Experiment 2

The procedure was identical to Experiment 1, with the differences that this study was computerized in order to minimize interaction between experimenter and participants, and that we included a “no-effort-rule” control condition. Participants were again presented with video excerpts to manipulate mood and performed a mental concentration task with the instruction to regulate their effort mobilization according to either one of two effort-rules. Cardiovascular activity was assessed during habituation, the mood inductions, and task performance. During performance, we expected higher cardiovascular reactivity (especially SBP) in a negative mood than in a positive mood in both the enough-rule condition and the no-rule control condition. By contrast, in the enjoy-rule condition cardiovascular reactivity was anticipated to be stronger in a positive mood than in a negative mood. We did not anticipate any mood effects on cardiovascular reactivity during the mood inductions.

4.2.1. Method Participants and design

Seventy-nine university students (all women) with various majors (average age 24 years) received 10 Swiss Francs (about 10 US$) for their anonymous and voluntary participation. They were randomly assigned in a 2 (mood: negative vs. positive) x 3 (effort-rule: enjoy-rule vs. enough-rule vs. no-rule) x 2 (time: mood inductions vs. task performance) mixed model design with repeated measures on the last factor.

Apparatus and physiological measures

Blood pressure was assessed with the same monitor as in Experiment 1 (Par Electronics Physioport III, Berlin, Germany). HR was assessed with an electrocardiogram (ECG) to obtain more precise measures of inter-beat intervals (IBIs) than in the first study. In order to continuously monitor the electrical activity of the heart muscle, two 16-mm Ag/AgCl electrodes were attached: one on the musculature between the neck and the distal end of the right collarbone, and one on the left lateral abdomen below the lower rib cage (Lead II). The ECG signal was filtered (band pass filter: 10–40 Hz) and sampled at 500 Hz. The resulting data were transferred to an internal R-wave detector (Psylab System, Contact Precision Instruments, London, England) that calculated IBIs. The assessed IBIs were then averaged for each minute, excluding values lower than 500 ms and higher than 1500 ms to control for movement artifacts, and converted to HR scores in beats per minute. The entire experiment was run on a personal computer using experiment generation software (INQUISIT, Millisecond Software). Beginning and end of the measurement periods (habituation, mood induction, and task performance) were synchronized via Transistor–Transistor Logic signals sent by the experimental software (Inquisit 2.0, Millisecond Software, Seattle, WA) through a parallel port. Experimenter and participants were ignorant of all physiological values measured over the course of the experiment.¹³

Procedure

Participants arrived individually at the laboratory and took a seat in front of a computer screen.

The study took 45 min and was introduced as an investigation in physiological activity during relaxation—with film excerpts to watch—and a work/challenge phase—with a concentration task. After having received signed consent, the experimenter attached the blood pressure cuff and the ECG electrodes. Instructions and questions were displayed on the screen and answers were given via computer keyboard or mouse. Participants were left alone to continue the experiment on their own pace. After a short description of the study, participants answered biographical questions and rated their current mood state on two items for positive (joyful, cheerful) and two items for negative mood (sad, depressed) of the UWIST mood adjective checklist (Matthews et al., 1990)¹⁴. These ratings—which were made on 7-points scales ranging from not at all (1) to very much (7)—were presented as a standard measure for participants’ states upon entering the laboratory and later constituted the mood baseline measure. The experiment continued with the so called “relaxation period” to determine

13 We also assessed electrodermal activity, but no significant results were found.

14 Other studies from our lab found that these two adjectives for positive and negative valence had the highest internal consistency among the UWIST items.

participants’ cardiovascular baseline values. Therefore participants were instructed to sit still and to relax during the presentation of a video excerpt—a hedonically neutral film about trains, which was 8-min long. Four blood pressure measures were taken in 2-8-min intervals. ECG was recorded continuously.

After the first video excerpt, which was presented to all participants, we presented the same 8 min long video excerpts as in Experiment 1 to manipulate mood (“Naked Gun 2½” in the positive mood condition; “Love Story” in the negative mood condition). Four blood pressure measures were taken in 2-min intervals; ECG was recorded continuously. After the videos, participants first answered some filler questions about the content of the film on 7-point rating scales (e.g., ‘‘Was the movie interesting?’’,

‘‘Was the movie pleasant?’’).

Next, participants worked on the mental concentration task. However, before task onset, participants rated the four items of the UWIST mood scale again on 7-point scales, introduced as a standard measure at the beginning of this new phase of the study. Then participants worked for 5 min on a computerized version of the “d2 mental concentration task” (Brickenkamp, 1981) with the instruction to identify as many ds with exactly 2 apostrophes. One stimulus was presented per trial on the screen until participants pressed either a “yes” key or a “no” key on the computer keyboard. Before performance, participants worked on 8 test trials with correctness of response feedback. No feedback was given during the 5 min of task performance to prevent feedback effects on mood. Participants in the no-rule control condition did not receive further instructions. Participants in the enjoy-rule condition were instructed to ask themselves during the mental concentration task if they enjoyed their task performance. If the answer was “yes” they should maintain or increase the amount of effort they were investing. If the answer was “no” they should reduce their effort. By contrast, participants in the enough-rule condition were instructed to ask themselves if they were investing enough effort. They should increase effort if the answer to this question was “no”, whereas they should reduce effort if the answer was “yes”. A reminder for these two effort-rules appeared on the computer screen for 5 s after the 25^th, and each further 50^th trial of the mental concentration task. Three blood pressure measures were taken in 2 min intervals starting at task onset; again ECG was recorded continuously. After the task, the experimenter interviewed participants with regard to suspicion, debriefed, paid, and thanked them.

4.2.2. Results

Mood manipulation check

Mood sum scores and change scores (Cronbach’s αs > .76) were created as in Experiment 1 after recoding the negative mood items. A 2 (mood) x 3 (effort-rule) between persons ANOVA of the mood baseline scores did not find any significant effects (ps > .10; average M = 19.44, SE = 0.54). The 2 x 3 between-persons ANCOVA of the mood change scores (mood baseline scores as covariate) revealed only a strong association between the mood baseline values and change scores, F(1, 79) = 20.27, p < .001, but surprisingly no other significant effect (ps > .09). Unexpectedly, the means in the positive (M = -0.46, SE

= 0.64) and negative mood condition (M = -0.18, SE = 0.68) indicated nearly no mood changes after the manipulation.

Cardiovascular baselines

The IBIs assessed with the ECG were integrated to four HR scores in 2 min intervals to be comparable with the blood pressure measures. The cardiovascular baseline scores were created by averaging the measures assessed during the last four minutes of the neutral video presentation (Cronbach’s αs >.84).¹⁵ Cell means and standard errors are presented in Table 7. According to 2 (mood) x 3 (effort-rule) between persons ANOVAs, there were no differences between the experimental conditions for DBP and HR (all ps > .06). Only the ANOVA of the SBP baseline values revealed a main effect of mood, F (1, 73) = 4.08, p < .05. This was considered in an ANCOVA presented below.

Cardiovascular reactivity

Reactivity scores (all Cronbach’s αs > .89) were constituted and preliminarily analyzed as in Experiment 1. Concerning associations between baselines and reactivity scores, 2 (mood) x 3 (effort-rule) x 2 (time) ANCOVAs did not find any significant effects (ps > .11) for SBP and DBP but a reliable association for HR: F(1, 72) = 75.83, p < .001.

SBP reactivity. Cell means and standard errors appear in Figure 10. The 2 (mood) × 3 (effort-rule)

× 2 (time) ANOVA revealed a significant main effect of time, F(1, 73) = 38.82, p < .001, reflecting stronger reactivity during task performance (M = 3.58, SE = 0.72) than during the mood inductions (M = 0.28, SE = 0.46). Most relevant, the expected three-way interaction between mood, effort-rule, and time was also significant, F(2, 73) = 9.56, p < .001. A 2 (mood) x 3 (effort-rule) between persons ANOVA of SBP

15 We calculated the physiological baseline values from the four last minutes of the habituation period because for all parameters the last two measures did not differ significantly from one another (ps > .15).

reactivity during the mood inductions found no reliable effects (ps > .26). However, for the task performance period a 2 (mood) x 3 (effort-rule) ANOVA revealed the expected reliable Mood x Effort-rule interaction, F(2, 73) = 9.28, p < .001. In clear support of the predictions, additional cell comparisons showed that SBP reactivity in the no-rule condition was significantly stronger in a negative mood (M = 6.88, SE = 2.05) than in positive mood (M = 1.42, SE = 1.28), t(73) = 2.19, p < .02. The same mood effect occurred in the enough-rule condition: Reactivity was stronger in a negative mood (M = 5.57, SE = 1.31) than in a positive mood (M = -0.74, SE = 1.31), t(73) = -2.56, p < .006. Most relevant, mood had the opposite effect in the enjoy-rule condition. Here SBP reactivity in a positive mood was significantly stronger (M = 7.80, SE = 2.11) than in a negative mood (M = 0.58, SE = 2.23), t(73) = 2.89, p < .003. These results completely support the predictions.

Table 7. Cell Means and Standard Errors (in Parentheses) of the Cardiovascular Baseline Values (Experiment 2).

no-rule enjoy-rule enough-rule

Negative

mood

Positive mood

Negative mood

Positive mood

Negative mood

Positive mood

SBP 95.96 100.85 98.73 102.77 95.21 98.31

(2.44) (2.44) (2.44) (2.44) (2.36) (2.44)

DBP 63.19 66.04 64.58 69.04 63.43 65.50

(2.28) (1.88) (1.30) (1.76) (2.11) (1.91)

HR 75.00 77.58 75.85 72.42 67.96 68.54

(3.12) (3.43) (2.59) (2.99) (4.70) (5.04)

Note: SBP: systolic blood pressure; DBP: diastolic blood pressure; HR: heart rate. Units of measure are millimeters of mercury for SBP and DBP, beats per minute for HR.

A: Mood induction phase

SBP reactivity (mmHg)

-2 0 2 4 6 8

10 Positive mood

Negative mood

enjoy-rule enough-rule no-rule

B: Task performance phase

SBP reactivity (mmHg)

-2 0 2 4 6 8

10 Positive mood

Negative mood

enjoy-rule enough-rule no-rule

Figure 10. Cell means and standard errors of systolic blood pressure (SBP) reactivity during the mood induction (top panel) and task performance (bottom panel) periods (Experiment 2).

DBP reactivity. Cell means and standard errors are presented in Table 8. As for SBP, the 2 (mood) x 3 (effort-rule) x 2 (time) mixed model ANOVA found significantly stronger DBP reactivity during task performance (M = 3.26, SE = 0.43) than during the mood induction (M = -0.13, SE = 0.33), due to a significant time main effect, F(1, 73) = 85.35, p < .001. Moreover, there was a reliable two-way interaction between effort-rule and time, F(2, 72) = 4.87, p < .01. A separate one-way ANOVA of reactivity in the three effort-rule conditions during the mood inductions did not find any effect (p > .70).

Also the one-way ANOVA for task performance was only marginally significant, F(2, 76) = 2.67, p < .08.

However, focused comparisons found weaker reactivity in the enough-rule condition (M = 1.92, SE = 0.63) than in both the enjoy-rule condition (M = 4.05, SE = 0.80), t(76) = 2.08, p < .04, and the no-rule condition (M = 3.86, SE = 0.75), t(76) = 1.94, p < .06. The difference between the no-rule and the enjoy-rule conditions was not reliable (p > .86).

HR reactivity. Cell means and standard errors are represented in Table 8. The 2 (mood) x 3 (effort-rule) x 2 (time) baseline-adjusted ANOVA of HR reactivity only found a reliable time effect, F(1, 72) = 4.47, p < .04, reflecting stronger reactivity during task performance (M = 0.67, SE = 1.60) than during the mood inductions (M = -2.75, SE = 1.42). No other effect or interaction approached the conventional level of statistical significance (ps > .08).

Table 8. Cell Means and Standard Errors (in Parentheses) of the DBP and HR reactivity (Experiment 2).

no-rule enjoy-rule enough-rule

Note: DBP: diastolic blood pressure; HR: heart rate. Units of measure are millimeters of mercury for DBP, beats per minute for HR.

Task performance

As in the previous study, task performance was analyzed in terms of the total number of performed stimuli and the net performance index (i.e., detected symbols minus errors). A 2 (mood) x 3 (effort-rule) between-persons ANOVA of the total number of performed stimuli revealed only a significant effort-rule main effect, F(2, 79) = 3.84, p < .03. Follow-up comparisons found that more stimuli were performed in the no-rule condition (M = 268.69, SE = 5.33) than in the enough-rule condition (M = 245.30, SE = 7.73), t(73) = 2.74, p < .01. The differences to the enjoy-rule condition (M = 253.54, SE = 4.48) were not significant (ps > .09). Also the ANOVA of the net performance index found an effort-rule main effect, F(2, 79) = 3.36, p < .05, reflecting better performance in the no-rule condition (M

= 255.88, SE = 5.57) than in the enough-rule condition (M = 232.30, SE = 8.12), t(73) = 2.58, p < .01. The differences to the enjoy-rule condition (M = 241.69, SE = 5.09) were not significant (ps > .13). Cell means and standard errors are depicted in Table 9.

Note: Net performance index = detected symbols minus errors

4.2.3. Discussion

The manipulation effects on SBP reactivity, our primary dependent variable, supported the predictions and replicate the initial findings of Experiment 1—this time all effects and cell comparisons attained the conventional level of statistical significance. When participants asked themselves if they mobilized enough resources or worked on the mental concentration task without an explicit effort-rule, systolic reactivity was stronger in a negative mood than in a positive mood. Most relevant, this effect was inversed, resulting in significantly stronger systolic reactivity in a positive mood than in a negative mood, when participants asked themselves if they enjoyed task performance. The no-rule control condition replicated previous research on mood effects on effort mobilization and revealed stronger reactivity in a negative mood than in a positive mood, suggesting that an enough-rule is the default judgment in resource mobilization. Similar effects have been reported by Martin et al. (1993) concerning mood effects on persistence. The present effects in the no-rule condition are in accordance with the idea that effort mobilization is guided by the general principle of resource conservation, as posited in motivational intensity theory (Brehm & Self, 1989) and supported by numerous studies that investigated resource mobilization without considering the effects of moods (see Wright & Kirby, 2001 for a review).

This study did again not provide any evidence for mood effects on resource mobilization in the context of the mood inductions, i.e. before onset of the mental concentration task that explicitly asked for effort mobilization and in which participants could use their moods as information for their effort mobilization rule. Together with the evidence for the context-dependency of moods’ effect on resource mobilization during task performance, this lends further support to the idea that moods themselves are not motivational states (Gendolla, 2000). As in Experiment 1, effects on the reactivity of DBP and HR were less sensitive to the manipulations, which is not surprising for the physiological reasons discussed above.

One obvious shortcoming of the present study is that the verbal mood manipulation check was not significant. This leads to the puzzle that the mood manipulation had the predicted significant effect on the main dependent variable, resulting in the predicted complex interaction effect on SBP reactivity, while there is no direct evidence for experienced mood changes due to the manipulation. However, it is clear that self-report measures of internal states have their own problems (Wilson, 2002), and that verbal manipulation checks are of limited validity as indicators of efficiently manipulated psychological processes—especially when no plausible alternative explanation for predicted effects on dependent

variables exists (Sigall & Mills, 1998). Given that the here applied mood manipulation had strong effects on effort mobilization and both verbal mood manipulation checks (e.g., Gendolla & Krüsken, 2002a, 2002b) and facial muscular activity (Silvestrini & Gendolla, 2007, in press-b) in our past research, and given further that the present effects on the dependent variable were as predicted, we are confident that our mood manipulation was effective. Moreover, it is of note that the verbal mood manipulation was also significant in Experiment 1. However, we run another study to assure that the present computerized procedure has significant effects on both participants’ self-reported moods and resource mobilization.