Article
Reference
The effort-related cost of implicit pain
SILVESTRINI, Nicolas
Abstract
The present study investigated implicit processes associated with pain and tested the idea that priming pain during task performance systematically influences effort mobilization—i.e., motivational intensity. Primed pain was predicted to increase perceived task difficulty and in turn effort mobilization but only when success was justified by a high incentive. Effort-related cardiovascular reactivity was assessed during a habituation period and a difficult short-term memory task presenting pain-related or neutral words together with a moderate or high incentive for success. Results fully supported the predictions. Cardiovascular reactivity was especially strong in the pain-prime/high-incentive condition compared to the other three conditions. Moreover, participants felt less capable to perform the task in the pain-prime than in the neutral-prime condition. Participants made also more errors during the task in the painprime condition than in the neutral-prime condition. These findings show that implicit pain has a systematic influence on effort mobilization and a similar detrimental effect on task performance as physical [...]
SILVESTRINI, Nicolas. The effort-related cost of implicit pain. Motivation science, 2015, vol.
1, no. 3, p. 151-164
DOI : 10.1037/mot0000020
Available at:
http://archive-ouverte.unige.ch/unige:88385
Disclaimer: layout of this document may differ from the published version.
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Running head: Implicit Pain and Effort
The Effort-Related Cost of Implicit Pain
Nicolas Silvestrini
University of Geneva, Switzerland
Published manuscript: Silvestrini, N. (2015). The effort-related cost of implicit pain. Motivation Science, 1(3), 151-164. doi: 10.1037/mot0000020
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Author Notes: I would like to thank Julie Dehan for her help as hired experimenter and Michael Richter and Guido Gendolla for their helpful remarks on a previous version of this manuscript.
Mailing Address: Nicolas Silvestrini
Dpt. of Psychology, UNI-MAIL 40, boulevard du Pont d'Arve CH-1205 Geneva
Tel: +41 22 379 92 68 Fax: +41 22 379 92 29
Email : nicolas.silvestrini@unige.ch
Abstract
The present study investigated implicit processes associated with pain and tested the idea that priming pain during task performance systematically influences effort mobilization—i.e., motivational intensity. Primed pain was predicted to increase perceived task difficulty and in turn effort mobilization but only when success was justified by a high incentive. Effort-related cardiovascular reactivity was assessed during a habituation period and a difficult short-term memory task presenting pain-related or neutral words together with a moderate or high incentive for success. Results fully supported the predictions. Cardiovascular reactivity was especially strong in the pain-prime/high-incentive condition compared to the other three conditions. Moreover, participants felt less capable to perform the task in the pain-prime than in the neutral-prime condition. Participants made also more errors during the task in the pain- prime condition than in the neutral-prime condition. These findings show that implicit pain has a systematic influence on effort mobilization and a similar detrimental effect on task
performance as physical pain. Implications for other effortful processes associated with self- regulation and pain condition are discussed.
Keywords: Effort, priming, pain, incentive, cardiovascular response
Introduction
Starting three decades ago, research on priming has revealed evidence that human behavior may be influenced by implicitly processed stimuli (see Bargh, 2006; Bargh &
Chartrand, 1999; Custers & Aarts, 2005; Dijksterhuis & Aarts, 2010). Representations of attitudes, stereotypes but also goals and emotions can be activated implicitly and influence behavior (Gendolla, 2012; Greenwald & Banaji, 1995; Winkielman & Berridge, 2004).
Extending this previous research, the present study aimed to investigate implicit processes associated with pain and tested the idea that priming pain influences effort mobilization—i.e., the intensity aspect of motivation.
Implicit Affect and Effort Mobilization
A recent research program revealed a systematic influence of implicit affect primes on effort mobilization during task performance (Freydefont, Gendolla, & Silvestrini, 2012;
Gendolla, 2012; Gendolla & Silvestrini, 2011; Lasauskaite Schüpbach, Gendolla, &
Silvestrini, 2014; Silvestrini & Gendolla, 2011b). According to the implicit-affect-primes-effort model (Gendolla, 2012), individuals acquire knowledge about affective states through learning and life experiences. This knowledge can later be implicitly activated by primes without eliciting explicit emotions. In the context of task performance, implicit affect, which can be defined as automatic activation of affective states' mental representations (e.g., Quirin, Kazén, & Kuhl, 2009), are expected to activate knowledge about ease or difficulty experiences typically associated with different affective states—e.g. sadness and fear with difficulty, happiness and anger with ease. This knowledge is expected to influence the evaluative judgment of task difficulty and in turn effort mobilization because effort increases with experienced task difficulty as long as success is possible and justified (Brehm & Self, 1989). So far the predictions of the model were supported for the emotions of sadness, happiness, and anger. However, the model aims to apply to any affective states that are associated with ease or difficulty. The present study aimed to investigate the influence of
primes related to the experience of pain on effort mobilization with the assumption that pain can be considered as an affective state associated with difficulty.
Pain, Attention, and Implicit Pain
Defined as ‘‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage’’ (Merskey, 1986), pain is a very common affective experience. Unless having a pathological condition, every individual has felt pain a countless number of times in his/her life. Actually, pain plays a very important role in survival due to its alarm function that enables the organism to avoid or minimize threat. Some authors consider pain as part of a complex and hierarchical motivational system that allows interrupting ongoing actions to cope with potential or actual threat (Eccleston & Crombez, 1999). Following this idea and in the context of the relationship between pain and cognitive functioning, it is now a common assumption that pain automatically demands attention to allow interrupting ongoing actions (Keogh, Moore,
Duggan, Payne, & Eccleston, 2013; Moore, Keogh, & Eccleston, 2012). Supporting this idea, numerous studies using a cognitive task together with painful stimuli showed impaired
performance in difficult cognitive tasks when experiencing pain (for a review and a conclusive experiment, see Buhle & Wager, 2010). This finding suggests that overlapping cognitive resources play a role in both pain processing and cognitive performance. Moreover, this finding also suggests that pain increases the perceived difficulty of executing a task due to additional demand on executive functioning. Therefore, it is expected that the experience of pain is associated with the feeling of difficulty in the context of task performance and that this association is represented in memory through learning and life experiences as for other affective states (Gendolla, 2012).
Learning associations between painful experiences and objects or situations is perhaps one of the most important and oldest systems to promote survival. Therefore, a strong associative memory network can be expected for pain, which could be activated by cues related to pain as other associative networks (Bargh, 2006; Collins & Loftus, 1975).
Recent research supported this idea and showed that representations of pain can be activated by priming (Dillmann, Miltner, & Weiss, 2000; Meerman, Verkuil, & Brosschot, 2011). Prime words related to pain or illness resulted in an increase of following pain
responses suggesting an activation of a pain memory network. However, no study has tested the influence of pain primes during a cognitive task. As presented above for other affective states (see Gendolla, 2012), priming pain words is expected to activate mental
representations about past pain experience. In the context of task performance, priming pain is expected to activate the information that performing a cognitive task when coping with pain is more difficult. Therefore, it is expected that priming pain leads to increased subjective task difficulty and in turn effort mobilization as long as success is possible and worthwhile (Brehm
& Self, 1989).
Effort Mobilization and Cardiovascular Reactivity
Integrating motivational intensity theory (Brehm & Self, 1989) with the active coping approach (Obrist, 1981), Wright (1996) proposed that effort mobilization can be assessed as performance-related changes in beta-adrenergic sympathetic activity on the heart.
Accordingly, cardiac preejection period (PEP), the time interval between left ventricular excitation and the opening of the aortic valve (Berntson, Lozano, Chen, & Cacioppo, 2004), represents the best noninvasive measure of effort mobilization because PEP reflects myocardial contractility, which is primarily controlled by beta-adrenergic influences (e.g., Newlin & Levenson, 1979). In support of this idea, PEP has been found to sensitively
respond to variations in experienced task demand, incentive value, and combinations of both (Richter, Friedrich, & Gendolla, 2008; Richter & Gendolla, 2009; Silvestrini & Gendolla, 2011a).
Also systolic blood pressure (SBP) has been used to quantified effort as it is systematically influenced by sympathetic activity through cardiac contractility (Gendolla &
Richter, 2010; Wright, 1996; Wright & Kirby, 2001). However, beside cardiac contractility, SBP is also influenced by peripheral resistance, which is not systematically influenced by
sympathetic activity (Levick, 2003). Diastolic blood pressure (DBP) is still more strongly influenced by peripheral resistance than SBP but some evidence indicates that DBP sometimes responds together with PEP (Lovallo et al., 1985) and SBP (Silvestrini &
Gendolla, 2011a). Heart rate (HR) may also responds together with PEP and SBP but only when the sympathetic impact is stronger than the parasympathetic impact, which is not always the case (Berntson et al., 2004). To resume, PEP is the most reliable indicator of effort mobilization among these cardiovascular measures due to the direct impact of beta- adrenergic sympathetic activity on this parameter.
The Present Study
The present study tested the impact of pain primes on effort-related cardiovascular reactivity and performance. The experiment started with a habituation period where cardiovascular baseline values were assessed. Then, participants worked on a difficult cognitive task integrating briefly presented and masked words related to pain or neutral words during which cardiovascular reactivity was assessed. Moreover, participants could receive either a moderate or a high monetary incentive in case of success. Task incentive was manipulated for two reasons: 1) To test the predictions of motivational intensity theory regarding the interplay between task difficulty and importance of success (see below for the specific predictions); 2) To simulate a situation where someone is in pain and has no specific motivation to realize a concurrent difficult action compared to a situation where he/she is highly motivated to realize this action. As described below, incentive is expected to play a crucial role in determining effort mobilization when the task is perceived as highly difficult.
Participants primed with pain words were expected to perceive the task as more difficult. According to motivational intensity theory (Brehm & Self, 1989), effort mobilization is determined by subjective difficulty but only as long as success is possible and justified. In other words, if a task is too difficult and the necessary amount of effort for its execution exceeds the level of justified effort, which is determined by needs or incentive, effort mobilization should be low to avoid wasting resources. Consequently, low effort-related
cardiovascular reactivity was expected in the pain-prime/moderate-incentive condition. Here, the difficult task and the increased difficulty induced by the pain primes were predicted to result in very high subjective difficulty. This high difficulty combined with a moderate incentive that did not justify the required effort was expected to lead to disengagement and low effort.
In contrast, stronger reactivity was predicted in the pain-prime/high-incentive condition because here the necessary high effort was justified by the high incentive. The neutral-prime conditions were expected to fall in between, leading to moderate cardiovascular reactivity.
Some previous studies found a relationship between effort and performance
(Gendolla & Richter, 2006; Silvestrini & Gendolla, 2013) but others did not (Freydefont et al., 2012; Silvestrini & Gendolla, 2011b). This may be explained by the fact that performance in a task is also dependent on variables such as ability or strategy, and not only on exerted effort (Locke & Latham, 1990). Moreover, regarding evidence on the detrimental effect of physical pain on performance (Buhle & Wager, 2010), priming the concept of pain could also be anticipated to mainly impair task performance. Therefore, performance was analyzed without clear a priori predictions.
Method Participants and Design
Sixty-one healthy University students (45 women, mean age 24 years) were randomly assigned to a 2 (prime: pain, neutral) 2 (incentive: moderate, high) between-persons design. Sample size was determined according to previous studies showing word priming effects on effort mobilization and which included about 15 participants per cell (Gendolla &
Silvestrini, 2010; Silvestrini & Gendolla, 2013). The experiment was stopped once the
targeted sample size was reached and no additional participants were included. Participation was voluntary and recompensed with 10 Swiss Francs (i.e., 11 USD). All participants
provided signed informed consent and the study protocol was approved by the local ethics committee. Three participants were excluded because of extreme PEP or SBP reactivity values (> 2.5 SD of the condition means), resulting in a final sample of N = 58 (42 women).
Apparatus and Physiological Measures
The procedure was computerized with a script running in E-prime 2.0 (Psychology Software Tools Inc., Pittsburgh, PA). PEP (in milliseconds) and HR (in beats per minute) were assessed using a Cardioscreen 1000 system (Medis, Ilmenau, Germany), that
continuously measured ECG (electrocardiogram) and ICG (impedance cardiogram) signals.
Four pairs of spot electrodes were attached on the right and the left side of the base of participants’ neck and on the left and right middle axillary line at the height of the xiphoid to sample (1000 Hz) thoracic impedance and electrocardiogram signals (Scherhag, Kaden, Kentschke, Sueselbeck, & Borggrefe, 2005).
Systolic and diastolic blood pressures were measured with a Vasotrack APM205A monitor (Medwave, St. Paul, Minnesota, USA). The Vasotrack system uses applanation tonometry with a pressure sensor placed on the wrist on top of the radial artery applying a varying force on the artery. Internal algorithms yield systolic and diastolic pressure each 12- 15 heart beats, i.e. 4-5 values per minute (see Belani et al., 1999, for a validation study). Due to technical problems with the Vasotrac monitor, blood pressure was measured for 25
participants with a Dinamap ProCare monitor (GE Medical Systems, Information
Technologies Inc., Milwaukee, WI) that uses oscillometry. A blood pressure cuff placed over the brachial artery above the elbow of participants’ non-dominant arm was automatically inflated in 1 min intervals. All cardiovascular measures and signals were directly stored on computer disk.
Procedure
The experiment was announced as a study on physiological responses during a cognitive task. Participants were seated in a comfortable chair in front of a desktop computer.
After preparation for the physiological measures and having obtained informed consent, the experimenter—who was hired and unaware of both the hypotheses and the experimental condition—left the participant alone and went to an adjacent control room. The experiment started with the rating of two positive (happy and joyful) and two negative (sad and
depressed) hedonic tone items of the UWIST scale (Matthews, Jones, & Chamberlain, 1990) on scales ranging from 1 (not at all) to 7 (very much) to control for differences in affective state before the manipulation that may influence subsequent effort mobilization (e.g.,
Brinkmann & Gendolla, 2008). This was followed by a habituation period (8 min) to determine participants’ cardiovascular baseline values. Participants watched a hedonically neutral documentary film on Portugal and cardiovascular activity was assessed continuously. After baseline assessment participants received instructions for a difficult Sternberg-type short- term memory task (Sternberg, 1966) calibrated according to a previous experiment (Freydefont et al., 2012).
Task trials started with a fixation cross (1000 ms) followed by a word related to pain vs. a neutral word (53 ms) that was backward masked by a string of the letter “X” (133 ms).
The prime words (pain: pain, suffer, burn, sting; neutral: color, describe, border, seam;
presented in French) were selected according to a pretest and matched in length and frequency of occurrence. Moreover, instead of primes, half of the trials presented senseless series of letters created by juggling the letters of the pain and neutral primes to prevent fast habituation to the prime words. The mask was followed by a string of 7 letters presented for 1750 ms and followed by another backward mask (a string of 7 letters “X”) and a target letter above the mask. Participants had to indicate if that letter was part of the previously presented string by pressing a “yes” or a “no” key within a response time window of 2 sec. The words and strings were displayed in capital letters and in bold (Verdana, font size = 26, screen resolution = 1280 x 1024, screen size = 11.8'' x 15''). Participants first performed 10 training trials in order to get an impression of task difficulty. The training trials comprised correctness feedback and only senseless series of letters as primes. After training, participants in the moderate-incentive condition learned that they would receive 2 Swiss Francs (about 2 USD) if they correctly responded in at least 90% of the trials. Participants in the high-incentive condition were promised 12 Swiss Francs (about 13 USD) for meeting this success criterion.
Then participants performed 32 experimental trials without feedback (i.e., in the pain
condition: 16 trials with pain words, each pain word being presented four times, and 16 trials
with senseless strings of letters as primes; in the neutral condition: 16 trials with neutral words, each neutral word being presented four times, and 16 trials with senseless strings of letters as primes). After responding, the message “response entered” appeared for 3250 ms minus participants’ reaction time, assuring that all participants worked for the same time (5 min). The inter-trial interval varied between 2 to 5 sec.
After the task participants rated experienced task difficulty, subjective ability, success importance, and attractiveness of the reward (1 = not at all, 7 = very much) and also rated again the 4 UWIST scale mood items to test for possible affective changes due to the priming. Then, participants were interviewed in a funnel debriefing procedure (Chartrand &
Bargh, 1996) about the study purpose and what they had seen during the trials. Participants who mentioned “flickers” were asked about their content.
Data Analyses
R-peaks in the ECG signal were identified using a threshold peak-detection algorithm and visually confirmed (ectopic beats were deleted). Only artifact-free cardiac cycles were included. ICG analysis software (Richter, 2010) computed the change in thoracic impedance (first derivate) and then applied a 50Hz low-pass filter to the dZ/dt signal (e.g., Hurwitz et al., 1993). The resulting dZ/dt signal was ensemble averaged (1 min periods) using the detected R-peaks (Kelsey et al., 1998). B-point location was estimated based on the RZ interval (Lozano et al., 2007), visually inspected, and corrected as recommended (Sherwood et al., 1990). The correction was applied when a notch corresponding to the B-point was clearly visible on the dZ/dT signal. PEP was determined as the time interval between R-onset in the ECG signal and B-point in the ICG signal (Berntson et al., 2004). Shorter PEP indicates a stronger beta-adrenergic impact on the heart—i.e., stronger effort.
The theory-based predictions were tested with an a priori contrast—the most powerful and thus most appropriate statistical tool to test predicted patterns of cell means (Rosenthal
& Rosnow, 1985; Wilkinson & The Task Force on Statistical Inference, 1999). As outlined in the introduction and also used in a previous experiment (Freydefont & Gendolla, 2012), the
pattern of PEP reactivity was expected to result in low responses in the moderate-
incentive/pain condition (contrast weight = - 4), stronger responses in the neutral condition in both moderate and high incentive (contrast weight = + 1), and still stronger responses in the high-incentive/pain condition (contrast weight = + 2). One-tailed tests were used for
additional cell comparisons testing directed predictions. Task performance (accuracy and reaction times) and task ratings for which there were no theory-based predictions were analyzed with conventional 2 (prime) x 2 (incentive) between-persons ANOVAs. Moreover, mood scores were analyzed with a 2 (prime) x 2 (incentive) x 2 (time) mixed-model ANOVA with repeated measures on the last factor.1
Results Cardiovascular Baselines
Cardiovascular baseline values were calculated by averaging the last 3 min of the habituation period, which were highly consistent (α > .98).2 Cell means and standard errors are presented in Table 1. Preliminary 2 (prime) 2 (incentive) ANOVAs on these baseline scores did not reveal any main effect or interaction between the conditions for all parameters (all ps > .07). Reactivity scores were obtained by subtracting the baseline values from the averaged task-related values (αs > .98). Preliminary 2 (prime) 2 (incentive) ANCOVAs with baseline scores as covariate did not reveal any association between baselines and reactivity scores (all ps > .18).
Cardiovascular Reactivity
Pre-Ejection Period. The a priori contrast on PEP reactivity was significant, F(1, 51) = 8.13, p = .006, η2 = .13. As depicted in Figure 1 (Panel A), PEP reactivity showed the
anticipated pattern. Follow-up comparisons revealed that PEP response in the pain-
prime/high-incentive condition (M = -8.89, SE = 1.67) was, as expected, stronger than in the pain-prime/moderate-incentive condition (M = -1.19, SE = 1.06), t(51) = 3.77, p < .001, η2 = .22, the neutral-prime/high-incentive condition (M = -3.18, SE = 1.52), t(51) = 2.96, p = .002,
η2 = .15, and the neutral-prime/moderate-incentive condition (M = -3.43, SE = 1.13)
conditions, t(51) = 2.78, p = .004, η2 = .13. Other comparisons were not significant (all ps >
.13).
Systolic Blood Pressure. The a priori contrast on SBP reactivity was significant, F(1, 53) = 9.82, p = .003, η2 = .16. As depicted in Figure 1 (Panel B), SBP reactivity showed the anticipated pattern. Follow-up comparisons revealed that SBP response in the pain-
prime/high-incentive condition (M = 13.58, SE = 2.50) was, as expected, stronger than in the pain-prime/moderate-incentive (M = 3.11, SE = 1.35), the neutral-prime/high-incentive (M = - 6.33, SE = 1.75), and the neutral-prime/moderate-incentive (M = 6.39, SE = 1.66) conditions (ts53 > 2.45, ps < .02, η2s > .10). Other comparisons were not significant (all ps > .08).
Diastolic Blood Pressure. The a priori contrast on DBP reactivity was also significant, F(1, 53) = 8.42, p = .005, η2 = .14. As depicted in Figure 1 (Panel C), DBP reactivity showed the same pattern than PEP and SBP. Follow-up comparisons revealed that DBP response in the pain-prime/high-incentive condition (M = 8.01, SE = 1.66) was stronger than in the pain- prime/moderate-incentive (M = 2.04, SE = 0.72), the neutral-prime/high-incentive (M = 4.77, SE = 1.13), and the neutral-prime/moderate-incentive (M = 4.63, SE = 1.30) conditions (ts53 > 1.86, ps < .04, η2s > .06). Other comparisons were not significant (all ps > .06).
Heart Rate. The a priori contrast on HR reactivity was also significant, F(1, 54) = 15.35, p < .001, η2 = .22. As depicted in Figure 1 (Panel D), HR reactivity showed a similar pattern than PEP and SBP. Follow-up comparisons revealed that HR response in the pain- prime/high-incentive condition (M = 9.36, SE = 1.97) was stronger than in the pain-
prime/moderate-incentive (M = 1.53, SE = 0.77), the neutral-prime/high-incentive (M = 6.31, SE = 0.88), and the neutral-prime/moderate-incentive (M = 3.55, SE = 0.57) conditions, (ts54 > 1.81, ps < .04, η2s > .05). The difference between HR response in the neutral- prime/high-incentive and in the pain-prime/moderate-incentive was also significant, t(54) = 2.79, p = .004, η2 = .13. Other comparisons were not significant (ps > .05).
Task Performance
Participants were more accurate in the neutral (M = 93.30%, SE = 1.18) than in the pain condition (M = 88.74%, SE = 1.86), as revealed by a main effect of prime, F(1, 54) = 4.35, p = .042, η2 = .07, in a 2 (prime) x 2 (incentive) ANOVA. Other effects were not
significant (ps > .25). Cell means are depicted in Figure 2. A 2 (prime) x 2 (incentive) ANOVA on the reaction times of correct responses did not reveal any significant effect (ps > .61).
Means and standard errors were as follow: pain-prime/high-incentive (M = 1006.45, SE = 38.76), pain-prime/moderate-incentive (M = 1018.86, SE = 51.49), neutral-prime/high- incentive (M = 1013.05, SE = 38.73), neutral-prime/moderate-incentive (M = 1043.54, SE = 37.84).
Task Ratings and Mood Scores
Participants in the pain-prime conditions felt less capable to execute the task (M = 4.93, SE = 0.23) than participants in the neutral-prime conditions (M = 5.52, SE = 0.18) as revealed by a main effect of prime in a 2 (prime) x 2 (incentive) ANOVA, F(1, 54) = 4.09, p = .048, η2 = .07, in absence of other effects (ps > .67). Cell means are depicted in Figure 3.
The task difficulty ratings were strongly correlated with subjective capability, r(58) = - .44, p <
.001, but did not reveal any significant effect in a 2 x 2 ANOVA (ps > .80). Moreover, in accordance with a successful incentive manipulation, participants rated the reward as more attractive in the high-incentive (M = 5.13, SE = 0.26) than in the moderate-incentive
conditions (M = 4.25, SE = 0.29), according to a 2 (prime) x 2 (incentive) ANOVA, F(1, 54) = 4.90, p = .031, η2 = .08, in absence of other effects (ps > .79). The ratings of the importance of success did not reveal any significant effect (ps > .56). Finally, a 2 (prime) x 2 (incentive) x 2 (time) ANOVA on the mood scores did not reveal any effects (ps > .16). Means and
standard errors of perceived difficulty, attractiveness of the reward, success importance, and mood scores are presented in Table 2.
Funnel Debriefing
The funnel debriefing procedure revealed that no participant could report the aim of the study. 22% of the participants mentioned having seen a flicker, letter, or word in the trials, but only 3 participants reported having seen words related to pain and 2 participants could mention some of the primed neutral words. This suggests that at least 91% of the
participants processed the primes without awareness of their content.
Discussion
The present study investigated the influence of primed pain on effort-related
cardiovascular reactivity and task performance. Supporting our predictions, results showed that priming pain increased effort mobilization when incentive was high. Moreover, priming pain impaired task performance, and decreased perceived capability to execute the task.
Taken together, these findings offer new insights in the interaction between pain and cognition showing the implication of implicit processes in pain experience and the influence of implicit pain on effort mobilization.
First of all, priming pain had a systematic influence on effort-related cardiovascular response. PEP reactivity presented the expected pattern with stronger reactivity in the pain- primes/high-incentive condition, lower reactivity in the pain-primes/moderate-incentive
condition, and moderate reactivity in the neutral-primes conditions. Also systolic and diastolic blood pressure and heart rate presented a similar pattern than PEP. Although PEP is the most sensitive measures of beta-adrenergic activity, some previous research also found evidence for adjustments during task performance for systolic and diastolic blood pressures or heart rate (Freydefont et al., 2012; Wright & Dill, 1993). Taken together, these findings on several cardiovascular parameters suggest a strong influence of primed pain and incentive on effort mobilization.
As expected, pain primes led to stronger effort mobilization in the high incentive condition. According to the predictions based on the implicit-affect-primes-effort model
(Gendolla, 2012), this effect occurred because priming pain was expected to activate mental representations of pain including knowledge about the experience of difficulty typically associated with pain in the context of cognitive performance. The activation of the difficulty concept by pain words was expected to increase subjective difficulty. Increased subjective difficulty associated with the objectively difficult task was predicted to result in stronger required effort that was justified by the high incentive and therefore mobilized in this condition (see Brehm & Self, 1989). In comparison, effort was low in the pain-primes/moderate-
incentive condition because, according to the predictions, the high effort required by the task and the pain words was not justified by the incentive and participants disengaged. Effort mobilization in the neutral conditions was in the middle range and not affected by incentive, which corresponds to the prediction that the effort required by the task and the neutral words was still justified by the moderate incentive.
Previous research on the interaction between pain and the cardiovascular system has revealed that pain may elicit responses like changes in heart rate (Rainville, Bao, & Chrétien, 2005). In the present study, however, the main effect of pain primes on cardiovascular reactivity was not significant suggesting that cardiovascular adjustments were not a direct response to primed pain but were rather determined by the interaction between pain primes and incentive. Also, primed pain did not significantly influence mood states making it
implausible that the effects of primed pain on effort were due to changes in mood (e.g., Brinkmann & Gendolla, 2008; Silvestrini & Gendolla, 2007).
Moreover, participants felt significantly less capable to perform the task when primed with pain words. This finding is in accordance with the prediction that priming pain should increase subjective difficulty. However, although perceived capability and perceived task difficulty were highly correlated, the effect of pain primes was only significant on perceived capability and not on perceived task difficulty. It is of note here that both ratings are expected to reflect the same construct of subjective difficulty and are very often highly correlated (as in the present study) and sometimes even combined (e.g., Silvestrini & Gendolla, 2013).
However, in some case one of these ratings may be more sensitive to variations in subjective
difficulty than the others for several reasons. Here, the high objective difficulty level that was fixed for the task maybe prevented for an effect of the primes on the rating of task difficulty whereas perceived capability rating was sensitive to the influence of the pain primes. Finally, given the potential limitations of self-reports (see Wilson, 2002), it is most relevant that the physiological findings are in support of the predictions.
Results also revealed that priming the concept of pain impaired task performance:
Participants primed with pain words made more errors than participants primed with neutral words. This result is in accordance with previous research showing decreased task
performance during physical pain experience (Buhle & Wager, 2010) and the present study is the first to find an effect of implicit pain on a concurrent cognitive task. As outlined in the introduction, task performance is not only determined by effort but also by ability or strategy (Locke & Latham, 1990). In some situation more effort may result in better performance (e.g., Gendolla & Richter, 2006; Silvestrini & Gendolla, 2013) but here effort was dissociated from performance, which has also been found in previous studies (Freydefont et al., 2012;
Silvestrini & Gendolla, 2011b). Here, the main effect of pain primes on performance may be interpreted with a different mechanism than the one for effort. It may be possible that priming pain interferes with ongoing cognitive processes in a similar way than physical pain can interrupts ongoing behavior due to its alarm function (Eccleston & Crombez, 1999). Primed pain words may be implicitly detected by the attentional system as a potential signal for threat and impairs ongoing higher-order cognitive processes relying on limited attentional resources. Consequently, this interference may decrease task performance. Interestingly, this interference may also lead to a higher subjective difficulty influencing in turn effort mobilization, which would offer an alternative explanation to the implicit-affect-primes-effort model in the context of pain. Further studies are required to distinguish between these two competing mechanisms.
Also, one might consider other alternative mechanisms that could explain the effect of pain primes on effort. For instance, pain primes may have influenced effort through the activation of the concept of fear. As pain is most of the time an unpleasant emotional
experience, one may expect that the anticipation of pain can induce fear and that the pain and the fear concepts are closely associated in memory. In the present study, words directly related to pain were used so it was expected that pain was the first concept activated. But then, it might be possible that the fear concept was in turn activated by the pain primes and influenced subjective difficulty and effort. Actually, the implicit-affect-primes-effort model (Gendolla, 2012) proposes some predictions on the influence of fear priming on effort, which correspond to the predictions proposed for pain (see Chatelain & Gendolla, 2015). Therefore, it remains an open question whether the activation of the pain concept activates the difficulty concept directly due to an association between pain and difficulty (as proposed in the
introduction) or whether it is mediated by the activation of the fear concept.
Moreover, one may also argue that pain words influenced effort because they are associated with a negative valence (see Richter et al., 2014). It is of note that previous studies suggest that the effect of affective primes on effort are emotion category-specific rather than valence-specific (Freydefont et al., 2012), but this issue has still to be
investigated in the context of pain. Therefore, although the present findings support the predictions based on the implicit-affect-primes-effort model (Gendolla, 2012), further studies are required to disentangle the issue of the underlying mechanisms. For instance, future studies may investigate more directly the semantic association between the pain concept and the difficulty concept, which should drive the effect of pain primes on effort according to the implicit-affect-primes-effort model.
The present study may have several implications. Most important, our results support the idea that pain can have an impact on effort mobilization. In the present study, this effect was found for implicit pain. However, a similar effect may be expected for physical pain.
Therefore, it is reasonable to predict that pain induces repeated increases in effort
mobilization during daily cognitive challenges. This finding can be related to models of limited and domain-general self-regulatory capacity (Baumeister, Vohs, & Tice, 2007; Solberg Nes, Roach, & Segerstrom, 2009). In the model of Solberg Nes and colleagues (2009), pain is predicted to induce self-regulatory demands, like executing challenging cognitive activities
despite the pain or exerting control over negative emotions or thoughts associated with pain.
These demands are expected in turn to impair subsequent self-regulation due to a limited capacity to exert control leading to the worsening of the pain condition and also to self- regulatory deficits like irritability, depression, or interpersonal distress. To support their model, these authors present striking similarities between impaired self-regulation in experimental studies and self-regulatory deficits observed in clinical pain populations. The present study offers more direct evidence for the consequences of pain-related stimuli on effortful demands. According to our finding, pain may result in stronger effort mobilization during daily cognitive challenges due to higher perceived difficulty, which may decrease in turn the limited and domain-general capacity to exert control and to self-regulate. In consequence, these repeated additional demands may lead to the worsening of the pain condition and the development of chronic self-regulatory deficits.
It is also noteworthy that increased effort mobilization was only observed when incentive was high. When incentive was low, effort mobilization was low suggesting disengagement due to the too high subjective demand. This finding can be related to disengagement in daily-life activities in chronic pain (Breivik, Collett, Ventafridda, Cohen, &
Gallacher, 2006). Accordingly, one can imagine that chronic pain leads individuals to perceive some daily-life activities as too challenging resulting in disengagement from these activities. In this context, our results support the idea that an increase in motivation can compensate for these increased challenges and help people to stay engaged in their daily- life activities. This finding further highlights the importance of motivation in chronic pain, as also visible in the growing literature on this topic in the past few years (Karsdorp & Vlaeyen, 2011; Schrooten et al., 2012; Van Damme, Legrain, Vogt, & Crombez, 2010; Verhoeven et al., 2010).
In conclusion, the present findings supported our predictions on the implicit influence of primed pain on effort mobilization. Interestingly, pain is most often a conscious experience.
However, in the present study, our findings suggest implicit processes in pain experience and also in interaction with cognitive functioning. These findings and also previous evidence
(Dillmann et al., 2000; Weiss, Miltner, & Dillmann, 2003) indicate that mental representations of pain can be activated implicitly as attitudes, stereotypes, goals or emotions (Bargh, 2006;
Bargh & Chartrand, 1999; Custers & Aarts, 2005; Dijksterhuis & Aarts, 2010; Gendolla, 2012). These implicit pain processes may have important consequences in acute and chronic pain conditions influencing how people process and cope with present or upcoming painful information. Further studies on these implicit processes may therefore be needed to offer a deeper understanding of pain experience. Moreover, although different mechanisms may be expected, a similar effect on effort mobilization should be found with physical compared to primed pain—which should be systematically tested in future studies. These results may therefore have clinical implications in the treatment of chronic pain condition: If pain experience increases effort mobilization and decreases a limited and domain-general capacity to exert control and to self-regulate (Baumeister et al., 2007; Solberg Nes et al., 2009), this may explain several deficits in self-regulation frequently associated with chronic pain—i.e., irritability, depression, or interpersonal distress. In this context, finding appropriate motivational incentives and fixing goals with adequate difficulty levels may play a crucial role to help chronic pain patients to overcome these deficits and cope with their pain.
Footnotes
1 Due to technical measurement problems, there were missing data for some participants. Therefore, the sample sizes slightly varied across the analyses of the single dependent variables: N=55 for PEP, N=57 for SBP and DBP, and N=58 for HR.
2 Cardiovascular baseline values were calculated from the three last minutes of the habituation period, because there was a decline in assessed values over the first 5 minutes.
However, for the last 3 minutes of the habituation period the values were stable and did not differ significantly from one another (ps > .16).
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Figure Captions
Figure 1. Cell means and standard errors of pre-ejection period (PEP, Panel A), systolic blood pressure (SBP, Panel B), diastolic blood pressure (DBP, Panel C), and heart rate (HR, Panel D) reactivity during task performance.
Figure 2. Cell means and standard errors of accuracy during task performance.
Figure 3. Cell means and standard errors of perceived capability.
Table 1
Cell Means and Standard Errors (in Parentheses) of Cardiovascular Baseline Values
Moderate Incentive High Incentive
Pain Neutral Pain Neutral
PEP
103.36 (4.18)
103.55 (4.21)
101.43 (2.68)
92.02 (3.68)
SBP
115.54 (4.01)
111.19 (4.44)
118.41 (6.26)
112.57 (7.59)
DBP
63.21 (2.17)
62.94 (3.27)
66.57 (3.75)
63.95 (5.03)
HR
74.50 (2.68)
74.19 (4.14)
76.44 (3.91)
71.27 (2.23)
Note: Cell ns = 12-15; PEP: pre-ejection period; SBP: systolic blood pressure; DBP: diastolic blood pressure; HR: heart rate. Units of measure are milliseconds for PEP, millimeters of mercury for SBP and DBP, and beats per minute for HR.
Table 2
Cell Means and Standard Errors (in Parentheses) of Perceived Difficulty, Attractiveness of the Reward, Success Importance, and Mood Scores
Moderate Incentive High Incentive
Pain Neutral Pain Neutral
Perceived Difficulty
3.64 (0.43)
3.57 (0.49)
3.53 (0.34)
3.67 (0.37)
Attractiveness of the Reward
4.29 (0.35)
4.21 (0.48)
5.20 (0.38)
5.07 (0.37)
Success Importance
5.50 (0.29)
5.64 (0.34)
5.60 (0.25)
5.40 (0.29)
Mood Baseline
22.29 (0.78)
22.64 (0.84)
20.13 (1.32)
22.73 (0.75)
Mood After Task Performance
22.71 (0.70)
22.79 (0.60)
20.73 (1.08)
22.40 (0.75)
Note: Cell ns = 14-15. The ratings of perceived difficulty, attractiveness of the reward, and success importance were scaled from 1 to 7. The mood scores were scaled from 4 (lowest mood possible) to 28 (highest mood possible).
A: PEP Reactivity
Incentive
Moderate High
[ms]
-12 -10 -8 -6 -4 -2 0
Pain Neutral
B: SBP Reactivity
Incentive
Moderate High
[mm Hg]
0 2 4 6 8 10 12 14 16
18 Pain
Neutral
C: DBP Reactivity
Incentive
Moderate High
[mm Hg]
0 2 4 6 8 10
12 Pain
Neutral
D: HR Reactivity
Incentive
Moderate High
[bpm]
0 2 4 6 8 10
12 Pain
Neutral
Figure 1
Accuracy
Incentive
Moderate High
[%]
80 85 90 95
100 Pain
Neutral
Figure 2
Perceived Capability
Incentive
Moderate High
[1 - 7]
1 2 3 4 5 6
7 Pain
Neutral
Figure 3
