulatio avoiders. Thus, we would expect extraverts to avoid vigilace-type tasks but to seek out ad do well o those tasks that produce higher

4 REVELLE, HUPHREYS, SION, AND GILLILAND arousal levels. Itroverts, o the other had, should seek out those tasks that iduce lower levels of arousal ad avoid those that produce high levels. These prefereces, of course, are see i our everyday stereotypes of itroverts ad extraverts, ad ca also be demostrated i the laboratory. Thus, Elliot (1971) ad Ludvigh ad Happ (1974) have show that extraverts prefer higher levels of auditory stimulatio tha do itroverts. Similarly, Gale (1969) has show that i a operat situatio where a icrease i Visual stimulatio was used as a reward, extraverts work harder tha itroverts. The greater caffeie preferece of extraverts (Bartol, 1975) may be see as their way of achievig a higher, ad for them a more pleasat, level of arousal. Limitatios of the Arousal Theory A difficulty with such a simple explaatio of stimulatio seekig is that it fails to take accout of differeces i stimulus value betwee self-paced ad exterally paced tasks. That is, is moutai climbig a highly arousig situatio because of the high risk, or is it a relaxig avocatio because of the self-paced ature of the task? This theory of stimulatio seekig also fails to take accout of idividual differeces i prefereces ad abilities. For example, is attedig a dace arousig because of the social stimulatio, or is it relaxig because you are a good dacer? These examples illustrate the difficulty i decidig which tasks or situatios are most arousig. Clearly, more effort ad thought are eeded before arousal theory ca predict situatioal prefereces. Yet aother coceptual weakess i the theory as outlied is that differeces i preferred level may or may ot be correlated with differeces i restig level. It is quite possible to costruct a model i which preferred level ad restig level are idepedet. This would lead to the predictio that high stimulatio seekers are either those with low restig levels or high ideal levels, or both. The preset theory does ot predict the behavioral cosequeces of differeces i ideal arousal level separate from differeces i basal level. A fial problem with the theory as outlied above is the cocept of arousal itself. What does it mea to say that someoe is more aroused tha someoe else? Arousal is ormally a withi-subjects cocept cotrastig states of extreme sleepiess with extreme excitemet. Withi-subjects icreases i arousal are associated with icreases i heart rate, breathig rate, umber of spotaeous galvaic ski resposes (GSRs), icreases i ski coductace, ad icreases i the domiat electroecephalogram (EEC) frequecy. I additio to these psychophysiological idicators of arousal, it is possible to assess withi-subjects differeces by self-report (Kjellberg & Bohli, 1974; Thayer, 1967). I fact, i oe study, self reports of arousal were foud to correlate more with the physiological idicators tha ay two idicators correlated with each other (Clemets, Hafer, & Vermillio, 1976). What does it mea, however, to perform betwee-subjects comparisos usig procedures validated withi subjects? Is it eve possible to cosider betwee-subjects differeces o the same dimesio as withisubjects differeces? That is, withi subjects, a perso is more aroused with a heart rate of 80 beats per miute (bpm) tha with 60 bpm, but is someoe with a 80-bpm rate more aroused tha someoe else is with a 60-bpm rate? It is perhaps these difficulties that lead to the fidigs that although itroverts ad extraverts do ot differ o self-report measures of arousal, itroversio iteracts with self-reported arousal o a measure of sematic memory retrieval (. W. Eyseck, 1974). Similarly, i a study relatig itroversio/extraversio, ski coductace, ad performace (Revelle, 1974), it was foud that although either ski coductace or itroversio was related to aagram performace, the iteractio betwee itroversio ad ski coductace was sigificat. Itroverts with low ski coductace performed better tha itroverts with high ski coductace, whereas extraverts with moderate levels of ski coductace did better tha those with either lower or higher levels. A fial poit about the utility of the curviliear arousal-performace hypothesis is

5 PERSONALITY AND AROUSAL that the curviliear hypothesis serves as a descriptio rather tha a explaatory device. It does ot provide a explaatio for performace icremets or decremets uder icreases i arousal. If o a particular task extraverts are observed to do better ad itroverts worse (with a moderate icrease i stress), there is o guaratee that the same mechaism was resposible for both the icremet ad the decremet. It may be that oe theory will be eeded for the performace icremets ad a secod for the performace decremets. A similar poit has bee made by Poulto (1977) i his discussio of the performace chages iduced by icreases i ambiet oise levels. Poulto proposes that the performace icreases with oise are due to the arousig properties of oise but that the performace decremets are due to icreases i the distractig effects of oise (maskig of ier speech, etc.). Other critics of the iverted-u hypothesis (viz., Naatae, 1973) also hold that decremets are due to distractios cofouded with the icrease i stress. Thus, oise (Davies & Hockey, 1966), the presece of others (Gee, 1973), or testlike versus relaxed coditios may be thought of as beig more distractig tha the cotrol coditios. Caffeie as a Stressor A cetral poit to our discussio of the effects of caffeie upo performace is the assumptio that caffeie icreases arousal. A excellet review of the effects of caffeie upo humas is that of Gilbert (1976), from which this sectio will borrow heavily. Oe of the best kow behavioral effects of caffeie is, of course, that it delays the oset ad reduces the quality of sleep. With awake subjects, caffeie facilitates performace o simple repetitive tasks (the facilitatio occurs after may repetitios of the task), probably through its fatigue-alleviatig properties. With chroically high doses, caffeie iduces symptoms cliically idistiguishable from axiety (Grede, 1974). Normal caffeie cosumptio also has bee related to symptoms of axiety amog workers cofroted with the stress of a factory closig (Cobb, 1969). For extraverts, caffeie has bee show to improve performace o a vigilace task by reducig the characteristic declie i performace as the work progresses (Keister & claughli, 1972). With respect to psychophysiological measures, caffeie reduces the habituatio rate of the GSR to auditory stimuli. Neurochemically, it is thought that the effect of caffeie is to ihibit the breakdow by phosphodiesterase of cyclic adeosie moophosphate (AP), which results i higher cylic- AP levels. A related pheomeo is that caffeie raises blood-sugar levels as well as the plasma level of free fatty acids. Whe take orally, caffeie reaches peak plasma levels withi 30 mi. ad remais i the blood stream with a half-life betwee 2 ad 4 hr. A ormal cup of coffee has bee estimated to cotai about 75 mg of caffeie, although some idividuals cosume cups with upwards of 300 mg of caffeie (Gilbert, Schwieder, arshma, & Berg, 1976). The effect of caffeie o performace appears to be iterestig i its ow right. Whether this effect is i ay way similar to the effects of such presumed arousers as oise, social stimulatio, or axiety remais to be determied. That is, it remais to be determied whether caffeie ad the other presumed arousers have the same behavioral effects. Beyod this, it also remais to be determied whether these effects are mediated by a commo physiological mechaism. I our studies we specifically ivestigated the behavioral effects of caffeie. However, we believe that the assumptio that the effect of caffeie ad other stressors (e.g., oise, social stimulatio, or axiety) ca be subsumed uder a commo costruct (arousal) is theoretically fruitful. The easuremet of I troversio/extraversio Some commets are also eeded about the persoality dimesio of itroversio/extraversio. I order to assess this dimesio, subjects are asked to aswer questios about their life-styles ad behavioral tedecies. Do they like parties? Will they do aythig o a dare? The items ad the aswers to

6 REVELLE, HUPHREYS, SION, AND GILLILAND these items that defie the itroversio/ extraversio scale have bee selected primarily o the basis of psychometric criteria (Eyseck & Eyseck, 1969). Basically, a set of items were selected that correlated with each other ad did ot correlate with other items. There is some dispute whether by this criterio itroversio/extraversio is oe or two scales. Thus, Guilford (1975, 1977) ad Carriga (1960) have suggested that it is more useful to cosider the subscales of impulsivity ad sociability as separate costructs ad ot to combie them ito the higher order factor of itroversio/ extraversio. See H. J. Eyseck (1977) for a rebuttal of this positio. While it is clear that there is a relatioship betwee itroversio/extraversio ad arousal-related measures, it would be quite surprisig if items selected o these psychometric criteria would prove to be the best predictors of performace i arousig situatios. The assumptio that we iitially made i this series of experimets was that the dimesio of itroversio/extraversio was our best lead to idividuals who will perform well or poorly uder stress. I aalyzig our results we looked at the itroversio/extraversio scale as well as the two subscales of impulsivity ad sociability. The object was to determie whether the itroversio/ extraversio scale or oe of the two subscales would be the best predictor of performace icremets ad decremets uder stress. The aswer was complex ad will be discussed i more detail later. The First Replicatio The first replicatio of the Revelle et al. (1976) study was udertake as part of a doctoral dissertatio at Northwester Uiversity (Gillilad, 1977). The procedures employed by Gillilad will be described, ad those aspects of the procedures that differed from the Revelle et al. study will be oted. I the Gillilad experimet subjects served i a sigle, 2-hr, sessio as compared to three 1-hr, sessios i Revelle et al. The subjects were give oe of two forms of the Graduate Record Examiatio (GRE) practice tests (see Gruber & Gruber, 1973; Revelle et al., 1976). The, each subject was give oe of three doses of caffeie adjusted accordig to the body weight of the subject: 0 mg/kg of body weight (the placebo coditio), 2 mg/kg of body weight, or 4 mg/kg of body weight. Forty-five miutes after the admiistratio of caffeie, the subjects were tested o a equivalet form of the GRE practice test. Both the pre- ad the posttest were give uder high time pressure (10 mi.) to complete the test. The data of pricipal iterest i this study were the chage scores (the differece i the umber correct betwee pre- ad posttests). Gillilad reports that there was a sigificat Extraversio X Drug Level iteractio; however, the patter of results was somewhat differet tha was expected. It had bee aticipated from the iverted-u hypothesis that the admiistratio of caffeie i either dose would harm the performace of itroverts. The performace of extraverts was expected to be ehaced by the small dose but perhaps be harmed by the large dose. Cotrary to those expectatios, the performace of the itroverts as dosage icreased first became better (0 mg/kg to 2 mg/kg) ad the became worse (2 mg/kg to 4 mg/kg). The performace of the extraverts steadily improved with icreasig dosages of caffeie. Whe the itroversio/extraversio scale was broke dow ito the two subscales (impulsivity ad sociability), it was apparet that most of the caffeie effects were due to the impulsivity scale. For low impulsives there was a sigificat quadratic tred as the performace of low impulsives first icreased the decreased with a icreasig dose of caffeie. For high impulsives there was a sigificat liear tred as the performace of those subjects icreased steadily across the levels of the drug variable. The iteractio of liear treds was statistically sigificat. The oly sigificat effect o the sociability scale was the quadratic tred for low sociables. These subjects first icreased the decreased across the levels of the drug variable. Gillilad cocluded that his results supported the iverted-u hypothesis ad the arousal iterpretatio of itroversio/ extraversio. His data did cast doubts,

7 PERSONALITY AND AROUSAL however, upo the uitary ature of the costruct. Experimets 1-5 As a result of the Revelle et al. (1976) ad Gillilad (1977) studies there seemed to te little doubt that there was a iteractio betwee the persoality dimesio of itroversio/extraversio ad the dosage of caffeie, However, the exact form of the iteractio was ot clear, ad it seemed possible that a task or a evirometal variable (stage of practice, time of day, the use of a pretest, etc.) might be moderatig this iteractio. Furthermore, as a result of Gillilad's observatio about the importace of the impulsivity subscale, it was ot clear whether the etire itroversio/extraversio scale or oe of its compoets was resposible for this Drug X Persoality iteractio. This sectio of the article reports o the results from five experimets desiged to look at some aspect of this iteractio. Experimets 1 ad 2 were relatively direct attempts to replicate the Revelle et al. experimet. Experimet 1 was a two-sessio experimet coducted i the morig. Experimet 2 was a sigle-sessio experimet usig the pre- ad posttest desig previously used by Gillilad. Experimet 1 icluded oly the timed placebo ad caffeie coditios. Experimet 2 crossed time ad relaxed coditios with the placebo caffeie maipulatio. Experimets 3 ad 4 looked at the effect of time of day as well as caffeie versus placebo. I Experimet 3, subjects were required to atted two sessios, oe i the morig ad the other i the eveig. Experimet 4 differed from the precedig experimets i that a differet cogitive task was used. Experimet 5 was a two-sessio experimet coducted i the eveig. I Experimet 5, a variety of ability tests were admiistered i a attempt to assess the geerality of the Revelle et al. fidigs. Geeral Procedure ethod The subjects were asked ot to take ay caffeie (coffee, tea, cola, stay-awake pills) for 6 hr. prior to the experimet. The experimets were coducted i group sessios with betwee 2 ad 12 subjects per sessio. The subjects were asked to sig a coset form idicatig the possible side effects of caffeie, were screeed for medical cotraidicatios, ad the were asked to drik a glass of Tag cotaiig either caffeie or flat quiie water (to approximate the bitteress of the caffeie solutio). After drikig the Tag, the subjects waited 30 mi. before startig o the performace tasks. Durig this time the persoality ad behavioral questioaires were admiistered. I some of the experimets (1, 2, ad 5), a additioal performace task was also icluded. The results from these additioal tasks will ot be discussed i this article. aterials The persoality questioaires icluded the followig: (a) the Eyseck Persoality Ivetory (EPI), which icludes 24 itroversio/extraversio items, 24 stability/euroticism items, ad 9 lie items. (Withi the itroversio/extraversio scale there are subscales for sociability ad impulsivity [see Table 1]) ; (b) a experimetal versio of the Eyseck Persoality Questioaire that cotais scales for itroversio/extraversio, stability/ euroticism, psychoticism, lie, ad four differet impulsivity scales; 1 (c) a questioaire cosistig of 92 items derived from the Sells, Dearee, ad Will (Note 1) study of the Guilford ad Cattell persoality ivetories. Items were selected to measure impulsivity, activity, sociability, ad axiety. I additio, items cocerig caffeie cosumptio, sleep ad study habits, ad how hard subjects tried i the experimet were icluded. A short adjective check list (Thayer, 1967) i which subjects report their curret mood or feeligs was also icluded. Not all of these additioal questioaires were give i every experimet. Where relevat, the exceptios will be oted. The stadard performace task (used i three of the five experimets as well as i the Revelle et al. ad Gillilad studies) is similar i format to the verbal form of the Graduate Record Exam. Two forms of the test were used. Each test cosisted of each of aalogies, atoyms, ad setece completios. The questios were take from Gruber ad Gruber (1973). This test is referred to as the practice GRE. Experimet 1 Subjects. The subjects were 108 studets from the itroductory psychology class at Northwester Uiversity. They served i the experimet as part of a course requiremet. 1 This form was kidly provided by S. B. G, Eyseck.

8 REVELLE, HUPHREYS, SION, AND GILLILAND Table 1 ad Subscales of the EPI scale" Logs for excitemet Is usually carefree Does ot stop ad thik thigs over before doig aythig Geerally does ad says thigs quickly without stoppig to thik Would do almost aythig for a dare Ofte does thigs o the spur of the momet Ofte shouts back whe shouted at Likes doig thigs i which he/she has to act quickly Is ot slow ad uhurried i movemet scale b Does ot feel shy whe he/she wats to talk to a attractive strager Does ot prefer readig to meetig people Likes goig out a lot Does ot prefer to have few but special frieds Ca usually let him-/herself go ad ejoy him-/herself at a lively party Other people thik of him/her as beig very lively Is ot quiet whe with other poeple If there is somethig he/she wats to kow about, he/she would ot rather look it up i a book tha talk to someoe about it Does ot hate beig with a crowd who plays jokes o oe aother Likes talkig to people so much that he/she would ever miss a chace of talkig to a strager Would be very uhappy if he/she could ot see lots of people most of the time Does ot fid it hard to really ejoy him-/herself at a lively party Ca easily get some life ito a rather dull party a Items 1, 3, 5, 8, 10,, 22, 39, ad 41 are from the Eyseck Persoality Ivetory (EPI), Form A. b Items 11, 15, 17,, 25, 27, 29, 32, 37, 44, 46, 51, ad 53 are from the Eyseck Persoality Ivetory, Form A. Desig ad procedure. Each subject was tested Experimet 3 o 2 cosecutive days at either 9:00 or 10:00 a.m. O Day 1, the subjects were radomly assiged to Subjects. The subjects were 157 studets from receive caffeie or placebo. O Day 2, subjects. the same source as used i previous experimets, were switched to the alterative drug coditio. That is, if they had received caffeie o Day 1, De?9 ad Procedure. Each subject served i 1-hr, sessios. The sessios were held at 9:00 they received placebo o Day 2. The dosage of caffeie was 0 mg (400 mg of caffeie citrate). a." 1 ' ad 7: 0 P- m - Approximately half of the sub- Jects were first tested m the morig ad the i The performace task was the practice GRE. A the eveig. The remaiig subjects were first differet form of this test was used o each of the 2 days. Subjects were allowed 10 mi. to aswer fted m the eveig ad the i the morig. Approximately 36 hr. separated the two sessios the 60 questios. for a S lve sub J ect - Whe sigig up for the experimet, subjects had a choice of whether to serve first i the Fx-beritet? «or eveig. Subjects ^ - were ra(j om iy assig e d to receive caffeie durig Subjects. The subjects were 90 studets from the first sessio ad placebo durig the secod or the same source used i the previous experimet. to receive placebo first ad caffeie secod. The Desig ad procedure. Each subject served for combiatio of the two variables (drug ad time of oe Hz-hr. sessio. The experimetal sessios day) resulted i four betwee-subjects coditios started at 10:00 a.m. Subjects were give 10 mi. with approximately equal umbers of subjects i to complete a pretest o oe of the two forms of the practice GRE prior to drikig the Tag solueach coditio. The four coditios were (a) caffeie i the morig of Day 1 ad placebo i tio. They the filled out the persoality ques- the eveig of Day 2, (b) placebo i the morig tioaires for 30 mi. before takig the secod of Day 1 ad caffeie i the eveig of Day 2, (c) form of the practice GRE. I half of the experi- caffeie i the eveig of Day 1 ad placebo i the metal sessios the subjects were allowed 10 mi. morig of Day 2, (d) placebo i the eveig of to complete the secod test, ad i the other half Day 1 ad caffeie i the morig of Day 2. The they were allowed mi. The dosage of caffeie experimeter was blid to the drug maipulatio, was 0 mg. The dosage of caffeie was 0 mg.

9 Experimet 4 PERSONALITY AND AROUSAL Subjects. The subjects were 153 studets from the same source as the previous experimets. Desig ad procedure. The subjects served i oe 1-hr, sessio at either 9:00 a.m. or 7:00 p.m. They assiged themselves to either the morig or eveig sessio whe they siged up for the experimets. The subjects were uaware util they arrived for the experimet that they would be asked to take caffeie. Subjects were radomly assiged to either the caffeie or the placebo coditio. The amout of caffeie was 0 mg. The experimeter was blid to the drug maipulatio. The performace task was 68 4-choice aalogy problems (A:B::C:t). Distractors were used i these problems that were related to or were strog associates of the C terms. For example, Pig:Boar: :Dog:? was oe of the problems. The correct aswer was Wolj ad oe of the distractors was Cat. The subjects were give 5 mi. to aswer the aalogy problems ad were ecouraged to aswer as may problems as possible. Experimet 5 Subjects. The subjects were 121 members of the Northwester Uiversity commuity. They had bee recruited through a advertisemet i the studet ewspaper. They were each paid $2.50 a hour for participatig i the experimet. Desig ad procedure. Each subject served i two 1-hr, sessios at 7:00 p.m. The sessios for a give subject were held o cosecutive days. Subjects were radomly assiged to receive caffeie o Day 1 ad placebo o Day 2 or placebo o Day 1 ad caffeie o Day 2. The experimeter was blid to the drug coditio. Three ew performace tasks were used for the first time. These were the verbal, quatitative, ad abstract reasoig tests from the Differetial Aptitude Test (DAT). Oe form of each test was used o Day 1, ad the alterative form was used o Day 2. Subjects were allowed 10 mi. to complete each of the three subtests of the DAT. There were 50 items o each form of the verbal reasoig ad abstract reasoig tests ad 40 items o each form of the quatitative reasoig test. The dosage was 4 mg/kg of body weight. Results Take together, these five experimets, i additio to the two previously reported, show very cosistet patters for some variables. Before reportig the results from each experimet ad discussig their implicatios, we thik it is worthwhile to cosider this overall patter. I order to make this patter as clear as possible, the media performace expressed i stadard score uits (stadardized withi experimets) for Experimets 1-5 plus Revelle et al. (1976) ad Gillilad (1977) has bee plotted i Figures 1-3. These figures show the media performace as a fuctio of experimetal coditios ad the persoality variables of impulsivity (Figure 1), sociability (Figure 2), ad itroversio/extraversio (Figure 3). It should be oted that impulsivity ad sociability, although subscales of itroversio/extraversio, do ot iclude all of the items from the etire itroversio/extraversio scale. Thus, the results from the itroversio/extraversio scale are ot simply the sum of the results from the impulsivity ad sociability subscales. The experimetal maipulatios show i Figures 1-3 are the drug coditio (caffeie/ placebo), the time of day whe the subjects were tested (morig/eveig), ad the stage of practice (Day I/Day 2). The most strikig results are for the impulsivity subscale o Day 1. There is a crossover iteractio i the morig (Figure 1, Pael a) ad this iteractio reverses i the eveig (Figure 1, Pael b). That is, although low impulsives performed more poorly with tha without caffeie i the morig of Day 1, they performed better with tha without caffeie i the eveig. The opposite is true for high impulsives, who were helped by caffeie i the morig ad hidered by it i the eveig. For impulsivity, the effects o Day 2 are ot large, ad i the eveig the patter of who is helped ad who is hidered reverses from Day 1 to Day 2 (Figure 1, Paels b ad d). The results usig the sociability subscale are i may ways dissimilar to the results usig the impulsivity subscale. Compare the results i the morig for impulsivity ad sociability (Figure 1, Pael a vs. Figure 2, Pael a, ad Figure 1, Pael c vs. Figure 2, Pael c). For sociability, the Day 2 results are the most strikig. I the morig, low sociables were helped by caffeie whereas high sociables were hidered (Figure 2, Pael c). This patter reverses i the eveig, where low sociables were hidered ad high sociables helped by caffeie (Fig-

10 10 REVELLE, HUPHREYS, SION, AND GILLILAND DAY A P Caffeie Caffeie DAY A. Caffeie Caffeie Figure 1. edia performace (i stadard scores) as a fuctio of impulsivity, placebo or caffeie, time of day, ad experimet duratio for Revelle et al. (1976), Gillilad (1977), ad Experimets 1-5. ( impulsives ; high impulsives D O) ure 2, Pael d). Agai ote that i the eveig there is a reversal i the patter of who is helped ad who is hidered by caffeie betwee Day 1 ad Day 2 (Figure 2, Paels b ad d). Usig the etire itroversio/extraversio scale (Figure 3) appears to add othig ad may eve detract from the effects oted for the subscales of impulsivity ad sociability. I fact, the Day 1 effects for impulsivity are elimiated whe the etire itroversio/ extraversio scale is used (Figure 1, Pael a vs. Figure 3, Pael a, ad Figure 1, Pael b vs. Figure 3, Pael b). I the remaider of the results sectio, the data from idividual experimets will be reported. Because the iteractive effects of drug ad persoality are larger ad more cosistet for the subscales of impulsivity ad sociability tha they are for the itroversio/extraversio scale, oly the results from these subscales will be reported. Experimet 1 Experimet 1 was a 2-day, crossover desig coducted i the morig. The variables were Day 1 versus Day 2 (day) ad

11 PERSONALITY AND AROUSAL A DAY P I"' 3 E-.4, Caffeie Caffeie DAY 2.3 A P ' -.4' Caffeie Caffeie Figure 2. edia performace (i stadard scores) as a fuctio of sociability, placebo or caffeie, time of day, ad experimet duratio for Revelle et al. (1976), Gillilad (1977), ad Experimets 1-5. ( sociables ; high sociables Q D-) caffeie versus placebo (drug). I additio, the subjects were divided ito groups of high ad low impulsives ad high ad low sociables. I this ad all subsequet experimets these groups were determied by takig a media split of the scores o the impulsivity ad sociability scales from the EPI. The results for both the impulsivity ad sociability dimesios are give i Table 2. The etries i Table 2 are the mea umber correct out of the 60 items o the test. O Day 1, low impulsives ad low sociables appear to have bee hidered by the admiistratio of caffeie, dow 1.39 ad 1.60 poits, respectively. I cotrast to this declie, high impulsives ad high sociables appear to have improved with the admiistratio of caffeie, up 1.81 ad 2.34 poits, respectively. O Day 2, all subjects appear to have doe better with caffeie. Statistical aalysis partially cofirms the differetial effect of caffeie o Day 1 ad Day 2. The X Drug X Day iteractio was ot sigificat, 2 F(l, 104) 2 The level of sigificace chose for these experimets was p <..05.

12 12 REVELLE, HUPHREYS, SION, AND GILLILAND.4.3 DAY 2 A P !-> *- ' 1,4 & Caffeie Caffeie I' 3.2 A DAY Caffeie Caffeie Figure 3, edia performace (i stadard scores) as a fuctio of itroversio/extraversio, placebo or caffeie, time of day, ad experimet duratio for Revelle et al. (1976), Gillilad (1977), ad Experimets 1-5. (Itroverts ; extraverts Q O) = 2.86, S e = However, the X Drug X Day iteractio was sigificat, F(l, 104) = 8.17, S e = There was also a sigificat improvemet from Day 1 to Day 2, F(l, 104) =4.94. Thus, this experimet showed that stage of practice was moderatig the Persoality X Drug iteractio. I additio, the crossover iteractio betwee impulsivity ad drug was clearly show to occur i the morig of Day 1 (see Figure 1, Pael a). Experimet 2 Experimet 2 cosisted of a sigle experimetal sessio i which both a pre-ad a postdrug performace measure were obtaied. The variables were drug ad time allowed to take the test (pacig). The results are show i Table 3 for both the pre- ad the posttest as a fuctio of drug, pacig, ad the persoality variables of impulsivity ad sociability. O the pretest there was a tedecy for low impulsives ad

13 PERSONALITY AND AROUSAL Table 2 ea Number Correct for edia Splits o the ad Dimesios for Experimet 1 Day 1 Day 2 Caffeie Caffeie dimesio» low sociables who were to be give caffeie to do worse tha those who were to be give placebos. Also high impulsives ad high sociables who were to be give caffeie did better tha those who were to be give placebos. However, either the X Drug iteractio or the X Drug iteractio was sigificat, F(l, 86) = 2.25, S e = 41.37, ad F(l, 86) = 3.05, S e = 39.71, respectively. Noe of the other iteractios or mai effects was sigificat o the pretest. Although the Persoality X Drug iteractios were ot sigificat o the pretest, it should be oted that the patter o the pretest was the same as the patter o the posttest. To some extet, the, the patter o the posttest may have resulted from the fortuitous assigmet of subjects to coditios. O the posttest, as expected, the subjects i the relaxed coditios did substatially better tha subjects i the timed coditios. However, the patter of results was the same for the relaxed ad timed coditios. Neither the X Drug X Pacig iteractio, F(l, 82) =.26, S e = 77.45, or the X Drug X Pacig iteractio, F(l, 82) =.25, S e = 88.26, was sigificat. The X Drug iteractio was ot sigificat, F(l, 82) =2., Table 3 ea Number Correct for edia Splits o the ad Dimesios for Experimet 2 Pacig Relaxed Timed Persoality dimesio Test Caffeie Caffeie Pretest Posttest Pretest Posttest

14 14 REVELLE, HUPHREYS, SION, AND GILLILAND Table 4 ea Number Correct for edia Splits o the ad Dimesios for Experimet 3 Day 1 Day 2 Persoality dimesio Time of day Caffeie Caffeie A P A P Note, A = morig; P = eveig. or was the X Drug iteractio, F(l, 82) = Although the iteractios betwee persoality ad drug coditio were ot sigificat, the patter was the same as i the first experimet, ad, for impulsivity, the same as i Figure 1, Pael a. That is, low impulsives ad low sociables did worse with tha without caffeie, whereas high impulsives ad high sociables did better with tha without caffeie. However, whe chage scores are calculated (the posttest mea mius the pretest mea), oly the impulsives i the timed coditio show this patter. I chage scores, the low impulsives i the timed coditio did.75 poits worse with tha without caffeie, ad the high impulsives did.59 poits better with tha without caffeie. The chage scores for the relaxed coditio showed that high impulsives were helped more by caffeie tha were low impulsives, but the crossover patter was ot preset. The low impulsives did.67 poits better with tha without caffeie, ad the high impulsives did 2.75 poits better with tha without caffeie. For the sociability dimesio, o discerable patter was preset i the chage scores. I the timed coditio, the low sociables did.25 poits worse with tha without caffeie, ad the high sociables did.06 poits worse with tha without caffeie. I the relaxed coditio, the low sociables did 2.04 poits better with tha without caffeie, ad the high sociables did 1.12 poits better with tha without caffeie. Experimet 3 Like Experimet 1, Experimet 3 was a 2-day, crossover desig. I additio to the day ad drug variables, Experimet 3 icluded a time of day variable. All subjects were tested i both the morig ad eveig. The mea umber correct as a fuctio of persoality, day, drug, ad time of day is show i Table 4. The most importat result from this experimet was the demostratio that time of day was affectig the Persoality X Drug iteractio. The X Drug X Time of Day iteractio was sigificat, F(l, 149) = 27.99, S e = I the morig, the low impulsives did 2.52 poits worse with tha without caffeie, whereas the high impulsives did 2.90 poits better with tha without caffeie. I the eveig, this patter reverses, with low impulsives doig 3.29 poits better with tha without caffeie while high impulsives were doig.83 poits worse with tha without caffeie.

15 PERSONALITY AND AROUSAL 15 With respect to the sociability dimesio, there was also a sigificat three-way iteractio with the drug ad time of day variables, F(l, 149) =5.43, S e = I the morig, the low sociables did 1.61 poits better with tha without caffeie, whereas high sociables did.17 poits worse with tha without caffeie. I the eveig, the patter chaged as low sociables did oly.95 poits better with tha without caffeie, ad high sociables did 1.60 poits better with tha without caffeie. As will be oted later, Day 2 performace i this experimet did ot coform to the patter foud i the other studies. Because of the possibility that switchig both the drug coditio ad the time of day o these subjects may have affected the Day 2 results, the Day 1 results were aalyzed by themselves. This aalysis cofirmed the X Drug X Time of Day iteractio, F(l, 149) =6.58, S e = 52,33. I the morig, the low impulsives did 3.95 poits worse with tha without caffeie, whereas the high impulsives did 4.49 poits better with tha without caffeie. I the eveig, this patter was reversed as the low impulsives did 3.33 poits better with tha without caffeie, ad the high impulsives did.29 poits worse with tha without caffeie. The patter here is the same as the media patter show i Figure 1, Paels a ad b. However, the X Drug X Time of Day iteractio was ot cofirmed, F(l, 149) =.16, S e = Furthermore, the Day 1 sociability patter is ot the same as the Day 1 impulsivity patter, as it was for both days combied. I the morig of Day 1, both the low ad high sociables did better with tha without caffeie (.31 ad 1.29 poits, respectively). I the eveig, the low sociables did.45 poits worse with tha without caffeie, whereas the high sociables did 2.36 poits better with tha without caffeie. Experimet 4 I Experimet 4, the subjects themselves chose whether to be tested i the morig or eveig. The depedet variable was the umber correct o a 68-item aalogies test. The results as a fuctio of persoality, drug, ad time of day are give i Table 5. The iteractio of X Drug X Time of Day was ot sigificat, F(l, 6) = 3.86, S e = However, the patter of results was the same as the media patter i Figure 1, Paels a ad b. I the morig, low impulsives did 2.74 poits worse with tha without caffeie, ad high impulsives did 8.46 poits better with tha without caffeie. This patter was reversed i the eveig, whe low impulsives did 2.17 poits better with tha without caffeie, ad high impulsives did.98 poits worse with tha without caffeie. The triple iteractio with sociability, drug, ad time of day was ot sigificat (F < 1). However, the X Drug iteractio was sigificat, F(l, 6) = 12.14, S e = These results differ from the impulsivity results i this experimet ad from the sociability results i the previous experimet. I the morig, the low sociables did 9.19 poits better with tha without caffeie, ad the high sociables did 5.30 poits worse with tha without caffeie. I the eveig, the low sociables did 6.93 poits better with tha without caffeie, ad the high sociables did 3.28 poits worse with tha without caffeie. Oe possible explaatio for the differece with the previous study could be i the amout of caffeie cosumed prior to participatio i this study. I Experimet 4, we had bee primarily cocered with the characteristics of the subjects who would ad would ot take caffeie ad who would select themselves for the morig or eveig sessios (these results will be discussed later). For this reaso, the subjects i Experimet 4 were ot wared about the caffeie maipulatio, ad as a cosequece, they were ot told to abstai from caffeie for 6 hours prior to participatig. If prior caffeie cosumptio was varyig with time of day or with the sociability dimesio, this might accout for these discrepat results. Ufortuately, due to experimeter error a caffeie cosumptio questioaire was ot admiistered i Experimet 4, so this speculatio caot be verified.

16 16 REVELLE, HUPHREYS, SION, AND GILLILAND Table 5 ea Number Correct for edia Splits o the ad Dimesios for Experimet 4 orig Eveig Persoality dimesio Caffeie Caffeie Experimet 5 Experimet 5 was a 2-day experimet coducted i the eveigs. Subjects served i both the placebo ad caffeie coditios. The performace tasks were the verbal reasoig, umerical ability, ad abstract reasoig subtests of the DAT. The umbers correct o each test as a fuctio of persoality, drug coditio, ad day are give i Table 6. The maximum umbers correct o the verbal, quatitative, ad abstract tests are 50, 40, ad 50, respectively. The experimet cofirmed the fidigs of Experimets 1 ad 3 i showig that the X Caffeie iteractio is moderated by stage of practice. For the verbal, umerical ability, ad abstract reasoig tests, the X Drug X Day iteractios were sigificat, f(l, 117) =30.32,.S e = 8.75; F(l, 117) = 4.73, S, = 7.56; ad F(l, 117) = Table 6 ea Number Correct for edia Splits o the ad Dimesios for Experimet 5 Day 1 Day 2 rersuuaiily dimesio ur\ i subtest Caffeie Caffeie Verbal Quatitative Abstract Verbal Quatitative Abstract Note. DAT = Differetial Aptitude Test.

17 PERSONALITY AND AROUSAL 17.57, S e 11.67, respectively. oreover, the patter for all three tests was the same as the media patter i Figure 1, Paels b ad d. O Day 1, the low impulsives did better with tha without caffeie, ad the high impulsives were worse with tha without caffeie. O Day 2, this patter reversed, so that the low impulsives did worse with tha without caffeie, ad the high impulsives did better with tha without caffeie. With respect to the sociability dimesio, the effects were i the same directio as they were with the impulsivity dimesio. For the verbal reasoig, umerical ability, ad abstract reasoig tests, the X Drug X Day iteractio was sigificat, F(l, 117) = 29.91, S e = 8,88; F(l, 117) = 35.82, S e = 7A5; ad F(l, 117) = 42.41, S e = 11.54, respectively. The Day 2 patter for all three tests was the same as the media patter show i Figure 2, Pael d. I additio, for both the umerical ability ad the abstract reasoig tests, there was a sigificat improvemet from Day 1 to Day 2, F(l, 117) =60.61, ad F(l, 117) = 67.50, respectively. The effect of days was ot sigificat for the verbal reasoig test, F(l, 117) = Persoality Variables Experimet 4 was desiged to aswer questios about whether the traits of impulsivity ad sociability were related to subject's decisios to participate i these studies. I this experimet subjects were allowed to sig up for either a morig or a eveig sessio, ad a roughly costat umber were allowed to sig up each weeli durig the academic term. I Table 7, the mea impulsivity ad sociability scores are show as a fuctio of the time of day, time durig the term, ad drug coditio. The impulsivity ad sociability scores are from the EPI, which was admiistered after the drug or placebo was give to the subjects ad before the performace test. For the impulsivity scores, either time of day, F(l, 127) =.02; drug coditio, F(l, 127) =.25, S e = 2.62; or ay of the other mai effects or iteractios were sigificat. For the sociability scores the iteractio betwee drug ad time durig the term was sigificat, F(3, 5) =6.63, S e = Noe of the other iteractios ad oe of the mai effects were sigificat. This iteractio betwee drug coditio ad time durig the term was surprisig ad somewhat discocertig. We had thought that subjects with differet persoality characteristics might be sigig up for the experimet at differet times durig the term or might be selectig themselves for the morig or eveig sessios. However, we had ot aticipated ay effects due to the admiistratio of caffeie. The fidig was discocertig, because ay effect of drug coditio o the persoality scores would lead to iterpretive problems. The issue here cocers the directio of causatio. Is a stable persoality trait causig the effects, or are the persoality scores we are obtaiig simply aother maifestatio of the basic effect? To ivestigate further the effect of drug o persoality, the results from the other four experimets were aalyzed. I these aalyses the depedet measures were the impulsivity ad sociability scores from the EPI. I the 2-day experimets, the EPI results are from Day 1. The idepedet variables were drug coditio ad time durig the term (except for Experimet 5, which did ot ivolve itroductory psychology studets). I additio, for Experimet 3, the time of the Day 1 testig sessio was icluded as a variable. I oe of these experimets was the mai effect of drug coditio, or ay of the iteractios ivolvig the drug coditio, sigificat. For Experimets 1 ad 2, the mai effect of time durig the term was sigificat for impulsivity, -F(3, 99) = 3.98, S* = 2.92, ad F(3, 82) = 3.75, S e = 3.00, respectively. Thus, there is o evidece that caffeie affected the impulsivity scores. For each of Experimets 1-5 the mea score for the caffeie coditio mius the score for the placebo coditio was.01,.07,.07,.12, ad.09, respectively. For the sociability scores, the sigificat iteractio foud i Experimet 4 was ot foud i the other experimets. Furthermore, the patter of results i these experimets did ot resemble

18 REVELLE, HUPHREYS, SION, AND GILLILAND Table 7 ad Scores for Experimet 4 as a Fuctio of Time i Term, Time of Day, ad Drug Coditio Time i term (i quarters) Time of day ad drug coditio Score 1st Score 2d Score 3rd 4th Score» orig Caffeie Eveig Caffeie orig Caffeie Eveig Caffeie the Experimet 4 patter. The differeces i the sociability scores betwee the caffeie ad placebo coditios were.23,.21,.70,.25, ad.24, for Experimets 1-5, respectively. The slight tred here (four out of five studies i the same directio), alog with the sigificat iteractio foud i oe out of five experimets, suggests at most a small effect of caffeie o sociability scores. The ext issue was whether there were ay differeces betwee the experimets i terms of subject characteristics. I Table 8 Table 8 eas, Stadard Deviatios, Reliabilities (a), ad Itercorrelatios of ad Scales Scale SD a SD a X Experimet the mea impulsivity ad sociability scores, the stadard deviatios of these scores, the reliability of the impulsivity ad sociability scales, ad the itercorrelatio betwee these scales is give for Experimets 1-5. The differeces betwee the experimets i these statistics are relatively small ad appear to be largely urelated to the magitude of the observed effects. However, there was a differece betwee the reliabilities for the impulsivity ad sociability scales. For all five experimets the impulsivity scale had a lower reliability tha did the sociability scale. The media reliabilities were.48 ad.71 for impulsivity ad sociability, respectively. The media* correlatio,.25, betwee impulsivity ad sociability was ot very large ad suggests that impulsivity ad sociability eed ot always be cosidered as compoets of a higher order itroversio/extraversio factor. (See also Revelle & JRockli, 1979). Discussio Cosistecies Betwee Experimets To facilitate comparisos betwee these five experimets ad the two experimets previously coducted i our laboratory

19 PERSONALITY AND AROUSAL 19 (Gillilad, 1977; Revelle et al., 1976), data from all seve experimets have bee combied ito two tables. Table 9 summarizes the effects of caffeie o low ad high impulsives. For each experimet, idividual scores were first coverted to stadard scores usig the withi-cell error term. The average stadard score i the placebo coditios was the subtracted from the average stadard score i the caffeie coditio. For Experimet 2, differeces betwee the stadardized chage scores i the timed coditios are reported. For the Gillilad experimet, stadardized chage scores i the placebo ad the 4 mg/kg of body weight coditios are reported. For the Revelle et al. experimet, the data from the timed coditios are reported, ad the results from Days 2 ad 3 are combied ad reported i the Day 2 colum. The patter i the morig of Day 1 is especially clear. I each of the five studies coducted i the morig, the low impulsives were hidered ad the high impulsives were helped by caffeie. The media loss (i stadard deviatios) was.22 for the low impulsives, ad the media gai was.58 for the high impulsives. The patter i the eveig of Day 1 is also fairly clear. I Experimets 3 ad 4 ad for all three subtests used i Experimet 5, the low impulsives were helped by the admiistratio of caffeie ad the high impulsives were hidered. The oly exceptio to this Day 1 patter is the Revelle et al. study, i which low impulsives were slightly hurt by caffeie. However, i this study the high impulsives were hidered more by caffeie tha were the low impulsives. Across all of these studies ad tests, the media improvemet for low impulsives was.27, ad the media loss for high impulsives was.15. Overall, the prevailig patter for the impulsivity dimesio o Day 1 i the morig was reversed i the eveig. impulsives were hidered by caffeie i the morig ad helped i the eveig. impulsives were helped by caffeie i the morig ad hidered i the eveig. Experimet 3 showed that this reversal i the X Drug iteractio was ot the result of differet subjects selectig themselves for the morig ad eveig experimets, as this iteractio was sigificat o Day 1. I Experimet 3, subjects were required to sig up for both a eveig ad a morig sessio. It seems highly ulikely that subjects who siged up to serve i the morig of Day 1 ad the eveig of Day 2 would differ from those who siged up to serve i the eveig of Day 1 ad the morig of Day 2. The results of Experimet 4 also support the coclusio that time of day was affectig the X Drug iteractio. I that experimet, subjects had a opportuity to sig up for either a morig or a eveig sessio. With respect to the perso- Table 9 Stadard Score Differeces Betwee the Caffeie ad Coditios as a Fuctio of for Revelle et al. (1976), Gillilad (1977), ad Experimets 1-5 Day 1 Day 2 A impulsivity P impulsivity A impulsivity P impulsivity Experimet Revelle et al. Gillilad (Verbal) 5 (Numerical) S (Abstract) Note. A = morig; P = eveig

20 REVELLE, HUPHREYS, SION, AND GILLILAND Table 10 Stadard Score Differeces Betwee the Caffeie ad Coditios as a Fuctio of for Revelle et al. (1976), Gillilad (1977), ad Experimets 1-5 Day 1 Day 2 A sociability P sociability A sociability P sociability Experimet Revelle et al. Gillilad (Verbal) 5 (Numerical) 5 (Abstract), Note. A = morig; P = eveig. ality dimesios beig cosidered here (impulsivity ad sociability), there were oly mior differeces betwee the morig ad eveig subjects, though there was some evidece for selectio effects as a fuctio of time durig the term. This suggests that the sig-up procedures used i most of these experimets (except for Experimet 5 ad Revelle et al., 1976) did ot produce strog selectio effects. Stage of practice clearly affected the X Drug iteractio. I Experimet 5, this iteractio was sigificat for all three tests. It was also sigificat for Revelle et al. (1976), F(2, 8) = 3.95, S K = However, the ature of the chage from Day 1 to Day 2 is ot readily apparet. Table 10 summarizes the effects of caffeie o high ad low sociables. As i Table 9, the etries i Table 10 are the differeces betwee the caffeie ad placebo coditios i stadard scores. Ulike the impulsivity results the sociability results are ot cosistet o the first day of testig. This is true for both the morig ad eveig sessios. As with impulsivity, there was a clear effect of stage of practice. The X Drug X Day iteractio was sigificat i Experimet 1 ad for all three tests i Experimet 5. For Revelle et al. (1976), however, this iteractio was ot sigificat, F(2, 8) = 1.26, S e Probably the oly way to make sese out of the Day 2 results for both impulsivity (Table 9) ad sociability (Table 10) is to igore the results of the third experimet. This was the oly experimet without a sigificat Persoality X Drug X Day iteractio. Perhaps this was due to the desig of the experimet, which provided for a switch i both the drug ad the time of day coditios from Day 1 to Day 2. Igorig Experimet 3, o the secod day of testig, impulsivity ad sociability seem to have affected performace i a similar maer. All subjects appeared to do better whe give caffeie i the morig. I the eveig, low impulsives ad low sociables did worse whe give caffeie, whereas high impulsives ad high sociables did better whe give caffeie. This fidig was reported by Revelle et al. (1976) ad appears i retrospect to be due to the fact that their subjects were give three testig sessios. That is, the results from Sessios 2 ad 3 overshadowed the results from Sessio 1. Whe the results from Day 2 are cosidered, it should be remembered that all of the multiday experimets ivolved a crossover desig. That is, subjects who served i the caffeie coditio o Day 1 were give placebos o Day 2, ad subjects who were give placebos o Day 1 were give caffeie o Day 2. This desig is iappropriate if

21 there was differetial trasfer from the Day 1 coditios. Before we draw ay strog coclusios from the Day 2 results, it will be ecessary to make use of a complete desig i which some subjects do ot receive both caffeie ad placebo. Arousal Theory of Itroversio/Extraversio Revisited Give the cosistet patters i the data, it is appropriate to ask how well they fit the arousal theory of itroversio/extraversio. I order to fit a arousal model to these data we are makig the followig assumptios: 1. The admiistratio of caffeie icreases arousal; 2. If a performace decremet results from the admiistratio of moderate doses of caffeie, the the subjects must have bee iitially optimally aroused or overaroused; 3. If a performace icremet results from the admiistratio of caffeie, the the subjects must have bee iitially uderaroused. I additio to these assumptios, the simple model outlied i the itroductio hypothesized that itroverts are more aroused tha extraverts. With respect to the impulsivity subscale, this model fits the morig data: Caffeie hurt the performace of presumably highly aroused low impulsives ad helped the performace of presumably less tha optimally aroused high impulsives. This traditioal model is uable, however, to explai the results i the eveig of Day 1, the iteractio betwee morig ad eveig, or the iteractio betwee Day 1 ad Day 2. A more plausible model that fits our Day 1 data ad that follows from the research by Blake ad his associates (Blake, 1967, 1971; Blake & Corcora, 1972) is that high ad low impulsives differed ot so much i their overall arousal but i the phase of their diural arousal rhythms. Blake (1967, 1971) demostrated that the body temperature of itroverts both rises to its highest value ad falls off from this peak several hours before that of extraverts. If we ca assume that Blake's fidig applies to the impulsivity dimesio, the the Day 1 results support a modified arousal theory: impulsives achieve their peak arousal PERSONALITY AND AROUSAL 21 level earlier i the day tha do high impulsives. This modified formulatio suggests that i the morig, the low impulsives are optimally aroused without caffeie but that caffeie makes them too aroused ad iduces decremets i performace. impulsives, o the other had, are below their optimal level ad become more aroused ad more efficiet with caffeie. I the eveig, however, the arousal model oly fits if the assumptio is made that the low impulsives are ow suboptimally aroused (o the dow limb of their diural arousal curve) while the high impulsives are optimally aroused without caffeie. This follows from our assumptio ad the results, which showed that i the eveig, the low impulsives were helped by caffeie, whereas the high impulsives were hidered by caffeie. The impulsivity data from Day 2 i the morig are ot cosistet eough to be iterpreted (perhaps due to the chage i both the time ad drug coditio i Experimet 3). The eveig data, however, are cosistet eough to attempt to fit the modified arousal model. I order for the modified arousal model to fit the Day 2 eveig data, it is ecessary to make two post hoc assumptios. First, the high impulsive subjects must be assumed to have had a lower level of arousal i the eveig of Day 2 tha they had i the eveig of Day 1. Perhaps they had habituated to the experimetal situatio ad o loger foud it particularly arousig. Secod, the low impulsives must be assumed to have had a higher level of arousal i the eveig of Day 2 tha they had i the eveig of Day 1. Perhaps they had experieced higher levels of discomfort tha did the high impulsives durig the Day 1 testig sessio. Because of this higher level of discomfort o Day 1, they might have bee more apprehesive ad thus more aroused durig the Day 2 testig sessio. With these additioal assumptios, the modified arousal model ca fit the eveig data o Day 2. That is, the low impulsives are ow optimally aroused without caffeie ad overaroused with caffeie, whereas the high impulsives are suboptimally aroused without caffeie ad optimally aroused with

22 22 REVELLE, HUPHREYS, SION, AND GILLILAND caffeie. This accout of the Day 2 results is highly speculative ad is without idepedet evidece supportig the two post hoc assumptios. Such evidece would cosist of a demostratio that physiological or selfreport idicators of arousal icreased from Day 1 to Day 2 for low impulsives ad decreased for high impulsives. The lack of a cosistet patter o Day 1 for the sociability dimesio egates the possibility of fittig a arousal curve to these sociability data. By the secod day, however, the patter does suggest that i the eveig, low sociables were optimally aroused without caffeie ad overaroused by the admiistratio of caffeie, whereas the high sociables were suboptimally aroused without ad optimally aroused with caffeie. It is iterestig to ote that although the impulsivity ad sociability scales have differet patters o Day 1, they have coverged ito the classic itroversio/extraversio iterpretatio by the eveig of Day 2. That is, it appears as if itroverts (low impulsives, low sociables) were optimally aroused without ad overaroused with caffeie, whereas extraverts (high impulsive, high sociable) were uderaroused without ad optimally aroused with caffeie. These differeces betwee Day 1 ad Day 2 suggest that it is importat to cosider impulsivity ad sociability separately as well as i combiatio at the higher order factor of itroversio/extraversio. It is ufortuate that much previous research has ot bee broke dow with respect to these two primary dimesios. It is particularly ufortuate that the work relatig persoality to differeces i the diural rhythm of arousal has ot made this distictio betwee impulsivity ad sociability. Blake's iitial fidig (1967) ad subsequet studies with Corcora (Blake & Corcora, 1972) made use of the Hero (1956) scale of itroversio/extraversio, which has both impulsivity ad sociability compoets i uspecified amouts. Similarly, Patkai (1971) reported differeces i the diural rhythm of adrealie secretio i its relatio to itroversio/extraversio as assessed by the audsley Persoality Ivetory (Eyseck, 1959), a early form of the EPI. Fially, Folkard (1976) related differeces i itroversio/extraversio assessed with the EPI to the diural rhythm of pai sesitivity. Sice oe of these studies examied phase differeces i terms of either impulsivity or sociability, it is impossible to coclude with certaity that impulsivity is the importat compoet. However, o the basis of their fidigs, take together with ours, which show that impulsivity iteracts with time of day ad sociability does ot, we suggest that impulsivity ad ot sociability is related to the diural rhythm of arousal. The complex patter of results ivolvig persoality, time of day, stage of practice, ad performace should be take as either cofirmig or discofirmig arousal models. With some additioal assumptios, a arousal model ca be fit to these data. Alterative versios of arousal models that we have ot explored may also fit these data. What the data do show, however, is that replicable results ca be obtaied, at least o Day 1. The stability of these results should permit the formulatio ad testig of more precise arousal models. Fially, these results show that the situatio with respect to arousal maipulatios is more complex tha has geerally bee recogized. This poit has bee made quite well by Gale (1977) i his discussio of the determiats of arousal ad its relatioship to vigilace. Gale lists ie potetial sources of arousal i experimetal situatios: (a) arousal due to stable idividual differeces; (b) arousal due to biological rhythms such as the mestrual ad diural cycles; (c) arousal due to subject recruitmet effects; (d) arousal due to experimeter-subject rapport ad subject uderstadig of the purpose ad covetios of the task; (e) arousal due to task mastery ad choice of a proper strategy; (f) arousal due to task-specific effects (e.g., some tasks such as ours probably are arousal-iducig by themselves, whereas others, such as vigilace, are thought to be the opposite); (g) arousal due to situatioal effects of the experimet (e.g., group versus idividual sessios, pleasat versus oxious evirometal coditios); (h) arousal due

23 PERSONALITY AND AROUSAL 23 to feedback o how well the subject is doig; ad (i) arousal due to extrisic ad itrisic motivatioal characteristics of the subject ad the experimetal procedure. I our studies we have foud several of these sources of arousal to be importat. Obviously the most importat coceptually is the effect of stable idividual differeces i arousal. This effect was iitially uder ivestigatio ad is fudametal to the Eyseckia model. However, our data do ot support the existece of such stable idividual differeces, but rather suggest that stable differeces i the phase of the diural rhythm have a effect o the relatioships betwee persoality, stress, ad performace. The previous iterpretatio of time of day results (e.g., Colquhou & Corcora, 1964) has bee that itroverts, who are ormally more aroused tha extraverts, become overaroused as the day progresses, ad thus their performace deteriorates. However, our data, i cojuctio with the earlier studies by Blake (1967) ad Blake ad Corcora (1972) imply that this is ot the case. Rather, they suggest that itroverts, or specifically low impulsives, are more aroused tha high impulsives early i the day ad less aroused later i the day due to a earlier peakig of their diural arousal rhythm. If the low impulsives had bee overaroused as Colquhou ad Corcora (1964) suggested, the admiistratio of caffeie should have further icreased arousal ad thus hurt performace. Sice caffeie helped the performace of low impulsives, we coclude that they were uderaroused. I additio to differeces i arousal betwee subjects, our studies also demostrate the importace of several more of the determiats of arousal listed by Gale. It is quite likely that takig a test similar to the Graduate Record Examiatio is a very arousig maipulatio for udergraduates. This is probably a more arousig task for this type of subject tha it would be for may others. It is also possible that the arousal value of the task chages from Day 1 to Day 2. As a fial poit, it should be oted that the experimeter eeds to cotrol ad preferably maipulate all of these possible sources of arousal i order to uderstad the relatioship betwee arousal ad performace. Idividual differeces must be take ito cosideratio, because there appears to be o mai effect associated with caffeie ad there may be few mai effects associated with other arousal maipulatios. I additio, we would ot have observed a Persoality X Caffeie iteractio if we had collapsed the morig ad eveig coditios. It appears that the stadard experimetal practice of testig subjects at various times durig the day may have preveted other ivestigators from fidig these iteractive effects betwee persoality ad maipulated arousal. The admiistratio of caffeie (assumig that this icreases arousal) is what permits us to determie whether the poor performace of itroverts i the eveig is due to uderarousal or overarousal. Fially, stage of practice ad/or degree of adaptatio to the experimetal settig must be cosidered i ay aalysis of the effects of arousal o performace. Processes Uderlyig Performace Chages Our experimets had bee desiged to replicate, exted, ad test the geerality of the Revelle et al. (1976) fidigs but ot to elucidate the processes resposible for the performace icremets ad decremets. However, it is still possible to draw some tetative coclusios about these processes. The priciple questio about the process is whether it is peripheral or cetral. Although we caot aswer this questio i geeral, it appears possible to elimiate a variety of peripheral processes, thereby ledig some support to the idea that the chages are due to some fudametal chage i the efficiecy with which iformatio is processed. Distractio as a explaatio for the performace decremets ca probably be rejected. Some of our subjects reported gastric disturbaces after takig caffeie, so a distractio effect seemed possible. However, the complex ad apparetly stable patter of effects observed o Day 1 seems to rule out distractio as a geeral explaatio. Idividuals similar to those helped by caffeie i the morig were hidered by it i the

24 24 REVELLE, HUPHREYS, SION, AND GILLILAND eveig, ad idividuals similar to those who were hidered i the morig were helped i the eveig. It is ulikely that a perso who was susceptible to caffeie-iduced gastric upsets, or ay other form of caffeie-iduced distractio, at oe time of day would be helped by caffeie at aother time of day. Furthermore, most of the subject reports that we got did ot suggest that our subjects were particularly aware of the drug coditio, at least o the first day of the experimet. Related to the distractio hypothesis is the possibility that our subjects differed i terms of their ormal caffeie itake. Thus, those who showed improvemets with caffeie might have bee sufferig from caffeie withdrawal symptoms (they had bee asked ot to take caffeie for 6 hours prior to the experimet). Those who showed decremets with caffeie might have bee uaccustomed to caffeie ad they might have suffered from gastric upsets, distractio effects, ad so o. Agai, the complex patter of results o Day 1 does ot support this explaatio. I additio, whe self-reports of caffeie cosumptio are examied, the amout of caffeie cosumed appears to be small, suggestig that there would be little effect of caffeie withdrawal (see Gilbert, 1976). There was also o oticeable relatioship with the persoality variables except i Experimet 5. Subjects were asked to report average daily cosumptio of caffeie-cotaiig substaces such as coffee, tea, colas, stay-awake pills, ad the like. Their resposes were coverted to cups of coffee equivalet (weightig tea ad colas as.5 cups of coffee ad stay-awake pills as 1.25 cups; see Gilbert, 1976). Subjects, whether high or low i impulsivity, reported drikig the equivalet of slightly more tha 1.5 cups of coffee a day. The oly exceptio to this fidig was Experimet 5, where the high impulsives reported drikig 2.2 cups ad the lows 1.5 cups per day. The differece was sigificat, F(l, 119) =7.34, 5 e = It is importat to poit out that the subjects i this experimet were somewhat older (mea age 19.5 years) tha were the subjects i the other experimets (mea age =.8). It thus seems possible that i this populatio, differetial caffeie cosumptio as a fuctio of persoality develops after a few years at college (see Bartol, 1975). Aother explaatio that ca probably be elimiated is some chage i the willigess of the subjects to guess. Agai, the complex patter of results rules out ay simple relatioship betwee caffeie ad willigess to guess. I additio, a examiatio of the umber of overt errors did ot reveal a cosistet relatioship betwee this statistic ad the umber correct. If chages i guessig were resposible for chages i the umber correct, a positive correlatio would be expected. With respect to the impulsivity dimesio over all five experimets, there were 15 occasios whe the umber correct was greater for the subjects give caffeie tha for those ot give caffeie. I 8 of these 15 occasios, the umber of errors was also greater for those give caffeie. There were 17 occasios whe the umber correct was less for the subjects give caffeie tha for those ot give caffeie. O 8 of these 17 occasios, the umber of errors was greater for those give caffeie. The time of day effect ad the stage of practice effect also appear to be largely urelated to the chages i the error scores (The error data for Experimets 1-5 are give i the Appedix, Tables A1-A5.) It also seemed possible that a chage i some geeral test-takig strategy such as skippig the hard questios to aswer the easy questios might be resposible for these results. However, fidig the same basic results for tests that vary widely i» difficulty ad for varyig degrees of time pressure does ot support such a explaatio. The aalogies test used i Experimet 4 does ot cotai difficult items, as our subjects would be correct almost 100% of the time without the extreme time pressure employed (5 mi. to aswer 68 questios). The DAT subtests were also substatially easier for our subjects tha were the practice GREs. Experimet 2, however, cotaied the oly coditio approachig the time pressure of a stadard power test ( mi. to aswer 60 questios). The patter of

25 PERSONALITY AND AROUSAL 25 results i the posttest data for this coditio was the same as i the other experimets. However, the chage scores suggest that the Persoality X Drug iteractio may be atteuated at the slower rate. Obviously, we have ot elimiated all possible peripheral or strategic explaatios for the observed icremets ad decremets. However, the stability of the effects (especially the Day 1 effects) over the rage of cogitive tasks employed suggests that we are dealig with somethig more basic or fudametal. There is evidece from other experimets o itroversio/extraversio ad arousal that respose competitio may be ivolved (see Broe & Storms, 1961;. W. Eyseck, 1976). There is also evidece supportig some disturbace i ecodig processes (Hamilto, Hockey, & Qui, 1972; Schwartz, 1975). Either of these otios might provide the basis for a explaatio of our results. Easterbrook's (1959) suggestio that arousal leads to a arrowig of attetio is harder to recocile with these results o forced-choice tests. Possibly, arrowig of attetio could be equated with iflexible ecodig. Alteratively, arrowig of attetio could result from iability to rapidly switch attetio from oe task to aother. This i tur could result from some geeral deficit i workig memory operatios. Implicatios for Persoality Theory ad Research These fidigs regardig the relatioship betwee persoality differeces ad performace i stressful situatios are relevat to the curret cotroversy i persoality theory with respect to the cosistecy, stability, ad utility of traits (e.g., Block, 1977; Bowers, 1973; ischel, 1968, 1973, 1977). The lack of a mai effect for traits implies that a simple model of trait cosistecy is iadequate. The complex patter of iteractios with time of day could be take as showig that traits are ot very useful predictors of performace. This, however, would be a mistake, because the effects of caffeie, time of day, ad stage of practice would ot have bee apparet without the iclusio of the idividual differeces variable. With the appropriate idividual differeces variable icluded, relative chages i cogitive performace greater tha oe stadard deviatio are observed. I additio, these fidigs are relevat to the iteractioist positio that traits are oly importat i the way they iteract with situatioal variables. Our results clearly show that the effects of impulsivity ad sociability deped o situatioal determiats of arousal. However, the process of teasig out the Trait X Situatio iteractios has bee greatly aided by our theoretical framework (the curviliearity assumptio ad the assumptio about stable idividual differeces i some aspect of arousal). It seems as if much of the curret emphasis o Trait X Situatio iteractios igores this poit about the usefuless of theory i directig the search for the Trait X Situatio iteractio. Also, it should be oted that our results suggest that the classic formulatio of itroversio/extraversio (Eyseck, 1967) eeds to be recosidered. O the first day i our studies, the two compoets of itroversio/extraversio fuctio i such a differet fashio as to make the aalysis of the secodary factor of itroversio/extraversio of dubious value. This emphasizes the importace of suggestios by Gray (1973) ad Schallig (1978) to look at impulsivity ad sociability separately. It is possible, however, that i repeated-day studies, the fuctioal idepedece of these two subscales is reduced. This eeds to be explored i further ivestigatios. It is also clear that o Day 1, the iterpretatio of mai effect differeces i arousal betwee high ad low impulsives is icorrect. The more compellig explaatio, compatible with our results ad the earlier results of Blake (1967), Folkard (1976), ad Patkai (1971), is that low impulsives reach their peak of arousal earlier i the day tha do high impulsives. The result is that low impulsives are more aroused i the morig ad less aroused i the eveig tha are high impulsives. However, it is also importat to poit out that the meaig of impulsivity, as used i

26 26 REVELLE, HUPHREYS, SION, AND GILLILAND this article, is ot completely clear. We started this series of studies with the belief that itroversio/extraversio was the best lead to follow i tryig to uderstad idividual differeces i susceptibility to stress. We ow feel that a subcompoet of this dimesio, impulsivity, is a better lead. But impulsivity as we have measured it is clearly a complex costruct. The ie-item impulsivity subscale of the EPI itroversio/ extraversio scale is ot a psychometrically pure measure of aythig. It icludes items about ot stoppig to thik, doig thigs o the spur of the momet, persoal tempo, ad risk-takig behavior. It is possible that this scale is a complex bled of differet costructs, but it is also clear that there is eough i commo i these items to produce the cosistet patter of results that we have observed i our studies. Clearly, further psychometric ad experimetal work refiig the costruct of impulsivity is i order. Fially, our results suggest that the debate betwee Eyseck, o the oe had, ad Cattell ad Guilford, o the other, as to the importace of itroversio/extraversio i a multivariate theory of persoality caot be resolved by factor aalysis aloe, but eeds to take ito accout the results of carefully plaed ad executed experimetal studies. Coclusios The most importat coclusio from this series of studies is that it is possible to show reliable performace icremets ad decremets as a fuctio of how people respod about their prefereces ad activities o a paper-ad-pecil test ad the admiistratio of caffeie. The stable patter of results from the first day allows us to specify those coditios i which we expect certai subjects to do well or badly uder caffeie-iduced stress. I the morig, low impulsives are hidered by the admiistratio of caffeie, whereas high impulsives are helped by it. I the eveig, low impulsives are helped by caffeie, whereas high impulsives are hidered by it. The results from the secod day are ot as powerful or as easily uderstadable. It is clear that somethig is happeig betwee Day 1 ad Day 2, but we are ot able to specify what is accoutig for the effect. A secod coclusio is that arousal theory ca be profitably applied to our results. It should be reiterated, however, that by this we do ot mea that itroversio/extraversio has a mai effect o arousal. It seems as if the relatioship betwee persoality ad arousal is oe of phase differeces i the diural rhythm rather tha a differece i chroic arousal, as was previously postulated. Although we are uable to specify ay particular cogitive process that could accout for our effects, we have elimiated a variety of peripheral or strategic explaatios. The complex patter of iteractios ivolvig time of day ad caffeie-iduced stress certaily elimiates motivatio ad ability ad probably elimiates distractio as possible explaatios for the persoality effects. Lookig for some basic chage i the efficiecy with which iformatio is processed seems worthwhile. Referece Note 1. Sells, S. B., Dearee, R. C, & Will, D. P., Jr. A taxoomic ivestigatio of persoality. Cojoit factor structure of Guilford ad Cattell trait markers (Tech. Rep.). Fort Worth, Texas : Texas Christia Uiversity Istitute of Behavioral Research, Refereces Bartol, C. R. Extraversio ad euroticism ad icotie, caffeie, ad drug itake. Psychological Reports, 1975, 36, Blake,. S. F. Relatioship betwee circadia rhythm of body temperature ad itroversioextra versio. Nature, 1967, 215, Blake,. S. F. Temperamet ad time of day. I W. P. Colquhou (Ed.), Biological rhythms ad huma performace. Lodo: Academic Press, Blake,. S. F., & Corcora, D. W. Itroversioextraversio ad circadia rhythms. I W. P. Colquhou (Ed.), Aspects of huma efficiecy. Lodo: The Eglish Uiversity Press, Block, J. Advacig the psychology of persoality: Paradigmatic shift or improvig the quality of research. I D. agusso & N. S. Edler (Eds.), Persoality at the crossroads. Hillsdale, NJ.: Erlbaum, 1977.

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