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Is distraction less effective when pain is threatening? An experimental investigation with the cold pressor task
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European Journal of Pain 12 (2008) 60–67 www.EuropeanJournalPain.com
Is distraction less effective when pain is threatening? An experimental investigation with the cold pressor task Stefaan Van Damme *, Geert Crombez, Kathleen Van Nieuwenborgh-De Wever, Liesbet Goubert Department of Experimental-Clinical and Health Psychology, Ghent University, Belgium Received 2 November 2006; received in revised form 1 February 2007; accepted 1 March 2007 Available online 12 April 2007
Abstract Distraction is a commonly used strategy to control pain. However there is doubt about its effectiveness as a clinical tool, and results from both experimental and clinical studies remain inconclusive. Recent theoretical advancements suggest that distraction of attention may be less effective when pain is threatening. The aim of the present study was to experimentally investigate this hypothesis. Pain-free volunteers (N = 101) participated in a cold pressor test. Half of the participants simultaneously performed a cognitive distraction task, the other half did not. The threat value of the pain was manipulated by means of verbal information. The results showed that distraction resulted in less attention to the pain and lower pain ratings once the cold pressor procedure was halted. The hypothesis that the effectiveness of distraction is modulated by the threat value of pain could not be confirmed. However, threatening information increased catastrophic thoughts and anxiety, and interfered with performance on the distraction task. These findings suggest that caution is required in using distraction as a pain control strategy when the threat value is high, because fearful appraisal of pain is associated with less engagement in distraction tasks. 2007 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. All rights reserved. Keywords: Distraction; Attention; Threat; Experimental pain
1. Introduction Distraction of attention is a commonly used coping strategy to control pain in everyday situations. Distraction techniques are also often part of packages of cognitive behavioural therapy in clinical situations (Morley et al., 2004). The underlying assumption is that attention allocated to other demands cannot be applied to pain, and therefore diminishes the pain experience (McCaul and Malott, 1984; Villemure and Bushnell, 2002). Despite its intuitive appeal, the effectiveness of distrac*
Corresponding author. Tel.: +32 09 2649149; fax: +32 09 2646489. E-mail address: [email protected] (S. Van Damme).
tion as a clinical tool is debatable, and results from clinical and experimental research remain inconclusive (Leventhal, 1992). Several reasons for the contradictory findings have been proposed. First, the literature suffers from a number of methodological problems, such as the lack of standardization in samples, pain induction procedure, and type of distraction task. Most problematic however is that most studies fail to test for the actual engagement in the distraction task, making any profound interpretation of the results difficult (Eccleston, 1995). Second, empirical and theoretical advancements have suggested that distraction may only be effective in some situations. It has been shown that pain has a strong attentional
1090-3801/$32 2007 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ejpain.2007.03.001
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demand, particularly when it is perceived as highly threatening (Eccleston and Crombez, 1999). Consequently it can be argued that a high threat value may interfere with the effects of distraction (Crombez et al., 2005). However, these hypotheses have not yet been systematically addressed. Several studies have shown that a threatening appraisal of pain makes it difficult to ignore or direct attention away from pain (Crombez et al., 1998a; Goubert et al., 2004b; Heyneman et al., 1990; Van Damme et al., 2004a,b). However, these studies did not include adequate control conditions allowing conclusions about the efficacy of distraction. Third, distraction from pain may be considered as the result of controlled processes and not of automatic processes. The continuous recruitment of controlled processes is effortful and may bring about (paradoxical) costs (Koster et al., 2003; Wegner et al., 1987). Although such costs have been briefly mentioned in the pain literature (Cioffi and Holloway, 1993; Goubert et al., 2004a; Masedo and Esteve, 2007; Sullivan et al., 1997), there is a need of replication. In the present study we experimentally investigate whether the effectiveness of distraction during cold pressor pain is affected by the threat value of pain. In the distraction group, participants are required to perform an attention-demanding task, whereas in the control condition no distraction task is used. Performance on the distraction task is considered a test of attentional engagement. Furthermore, the threat value of pain is manipulated by verbal information about the cold pressor task. We expect that the distraction group will experience less pain, attend less to the pain, and catastrophize less about it, compared with the non-distraction group. Furthermore, we hypothesize that these effects will be smaller when threatening information about the pain is provided relative to neutral information.
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2.2. Cold pressor apparatus The cold pressor apparatus (Coolmatic, Waeco International) consisted of a plastic container (60 cm long, 35 cm wide, 45 cm high) of which the largest department was filled with water (approximately 30 l) at a temperature of 6–7 C. Participants were seated in a chair adjacent to the container, and immersed their non-dominant hand into the container. In between participants the temperature of the water was maintained by a cooling system, and was kept circulating by a pump. Maximum duration of immersion was two minutes, as a result of which temperature was constant during the test. The temperature used was considered appropriate for the purpose of the present experiment. We aimed at an ambiguous sensation allowing a manipulation of the threat value. Temperatures closer to freezing provoke more intense pain and numbing effects, and are threatening for everyone. Because we wanted to investigate the effects of distraction upon the self-reported pain, it was necessary that a sufficient number of participants were able to maintain their hand into the container for two minutes. 2.3. Distraction task The distraction task was a Random Interval Repetition (RIR) task (Vandierendonck et al., 1998). Participants were instructed to respond as quickly as possible to computer-generated tones (tone duration = 150 ms; tone pitch = 750 Hz), by pressing a one-button console held in the dominant hand as soon as a tone was perceived. Inter-trial intervals were 900 and 1500 ms, which were randomly distributed across trials. The RIR is an attention-demanding cognitive task. Performance of the RIR requires the continuous recruitment of central executive processes (Vandierendonck et al., 1998). 2.4. Measures
2. Methods 2.1. Participants One hundred and one undergraduate students (22 males and 79 females; mean age = 19.14 years, SD = 1.87; range 17–29 years) from Ghent University participated in order to fulfil course requirements. Exclusion criteria included presence of a circulatory disorder, hypertension, diabetes, Raynaud’s disease, and a heart condition. No participants had to be excluded for these reasons. The protocol of the study was approved by the local ethical committee. All participants gave informed consent and were free to terminate the experiment at any time. None of the students refused to participate. Nine participants withdrew their hand during the cold water procedure.
Catastrophic thinking about pain was assessed by the Dutch version of the Pain Catastrophizing Scale (PCS; Sullivan et al., 1995; Crombez et al., 1998a). This is a 13-item scale that measures the level of catastrophic thinking about pain in both non-clinical and clinical populations. Participants are asked to reflect on past painful experiences and to indicate the degree to which they experienced each of the 13 thoughts or feelings during pain (e.g., ‘I become afraid that the pain may get worse’) on a 5-point scale from 0 (not at all) to 4 (all the time). The Dutch version of the PCS has been shown to be valid and reliable (Van Damme et al., 2002). In the present study, Cronbach’s alpha of the PCS was .87. Participants also completed 20 questions on 11-point rating scales (developed by Goubert et al., 2004a). The first two items assessed pain intensity (0 = no pain;
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10 = worst imaginable pain). Participants assessed pain intensity immediately after the cold pressor procedure (how much pain do you have at this moment?). Furthermore they retrospectively assessed pain intensity during the cold pressor procedure (how much pain did you experience during the immersion of your hand in the cold water?). The other items retrospectively assessed three domains of interest. Attention to pain during the cold water procedure was assessed by three items (0 = not at all; 10 = very much). Cronbach’s alpha of this scale was .75. An example item is ‘‘I was continuously focusing on my pain during the cold water procedure’’. Catastrophic thinking about pain during the cold water procedure was assessed by 10 items (0 = not at all; 10 = very much). Cronbach’s alpha of this scale was .88. An example item is ‘‘During the cold water procedure, I felt I could not stand it any longer’’. General anxiety during the cold water procedure was assessed by five items (0 = not at all; 10 = very much). Cronbach’s alpha of this scale was .91. An example item is ‘‘I felt nervous’’. 2.5. Procedure When entering the experiment room, the experimenter informed participants about the study. They were told that the aim of the experiment was to examine pain perception by means of a cold pressor test. Exclusion criteria were checked and participants signed informed consent. Then they completed the PCS. Participants were randomly assigned to one of four conditions, based upon the manipulation of threat (threatening information versus non-threatening information) and attention (distraction task versus no distraction task). Distribution of sex did not differ across the several conditions. As the threat manipulation, two different instructions for the cold pressor procedure were used (see appendix). Instructions were adapted from a recent study by Jackson et al. (2005). In the threat condition, participants were told that ‘‘exposure to cold water can lead to freezing in the long term, and that this may be associated with pain, tingling, and numbness in the immersed hand’’. In order to further increase the threat value, there was a measurement of the blood pressure, and participants were falsely told that their blood pressure was ‘‘rather high, but just within the limit to allow participation to the cold water procedure’’. In the neutral condition, participants were told that ‘‘exposure to cold water is harmless, but that it can be associated with some discomfort or pain, which is absolutely normal and has no further consequences’’. In this condition there was no measurement of the blood pressure. After this, participants were seated in a chair adjacent to the container and were asked to immerse their nondominant hand in a basin with water at room tempera-
ture. Next they were instructed to immerse their forearm into the container with cold water and they were instructed to keep their hand as long as possible in the container. However it was emphasized that they could withdraw their hand at any time during the cold water procedure. As the attention manipulation, participants did or did not perform the distraction task. Participants in the distraction condition were asked to detect tones during the cold pressor procedure by pressing a response button. They were instructed to do this as quickly and accurately as possible. Participants were not informed that this task was intended to distract them from the cold pressor pain. The maximum duration of immersion was set at two minutes, but participants were not informed about this. The experimenter checked the duration using a digital stopwatch. After two minutes the experimenter asked participants to withdraw their hand from the container, and handed participants a towel to dry their arm. Immediately after this, participants were asked to complete the self-report scales assessing pain and negative pain cognitions. Finally, they were debriefed about the experiment, and particularly in the group receiving the threatening instructions it was made clear to the participants that the blood pressure registration was faked and that the immersion in the cold water was harmless. 2.6. Statistical analyses First, performance on the distraction task was examined. Data from 2 participants in the distraction group who were unable to keep their hand in the cold water for two minutes were excluded from the statistical analyses on the RIR distraction task, because shorter duration of this task may affect the reaction time pattern. For the other participants, mean response times (RT) and standard deviations on the RIR task were calculated. Participants failed to respond to the tone stimulus in 1.90% of the trials. RTs faster than 100 ms (2.90%) were considered as anticipatory responses and omitted. Also RTs slower than 900 ms (0.30%) were omitted, as the smallest inter-trial interval was 900 ms. The percentage of valid responses was over 95%. Because RT data were slightly skewed to the right (Skewness = 1.154, Standard error = 0.333), all RTs were log-transformed. In order to investigate the effect of the threatening instructions upon attentional engagement to the distraction task, mean log-transformed RTs, standard deviations on the log-transformed means, number of anticipations, and number of missed responses were subjected to one-way ANOVA’s with threat (threatening versus neutral information) as the independent factor. Log-transformed RTs fitted the normal distribution (Skewness = 0.488, Standard error = 0.333). For reasons of clarity, raw RT data are used to present means and standard devia-
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tions, although the analyses are conducted on the log-transformed data. Next, the effects of distraction and threat on early withdrawal from the cold pressor procedure were analyzed by v2–tests. Furthermore, the effects of distraction and threat on perceived pain and negative cognitions were tested by subjecting the mean self-report scores on pain variables (pain during and pain after cold pressor procedure) and process variables (attention, catastrophic thinking, and general anxiety) to 2 (distraction: RIR versus no RIR) · 2 (threat: threatening versus neutral) ANOVA’s. Cohen’s d was calculated to determine whether relevant results had a small (0.15), medium (0.40), or large (0.75) effect size.
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M = 10.36, SD = 6.43; F(1, 99) = 5.70, p = .019, d = 0.83) to and catastrophic thoughts (M = 39.56, SD = 12.73 versus M = 25.02, SD = 16.22; F(1, 99) = 6.79, p = .011, d = 0.90) about the cold water procedure compared to the other participants. They also tended to report more pain immediately after the cold water procedure (M = 4.00, SD = 2.29 versus M = 2.76, SD = 2.03; F(1, 99) = 2.98, p = .088, d = 0.60). There were no significant differences in self-reported pain (M = 5.78, SD = 1.09 versus M = 5.26, SD = 2.30; F(1, 99) = 0.44, p = .548, d = 0.23) and anxiety (M = 24.89, SD = 10.06 versus M = 19.13, SD = 11.45; F(1, 99) = 2.11, p = .149, d = 0.50) during the cold water procedure. 3.3. Self-report scales
3. Results All means of the self-report scales1 are displayed in Table 1. There were no differences in baseline level of catastrophic thinking about pain (PCS) as a function of distraction, threat, or an interaction between both (all Fs < 1). The distraction manipulation was successful, as participants in the distraction group reported less attention to the pain than participants in the non-distraction group (F(1, 97) = 5.45, p = .022, d = 0.46). Of particular interest, we found that distraction resulted in less pain once the cold pressor procedure was stopped than non-distraction (F(1, 97) = 4.43, p = .038, d = 0.41). Also catastrophic thinking during the cold water procedure tended to be lower in the distraction group than in the non-distraction group (F(1, 97) = 3.16, p = .079, d = 0.35). There were no effects of distraction upon retrospective pain during the cold pressor test (F(1, 97) = 1.75, p = .189, d = 0.26), and upon general anxiety (F(1, 97) = 0.20, p = .654, d = 0.09). The threat manipulation was successful, as participants in the threat group pain reported more catastrophic thoughts about the cold pressor pain (F(1, 97) = 4.25, p = .042, d = 0.40) and more anxiety (F(1, 97) = 5.56, p = .020, d = 0.47) than participants in the neutral group. There were no differences between the threat group and the neutral group upon retrospective pain during (F(1, 97) = 1.48, p = .227, d = 0.24) and after the cold pressor test (F(1, 97) = 2.39, p = .125, d = 0.30), and attention to the pain (F(1, 97) = 0.54, p = .463, d = 0.15).
3.1. Distraction task Participants performed substantially slower on the RIR task in the threat condition (M = 291 ms; SD = 90) compared to the neutral condition (M = 243 ms; SD = 46), F(1, 47) = 4.69, p = .035, d = 0.64. No significant group differences were found in the standard deviations of the RTs (F(1, 47) = 0.05, p = .821, d = 0.28), the number of anticipations (F(1, 47) = 0.55, p = .462, d = 0.32) and the number of missed responses (F(1, 47) = 1.21, p = .277, d = 0.22). 3.2. Cold pressor test Nine participants withdrew their hand before two minutes had passed (M = 67.78 s, SD = 26.77, range = 12–101). There tended to be less withdrawers in the distraction condition (N = 2) compared to the non-distraction condition (N = 7), v2(1) = 3.16, p = .075. There also tended to be more withdrawers in the threat condition (N = 7) compared to the neutral condition (N = 2), v2(1) = 2.94, p = .086. However there was no interaction between both factors (v2(1) = 0.14, p = .704). There was no difference in withdrawers and non-withdrawers in their level of catastrophic thinking about pain in general, as measured with the PCS (F(1, 99) = 0.16, p = .695, d = 0.14). However, participants who withdrew reported more attention (M = 15.67, SD = 5.55 versus
Table 1 Means and standard deviations of self-report measures in function of distraction and threat Total (N = 92)
Pain during Pain after Attention Catastrophic Anxiety
5.26 2.76 10.36 25.02 19.13
(2.30) (2.03) (6.43) (16.22) (11.45)
Threat (N = 44)
Neutral (N = 48)
Distract (N = 24)
No distract (N = 20)
Distract (N = 25)
No distract (N = 23)
5.17 2.54 8.46 25.67 23.67
5.90 3.65 11.40 31.90 20.25
4.84 2.24 9.72 20.72 16.08
5.26 2.78 12.12 23.04 16.74
(2.55) (2.02) (5.18) (13.49) (11.11)
(2.17) (2.39) (7.37) (19.66) (11.97)
(2.12) (1.59) (5.86) (14.60) (9.31)
(2.36) (2.02) (7.07) (16.23) (12.45)
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The effects of distraction were not modulated by threat. The hypothesized Distraction · Threat interaction failed to reach significance for all pain reports and negative cognitions (all Fs < 1.60, d’s < 0.30).
4. Discussion The aim of this study was to investigate whether distraction is less effective when pain is perceived as threatening. Pain-free volunteers performed a distraction task during a cold-pressor procedure. The threat value of cold-pressor pain was manipulated by instructions. The experimental manipulations were successful. Participants in the distraction condition reported less attention to the pain compared to participants in the non-distraction condition. Furthermore, participants receiving threatening information about the cold pressor procedure reported more catastrophic thoughts and anxiety than participants receiving neutral information. Several interesting results emerged from this study. First, distraction diminished pain ratings immediately after but not during the cold pressor procedure. Second, the hypothesis that threat instructions would hinder the effectiveness of distraction was not confirmed. However, threat instructions disrupted performance on the distraction task. The finding that distraction did not diminish pain during the cold pressor procedure is in line with a number of studies failing to find analgesic effects of distraction (Johnson et al., 1998; Goubert et al., 2004a; McCaul et al., 1992), but contradicts the results of several other studies showing beneficial effects of distraction (Hodes et al., 1990; James and Hardardottir, 2002; Johnson and Petrie, 1997; Miron et al., 1989; Petrovic et al., 2000). The finding that distraction resulted in less pain immediately after the cold pressor procedure, does not support several studies reporting paradoxical after-effects of distraction, showing more pain and distress as a result of distraction (Cioffi and Holloway, 1993; Feldner et al., 2006; Goubert et al., 2004a; Keogh et al., 2005; Masedo and Esteve, 2007; Sullivan et al., 1997). Although the present study was not designed to measure effects upon tolerance time, the results indicate that less participants withdrew from the cold pressor procedure when they were distracted. Possibly, distraction has effects upon behavioural decisions (escape and avoidance) rather than on the pain experience itself. In the present study we attempted to control for two issues that may be held responsible for the contradictory results of previous research. The first issue relates to the observation that most studies failed to test for the actual engagement of attention to the distraction task. As a result, it is not clear in which studies the distraction task consumed cognitive resources at the cost of pain pro-
cessing, making any profound interpretation of the findings impossible (Eccleston, 1995). In our study performance data on the distraction task suggest that attention was engaged to it. The second issue is about the theoretical proposition that a high threat value of pain may interfere with the effects of distraction (Crombez et al., 2005). A number of studies provide support for this thesis. In the context of physical therapy, it has been shown that distraction was not effective in patients with a high level of health anxiety (Hadjistavropoulos et al., 2000). Similar results were reported for healthy women scoring high on anxiety sensitivity (Keogh and Mansoor, 2001). Furthermore, it has been shown that distraction resulted in higher pain tolerance only in individuals who did not have catastrophic thoughts about the pain (Heyneman et al., 1990). In line with this, Roelofs et al. (2004) found that an auditory discrimination task reduced pain during a cold pressor task, but only in individuals with a low level of painrelated fear. We were not able to replicate the findings from these studies. In our study, distraction had the same effects upon pain ratings and negative pain cognitions in participants receiving threatening instructions about cold pressor pain compared with those receiving neutral instructions. However, an intriguing finding was that our manipulation of the threat value affected task performance. Participants in the threat condition were significantly slower than participants in the neutral condition, indicating less engagement in the distraction task. Our results are in line with the study of Goubert et al. (2004a) in chronic low back pain patients, who found that catastrophic appraisal of pain was related to less engagement in a similar distraction task as was used in our study. The results are also in line with primary task studies demonstrating that the threat of very intense pain increases the disruption of task performance by low-intense electrocutaneous pain stimuli (Crombez et al., 1998b). Of further interest in this context is the study by Jackson et al. (2005) who found that healthy individuals receiving threat instructions about a cold pressor procedure reported less use of distraction strategies. Also this is in line with our finding that participants in the threat group showed less engagement to the distraction task than those in the neutral group. However, it should be noted that in our study distraction was experimentally manipulated by instructing participants to perform an attention-demanding task, whereas the study by Jackson and colleagues examined distraction as a spontaneous coping strategy. In the same study it was found that the induction of threat increased catastrophic thinking about pain, which was confirmed in our study. Note that threatening instructions had no direct effect on perceived pain, although pain tolerance was significantly shortened, which is in line with our findings.
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This study has both theoretical and clinical implications. First, when pain is perceived as threatening, catastrophic and anxious thoughts emerge, and less cognitive resources are allocated to distraction tasks (Crombez et al., 2005). This puts restraints on the usefulness of distraction as a clinical tool in patients with chronic pain, who are frequently characterised by a catastrophic, fearful appraisal of their symptoms (Sullivan et al., 2001; Vlaeyen and Linton, 2000). Second, our findings suggest that the amount of attention actively engaged in the distraction task does not modulate its effectiveness in terms of pain intensity. This questions the key theoretical principle underlying the assumed beneficial effects of distraction, i.e., that attention engaged in non-pain demands cannot be allocated to pain processing, thereby diminishing the painful experience (McCaul and Malott, 1984). There are a number of issues concerning this study which require further consideration. First, we cannot rule out the possibility that participants in the non-distraction condition spontaneously used some form of distraction strategy. It could be useful to examine this possibility in future studies. Furthermore, an interesting approach to determine the exact impact of attentional engagement to the distraction task is assigning participants to distraction tasks with different degrees of attentional demand (McCaul et al., 1992). Second, we used a neutral distraction task. However, it has been argued that distraction with an emotional content might work better (Leventhal, 1992). This was illustrated in a recent study in cancer patients, showing that distractions were rated as more effective when they were interesting, important, and pleasant (Buck and Morley, 2006). As we did not control for the emotional involvement of the participants, this may have affected the results. Future research should also manipulate the emotional significance of the distraction task as a possible determinant of its effectiveness. Third, pain and negative cognitions during the task were rated retrospectively, which may have biased the effects. Memory biases in retrospective pain reports have been demonstrated even when the recall is relatively close in time to the painful event (Redelmeier et al., 2003). Future studies could use online measurements of pain, and other outcome measures such as tolerance. However, one should be mindful that these alternatives have been criticized (Eccleston, 1995). A better alternative could be to evaluate mean pain, worst pain, and pain at the end of the cold water procedure. Such combination has been argued to substantially the accuracy of retrospective pain evaluations (Kahneman et al., 1993). Fourth, at the moment behaviour and neurobiological knowledge about the interaction between distraction and pain perception mainly stems from separate research lines. The challenge for future research is to merge findings with both methods, which
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would allow obtaining a more complete picture of the processes associated with directing attention towards and away from pain, and the effects of this upon pain perception. For instance, it has been suggested that the anterior cingulate cortex (ACC) is activated during both pain perception and attention-demanding tasks, but that distinct sub-regions are involved (Buffington et al., 2005). This was confirmed in a study investigating distraction from cold pressor pain, showing that lower pain ratings during the distraction task could be due to both increased activation of attention-related ACC subregions and decreased activation of pain-related subregions (Frankenstein et al., 2001). Integration of such neurobiological observations with behavioural data could further our understanding of the underlying mechanisms of distraction. Fifth, the present research was conducted in pain-free undergraduate students. Replication of the results in other pain-free populations and clinical populations is necessary to allow definitive conclusions. Furthermore, distraction may have differential effects upon acute compared to chronic pain. Distraction seems most appropriate to control acute pain. In chronic pain situations, distraction has cognitive costs, possibly resulting in paradoxical effects (Crombez et al., 2005). Therefore, more dynamic attention strategies may be necessary, resulting in flexible switching of attention between pain and other task demands (Morley et al., 2004). In spite of several limitations, this study extends our knowledge about distraction and its underlying processes.
Notes 1 We repeated the analyses on the self-report data excluding the participants who were unable to keep their hand in the cold water for two minutes. However, this did not change the pattern of results presented in the paper.
Acknowledgement Stefaan Van Damme and Liesbet Goubert are postdoctoral researchers of the Fund for Scientific Research – Flanders (FWO). The authors want to thank Pascal Mestdagh (Ghent University) for technical assistance.
Appendix Threat instructions. In this experiment we work with the cold water test. This is a method to investigate pain perception. The intention is that you attempt to keep your hand in the cold water as long as possible.
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I will give you some more information about this procedure. The cold water test is a frequently used and safe method in pain research. However, exposure to ice cold water can lead to freezing in the long term. This is associated with pain, tingling, and numbness in the immersed hand. Before we start it is necessary that we check your blood pressure. Your blood pressure is rather high but just within the limits to allow participation to the cold water procedure. I would like to stress that you are free to participate to this study. You can stop your participation or withdraw your hand whenever you want. However try to leave your hand in the cold water as long as possible. Neutral instructions. In this experiment we work with the cold water test. This is a method to investigate pain perception. The intention is that you attempt to keep your hand in the cold water as long as possible. I will give you some more information about this procedure. First, the cold water test is a frequently used method in pain research. Second, the test is safe because the water temperature does not fall below the freezing point. Although exposure to cold water is harmless, it can be associated with some discomfort or pain, which is absolutely normal and has no further consequences. However, I would like to stress that you are free to participate to this study. You can stop your participation or withdraw your hand whenever you want. However try to leave your hand in the cold water as long as possible.
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Goubert L, Crombez G, Eccleston C, Devulder J. Distraction from chronic pain during a pain-inducing activity is associated with greater post-activity pain. Pain 2004a;110:220–7. Goubert L, Crombez G, Van Damme S. The role of neuroticism, pain catastrophizing and pain-related fear in vigilance to pain: a structural equations approach. Pain 2004b;107:234–41. Hadjistavropoulos HD, Hadjistavropoulos T, Quine A. Health anxiety moderates the effects of distraction versus attention to pain. Behav Res Ther 2000;38:425–38. Heyneman NE, Fremouw WJ, Gano D, Kirkland F, Heiden L. Individual differences and the effectiveness of different coping strategies for pain. Cogn Ther Res 1990;14:63–77. Hodes RL, Howland EW, Lightfoot N, Cleeland CS. The effects of distraction on responses to cold pressor pain. Pain 1990;41: 109–14. Jackson T, Pope L, Nagasaka T, Fritch A, Lezzi T, Chen H. The impact of threatening information about pain on coping and pain tolerance. Br J Health Psychol 2005;10:441–51. James JE, Hardardottir D. Influence of attention focus and trait anxiety on tolerance of acute pain. Br J Health Psychol 2002;7: 149–62. Johnson MH, Petrie SM. The effects of distraction on exercise and cold-pressor tolerance for chronic low back pain sufferers. Pain 1997;69:43–8. Johnson MH, Breakwell G, Douglas W, Humphries S. The effects of imagery and sensory detection distractors on different measures of pain: how does distraction works? Br J Clin Psychol 1998;37:141–54. Kahneman D, Fredrickson BL, Schreiber CA, Redelmeier DA. When more pain is preferred to less: adding a better end. Psychol Sci 1993;4:401–5. Keogh E, Mansoor L. Investigating the effects of anxiety sensitivity and coping on the perception of cold pressor pain in healthy women. Eur J Pain 2001;5:11–22. Keogh E, Bond FW, Hanmer R, Tilston J. Comparing acceptance- and control-based coping instructions on the coldpressor pain experiences of healthy men and women. Eur J Pain 2005;9:591–8. Koster EHW, Rassin E, Crombez G, Naring GWB. The paradoxal effects of suppressing anxious thoughts during imminent threat. Behav Res Ther 2003;41:1113–20. Leventhal H. I know distraction works even though it doesn’t. Health Psychol 1992;11:208–9. Masedo AI, Esteve MR. Effects of suppression, acceptance, and spontaneous coping on pain tolerance, pain intensity and distress. Behav Res Ther 2007;45:199–209. McCaul KD, Malott JM. Distraction and coping with pain. Psychol Bull 1984;95:516–33. McCaul KD, Monson N, Maki RH. Does distraction reduce painproduced distress among college students? Health Psychol 1992;11: 210–7. Miron D, Duncan GB, Bushnell MC. Effects of attention on the intensity and unpleasantness of thermal pain. Pain 1989;39:345–52. Morley S, Shapiro DA, Biggs J. Developing a treatment manual for attention management in chronic pain. Cogn Behav Ther 2004;33: 1–11. Petrovic P, Petersson KM, Ghatan PH, Stone_Elander S, Ingvar M. Pain related cerebral activation is altered by a distracting cognitive task. Pain 2000;85:19–30. Redelmeier DA, Katz J, Kahneman D. Memories of colonoscopy: a randomized trial. Pain 2003;104:187–94. Roelofs J, Peters ML, van der Zijden M, Vlaeyen JWS. Does fear of pain moderate the effects of sensory focusing and distraction on cold pressor pain in pain-free individuals? J Pain 2004;5:250–6. Sullivan MJL, Bishop SR, Pivik J. The pain catastrophizing scale: development and validation. Psychol Assess 1995;7:524–32.
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European Journal of Pain 12 (2008) 60–67 www.EuropeanJournalPain.com
Is distraction less effective when pain is threatening? An experimental investigation with the cold pressor task Stefaan Van Damme *, Geert Crombez, Kathleen Van Nieuwenborgh-De Wever, Liesbet Goubert Department of Experimental-Clinical and Health Psychology, Ghent University, Belgium Received 2 November 2006; received in revised form 1 February 2007; accepted 1 March 2007 Available online 12 April 2007
Abstract Distraction is a commonly used strategy to control pain. However there is doubt about its effectiveness as a clinical tool, and results from both experimental and clinical studies remain inconclusive. Recent theoretical advancements suggest that distraction of attention may be less effective when pain is threatening. The aim of the present study was to experimentally investigate this hypothesis. Pain-free volunteers (N = 101) participated in a cold pressor test. Half of the participants simultaneously performed a cognitive distraction task, the other half did not. The threat value of the pain was manipulated by means of verbal information. The results showed that distraction resulted in less attention to the pain and lower pain ratings once the cold pressor procedure was halted. The hypothesis that the effectiveness of distraction is modulated by the threat value of pain could not be confirmed. However, threatening information increased catastrophic thoughts and anxiety, and interfered with performance on the distraction task. These findings suggest that caution is required in using distraction as a pain control strategy when the threat value is high, because fearful appraisal of pain is associated with less engagement in distraction tasks. 2007 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. All rights reserved. Keywords: Distraction; Attention; Threat; Experimental pain
1. Introduction Distraction of attention is a commonly used coping strategy to control pain in everyday situations. Distraction techniques are also often part of packages of cognitive behavioural therapy in clinical situations (Morley et al., 2004). The underlying assumption is that attention allocated to other demands cannot be applied to pain, and therefore diminishes the pain experience (McCaul and Malott, 1984; Villemure and Bushnell, 2002). Despite its intuitive appeal, the effectiveness of distrac*
Corresponding author. Tel.: +32 09 2649149; fax: +32 09 2646489. E-mail address: [email protected] (S. Van Damme).
tion as a clinical tool is debatable, and results from clinical and experimental research remain inconclusive (Leventhal, 1992). Several reasons for the contradictory findings have been proposed. First, the literature suffers from a number of methodological problems, such as the lack of standardization in samples, pain induction procedure, and type of distraction task. Most problematic however is that most studies fail to test for the actual engagement in the distraction task, making any profound interpretation of the results difficult (Eccleston, 1995). Second, empirical and theoretical advancements have suggested that distraction may only be effective in some situations. It has been shown that pain has a strong attentional
1090-3801/$32 2007 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ejpain.2007.03.001
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demand, particularly when it is perceived as highly threatening (Eccleston and Crombez, 1999). Consequently it can be argued that a high threat value may interfere with the effects of distraction (Crombez et al., 2005). However, these hypotheses have not yet been systematically addressed. Several studies have shown that a threatening appraisal of pain makes it difficult to ignore or direct attention away from pain (Crombez et al., 1998a; Goubert et al., 2004b; Heyneman et al., 1990; Van Damme et al., 2004a,b). However, these studies did not include adequate control conditions allowing conclusions about the efficacy of distraction. Third, distraction from pain may be considered as the result of controlled processes and not of automatic processes. The continuous recruitment of controlled processes is effortful and may bring about (paradoxical) costs (Koster et al., 2003; Wegner et al., 1987). Although such costs have been briefly mentioned in the pain literature (Cioffi and Holloway, 1993; Goubert et al., 2004a; Masedo and Esteve, 2007; Sullivan et al., 1997), there is a need of replication. In the present study we experimentally investigate whether the effectiveness of distraction during cold pressor pain is affected by the threat value of pain. In the distraction group, participants are required to perform an attention-demanding task, whereas in the control condition no distraction task is used. Performance on the distraction task is considered a test of attentional engagement. Furthermore, the threat value of pain is manipulated by verbal information about the cold pressor task. We expect that the distraction group will experience less pain, attend less to the pain, and catastrophize less about it, compared with the non-distraction group. Furthermore, we hypothesize that these effects will be smaller when threatening information about the pain is provided relative to neutral information.
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2.2. Cold pressor apparatus The cold pressor apparatus (Coolmatic, Waeco International) consisted of a plastic container (60 cm long, 35 cm wide, 45 cm high) of which the largest department was filled with water (approximately 30 l) at a temperature of 6–7 C. Participants were seated in a chair adjacent to the container, and immersed their non-dominant hand into the container. In between participants the temperature of the water was maintained by a cooling system, and was kept circulating by a pump. Maximum duration of immersion was two minutes, as a result of which temperature was constant during the test. The temperature used was considered appropriate for the purpose of the present experiment. We aimed at an ambiguous sensation allowing a manipulation of the threat value. Temperatures closer to freezing provoke more intense pain and numbing effects, and are threatening for everyone. Because we wanted to investigate the effects of distraction upon the self-reported pain, it was necessary that a sufficient number of participants were able to maintain their hand into the container for two minutes. 2.3. Distraction task The distraction task was a Random Interval Repetition (RIR) task (Vandierendonck et al., 1998). Participants were instructed to respond as quickly as possible to computer-generated tones (tone duration = 150 ms; tone pitch = 750 Hz), by pressing a one-button console held in the dominant hand as soon as a tone was perceived. Inter-trial intervals were 900 and 1500 ms, which were randomly distributed across trials. The RIR is an attention-demanding cognitive task. Performance of the RIR requires the continuous recruitment of central executive processes (Vandierendonck et al., 1998). 2.4. Measures
2. Methods 2.1. Participants One hundred and one undergraduate students (22 males and 79 females; mean age = 19.14 years, SD = 1.87; range 17–29 years) from Ghent University participated in order to fulfil course requirements. Exclusion criteria included presence of a circulatory disorder, hypertension, diabetes, Raynaud’s disease, and a heart condition. No participants had to be excluded for these reasons. The protocol of the study was approved by the local ethical committee. All participants gave informed consent and were free to terminate the experiment at any time. None of the students refused to participate. Nine participants withdrew their hand during the cold water procedure.
Catastrophic thinking about pain was assessed by the Dutch version of the Pain Catastrophizing Scale (PCS; Sullivan et al., 1995; Crombez et al., 1998a). This is a 13-item scale that measures the level of catastrophic thinking about pain in both non-clinical and clinical populations. Participants are asked to reflect on past painful experiences and to indicate the degree to which they experienced each of the 13 thoughts or feelings during pain (e.g., ‘I become afraid that the pain may get worse’) on a 5-point scale from 0 (not at all) to 4 (all the time). The Dutch version of the PCS has been shown to be valid and reliable (Van Damme et al., 2002). In the present study, Cronbach’s alpha of the PCS was .87. Participants also completed 20 questions on 11-point rating scales (developed by Goubert et al., 2004a). The first two items assessed pain intensity (0 = no pain;
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10 = worst imaginable pain). Participants assessed pain intensity immediately after the cold pressor procedure (how much pain do you have at this moment?). Furthermore they retrospectively assessed pain intensity during the cold pressor procedure (how much pain did you experience during the immersion of your hand in the cold water?). The other items retrospectively assessed three domains of interest. Attention to pain during the cold water procedure was assessed by three items (0 = not at all; 10 = very much). Cronbach’s alpha of this scale was .75. An example item is ‘‘I was continuously focusing on my pain during the cold water procedure’’. Catastrophic thinking about pain during the cold water procedure was assessed by 10 items (0 = not at all; 10 = very much). Cronbach’s alpha of this scale was .88. An example item is ‘‘During the cold water procedure, I felt I could not stand it any longer’’. General anxiety during the cold water procedure was assessed by five items (0 = not at all; 10 = very much). Cronbach’s alpha of this scale was .91. An example item is ‘‘I felt nervous’’. 2.5. Procedure When entering the experiment room, the experimenter informed participants about the study. They were told that the aim of the experiment was to examine pain perception by means of a cold pressor test. Exclusion criteria were checked and participants signed informed consent. Then they completed the PCS. Participants were randomly assigned to one of four conditions, based upon the manipulation of threat (threatening information versus non-threatening information) and attention (distraction task versus no distraction task). Distribution of sex did not differ across the several conditions. As the threat manipulation, two different instructions for the cold pressor procedure were used (see appendix). Instructions were adapted from a recent study by Jackson et al. (2005). In the threat condition, participants were told that ‘‘exposure to cold water can lead to freezing in the long term, and that this may be associated with pain, tingling, and numbness in the immersed hand’’. In order to further increase the threat value, there was a measurement of the blood pressure, and participants were falsely told that their blood pressure was ‘‘rather high, but just within the limit to allow participation to the cold water procedure’’. In the neutral condition, participants were told that ‘‘exposure to cold water is harmless, but that it can be associated with some discomfort or pain, which is absolutely normal and has no further consequences’’. In this condition there was no measurement of the blood pressure. After this, participants were seated in a chair adjacent to the container and were asked to immerse their nondominant hand in a basin with water at room tempera-
ture. Next they were instructed to immerse their forearm into the container with cold water and they were instructed to keep their hand as long as possible in the container. However it was emphasized that they could withdraw their hand at any time during the cold water procedure. As the attention manipulation, participants did or did not perform the distraction task. Participants in the distraction condition were asked to detect tones during the cold pressor procedure by pressing a response button. They were instructed to do this as quickly and accurately as possible. Participants were not informed that this task was intended to distract them from the cold pressor pain. The maximum duration of immersion was set at two minutes, but participants were not informed about this. The experimenter checked the duration using a digital stopwatch. After two minutes the experimenter asked participants to withdraw their hand from the container, and handed participants a towel to dry their arm. Immediately after this, participants were asked to complete the self-report scales assessing pain and negative pain cognitions. Finally, they were debriefed about the experiment, and particularly in the group receiving the threatening instructions it was made clear to the participants that the blood pressure registration was faked and that the immersion in the cold water was harmless. 2.6. Statistical analyses First, performance on the distraction task was examined. Data from 2 participants in the distraction group who were unable to keep their hand in the cold water for two minutes were excluded from the statistical analyses on the RIR distraction task, because shorter duration of this task may affect the reaction time pattern. For the other participants, mean response times (RT) and standard deviations on the RIR task were calculated. Participants failed to respond to the tone stimulus in 1.90% of the trials. RTs faster than 100 ms (2.90%) were considered as anticipatory responses and omitted. Also RTs slower than 900 ms (0.30%) were omitted, as the smallest inter-trial interval was 900 ms. The percentage of valid responses was over 95%. Because RT data were slightly skewed to the right (Skewness = 1.154, Standard error = 0.333), all RTs were log-transformed. In order to investigate the effect of the threatening instructions upon attentional engagement to the distraction task, mean log-transformed RTs, standard deviations on the log-transformed means, number of anticipations, and number of missed responses were subjected to one-way ANOVA’s with threat (threatening versus neutral information) as the independent factor. Log-transformed RTs fitted the normal distribution (Skewness = 0.488, Standard error = 0.333). For reasons of clarity, raw RT data are used to present means and standard devia-
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tions, although the analyses are conducted on the log-transformed data. Next, the effects of distraction and threat on early withdrawal from the cold pressor procedure were analyzed by v2–tests. Furthermore, the effects of distraction and threat on perceived pain and negative cognitions were tested by subjecting the mean self-report scores on pain variables (pain during and pain after cold pressor procedure) and process variables (attention, catastrophic thinking, and general anxiety) to 2 (distraction: RIR versus no RIR) · 2 (threat: threatening versus neutral) ANOVA’s. Cohen’s d was calculated to determine whether relevant results had a small (0.15), medium (0.40), or large (0.75) effect size.
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M = 10.36, SD = 6.43; F(1, 99) = 5.70, p = .019, d = 0.83) to and catastrophic thoughts (M = 39.56, SD = 12.73 versus M = 25.02, SD = 16.22; F(1, 99) = 6.79, p = .011, d = 0.90) about the cold water procedure compared to the other participants. They also tended to report more pain immediately after the cold water procedure (M = 4.00, SD = 2.29 versus M = 2.76, SD = 2.03; F(1, 99) = 2.98, p = .088, d = 0.60). There were no significant differences in self-reported pain (M = 5.78, SD = 1.09 versus M = 5.26, SD = 2.30; F(1, 99) = 0.44, p = .548, d = 0.23) and anxiety (M = 24.89, SD = 10.06 versus M = 19.13, SD = 11.45; F(1, 99) = 2.11, p = .149, d = 0.50) during the cold water procedure. 3.3. Self-report scales
3. Results All means of the self-report scales1 are displayed in Table 1. There were no differences in baseline level of catastrophic thinking about pain (PCS) as a function of distraction, threat, or an interaction between both (all Fs < 1). The distraction manipulation was successful, as participants in the distraction group reported less attention to the pain than participants in the non-distraction group (F(1, 97) = 5.45, p = .022, d = 0.46). Of particular interest, we found that distraction resulted in less pain once the cold pressor procedure was stopped than non-distraction (F(1, 97) = 4.43, p = .038, d = 0.41). Also catastrophic thinking during the cold water procedure tended to be lower in the distraction group than in the non-distraction group (F(1, 97) = 3.16, p = .079, d = 0.35). There were no effects of distraction upon retrospective pain during the cold pressor test (F(1, 97) = 1.75, p = .189, d = 0.26), and upon general anxiety (F(1, 97) = 0.20, p = .654, d = 0.09). The threat manipulation was successful, as participants in the threat group pain reported more catastrophic thoughts about the cold pressor pain (F(1, 97) = 4.25, p = .042, d = 0.40) and more anxiety (F(1, 97) = 5.56, p = .020, d = 0.47) than participants in the neutral group. There were no differences between the threat group and the neutral group upon retrospective pain during (F(1, 97) = 1.48, p = .227, d = 0.24) and after the cold pressor test (F(1, 97) = 2.39, p = .125, d = 0.30), and attention to the pain (F(1, 97) = 0.54, p = .463, d = 0.15).
3.1. Distraction task Participants performed substantially slower on the RIR task in the threat condition (M = 291 ms; SD = 90) compared to the neutral condition (M = 243 ms; SD = 46), F(1, 47) = 4.69, p = .035, d = 0.64. No significant group differences were found in the standard deviations of the RTs (F(1, 47) = 0.05, p = .821, d = 0.28), the number of anticipations (F(1, 47) = 0.55, p = .462, d = 0.32) and the number of missed responses (F(1, 47) = 1.21, p = .277, d = 0.22). 3.2. Cold pressor test Nine participants withdrew their hand before two minutes had passed (M = 67.78 s, SD = 26.77, range = 12–101). There tended to be less withdrawers in the distraction condition (N = 2) compared to the non-distraction condition (N = 7), v2(1) = 3.16, p = .075. There also tended to be more withdrawers in the threat condition (N = 7) compared to the neutral condition (N = 2), v2(1) = 2.94, p = .086. However there was no interaction between both factors (v2(1) = 0.14, p = .704). There was no difference in withdrawers and non-withdrawers in their level of catastrophic thinking about pain in general, as measured with the PCS (F(1, 99) = 0.16, p = .695, d = 0.14). However, participants who withdrew reported more attention (M = 15.67, SD = 5.55 versus
Table 1 Means and standard deviations of self-report measures in function of distraction and threat Total (N = 92)
Pain during Pain after Attention Catastrophic Anxiety
5.26 2.76 10.36 25.02 19.13
(2.30) (2.03) (6.43) (16.22) (11.45)
Threat (N = 44)
Neutral (N = 48)
Distract (N = 24)
No distract (N = 20)
Distract (N = 25)
No distract (N = 23)
5.17 2.54 8.46 25.67 23.67
5.90 3.65 11.40 31.90 20.25
4.84 2.24 9.72 20.72 16.08
5.26 2.78 12.12 23.04 16.74
(2.55) (2.02) (5.18) (13.49) (11.11)
(2.17) (2.39) (7.37) (19.66) (11.97)
(2.12) (1.59) (5.86) (14.60) (9.31)
(2.36) (2.02) (7.07) (16.23) (12.45)
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The effects of distraction were not modulated by threat. The hypothesized Distraction · Threat interaction failed to reach significance for all pain reports and negative cognitions (all Fs < 1.60, d’s < 0.30).
4. Discussion The aim of this study was to investigate whether distraction is less effective when pain is perceived as threatening. Pain-free volunteers performed a distraction task during a cold-pressor procedure. The threat value of cold-pressor pain was manipulated by instructions. The experimental manipulations were successful. Participants in the distraction condition reported less attention to the pain compared to participants in the non-distraction condition. Furthermore, participants receiving threatening information about the cold pressor procedure reported more catastrophic thoughts and anxiety than participants receiving neutral information. Several interesting results emerged from this study. First, distraction diminished pain ratings immediately after but not during the cold pressor procedure. Second, the hypothesis that threat instructions would hinder the effectiveness of distraction was not confirmed. However, threat instructions disrupted performance on the distraction task. The finding that distraction did not diminish pain during the cold pressor procedure is in line with a number of studies failing to find analgesic effects of distraction (Johnson et al., 1998; Goubert et al., 2004a; McCaul et al., 1992), but contradicts the results of several other studies showing beneficial effects of distraction (Hodes et al., 1990; James and Hardardottir, 2002; Johnson and Petrie, 1997; Miron et al., 1989; Petrovic et al., 2000). The finding that distraction resulted in less pain immediately after the cold pressor procedure, does not support several studies reporting paradoxical after-effects of distraction, showing more pain and distress as a result of distraction (Cioffi and Holloway, 1993; Feldner et al., 2006; Goubert et al., 2004a; Keogh et al., 2005; Masedo and Esteve, 2007; Sullivan et al., 1997). Although the present study was not designed to measure effects upon tolerance time, the results indicate that less participants withdrew from the cold pressor procedure when they were distracted. Possibly, distraction has effects upon behavioural decisions (escape and avoidance) rather than on the pain experience itself. In the present study we attempted to control for two issues that may be held responsible for the contradictory results of previous research. The first issue relates to the observation that most studies failed to test for the actual engagement of attention to the distraction task. As a result, it is not clear in which studies the distraction task consumed cognitive resources at the cost of pain pro-
cessing, making any profound interpretation of the findings impossible (Eccleston, 1995). In our study performance data on the distraction task suggest that attention was engaged to it. The second issue is about the theoretical proposition that a high threat value of pain may interfere with the effects of distraction (Crombez et al., 2005). A number of studies provide support for this thesis. In the context of physical therapy, it has been shown that distraction was not effective in patients with a high level of health anxiety (Hadjistavropoulos et al., 2000). Similar results were reported for healthy women scoring high on anxiety sensitivity (Keogh and Mansoor, 2001). Furthermore, it has been shown that distraction resulted in higher pain tolerance only in individuals who did not have catastrophic thoughts about the pain (Heyneman et al., 1990). In line with this, Roelofs et al. (2004) found that an auditory discrimination task reduced pain during a cold pressor task, but only in individuals with a low level of painrelated fear. We were not able to replicate the findings from these studies. In our study, distraction had the same effects upon pain ratings and negative pain cognitions in participants receiving threatening instructions about cold pressor pain compared with those receiving neutral instructions. However, an intriguing finding was that our manipulation of the threat value affected task performance. Participants in the threat condition were significantly slower than participants in the neutral condition, indicating less engagement in the distraction task. Our results are in line with the study of Goubert et al. (2004a) in chronic low back pain patients, who found that catastrophic appraisal of pain was related to less engagement in a similar distraction task as was used in our study. The results are also in line with primary task studies demonstrating that the threat of very intense pain increases the disruption of task performance by low-intense electrocutaneous pain stimuli (Crombez et al., 1998b). Of further interest in this context is the study by Jackson et al. (2005) who found that healthy individuals receiving threat instructions about a cold pressor procedure reported less use of distraction strategies. Also this is in line with our finding that participants in the threat group showed less engagement to the distraction task than those in the neutral group. However, it should be noted that in our study distraction was experimentally manipulated by instructing participants to perform an attention-demanding task, whereas the study by Jackson and colleagues examined distraction as a spontaneous coping strategy. In the same study it was found that the induction of threat increased catastrophic thinking about pain, which was confirmed in our study. Note that threatening instructions had no direct effect on perceived pain, although pain tolerance was significantly shortened, which is in line with our findings.
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This study has both theoretical and clinical implications. First, when pain is perceived as threatening, catastrophic and anxious thoughts emerge, and less cognitive resources are allocated to distraction tasks (Crombez et al., 2005). This puts restraints on the usefulness of distraction as a clinical tool in patients with chronic pain, who are frequently characterised by a catastrophic, fearful appraisal of their symptoms (Sullivan et al., 2001; Vlaeyen and Linton, 2000). Second, our findings suggest that the amount of attention actively engaged in the distraction task does not modulate its effectiveness in terms of pain intensity. This questions the key theoretical principle underlying the assumed beneficial effects of distraction, i.e., that attention engaged in non-pain demands cannot be allocated to pain processing, thereby diminishing the painful experience (McCaul and Malott, 1984). There are a number of issues concerning this study which require further consideration. First, we cannot rule out the possibility that participants in the non-distraction condition spontaneously used some form of distraction strategy. It could be useful to examine this possibility in future studies. Furthermore, an interesting approach to determine the exact impact of attentional engagement to the distraction task is assigning participants to distraction tasks with different degrees of attentional demand (McCaul et al., 1992). Second, we used a neutral distraction task. However, it has been argued that distraction with an emotional content might work better (Leventhal, 1992). This was illustrated in a recent study in cancer patients, showing that distractions were rated as more effective when they were interesting, important, and pleasant (Buck and Morley, 2006). As we did not control for the emotional involvement of the participants, this may have affected the results. Future research should also manipulate the emotional significance of the distraction task as a possible determinant of its effectiveness. Third, pain and negative cognitions during the task were rated retrospectively, which may have biased the effects. Memory biases in retrospective pain reports have been demonstrated even when the recall is relatively close in time to the painful event (Redelmeier et al., 2003). Future studies could use online measurements of pain, and other outcome measures such as tolerance. However, one should be mindful that these alternatives have been criticized (Eccleston, 1995). A better alternative could be to evaluate mean pain, worst pain, and pain at the end of the cold water procedure. Such combination has been argued to substantially the accuracy of retrospective pain evaluations (Kahneman et al., 1993). Fourth, at the moment behaviour and neurobiological knowledge about the interaction between distraction and pain perception mainly stems from separate research lines. The challenge for future research is to merge findings with both methods, which
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would allow obtaining a more complete picture of the processes associated with directing attention towards and away from pain, and the effects of this upon pain perception. For instance, it has been suggested that the anterior cingulate cortex (ACC) is activated during both pain perception and attention-demanding tasks, but that distinct sub-regions are involved (Buffington et al., 2005). This was confirmed in a study investigating distraction from cold pressor pain, showing that lower pain ratings during the distraction task could be due to both increased activation of attention-related ACC subregions and decreased activation of pain-related subregions (Frankenstein et al., 2001). Integration of such neurobiological observations with behavioural data could further our understanding of the underlying mechanisms of distraction. Fifth, the present research was conducted in pain-free undergraduate students. Replication of the results in other pain-free populations and clinical populations is necessary to allow definitive conclusions. Furthermore, distraction may have differential effects upon acute compared to chronic pain. Distraction seems most appropriate to control acute pain. In chronic pain situations, distraction has cognitive costs, possibly resulting in paradoxical effects (Crombez et al., 2005). Therefore, more dynamic attention strategies may be necessary, resulting in flexible switching of attention between pain and other task demands (Morley et al., 2004). In spite of several limitations, this study extends our knowledge about distraction and its underlying processes.
Notes 1 We repeated the analyses on the self-report data excluding the participants who were unable to keep their hand in the cold water for two minutes. However, this did not change the pattern of results presented in the paper.
Acknowledgement Stefaan Van Damme and Liesbet Goubert are postdoctoral researchers of the Fund for Scientific Research – Flanders (FWO). The authors want to thank Pascal Mestdagh (Ghent University) for technical assistance.
Appendix Threat instructions. In this experiment we work with the cold water test. This is a method to investigate pain perception. The intention is that you attempt to keep your hand in the cold water as long as possible.
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I will give you some more information about this procedure. The cold water test is a frequently used and safe method in pain research. However, exposure to ice cold water can lead to freezing in the long term. This is associated with pain, tingling, and numbness in the immersed hand. Before we start it is necessary that we check your blood pressure. Your blood pressure is rather high but just within the limits to allow participation to the cold water procedure. I would like to stress that you are free to participate to this study. You can stop your participation or withdraw your hand whenever you want. However try to leave your hand in the cold water as long as possible. Neutral instructions. In this experiment we work with the cold water test. This is a method to investigate pain perception. The intention is that you attempt to keep your hand in the cold water as long as possible. I will give you some more information about this procedure. First, the cold water test is a frequently used method in pain research. Second, the test is safe because the water temperature does not fall below the freezing point. Although exposure to cold water is harmless, it can be associated with some discomfort or pain, which is absolutely normal and has no further consequences. However, I would like to stress that you are free to participate to this study. You can stop your participation or withdraw your hand whenever you want. However try to leave your hand in the cold water as long as possible.
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