siology 63 (2007) 294–301www.elsevier.com/locate/ijpsycho

International Journal of Psychophy

Incentive value, unclear task difficulty, and cardiovascularreactivity in active coping☆

Michael Richter ⁎, Guido H.E. Gendolla

University of Geneva, Switzerland

Received 25 April 2006; received in revised form 6 December 2006; accepted 6 December 2006Available online 15 December 2006

Abstract

An experiment with 44 participants assessed the moderating effects of four levels of incentive value on cardiovascular responses in activecoping. Randomly assigned to one of four different incentive conditions, participants performed a memory task without knowing its difficulty inadvance. By means of successfully performing the task participants could either win no reward, 10 Swiss Francs, 20 Swiss Francs, or 30 SwissFrancs. In accordance with the theoretical predictions derived from motivational intensity theory, reactivity of systolic blood pressure and heartrate monotonically increased with incentive value. Thereby, these findings provide additional empirical evidence for the predictions ofmotivational intensity theory with regard to unclear task difficulty and extend recent research (Richter, M., Gendolla, G.H.E., 2006. Incentiveeffects on cardiovascular reactivity in active coping with unclear task difficulty. Int. J. Psychophysiol. 61, 216–225.), which was not conclusiveregarding the predicted monotonic relationship between incentive value and cardiovascular reactivity under conditions of unclear task difficulty.© 2006 Elsevier B.V. All rights reserved.

Keywords: Incentive value; Unclear task difficulty; Cardiovascular reactivity; Active coping

1. Introduction

Evidence supporting an integrative perspective of perfor-mance-related cardiovascular reactivity (Wright, 1996) built onthe predictions of motivational intensity (Brehm and Self, 1989)and Obrist's active coping approach to cardiovascular adjust-ments (Obrist, 1981, 1976) is accumulating. Motivationalintensity theory deals with the mobilization of resources ininstrumental behavior (i.e., the mobilization of energy for goalattainment). Based on the assumption that organisms orient theirinvestment of energy on a resource conservation principle whenthey execute instrumental behavior (i.e., organisms try to avoidthe waste of resources), the theory makes two fundamentalpredictions: (1) If task demands are clear, resource mobilization

☆ We would like to thank Sandrine Oliveira for her help by serving as hiredexperimenter, and Kerstin Brinkmann, Joana Isabel de Burgo de Lima Ramos,and Nicolas Silvestrini for helpful comments on an early draft of thismanuscript.⁎ Corresponding author. University of Geneva, FPSE, Department of Psychol-

ogy, 40, Bd. du Pont d'Arve, CH-1211 Geneva 4, Switzerland. Tel.: +41 22 379 9232; fax: +41 22 379 92 19.

E-mail address: Michael.Richter@pse.unige.ch (M. Richter).

0167-8760/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.ijpsycho.2006.12.002

should be proportional to task difficulty as long as the necessaryamount of energy is justified by the importance of success(which determines the hypothetical maximum of energy that ismobilized for a given task). If task demands exceed the maximalresources that are justified for goal attainment, organisms do notmobilize any energy to cope with it. (2) If task demands areunclear (unclear difficulty) or the difficulty of a task can bechosen by the performers themselves (unfixed difficulty),resource mobilization should correspond to the importance ofsuccess. Integrating Obrist's observations that the cardiovascu-lar system reacts proportionally to the level of task demandwhen individuals can actively cope with a challenge, Wright(1996) has postulated that the predictions of motivationalintensity theory should also apply to cardiovascular responses.During the last twenty years numerous experimental studiessupported this integrative perspective.

Researchers have demonstrated that the cardiovascularsystem responds proportionally to task difficulty as long astask success is possible and the necessary resources are justifiedwhen the difficulty of instrumental behavior is fixed on a certainlevel ( fixed difficulty) (Bongard, 1995; Bongard and Hodapp,1997; Gellatly and Meyer, 1992; Gerin et al., 1995; Gendolla

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and Richter, 2006a,b; Light, 1981; Lovallo et al., 1985; Smithet al., 1990, 1997, 2000; Storey et al., 1996; Sherwood et al.,1990). Empirical research also supported the second part of theintegrative model: when task difficulty could be chosen by theperformers themselves (Fowles et al., 1982; Gendolla andRichter, 2005; Tranel et al., 1982; Wright et al., 2002, 1995,Experiment 2), cardiovascular reactivity was directly related tothe importance of task success. However, a third part of theintegrative model has nearly completely been ignored: incontrast to the vast bulk of research on cardiovascular reactivityunder conditions of fixed and unfixed task difficulty, researchinvolving tasks with fixed, but unclear task difficulty is veryrare.1

Early studies that were conducted outside the conceptualframework of motivational intensity theory (Belanger andFeldman, 1962; Fowles et al., 1982; Hahn et al., 1962; Tranelet al., 1982) have been quoted as evidence for unfixed difficultyeffects (see Wright et al., 2002). However, since these studiesdid not involve any direct manipulation of the clarity of taskdifficulty, they can also be interpreted as reflecting resourcemobilization processes under conditions of unclear taskdifficulty. Thus, it remains open if cardiovascular responseswere due to unfixed or due to unclear task difficulty. Introduc-ing a direct manipulation of unclear task difficulty, Wright,Heaton, and Bushman (reported in Wright and Brehm, 1989)were the first to empirically test the predictions of motivationalintensity theory for unclear task difficulty. Participants, whoexpected to perform a memory task, were either informed thatthey would receive an easy task (clear difficulty) or that one offive tasks that differed in difficulty would be randomly assignedto them (unclear difficulty). Supporting the predictions ofmotivational intensity theory systolic blood pressure reactivitywas only directly determined by the incentive presented forsuccessful task performance—either a music record or a pen—when participants were not informed in advance about thedifficulty of the task. When participants knew what they had toexpect, systolic blood pressure reactivity was low andindependent of the promised reward. However, assessing onlyanticipatory cardiovascular responses before task performance,the experiment of Wright et al. is not conclusive with regard tocardiovascular responses during performance. Furthermore, itis possible that the high systolic reactivity in the unclear/recordgroup resulted not from high success importance due to thevaluable record but reflected the resources necessary to copewith the highest task demand participants could expect to beconfronted with.

Recently, Richter and Gendolla (2006) investigated cardio-vascular reactivity under conditions of unclear task performancein two experiments that administered a stronger manipulation ofunclear task difficulty and assessed cardiovascular reactivityduring task performance. In both experiments participants

1 Unclear task difficulty refers to situations where the difficulty of a task isfixed on a certain level, but performers are ignorant of this level of taskdifficulty. Therefore, unclear task difficulty clearly differs from tasks wheretask difficulty can be chosen by the performers themselves (unfixed taskdifficulty) and from tasks where participants have a clear idea about taskdifficulty ( fixed task difficulty).

performed a memory task either knowing the level of taskdifficulty in advance or being ignorant of it. Furthermore,participants could win either a relatively valuable or a lessvaluable reward by succeeding. Cardiovascular reactivity wasdetermined by incentive value only when participants wereignorant of the objective task difficulty level (i.e. when taskdifficulty was unclear). This effect occurred independent of theobjective difficulty of the task—which was easy in Experiment1 and extremely difficult in Experiment 2. When participantshad received information concerning task difficulty, cardiovas-cular reactivity was low, independent of the reward they couldwin. These results seem to support the idea that successimportance and reward value, respectively, directly determinecardiovascular reactivity when task difficulty is unclear.However, an alternative explanation is also plausible.

As noted above, past research has shown that successimportance limits the proportional relationship between taskdifficulty and cardiovascular reactivity when participants havean idea about task difficulty (for reviews Wright, 1996; Wrightand Kirby, 2001). If success is impossible or if the necessaryresources for successful performance are not justified bysuccess importance, no resources are mobilized for taskperformance and cardiovascular reactivity is correspondinglylow (e.g., Gendolla and Richter, 2005). Supposing that Richterand Gendolla's difficulty manipulation did not create a situationof unclear task difficulty but resulted in an impression of a taskwith fixed high difficulty, one could alternatively explain thedifferences between the reward groups in the unclear conditionsby an interaction of task difficulty and success importance.Accordingly, expecting a “difficult” task, the reward conditionscould have differed with regard to the amount of justifiedresources. In the high reward conditions the necessary resourcescould have been seen as being justified, whereas they were notjustified in the low reward conditions. Consequently, a lowamount of resources was mobilized in the low rewardconditions—reflected by low cardiovascular reactivity—and ahigh amount of resources was mobilized in the high rewardconditions—reflected by high cardiovascular reactivity. Thus,the Richter and Gendolla (2006) findings could also beexplained in terms of an interaction between task difficultyand success importance. In summary, none of the past experi-ments did unequivocally support the predictions of motivationalintensity theory that cardiovascular reactivity directly dependson success importance or incentive value, respectively, whenperformers are ignorant of task difficulty.

The present experiment aimed to close this gap in theempirical evidence for the predictions of motivational intensitytheory by demonstrating for the first time the monotonic rela-tionship between success importance and cardiovascularreactivity under conditions of unclear task difficulty. Therefore,cardiovascular reactivity was assessed in the context of anunclear and difficult task. Furthermore, to create different levelsof success importance, incentive value was manipulated bymeans of presenting four different levels of monetary reward fora successful task performance. Since designs that compare onlytwo levels of incentive value are always open to interpreta-tions in terms of an interaction of task difficulty and success

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importance, using four levels of reward allowed us to unequiv-ocally investigate the relationship between incentive value andcardiovascular reactivity under conditions of unclear taskdifficulty. Based on the predictions of motivational intensitytheory for unclear task difficulty (Brehm and Self, 1989) and onthe psychophysiological literature (e.g., Belanger and Feldman,1962; Bongard, 1995; Fowles et al., 1982; Tranel et al., 1982;Gendolla and Krüsken, 2001; Gerin et al., 1995; Hahn et al.,1962; Light, 1981; Lovallo et al., 1985; Obrist, 1981; Sherwoodet al., 1990; Smith et al., 1997, 2000), we predicted thatcardiovascular reactivity—especially systolic blood pressurereactivity—should show a monotonic increase with increasingincentive value.

2. Experiment

Participants performed a memory task under one of fourincentive conditions. Being ignorant of the exact difficulty ofthe memory task, participants could either earn no reward, 10Swiss Francs (about 7 USD), 20 Swiss Francs (about 14 USD),or 30 Swiss Francs (about 21 USD) for successful task perfor-mance. Systolic blood pressure, diastolic blood pressure, andheart rate were assessed during a habituation period and duringtask performance to determine cardiovascular reactivity. Basedon our theoretical reasoning, we expected a linear trend acrossthe four incentive conditions: the higher the incentive value, thestronger the cardiovascular reactivity. Furthermore, based onthe preceding empirical evidence, we expected systolic bloodpressure to respond most sensitively to the manipulation.

2.1. Method

2.1.1. Participants and designForty-four university students with various majors (37

women and 7 men; mean age 22 years) were randomly assignedto either one of four experimental conditions (incentive value:no reward vs. 10 Swiss Francs vs. 20 Swiss Francs vs. 30 SwissFrancs).2 Despite the possible monetary reward for successfultask performance, all participants received course credit for theiranonymous and voluntary participation.

2.1.2. Apparatus and physiological measurementA computer-aided multi-channel monitor (Par Electronics

Physioport III-S) measured systolic blood pressure (in millime-ter mercury [mmHg]) and diastolic blood pressure (in mmHg)via oscillometry during two measurement periods: habituationand task performance. For that, a blood pressure cuff (Boso)was placed over the brachial artery above the elbow of theparticipants' left arm and automatically inflated in 1 minintervals. Cardiac interbeat interval (in milliseconds [ms]) was

2 Gender and age distributions were as follows: 9 women and 2 men in theno-reward-condition (mean age 23.64 years, age range from 19 to 49 years), 9women and 2 men in the 10-Swiss-Francs-condition (mean age 21.64 years,age range from 18 to 30 years), 11 women in the 20-Swiss-Francs-condition(mean age 23.36 years, age range from 18 to 46 years), and 8 women and 3men in the 30-Swiss-Francs-condition (mean age 21.00 years, age range from18 to 29 years).

continuously assessed using a Psylab system (Contact PrecisionInstruments) and two 16 mm Ag–AgCl electrodes (Red Dot,3M) placed on the musculature of the right side of the neck andon the left lateral abdomen (sampling rate of the ECG signalwas 500 Hz). All obtained measures were directly stored on acomputer disk. Both participants and experimenter were ig-norant of all values obtained during the experiment. Further-more, the experimenter was hired and ignorant of thehypotheses and the particular experimental condition. Experi-ment generation software (INQUISIT, Millisecond Software)controlled the presentation of all stimuli and instructions. Thesoftware also collected and stored participants' responses.

2.1.3. ProcedureRespondents individually participated in the experiment.

They took a seat in front of a personal computer and answeredsome biographical questions, while the experimenter applicatedthe blood pressure cuff and the electrodes. During the following10 min habituation period participants read an old issue of amagazine while 8 blood pressure measures were taken in 1 minintervals (due to calibration the intervals between the first andthe second measure in each measurement period were 2 min).Interbeat interval was continuously assessed during the 10 minof habituation. At the end of the habituation period participantsreceived instructions for the memory task.

2.1.3.1. Memory task and incentive value manipulation. Weused the same memory task that has been used in the studies byRichter and Gendolla (2006) and that differs only slightly fromtasks that have been successfully employed in other studiesinvestigating cardiovascular reactivity (e.g., Gendolla andRichter, 2006b; Richter et al., 2006). Participants had to memo-rize within 5 min a list of 10 senseless letter series (ALMP,MAPR, ACPT, WPQA, CLTW, SODZ, EPQZ, QPTA, TSAM,HLYC) and to correctly recall the series at the end of theperformance period. The letter series were successivelypresented in intervals of 30 s. That is, at the beginning of taskperformance only the first group of letters (ALMP) appeared onthe monitor screen. After 30 s the second group was added(MAPR), after 60 s the third letter group emerged (ACPT), andso on. 30 s before the end of performance period all of the 10series were visible on the screen. Participants were informedthat the letter series would successively appear, but they did notreceive any information concerning the exact number of letterseries, the total performance time, or the time interval betweenthe appearances of the different letter series. Using this proce-dure to present the letter series guaranteed that task difficultyremained unclear as long as possible. Furthermore, all partici-pants were instructed to correctly memorize all of the presentedletter series and to try to correctly recall them afterwards.Participants in three of the four inventive conditions addition-ally learned that they could earn a monetary reward—either 10Swiss Francs, 20 Swiss Francs, or 30 Swiss Francs—bycorrectly recalling all of the presented letter series.

After task instructions and incentive manipulation, partici-pants in the three monetary incentive conditions rated the at-tractiveness (“How attractive does winning the reward of 10

Table 1Cell means and standard errors of mean of evaluative ratings

Mean score Standard error

Noreward

10SwissFrancs

20SwissFrancs

30SwissFrancs

Noreward

10SwissFrancs

20SwissFrancs

30SwissFrancs

AR / 4.36 5.91 6.18 / 0.66 0.64 0.46IR / 3.82 4.36 5.00 / 0.69 0.53 0.52IS 5.64 6.55 6.73 6.36 0.43 0.37 0.47 0.41DT 7.45 6.55 7.55 7.64 0.51 0.41 0.34 0.31

n=11 in each cell. AR = attractiveness of the presented reward, IR = importanceof winning the presented reward, IS = importance of succeeding in the memorytask, DT = difficulty of the task.

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Swiss Francs appear to you?”) and the importance (“Howimportant is it for you to win the reward of 10 Swiss Francs?”)of winning the promised reward. Scales ranged from, respec-tively, not at all attractive and not at all important (1) to,respectively, very attractive and very important (9).3 Further-more, all participants indicated the importance of successfullyperforming the memory task (“How important is it for you tosuccessfully perform the memory task?”) on a scale from not atall important (1) to very important (9). Participants thenperformed the task for 5 min, while 4 blood pressure measureswere taken, starting 15 s after task onset. Interbeat interval wasassessed continuously. Following the performance period,participants noted all the letter series they could recall on asheet of paper. Furthermore, they indicated the difficulty of thetask (“How difficult was it for you to successfully perform thememory task?”) on a scale ranging from very easy(1) to verydifficult(9). Finally, participants were probed for suspicion,debriefed, and received their course credit.

2.2. Results

2.2.1. Preliminary analysesPreliminary 2 (gender)×4 (incentive value) ANOVAs of the

cardiovascular baseline values found only a gender main effecton systolic blood pressure baseline values, F(1, 37)=5.51,pb .03, (all other psN .22). Men had higher systolic blood pres-sure baselines (M=112.07, SE=1.82) than women (M=102.32,SE=1.48)—a common physiological finding (Wolf et al.,1997). Gender had no significant influence on cardiovascularreactivity (all psN .05).

2.2.2. Verbal manipulation checksAttractiveness and importance ratings were analyzed using

contrasts (Rosenthal and Rosnow, 1985) to test for the predictedlinear pattern. Results showed a significant linear contrast forreward attractiveness, F(1, 30)=4.57, pb .02, MSE=3.90,and a marginally significant linear contrast for reward impor-tance, F(1, 30)=2.05, pb .09, MSE=3.74.4 Furthermore, non-significant tests of the residuals revealed that the linear patternexplained all of the significant variance (both Fsb1). The linearcontrast for success importance was not significant, F(1, 40)=1.58, pN .10, MSE=1.95. Further analyzing reward attractive-ness and reward importance ratings with focused pairwisecomparisons showed that participants in the 10-Swiss-Francs-reward-condition rated winning the reward as significantly lessattractive than participants in the 20-Swiss-Francs-reward-condition and the 30-Swiss-Francs-reward-condition, ts(30)N1.83, psb .04. Furthermore, they rated winning the reward asless important than participants in the 30-Swiss-Francs-reward-condition, t(30)=1.43, pb .09 (all other psN .22). Thus, incontrast to the general measure of success importance, reward-

3 Participants in the 10-Swiss-Francs-condition rated the attractiveness andthe importance of 10 Swiss Francs. Participants in both the 20-Swiss-Francs-condition and in the 30-Swiss-Francs-condition rated the attractiveness and theimportance of their respective reward.4 Since we expected attractiveness and importance ratings to reflect our

incentive manipulation we applied one-tailed tests for the contrasts.

related ratings showed the expected linear pattern anddemonstrated a successful manipulation of incentive value.

A oneway ANOVA showed that participants did not differ intheir task difficulty impression after task performance, pN .20.Means and standard errors of all ratings can be found in Table 1.

2.2.3. Cardiovascular baselinesBaseline scores for systolic blood pressure and diastolic

blood pressure were computed using the arithmetic mean of thelast four measures taken during the habituation period; interbeatinterval baseline scores were computed using the arithmeticmean of the measures obtained during the last 4 min of thehabituation period (Cronbach's alphas were .94 for systolicblood pressure baseline, .93 for diastolic blood pressurebaseline, and .99 for interbeat interval baseline).5 For the easeof readability of the statistical analysis, heart rate scores (inbeats per minute [bpm]) were calculated based on interbeatintervals obtained during habituation and task performance andwere used for the analysis. Oneway between-persons ANOVAsof the baseline measures of systolic blood pressure, diastolicblood pressure, and heart rate did not find any significantdifferences between the incentive conditions (all psN .34).Means and standard errors of the baseline values of allcardiovascular measures are presented in Table 2.

2.2.4. Cardiovascular reactivityWe computed cardiovascular change (delta-) scores (Llabre

et al., 1991) for each participant and each cardiovascular mea-sure by subtracting the baseline value from the arithmetic meanof the values obtained during task performance (Cronbach'salphas were .93 for systolic blood pressure performance values,.94 for diastolic blood pressure performance values, and .99 forinterbeat interval performance values). Based on our clearpredictions about the impact of incentive value on cardiovas-cular reactivity, we analyzed the reactivity scores with linear apriori contrasts (Rosenthal and Rosnow, 1985). Since none ofthe cardiovascular reactivity scores were associated with its

5 We formed the cardiovascular baseline values of the last four measures,because for systolic blood pressure, diastolic blood pressure, and interbeatinterval values decreased over the first baseline measures and only the last fourmeasures did not differ significantly from one another (all psN .08). To comparethe interbeat interval measures to systolic blood pressure and diastolic bloodpressure measures, interbeat intervals were aggregated over 1 min intervals.

Table 2Cell means and standard errors of mean of cardiovascular baseline values

Mean score Standard error

Noreward

10SwissFrancs

20SwissFrancs

30SwissFrancs

Noreward

10SwissFrancs

20SwissFrancs

30SwissFrancs

SBP 104.16 105.01 100.03 106.28 2.93 2.73 2.21 3.09DBP 67.30 66.62 64.62 67.45 2.13 1.80 2.08 1.92HR 76.02 77.73 76.89 80.67 4.41 2.33 3.88 4.74

n=11 in each cell. SBP = systolic blood pressure, DBP = diastolic bloodpressure, HR = heart rate. Systolic blood pressure and diastolic blood pressure inmmHg, heart rate in bpm.

Fig. 1. Cell means and standard errors of systolic blood pressure reactivityduring task performance. mmHg=millimeter mercury.

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respective baseline values (− .13b rsb .15, all psN .33), weanalyzed the raw reactivity values (see Benjamin, 1967; Llabreet al., 1991).6

2.2.4.1. Systolic blood pressure reactivity. The a prioricontrast was significant, F(1, 40)=4.91, pb .02, MSE=49.07,reflecting the anticipated linear relationship between incentivevalue and systolic reactivity.7 Furthermore, a non-significanteffect for the residual (Fb1) indicated that the contrast capturedall significant variance. Further exploring the pattern of systolicreactivity with focused comparisons revealed a significantdifference between the no-reward-condition and the 30-Swiss-Francs-reward-condition, t(40)=2.13, pb .03, and a marginallysignificant difference between the 10-Swiss-Francs-reward-condition and the 30 Swiss-Francs-reward-condition, t(40)=1.54, pb .07. Although all other focused comparisons were notsignificant (all psN .11), Fig. 1 clearly shows that the patternemerged as predicted.

2.2.4.2. Diastolic blood pressure reactivity. The a prioricontrast was not reliable, F(1, 40)=1.01, pN .16, MSE=38.22and focused comparisons between the conditions did not revealany significant differences (all psN .18.). Cell means and stan-dard errors of the different reward conditions were as follows:M=3.20 and SE=1.44 in the no-reward-condition, M=3.77and SE=1.89 in the 10-Swiss-Francs-reward-condition,M=5.64 and SE=1.03 in the 20-Swiss-Francs-reward-condi-tion, M=5.37 and SE=2.68 in the 30-Swiss-Francs-reward-condition.

2.2.4.3. Heart rate reactivity. The linear a priori contrastshowed the predicted relationship between incentive value andheart rate reactivity, F(1, 40)=2.87, pb .05, MSE=74.12. Thetest of the residual was not reliable (Fb1). Focused compar-isons showed only a significant difference between the no-

6 Analyses of SBP, DBP, and HR reactivity with ANCOVAs using therespective baseline values as covariate did only change the significance of thea-priori contrast for HR, which was only marginally significant, F(1, 39)=2.59,pb .06. However, given that the effect for the covariate was not significant (Fb1),this result should be interpreted with caution. Including the baseline covariatesdid neither change the significance of the results for SBP or DBP, nor did itchange the significance of the focused comparisons for HR reactivity.7 Given our directed a priori hypothesis we used one-tailed tests for the a

priori contrast and the following focused comparisons.

reward-condition and the 30-Swiss-Francs-reward-condition,t(40)=1.82, pb .04 (all other psN .11). However, Fig. 2 showsthat heart rate reactivity largely reflected the predicted pattern.

2.2.5. Task performanceThe total number of recalled letter series, the number of

correctly recalled letter series, and the percentage of correctlyrecalled letter series (quotient of the number of correctly recalledseries and the total number of recalled series) were examined asperformance indicators. Oneway ANOVAs showed no signifi-cant main effects (all psN .23). Further examining the data forreliable associations between reactivity scores and performancevalues revealed no significant effects, as well,− .16b rsb .16,psN .31. Performance values for the respective conditions can befound in Table 3.

3. Discussion

The present experiment supports the predictions of motiva-tional intensity theory (Brehm and Self, 1989) and Wright's(1996) integrative analysis for cardiovascular reactivity under

Fig. 2. Cell means and standard errors of heart rate reactivity during taskperformance. bpm=beats per minute.

Table 3Cell means and standard errors of mean of performance values

Mean score Standard error

Noreward

10SwissFrancs

20SwissFrancs

30SwissFrancs

Noreward

10SwissFrancs

20SwissFrancs

30SwissFrancs

R 5.73 6.36 6.73 5.82 0.51 0.66 0.56 0.48CR 4.45 4.73 4.90 3.64 0.58 0.63 0.51 0.47PCR 76.35 74.99 74.63 60.93 5.81 6.08 6.17 5.77

n=11 in each cell. R = total number of recalled letter series, CR = number ofcorrectly recalled letter series, PCR = percentage of correctly recalled letterseries.

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conditions of unclear task difficulty and closes a gap in theevidence for this approach. Systolic reactivity monotonicallyincreased with increasing incentive value—our successfulmanipulation checks demonstrate that the attractiveness andimportance of winning the promised reward did indeed differbetween the incentive conditions—thereby demonstrating thepredicted relationship between cardiovascular reactivity andincentive value. Heart rate reactivity showed the same pattern.However, heart rate effects were not as pronounced as forsystolic blood pressure reactivity due to equally strongcardiovascular reactivity in the two intermediate incentiveconditions. Diastolic blood pressure reactivity did not changewith incentive value.

The lack of incentive effects on diastolic blood pressurereactivity in spite of significant influences on systolic bloodpressure and heart rate reactivity is not surprising consideringWright's (1996) theorizing and previous research (e.g., Al'absiet al., 1997; Bongard, 1995; Gendolla and Richter, 2005; Gerinet al., 1995; Lovallo et al., 1985; Smith et al., 1990; Storey et al.,1996; Wright and Dill, 1993). According to Wright's applica-tion of Obrist's (1981) active coping approach to motivationalintensity theory (Brehm and Self, 1989), resource mobilizationin active coping situations should be mediated by the impact ofthe sympathetic nervous system on the heart. Since systolicblood pressure is the most sensitive measure for sympatheticdischarge to the heart among our cardiovascular parameters(Berne and Levy, 1977; Brownley et al., 2000; Levick, 2003;Obrist, 1976, 1981; Papillo and Shapiro, 1990; Wright, 1996),effects of resource mobilization should be the most pronouncedfor systolic blood pressure reactivity—as it was in this case. Thepresent manipulation effect on heart rate reactivity might havebeen a result of sympathetic effects outweighing parasympa-thetic effects. As heart rate is determined by both sympatheticand parasympathetic influences, changes of sympathetic activ-ity are only visible if sympathetic influences are not masked byparasympathetic effects. In line with previous research that hasreliably found effects for systolic blood pressure but less con-sistently effects on diastolic blood pressure reactivity, we alsofound no effects for diastolic blood pressure (e.g., Al'absi et al.,1997; Bongard, 1995; Gerin et al., 1995; Lovallo et al., 1985;Smith et al., 1990; Storey et al., 1996; Wright and Dill, 1993).Diastolic blood pressure reactivity is not strongly related tosympathetic influences on the myocardium. However, strongchanges of myocardial contractility might result in parallel

increases in systolic blood pressure and diastolic blood pressure(e.g., Lovallo et al., 1985; Sherwood et al., 1990). But diastolicblood pressure effects might also result from greater vasocon-striction than vasodilation (e.g., Storey et al., 1996).

In sum, our data concur with the theoretical position ofWright and Obrist and with previous research investigating thepredictions of motivational intensity theory. However, giventhat we did not directly assess myocardial contractility orperipheral resistance in this experiment, we can only speculateabout the underlying autonomic mechanisms and alternativeexplanations might apply, as well. For instance, there isevidence that in certain situations incentive effects in activecoping might be mediated by influences on peripheral resistanceand parasympathetic withdrawal (Waldstein et al., 1997).However, beside the considerations concerning the role of theunderlying autonomic mechanisms our data are in line withprevious research on cardiovascular effects in active coping thathave demonstrated that motivational intensity theory can predictreliably systolic blood pressure reactivity in many differenttypes of active coping situations.

The most important result on the conceptual level is that ourdata clearly support the predictions of motivational intensitytheory for unclear task difficulty: when task difficulty is unclear,cardiovascular reactivity and resource mobilization, respective-ly, monotonically follow incentive value. Previous research haseither been concerned with cardiovascular reactivity under fixedand unfixed task difficulty (for reviews Wright, 1996; Wrightand Kirby, 2001), did not involve a direct manipulation ofunclear task difficulty (Belanger and Feldman, 1962; Fowleset al., 1982; Hahn et al., 1962; Tranel et al., 1982), or did onlyassess anticipatory resource mobilization (Wright et al., report-ed in Wright and Brehm, 1989). Moreover, recent studies byRichter and Gendolla (2006) that showed that effects of incen-tives are moderated by the clarity of task difficulty, are notconclusive concerning the predicted monotonic relationshipbetween incentive value and cardiovascular reactivity. Thus, thepresent experiment demonstrates for the first time that cardio-vascular reactivity is directly determined by incentive valuewhen the difficulty of a given task is unknown.

Our results also offer an alternative account for the results ofearlier studies, which found positive associations betweencardiovascular responses and incentive value (e.g., Elliot, 1969;Fowles et al., 1982; Tranel et al., 1982; Hahn et al., 1962). Interms of motivational intensity theory these results have beenexplained with the unfixed difficulty hypothesis: cardiovas-cular reactivity varies in dependence on incentive value due tounfixed task difficulty (Wright et al., 2002). However, in thelight of the present experiment and the studies by Richter andGendolla (2006), it seems as likely that the found associationbetween cardiovascular reactivity and incentive value was dueto unclear task difficulty. There is no way to rule out that inthese experiments the exact level of task difficulty was un-known for participants. For instance, in one experiment (Elliot,1969) that involved several trials cardiovascular reactivity wasrelated to incentive value only during the first trials. During latertrials there was no reliable association. During the first trialstask difficulty might have been unclear and, thus, participants

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used incentive value as indicator for resource mobilization. Inthe course of task performance participants then might haveformed an impression of task difficulty and orientated resourcemobilization on this impression of difficulty. Thus, both theunclear and the unfixed hypothesis offer a reasonableexplanation for these earlier studies.

The present findings for task performance add to previousresearch, which has shown that cardiovascular reactivity andtask performance are only loosely connected (e.g., Gendolla andKrüsken, 2002). Despite the fact that other studies that used thesame type of task sometimes found significant relationshipsbetween resource mobilization and performance (Richter andGendolla, 2006), none of our performance indicators wasrelated to the different incentive conditions or associated withcardiovascular measures. As already explained in detail inprevious articles, this is not surprising. Resource mobilizationor effort, respectively, is only one determinant of performancebut does not equal performance. Other variables like the abilityof the performer or the strategy used to cope with the taskinfluence performance, as well (see Locke and Latham, 1990).Effects of these variables can mask the relationship betweenresource mobilization and achievement and offer thereby anexplanation why empirical studies do not consistently findreliable associations between resource mobilization and perfor-mance. Furthermore, there is evidence that some types of tasksare more promising for finding associations between cardio-vascular responses and task performance than others. Forinstance, the association between resource mobilization andperformance seems to be strong in tasks that strongly rely onattention processes (Gaillard and Kramer, 2001; Gendolla andRichter, 2005)—which clearly does not apply to our memorytask. However, since performance was not in the focus of thepresent study, we used a memory task that was less sensitive forperformance effects but allowed a stronger manipulation ofunclear task difficulty.

In summary, the presented experiment supports the predic-tions of motivational intensity theory (Brehm and Self, 1989)and Wright's (1996) integrative analysis for active copingsituations with unclear task difficulty. For the first timeempirical data show that incentive value and cardiovascularreactivity are monotonically related under conditions of uncleartask difficulty: the more valuable the incentive promised for asuccessful task performance, the stronger the cardiovascularreactivity and resource mobilization, respectively.

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