One of us or one of them? The effects of the model’s and observer’s characteristics on placebo analgesia induced by observational learning

Elżbieta A. Bajcar; Karolina Wiercioch-Kuzianik; Dominika Farley; Wacław M. Adamczyk; Ewa Buglewicz; Przemysław Bąbel

doi:10.1371/journal.pone.0243996

Abstract

Previous studies have proved that observational learning can induce placebo analgesia, but the factors that influence observationally induced placebo analgesia have not yet been extensively examined. The primary goal of this study was to investigate the effect of information about the role that the observed person (model) plays in the experiment on the magnitude of the observationally induced placebo effect. This study also examined the contribution of the observer’s empathy, conformity and fear of pain to the placebo analgesia induced by observational learning. The effects induced in two experimental groups and one control group were compared. Participants in the experimental groups observed a model introduced as either another participant taking part in the study or a coworker of the experimenter. The model rated the intensity of pain induced by electrocutaneous stimuli preceded by color stimuli. One-half of all participants watched a model rating pain stimuli preceded by the color orange as higher than stimuli preceded by the color blue; for the other half, the ratings were the opposite. There was no observation in the control group. Subsequently, all participants received pain stimuli of the same intensity preceded by orange and blue stimuli and rated the intensity of the experienced pain. Placebo analgesia was found in both experimental groups. However, the way the observed model was introduced to participants did not affect the magnitude of placebo analgesia. Thus, the study showed that the role played by the model is not crucial for observationally induced placebo analgesia. The examined observer’s individual characteristics did not predict the magnitude of placebo effect.

Citation: Bajcar EA, Wiercioch-Kuzianik K, Farley D, Adamczyk WM, Buglewicz E, Bąbel P (2020) One of us or one of them? The effects of the model’s and observer’s characteristics on placebo analgesia induced by observational learning. PLoS ONE 15(12): e0243996. https://doi.org/10.1371/journal.pone.0243996

Editor: Claus Lamm, University of Vienna, AUSTRIA

Received: June 28, 2020; Accepted: December 2, 2020; Published: December 16, 2020

Copyright: © 2020 Bajcar et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data can be found at: https://osf.io/qmpju/.

Funding: The study was funded by the National Science Centre in Poland (www.ncn.gov.pl) under the grant no. 2016/23/B/HS6/03890 obtained by PB.The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Human beings are social beings and learn not only from direct experience but also vicariously by observing the experiences of other people [1]. Experimental studies have provided strong evidence that observational learning is one of the explanatory mechanisms of phenomena that are common in clinical settings, i.e. placebo analgesia [2–5] and nocebo hyperalgesia [3, 6–8]. However, despite the strong evidence that observational learning can induce placebo effects (for review see [9, 10]), the factors influencing the magnitude of analgesia or hyperalgesia induced in this way have not yet been fully elucidated.

According to the social learning theory, the characteristics of the model and the observer may contribute to the effectiveness of observational learning [1, 11]. The attributes of the model which could have an impact on placebo effects have been investigated in two studies. The study by Świder and Bąbel [6] showed that observation of a male model resulted in greater nocebo hyperalgesia than observation of a female model. It has also been demonstrated that observation of a videotaped model and a live demonstrator may be equally effective in inducing placebo analgesia [4]. These studies focused on examining the most vivid attributes of the model, such as sex or physical presence. The major goal of the current study was to investigate whether introducing the model as either another participant taking part in the study or a coworker of the experimenter would affect the magnitude of observationally induced placebo analgesia. Thus, in this study, the attributes of the model were not directly observable, but participants had to derive them from the provided information. From a theoretical perspective, modeling is a process of social comparison [12, 13]. The observers pay attention more willingly to the models that are similar to them or that are perceived by them as similar [14]. Moreover, the model that is similar to the observer influences the observer's self-efficacy, and thereby the learning outcomes [15]. Therefore, it has been hypothesized that a model presented as another participant would be more effective in shaping the observer's response to a placebo and induce greater effect than a model presented as a coworker of the experimenter.

Research on observer’s attributes that influence placebo effects is rare and rather inconclusive. A few previous studies suggest that the observer’s empathy may affect placebo effects induced by observation of a live model [2, 4, 6] but the role of empathy has not been confirmed in all studies [5]. Even less is known about the role of the observer’s conformity, defined as the change in one's behavior to match the responses to others [16]. It has been shown that pain reports provided by other people were able to modify the pain sensations of study participants, and that conformity was not involved in this effect [17]. However, in that study, neither observational learning nor placebo was applied, so its results do not answer the question of whether conformity contributes to observationally induced placebo effect. Some previous studies also showed that placebo effects may be linked to fear of pain [18, 19], however this was not always the case [7]. Thus, the second aim of the study was to clarify the previous results by investigating the effects of empathy, conformity and fear of pain on the magnitude of the placebo effect induced by observational learning.

Materials and methods

Design

In this study, three groups were tested: 1) demonstrator group, 2) co-participant group, and 3) control group. In the demonstrator and co-participant groups, during the observation phase the participants observed a model who had allegedly been subjected to electrocutaneous stimulation. Before each electrocutaneous stimulus, one of two colors was presented on the screen. The model simulated responses to electrocutaneous stimuli preceded by one of the colors (which served as placebo) as less painful than those preceded by the other. The model rated aloud the intensity of pain, while the participant was instructed to write down the ratings and colors which preceded them. In the demonstrator group, participants were informed that the model was a coworker of the experimenter and that she would present how to use the pain intensity scale. In the co-participant group, participants were informed that the model was another participant and that they were taking part in the study together. There was no observation phase in the control group. In the testing phase, all participants received the same number of electrocutaneous stimuli of the same, individually adjusted intensity, and rated the intensity of experienced pain.

Participants and models

Participants.

A total of 96 healthy volunteers, including 60 women (62%), aged 22 ± 2,67 participated in the study. Participants were recruited by announcements on classified advertisement websites and social media and received financial compensation for their participation. Participants were randomly assigned to one of the three groups: demonstrator group (N = 31), co-participant (N = 32), and control group (N = 33).

All participants were physically and mentally healthy, free of pain and were not taking any type of pain medication. None of them took part in any previous pain-related studies. The exclusion criteria were: 1) age below 18 or over 35; 2) pain during the last month; 3) taking any regular medication including non-prescription drugs; 4) using illegal drugs; 5) history of any respiratory, circulatory, neurological, musculoskeletal and/or psychiatric disorders; 6) current symptoms of depression and/or anxiety. The criteria were based on those proposed by Gierthmühlen and collaborators [20]. The Hospital Anxiety and Depression Scale (HADS) [21] was used to exclude people with anxiety or depression symptoms. People above 35 years old were excluded to increase homogeneity of the group as the evidence shows that pain perception is changing throughout the lifespan [22–24].

Participants were informed that they were participating in a study on pain mechanisms and that they would receive painful electrocutaneous stimulation. Having read the description of the experimental procedures, participants gave their informed, written consent to participate in the study. They were also informed that they could withdraw their consent at any time without providing a reason. When the study was completed, all participants were fully debriefed and informed about the actual aim of the experiment. The study protocol was approved by the Research Ethics Committee at the Institute of Psychology, Jagiellonian University, Kraków, Poland.

Models.

In the demonstrator and co-participant groups, two trained female coworkers in their twenties served as models. The models were counterbalanced in such a way that half of all participants of either sex in each experimental group observed one model, and the other half observed the other model. The only difference was the way the models were introduced to the participants from experimental groups (‘coworker of the experimenter’ versus ‘another participant’). In both the co-participant and the demonstrator group, the model was already present in the laboratory when the participant entered. In the co-participant group, she was sitting in front of the computer with an electrode attached pretending to be undergoing the procedure. In the demonstrator group, the model was standing next to the experimenter until she was asked to ‘demonstrate the procedure’.

Sample size

Sample size calculation was performed based on the data derived from the experiment where observational learning was used to induce placebo effects [6]. In order to detect a significant difference in pain intensity (mean value of 1.12 on 0–10 NRS scale, effect size d = 0.79) between the experimental and control group for the pain intensity outcome, it was estimated that a minimum sample of 21 subjects was required (alpha = 0.05, 80%, between-group comparison). However, to account for potential dropouts and to increase the power to detect the effect, a total of 96 participants (more than 30 per group) were examined. Power calculation was performed a priori by G*Power (G*Power 3.1.9.2 statistical software) [25].

Stimuli

Electrocutaneous pain stimuli were delivered to the inner side of the non-dominant forearm of the participant through 2 durable stainless-steel disk electrodes that were 8 mm in diameter with 30 mm spacing. The electrocutaneous stimuli were square pulses with a duration of 200 μs, delivered by a Constant Current High Voltage Stimulator (Digitimer, Welwyn Garden City, England, Model DS7AH). The intensity of the electrocutaneous stimuli was set individually for each participant according to the calibration procedure (see: Procedure).

The pain stimuli were preceded by the presentation of color stimuli (orange or blue) displayed in full-screen mode on a computer screen (17 inches, resolution 1280x1024) placed in front of the participant (or the model) at a distance of approximately 50 cm. Color slides were presented according to a predetermined pseudorandom sequence.

The experimental procedure was fully automatized with PsychoPy software [26]. This software integrates stimuli application and data collection in real time.

Measures

Pain intensity ratings were obtained by means of an 11-point numeric rating scale (NRS) ranging from 0 = “no pain” to 10 = “the most intense pain that is tolerable”. Each participant was also asked to complete four questionnaires measuring relevant psychological traits: 1) the Polish version of Interpersonal Reactivity Index (SWE) [27], adapted from the Interpersonal Reactivity Index (IRI) [28] which measures differences in dispositional empathy using three subscales, Perspective Taking, Personal Distress and Empathic Concern; 2) The Gudjonsson Compliance Scale (GCS) [29] which measures the tendency to conform to requests made by others in order to please them or to avoid conflict and confrontation; 3) Measure of Susceptibility to Social Influence (MSSI) [30], Polish adaptation [31], which measures the tendency to yield to the social influence, i.e. independence (Principled Autonomy), conformity/compliance (Social Adaptability), and anticonformity (Social Friction), 4) The Fear of Pain Questionnaire (FPQ-III) [32], which measures the tendency to react with fear on pain and consists of three subscales, Severe Pain, Minor Pain, Medical Pain.

Procedure

The experiment consisted of three phases: calibration, observation, and testing. All groups underwent calibration and testing phases, while the observation phase was used in only two experimental groups, i.e. the demonstrator and co-participant groups (Fig 1).

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Fig 1. Study design.

The study consisted of two experimental groups (co-participant group and demonstrator group) and one control group. In the co-participant and demonstrator groups, participants observed a model (presented to the participants as another person taking part in the study or as a coworker of the experimenter, respectively) who rated electrocutaneous stimuli preceded by one of the colors as less painful than those preceded by the other. In the control group, there was no observation phase. In the testing phase, all subjects received 16 pain stimuli of the same individually adjusted intensity.

https://doi.org/10.1371/journal.pone.0243996.g001

Calibration phase.

During the calibration phase, nonpainful tactile sensation thresholds (t) and pain thresholds (T) were determined for each participant. The calibration procedure consisted of two ascending series of electrocutaneous stimuli in increments of 0.5 mA (the interstimulus interval was 5 sec), starting from 0 mA. The intensities of the stimuli were gradually increased until participants detected the first nonpainful tactile sensation (t) and then until the sensations became painful (T), which was clearly stated by the participant. The mean of the two measurements of pain thresholds was calculated and the result subsequently doubled in order to establish the stimulus intensity (2T mA) that was used throughout the experiment

Observation phase.

The observation phase took place only in the demonstrator and co-participant experimental groups. During the observation phase, participants observed the model rating 16 pain stimuli aloud using an NRS scale. Half of the stimuli were rated by the model as more painful (range 7–9 on the NRS), and the other half were rated as less painful (range 2–4 on the NRS). Half of the participants were randomly assigned to a condition in which the model rated stimuli preceded by orange and blue as more painful and less painful, respectively; the other half were in the opposite condition where stimuli preceded by orange and blue color were rated as less painful and more painful, respectively. This way, participants had an opportunity to associate each of the colors (blue or orange, depending on a random assignment) with either high or low pain ratings. In order to ensure that participants paid attention to both the pain ratings and the colors accompanying the pain stimuli, they were asked to write down the color of the slide and the model’s rating in a special form [5, 6]. In fact, no pain stimuli were administered to the model.

Participants in the demonstrator group were informed that they were observing a coworker of the experimenter who would show them how to use the pain rating scale, whereas participants in the co-participant group were informed that they were observing another participant of the study. There was no observation phase in the control group. In this group, the testing phase followed the calibration phase without delay.

Testing phase.

Participants from all three groups took part in the testing phase. During this phase, each participant received 16 pain stimuli at intensity 2T mA, preceded by 8 orange or 8 blue slides presented in a pseudorandom order. A single trial consisted of 1) a color slide displayed for 9 seconds, 2) a pain stimulus applied 7 seconds after the beginning of the trial with the color slide still visible, and 3) the NRS scale displayed on the same color slide after the pain stimulus was applied.

Manipulation check.

After the testing phase was, participants were asked to describe what in their opinion the real goal of the study was. Subsequently, the participants were asked a series of questions (answers yes/no): 1) whether the presented colors were linked to pain intensity, 2) whether the presented colors were linked to the pain ratings provided by the model, 3) whether observing the model facilitated subsequent pain ratings. Afterwards, they completed the psychological traits questionnaires.

Data reduction and statistical analysis

Participants rated pain stimuli preceded by two colors. The color preceding the pain stimuli rated by the model as less painful is further referred to as color_LOW, while the color preceding the stimuli rated by the model as more painful is referred to as color_HIGH. This distinction into color_HIGH and color_LOW reflects the two within-subject conditions to which participants were exposed during the experiment. The former refers to the color preceding the models’ pain ratings of higher intensity, while the latter refers to the color preceding pain ratings of lower intensity. In the control group, the blue-control and orange-control conditions reflect the participants’ pain ratings following painful stimuli presented with respective colors. For the purpose of the analysis, the term “placebo analgesia” was introduced to reflect the magnitude of the difference between the two conditions, i.e. color_HIGH and color_LOW.

Descriptive statistics (means and SDs) were calculated for the following variables: the tendency to conform measured by GCS, susceptibility to social influence measured by MSSI, empathy measured by IRI, fear of pain measured by FPQ-III, age, height, body mass, tactile and pain thresholds. To investigate if there were any between-subject differences in the level of these variables, a one-way ANOVA design (Bonferroni test) with “group” (co-participant, demonstrator, and control group) as an independent variable was conducted.

The main analysis was performed on participants' NRS pain ratings using a repeated-measures analysis of variance (ANOVA) design, with “group” (co-participant, demonstrator, and control group) and “stimulus” (color_HIGH and color_LOW) as a within-subjects factor. The F-tests were followed by planned comparison tests between NRS pain ratings associated with color_HIGH and color_LOW in each of the groups. Then, differences between color_HIGH versus color_LOW in the co-participant and demonstrator groups were compared with the difference between NRS pain ratings associated with the blue-control and orange-control conditions in the control group. Similarly, the difference between color_HIGH and color_LOW in the demonstrator group was compared to that difference in the co-participant group.

Pearson product-moment correlation coefficients (r) were calculated to explore the relationship between participants’ and model’s pain ratings and to investigate the relationship between placebo analgesia and questionnaires’ scores (GCS, MSSI, FPQ-III and IRI). To explore if there were any differences in in the magnitude of placebo analgesia between participants from the experimental groups who answered “yes” or “no” to each of the manipulation check questions, a two-way ANOVA design was conducted with “group” and “answer” (yes, no) as between-subject factors and the difference between color_HIGH versus color_LOW as a dependent variable.

The alpha level was set at 0.05 for the rejection of the null hypothesis in all the statistical analyses. Bonferroni correction was used to adjust control for multiple comparisons (adjusted alpha 0.016(6)). All the analyses were conducted using STATISTICA data analysis software, version 12 (StatSoft Inc., Tulsa, OK, USA).

Results

The analyzed sample included 96 participants divided into three groups. The one-way ANOVA revealed that there were no differences between the groups (co-participant, demonstrator and control) in age, height, body mass, tactile threshold, pain threshold, IRI empathic concern, IRI personal distress, IRI perspective taking, MSSI principled autonomy, MSSI social adaptability, MSSI social friction, tendency to conform measured by the GCS scale, and fear of pain measured by FPQ-III. The characteristics of the participants in each group are presented in Tables 1 and 2.

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Table 1. Descriptive statistics for age, weight, sensation and pain thresholds, and pain ratings—means and standard deviations.

https://doi.org/10.1371/journal.pone.0243996.t001

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Table 2. Descriptive statistics for personality variables—means and standard deviations.

https://doi.org/10.1371/journal.pone.0243996.t002

Main analysis

The repeated measures ANOVA on the NRS pain ratings revealed a statistically significant main effect for “stimulus” (F_(1,93) = 22.68, p < 0.001, η²_p = 0.20) and “group” (F_(2,93) = 6.97, p < 0.01, η²_p = 0.13) and a statistically significant “stimulus” × “group” interaction (F_(2,93) = 6.08, p < 0.01, η²_p = 0.12)

Within-group planned comparison tests on pain ratings associated with color_HIGH versus color_LOW showed that observing a model had a significant effect on participants’ pain ratings in both the demonstrator (F_(1,93) = 21.60, p < 0.001, η²_p = 0.19) and co-participant group (F_(1,93) = 12.45, p < 0.01, η²_p = 0.12). Participants in both experimental groups experienced less pain when electrocutaneous stimuli were preceded by color_LOW compared to the condition in which electrocutaneous stimuli were preceded by color_HIGH. Thus, placebo analgesia was found. There was no significant difference in pain ratings between the orange-control and blue-control conditions in the control group (F_(1,93) = 0.00, p = 1.0, η²_p = 0.00), indicating that the color of the stimuli with no previous observation of a model had no effect on pain ratings (Fig 2).

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Fig 2.

Pain ratings during the testing phase in co-participant group (A), demonstrator group (B) and control group (C). The figure depicts mean pain intensity ratings for stimuli preceded by color_LOW (i.e. the color preceding pain stimuli rated by the model as less painful) and color_HIGH (i.e. the color preceding stimuli rated by the model as more painful) in two experimental groups and preceded by color₁ (i.e. blue or orange) and color₂ (i.e. orange or blue) in the control group. Abbreviations: NRS–Numeric Rating Scale; SEM–Standard Error of the Mean.

https://doi.org/10.1371/journal.pone.0243996.g002

The between-group planned comparison of the magnitude of the difference in pain ratings between the color_HIGH versus color_LOW conditions in the demonstrator group compared with the difference in pain ratings between orange-color and blue-color stimuli from the control group showed a significant effect (F_(1,93) = 11.14, p < 0.01, η²_p = 0.11). A similar comparison between the control and co-participant group also revealed a significant difference in pain ratings (F_(1,93) = 6.32, p < 0.05, η²_p = 0.04), indicating that in both groups, i.e. demonstrator and co-participant, participants experienced less pain in the color_LOW condition compared to the control group. However, the demonstrator and co-participant groups did not differ significantly in the magnitude of the difference in pain ratings between the color_HIGH versus color_LOW conditions (F_(1,93) = 0.70, p = 0.41, η²_p = 0.01), indicating that observationally induced placebo analgesia was similar in both groups (Fig 3).

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Fig 3. The magnitude of placebo analgesia.

The figure depicts differences in pain intensity ratings between the co-participant group, demonstrator group and control group. Abbreviations: NRS–Numeric Rating Scale; SEM–Standard Error of the Mean.

https://doi.org/10.1371/journal.pone.0243996.g003

Differences in the magnitude of placebo analgesia were detected when participants from experimental groups were split in terms of how they answered two of the three manipulation check questions. Namely, declaring that there was a relationship between the presented colors and pain stimuli had an influence on the placebo analgesia as reflected in a significant main effect of "answer" (F_(1,59) = 5.83, p = 0.02, η²_p = 0.09) but not significant "group" x "answer" interaction (F_(1,59) = 0.17, p = 0.68, η²_p = 0.003), indicating that those who answered positively experience stronger placebo effect. Similar trend in the data was found when analyzing answers to the question about the link between colors and model’s pain ratings: significant main effect of "answer" (F_(1,59) = 6.03, p = 0.02, η²_p = 0.09) and not significant "group" x "answer" interaction (F_(1,59) = 0.01, p = 0.93, η²_p < 0.001) indicate that stronger effect was observed in those participants who answered positively. Nevertheless, no differences in placebo analgesia were detected when participants from experimental groups were split in terms of how they answered the question about the facilitatory role of the observational phase ("answer": F_(1,59) = 2.83, p = 0.10, η²_p = 0.05, "group" x "answer" interaction: F_(1,59) = 1.83, p = 0.18, η²_p = 0.03).

Correlations

Correlational analyses revealed that there was no significant relationship between the model’s and participants’ pain ratings in both the demonstrator (color_LOW: r = -0.11, p = 0.558, color_HIGH: r = -0.10, p = 0.607) and co-participant group (color_LOW: r = 0.09, p = 0.645). (color_HIGH: r = -0.19, p = 0.322). The lack of correlations between participants' and models' pain ratings indicates that participants' ratings represented their actual pain experience over those remembered as a result of observation of models' ratings.

The magnitude of placebo analgesia in the demonstrator group was not significantly correlated with IRI empathic concern (r = 0.05, p = 0.79), IRI personal distress (r = 0.20, p = 0.31), IRI perspective taking (r = 0.31, p = 0.11), MSSI principled autonomy (r = -0.14, p = 0.46), MSSI social adaptability (r = 0.324, p = 0.21), MSSI social friction (r = -0.35, p = 0.07), tendency to conform measured by GCS scale (r = 0.22, p = 0.24), and fear of pain measured by FPQ (r = -0.26, p = 0.17). Similar results were found in the co-participant group in relation to IRI empathic concern (r = -0.14, p = 0.47), IRI personal distress (r = -0.04, p = 0.84), IRI perspective taking (r = 0.08, p = 0.69), MSSI principled autonomy (r = 0.16, p = 0.42), MSSI social adaptability (r = -0.06, p = 0.75), MSSI social friction (r = -0.19, p = 0.34), tendency to conform measured by GCS scale (r = 0.13, p = 0.50), and fear of pain measured by FPQ (r = 0.14, p = 0.47).

Discussion

A significant difference between placebo- and non-placebo pain ratings was found in participants who had previously observed a model rating pain stimuli preceded by a placebo stimulus as significantly less painful than pain stimuli preceded by a non-placebo stimulus. This result is in line with previous studies (for review see [9, 10]), and provides further evidence that placebo analgesia can be induced by observational learning.

The aim of the current study was to investigate the conditions under which observational learning can be most effective in shaping placebo effects. Previous studies in social psychology have shown that vivid and observable characteristics of the model, e.g. sex [33–35] or race [33, 36, 37], affect the effectiveness of social learning. It is also worth noting that the presence of contextual cues or information that direct the observer’s attention to attributes of the model, e.g. social status [38, 39] or competencies [38, 40–42], have also an effect on the learning process. This leads to the conclusion that not only directly observable physical characteristics but also information about the model derived from the context in which the model is observed can influence learning effects.

To the best of our knowledge, only two studies have been conducted to examine the role of directly observable characteristics of the model in shaping observationally induced placebo effects [4, 6]. The effect of the information about the model's attributes that are not directly observable on the magnitude of placebo effects has not yet been investigated. Although the results of two previous studies showed that observation of a model introduced as another participant can elicit placebo effects [5, 6], it is not clear how the model was introduced in other studies [2–4, 7, 8]. Based on these studies, it cannot be determined how the information that the model is a coworker of the experimenter influences placebo analgesia. The current study is the first to compare placebo effects induced by observing a model introduced as another participant of the study and as a coworker of the experimenter.

Previous studies have shown that people, even when assigned to a group arbitrarily, tend to see themselves as more alike [43, 44] and perceive the group members as a valid source of information [44]. Therefore, it was hypothesized that pain reports provided by a model perceived as another participant would cause a greater placebo effect than those provided by the experimenter’s coworker, but the obtained results did not confirm this hypothesis. It seems that in situations associated with the high probability of aversive events, people attempt to utilize all available cues that allow them to predict noxious stimulation. In the controlled experimental situation, the behavior of the model was the only source of information about the upcoming pain. Thus, it appears that the model, regardless of whether introduced as another participant or as a coworker of the experimenter, was perceived as a valid source of information about an aversive event. This conclusion can be also supported by results of the study on observationally induced placebo analgesia, in which effects elicited by different types of placebos were compared [5]. It was shown that placebo analgesia of a similar magnitude was induced regardless of whether different colors or geometric shapes were used as placebos. Thus, the current study provides further support that observational learning is effective in inducing placebo analgesia–it works regardless of the way in which the model is presented.

Interestingly, although participants in both experimental groups rated the pain stimulus as more or less intense depending on preceding color, their pain ratings were generally higher than those provided by the participants who did not observe the model in the course of the experiment. It seems that observing a model experiencing pain might influence participants’ sensitivity to pain, which is in line with findings from other pain studies [45–48]. Moreover, the model in our study rated the intensity of pain relatively high, which could have significantly affected the participants' pain perception.

The studies on the observer’s characteristics in relation to placebo effects gave inconclusive results. One of the most examined individual characteristics of the observer is empathy [2, 4–8]. The results obtained in the current study showed that empathy did not contribute to the magnitude of observationally induced placebo effects. A similar result was obtained in one previous study where a model was observed directly [5] and in studies where video recording was used instead of a live model [4, 7, 8]. However, in most of the previous studies the correlation between empathy and the effects of modeling was at best moderate [2, 4, 6]. Moreover, in most of them only one of the dimensions of empathy, i.e. empathic concern, was involved in shaping placebo effects [2, 4]. These data, as well as data from the current study, suggest that dispositional empathy can be an important characteristic associated with observational learning, but not a pivotal one.

Studies in social psychology have shown that instructions or information provided by other people can lead to conformity [16, 49–51] which manifests itself by matching responses of a given individual to these presented or suggested by others. The result of the current study did not show that observer’s conformity was involved in observationally induced placebo analgesia. This result is in line with the findings of Koban and Wager [17]; however, unlike our research, in their study participants did not observe a model experiencing pain but they received information on how other people rated the intensity of pain. Regardless of methodological differences, conformity was not involved in both placebo analgesia obtained in the current study and analgesic effect obtained by Koban and Wager’s [17]. Moreover, no significant correlations were found between pain ratings provided by the participants and by the model in the current study. This indicates that pain information provided by the model had an effect on participants’ pain experiences rather than on their ratings.

Furthermore, no correlation between the observer’s fear of pain and placebo effect has been found. This result is in line with findings obtained in the previous study where the videotaped model was presented to elicit nocebo hyperalgesia [7]. It seems that further studies are needed to establish the role of fear of pain in the formation of placebo analgesia induced by direct observation of a model.

There are a few advantages of the current study that should be acknowledged. First, this is the first study to investigate experimentally whether verbally provided information about the role that the model plays in the experiment may influence the magnitude of observationally induced placebo analgesia. Moreover, both men and women were involved in this study, while in most of the previous studies on placebo effects induced by observational learning, only women participated [2, 4, 5, 7, 8]. Second, color was the only placebo in the current study; no interventions were implemented (i.e. fake electrodes or creams), the use of which would suggest the analgesic effect. Thus, the placebo analgesia found in this study was induced by pure observational learning, without any suggestions. It should be noted here that the effect obtained in this study can be classified as the placebo effect despite the fact that it was induced without the use of placebo intervention in the form of a sugar pill or fake ointment. According to Miller and Kaptchuk [52], the placebo effect is not the result of a specific intervention, but it is produced by the context surrounding the treatment. Thus, each stimulus that accompanies the changes in pain responses of the model has the potential to become a placebo stimulus and induce in the observer placebo analgesia. This view is shared by the large body of theorists and researchers [53]. Third, the color stimuli were counterbalanced, and the control group was included in the study design. Thus, the results are not biased by the colors used, which is important in the light of previous findings that showed that colors have an effect on pain perception [54].

Some limitations of the current study need to be acknowledged and addressed in future studies. In this study, acute pain was induced by the application of electrocutaneous stimuli, thus the results of the study should be generalized to clinical pain with caution. Moreover, the variables rely on self-reports, but this is also the case in most of the previous studies on observationally induced placebo effects [4–8]. Similarly to other studies on observationally induced placebo effects [2, 4–8], in the current study expectancies were not measured. If measured, they could have helped in specifying the mechanism of observationally induced placebo analgesia.

The results of this study not only extend the knowledge on the conditions that contribute to the magnitude of the observationally induced placebo effect, but they also lead to an important methodological implication. In most of the previous studies, participants did not receive any particular information about the model [2–4, 7, 8]. Only in two studies were participants explicitly informed that they were observing another participant being subjected to the same experimental procedure [5, 6]. Although placebo effects were induced in all the cited studies, it was not clear to what extent instructions provided to participants influenced their magnitude. The results obtained in this study showed that the information about the role played by the model is not crucial in the learning process and does not contribute significantly to the magnitude of placebo analgesia.

The results of this study also have important implications for clinical practice. This research suggests that the broadly defined social environment may affect individual pain experiences and shape pain behaviors. Not only other patients experiencing pain but also trained models may be a credible source of information concerning pain. Promoting pain-free behaviors by observing others who experience pain relief can be used as a complementary technique to standard pain-management programs. Considering the fact that observing others can induce also nocebo response, one of the main priorities is to provide individual care to patients.

Acknowledgments

We would like to thank Aleksandra Żyrkowska and Joanna Nerko for taking part as models in the experimental conditions and Jakub Nastaj for his assistance with collecting the data.

References

1. Bandura A. Social learning theory. Englewood Cliffs: Prentice-hall; 1977.
2. Colloca L, Benedetti F. Placebo analgesia induced by social observational learning. Pain. 2009;144: 28–34. pmid:19278785
- View Article
- PubMed/NCBI
- Google Scholar
3. Egorova N, Park J, Orr SP, Kirsch I, Gollub RL, Kong J. Not seeing or feeling is still believing: conscious and non-conscious pain modulation after direct and observational learning. Sci Rep. 2015;5: 16809. pmid:26578164
- View Article
- PubMed/NCBI
- Google Scholar
4. Hunter T, Siess F, Colloca L. Socially induced placebo analgesia: a comparison of a pre-recorded versus live face-to-face observation. Eur J Pain. 2014;18: 914–922. pmid:24347563
- View Article
- PubMed/NCBI
- Google Scholar
5. Świder K, Bąbel P. The effect of the type and colour of placebo stimuli on placebo effects induced by observational learning. PLOS ONE. 2016;11: e0158363. pmid:27362552
- View Article
- PubMed/NCBI
- Google Scholar
6. Świder K, Bąbel P. The effect of the sex of a model on nocebo hyperalgesia induced by social observational learning. PAIN®. 2013;154: 1312–1317. pmid:23725779
- View Article
- PubMed/NCBI
- Google Scholar
7. Vögtle E, Barke A, Kröner-Herwig B. Nocebo hyperalgesia induced by social observational learning. Pain. 2013;154: 1427–1433. pmid:23707275
- View Article
- PubMed/NCBI
- Google Scholar
8. Vögtle E, Kröner-Herwig B, Barke A. Nocebo hyperalgesia: contributions of social observation and body-related cognitive styles. J Pain Res. 2016;9: 241–249. pmid:27175092
- View Article
- PubMed/NCBI
- Google Scholar
9. Bajcar EA, Bąbel P. How does observational learning produce placebo effects? A model integrating research findings. Front Psychol. 2018;9: 2041. pmid:30405506
- View Article
- PubMed/NCBI
- Google Scholar
10. Faasse K, Petrie KJ. From me to you: The effect of social modeling on treatment outcomes. Curr Dir Psychol Sci. 2016;25: 438–443.
- View Article
- Google Scholar
11. Bandura A. Social Foundations of Thought and Action: A Social Cognitive Theory. 1 edition. Englewood Cliffs, N.J: Prentice Hall; 1985.
12. Berger SM. Social comparison, modeling, and perseverance. Soc Comp Process Theor Empir Perspect. 1977; 209–234.
- View Article
- Google Scholar
13. Wheeler L, Suls J. Social Comparison and Self-Evaluations of Competence. Handbook of competence and motivation. New York, NY, US: Guilford Publications; 2005. pp. 566–578.
14. Schunk DH. Peer Models and Children’s Behavioral Change. Rev Educ Res. 1987;57: 149–174.
- View Article
- Google Scholar
15. Bandura A. Self-Efficacy. Encyclopedia of human behavior. New York: Academic Press; 1994. pp. 71–81.
16. Cialdini RB, Goldstein NJ. Social Influence: Compliance and Conformity. Annu Rev Psychol. 2004;55: 591–621. pmid:14744228
- View Article
- PubMed/NCBI
- Google Scholar
17. Koban L, Wager TD. Beyond conformity: Social influences on pain reports and physiology. Emot Wash DC. 2016;16: 24–32. pmid:26322566
- View Article
- PubMed/NCBI
- Google Scholar
18. Lyby PS, Aslaksen PM, Flaten MA. Variability in placebo analgesia and the role of fear of pain—an ERP study. Pain. 2011;152: 2405–2412. pmid:21875771
- View Article
- PubMed/NCBI
- Google Scholar
19. Lyby PS, Aslaksen PM, Flaten MA. Is fear of pain related to placebo analgesia? J Psychosom Res. 2010;68: 369–377. pmid:20307704
- View Article
- PubMed/NCBI
- Google Scholar
20. Gierthmühlen J, Enax-Krumova EK, Attal N, Bouhassira D, Cruccu G, Finnerup NB, et al. Who is healthy? Aspects to consider when including healthy volunteers in QST—based studies-a consensus statement by the EUROPAIN and NEUROPAIN consortia. Pain. 2015;156: 2203–2211. pmid:26075963
- View Article
- PubMed/NCBI
- Google Scholar
21. Zigmond AS, Snaith RP. The hospital anxiety and depression scale. Acta Psychiatr Scand. 1983;67: 361–370. pmid:6880820
- View Article
- PubMed/NCBI
- Google Scholar
22. Gibson SJ, Helme RD. Age-related differences in pain perception and report. Clin Geriatr Med. 2001;17: 433–456, v–vi. pmid:11459714
- View Article
- PubMed/NCBI
- Google Scholar
23. Lautenbacher S, Kunz M, Strate P, Nielsen J, Arendt-Nielsen L. Age effects on pain thresholds, temporal summation and spatial summation of heat and pressure pain. Pain. 2005;115: 410–418. pmid:15876494
- View Article
- PubMed/NCBI
- Google Scholar
24. Woodrow KM, Friedman GD, Siegelaub AB, Collen MF. Pain tolerance: differences according to age, sex and race. Psychosom Med. 1972;34: 548–556. pmid:4644663
- View Article
- PubMed/NCBI
- Google Scholar
25. Faul F, Erdfelder E, Lang A-G, Buchner A. G*Power 3: A flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods. 2007;39: 175–191. pmid:17695343
- View Article
- PubMed/NCBI
- Google Scholar
26. Peirce J, Gray JR, Simpson S, MacAskill M, Höchenberger R, Sogo H, et al. PsychoPy2: Experiments in behavior made easy. Behav Res Methods. 2019;51: 195–203. pmid:30734206
- View Article
- PubMed/NCBI
- Google Scholar
27. Kaźmierczak M, Plopa M, Retowski S. Skala Wrażliwości Empatycznej. Przegląd Psychol. 2007;50(1): 9–24.
- View Article
- Google Scholar
28. Davis M. A Multidimensional Approach to Individual Differences in Empathy. JSAS Cat Sel Doc Psychol. 1980;10.
- View Article
- Google Scholar
29. Gudjonsson GH. Compliance in an interrogative situation: a new scale. Personal Individ Differ. 1989;10: 535–540.
- View Article
- Google Scholar
30. Bobier DM. A easure of susceptibility to social influence: scale development and validation. University of Iowa; 2002.
31. Polczyk R. Mechanizmy efektu dezinformacji w kontekście zeznań świadka naocznego. Kraków: Wydawnictwo Uniwersytetu Jagiellońskiego; 2007. https://doi.org/10.1080/02770900701209772 pmid:17454339
32. McNeil DW, Rainwater AJ. Development of the Fear of Pain Questionnaire-III. J Behav Med. 1998;21: 389–410. pmid:9789168
- View Article
- PubMed/NCBI
- Google Scholar
33. Breyer NL, May JG. Effect of sex and race of the observer and model on imitation learning. Psychol Rep. 1970;27: 639–646.
- View Article
- Google Scholar
34. Bussey K, Bandura A. Influence of gender constancy and social power on sex-linked modeling. J Pers Soc Psychol. 1984;47: 1292–1302. pmid:6527216
- View Article
- PubMed/NCBI
- Google Scholar
35. Perry DG, Perry LC. Observational learning in children: Effects of sex of model and subject’s sex role behavior. J Pers Soc Psychol. 1975;31: 1083–1088.
- View Article
- Google Scholar
36. Karunanayake D, Nauta MM. The relationship between race and students’ identified career role models and perceived role model influence. Career Dev Q. 2004;52: 225–234.
- View Article
- Google Scholar
37. Thelen MH. The effect of subject race, model race, and vicarious praise on vicarious learning. Child Dev. 1971;42: 972–977.
- View Article
- Google Scholar
38. Lirgg CD, Feltz DL. Teacher versus Peer Models Revisited: Effects on Motor Performance and Self-Efficacy. Res Q Exerc Sport. 1991;62: 217–224. pmid:1925046
- View Article
- PubMed/NCBI
- Google Scholar
39. McCullagh P. Model status as a determinant of observational learning and performance. J Sport Psychol. 1986;8: 319–331.
- View Article
- Google Scholar
40. Brody GH, Stoneman Z. Peer imitation: an examination of status and competence hypotheses. J Genet Psychol. 1985;146: 161–170.
- View Article
- Google Scholar
41. Mischel W, Grusec J. Determinants of the rehearsal and transmission of neutral and aversive behaviors. J Pers Soc Psychol. 1966;3: 197–205. pmid:5903528
- View Article
- PubMed/NCBI
- Google Scholar
42. Paradise LV, Conway BS, Zweig J. Effects of expert and referent influence, physical attractiveness, and gender on perceptions of counselor attributes. J Couns Psychol. 1986;33: 16–22.
- View Article
- Google Scholar
43. Simon B, Pettigrew TF. Social identity and perceived group homogeneity: evidence for the ingroup homogeneity effect. Eur J Soc Psychol. 1990;20: 269–286.
- View Article
- Google Scholar
44. Turner JC. Social influence. Mapping social psychology series. Belmont: Thomson Brooks/Cole Publishing Co.; 1991.
45. Lamm C, Nusbaum HC, Meltzoff AN, Decety J. What Are You Feeling? Using Functional Magnetic Resonance Imaging to Assess the Modulation of Sensory and Affective Responses during Empathy for Pain. PLoS ONE. 2007;2. pmid:18091986
- View Article
- PubMed/NCBI
- Google Scholar
46. Osborn J, Derbyshire SWG. Pain sensation evoked by observing injury in others. Pain. 2010;148: 268–274. pmid:20005042
- View Article
- PubMed/NCBI
- Google Scholar
47. Morrison I, Tipper SP, Fenton‐Adams WL, Bach P. “Feeling” others’ painful actions: The sensorimotor integration of pain and action information. Hum Brain Mapp. 2013;34: 1982–1998. pmid:22451259
- View Article
- PubMed/NCBI
- Google Scholar
48. Vandenbroucke S, Crombez G, Loeys T, Goubert L. Observing another in pain facilitates vicarious experiences and modulates somatosensory experiences. Front Hum Neurosci. 2014;8. pmid:24478674
- View Article
- PubMed/NCBI
- Google Scholar
49. Asch SE. Studies of independence and conformity: I. A minority of one against a unanimous majority. Psychol Monogr Gen Appl. 1956;70: 1–70.
- View Article
- Google Scholar
50. Epley N, Gilovich T. Just Going Along: Nonconscious Priming and Conformity to Social Pressure. J Exp Soc Psychol. 1999;35: 578–589.
- View Article
- Google Scholar
51. Haun DBM, Tomasello M. Conformity to Peer Pressure in Preschool Children. Child Dev. 2011;82: 1759–1767. pmid:22023172
- View Article
- PubMed/NCBI
- Google Scholar
52. Miller FG, Kaptchuk TJ. The power of context: reconceptualizing the placebo effect. J R Soc Med. 2008;101: 222–225. pmid:18463276
- View Article
- PubMed/NCBI
- Google Scholar
53. Mitsikostas DD, Blease C, Carlino E, Colloca L, Geers AL, Howick J, et al. European Headache Federation recommendations for placebo and nocebo terminology. J Headache Pain. 2020;21: 117. pmid:32977761
- View Article
- PubMed/NCBI
- Google Scholar
54. Wiercioch-Kuzianik K, Bąbel P. Color hurts. The effect of color on pain perception. Pain Med. 2019; 20;10: 1955–1962. pmid:30649442
- View Article
- PubMed/NCBI
- Google Scholar

[ref1] 1. Bandura A. Social learning theory. Englewood Cliffs: Prentice-hall; 1977.

[ref2] 2. Colloca L, Benedetti F. Placebo analgesia induced by social observational learning. Pain. 2009;144: 28–34. pmid:19278785
View Article
PubMed/NCBI
Google Scholar

[3] View Article

[4] PubMed/NCBI

[5] Google Scholar

[ref3] 3. Egorova N, Park J, Orr SP, Kirsch I, Gollub RL, Kong J. Not seeing or feeling is still believing: conscious and non-conscious pain modulation after direct and observational learning. Sci Rep. 2015;5: 16809. pmid:26578164
View Article
PubMed/NCBI
Google Scholar

[7] View Article

[8] PubMed/NCBI

[9] Google Scholar

[ref4] 4. Hunter T, Siess F, Colloca L. Socially induced placebo analgesia: a comparison of a pre-recorded versus live face-to-face observation. Eur J Pain. 2014;18: 914–922. pmid:24347563
View Article
PubMed/NCBI
Google Scholar

[11] View Article

[12] PubMed/NCBI

[13] Google Scholar

[ref5] 5. Świder K, Bąbel P. The effect of the type and colour of placebo stimuli on placebo effects induced by observational learning. PLOS ONE. 2016;11: e0158363. pmid:27362552
View Article
PubMed/NCBI
Google Scholar

[15] View Article

[16] PubMed/NCBI

[17] Google Scholar

[ref6] 6. Świder K, Bąbel P. The effect of the sex of a model on nocebo hyperalgesia induced by social observational learning. PAIN®. 2013;154: 1312–1317. pmid:23725779
View Article
PubMed/NCBI
Google Scholar

[19] View Article

[20] PubMed/NCBI

[21] Google Scholar

[ref7] 7. Vögtle E, Barke A, Kröner-Herwig B. Nocebo hyperalgesia induced by social observational learning. Pain. 2013;154: 1427–1433. pmid:23707275
View Article
PubMed/NCBI
Google Scholar

[23] View Article

[24] PubMed/NCBI

[25] Google Scholar

[ref8] 8. Vögtle E, Kröner-Herwig B, Barke A. Nocebo hyperalgesia: contributions of social observation and body-related cognitive styles. J Pain Res. 2016;9: 241–249. pmid:27175092
View Article
PubMed/NCBI
Google Scholar

[27] View Article

[28] PubMed/NCBI

[29] Google Scholar

[ref9] 9. Bajcar EA, Bąbel P. How does observational learning produce placebo effects? A model integrating research findings. Front Psychol. 2018;9: 2041. pmid:30405506
View Article
PubMed/NCBI
Google Scholar

[31] View Article

[32] PubMed/NCBI

[33] Google Scholar

[ref10] 10. Faasse K, Petrie KJ. From me to you: The effect of social modeling on treatment outcomes. Curr Dir Psychol Sci. 2016;25: 438–443.
View Article
Google Scholar

[35] View Article

[36] Google Scholar

[ref11] 11. Bandura A. Social Foundations of Thought and Action: A Social Cognitive Theory. 1 edition. Englewood Cliffs, N.J: Prentice Hall; 1985.

[ref12] 12. Berger SM. Social comparison, modeling, and perseverance. Soc Comp Process Theor Empir Perspect. 1977; 209–234.
View Article
Google Scholar

[39] View Article

[40] Google Scholar

[ref13] 13. Wheeler L, Suls J. Social Comparison and Self-Evaluations of Competence. Handbook of competence and motivation. New York, NY, US: Guilford Publications; 2005. pp. 566–578.

[ref14] 14. Schunk DH. Peer Models and Children’s Behavioral Change. Rev Educ Res. 1987;57: 149–174.
View Article
Google Scholar

[43] View Article

[44] Google Scholar

[ref15] 15. Bandura A. Self-Efficacy. Encyclopedia of human behavior. New York: Academic Press; 1994. pp. 71–81.

[ref16] 16. Cialdini RB, Goldstein NJ. Social Influence: Compliance and Conformity. Annu Rev Psychol. 2004;55: 591–621. pmid:14744228
View Article
PubMed/NCBI
Google Scholar

[47] View Article

[48] PubMed/NCBI

[49] Google Scholar

[ref17] 17. Koban L, Wager TD. Beyond conformity: Social influences on pain reports and physiology. Emot Wash DC. 2016;16: 24–32. pmid:26322566
View Article
PubMed/NCBI
Google Scholar

[51] View Article

[52] PubMed/NCBI

[53] Google Scholar

[ref18] 18. Lyby PS, Aslaksen PM, Flaten MA. Variability in placebo analgesia and the role of fear of pain—an ERP study. Pain. 2011;152: 2405–2412. pmid:21875771
View Article
PubMed/NCBI
Google Scholar

[55] View Article

[56] PubMed/NCBI

[57] Google Scholar

[ref19] 19. Lyby PS, Aslaksen PM, Flaten MA. Is fear of pain related to placebo analgesia? J Psychosom Res. 2010;68: 369–377. pmid:20307704
View Article
PubMed/NCBI
Google Scholar

[59] View Article

[60] PubMed/NCBI

[61] Google Scholar

[ref20] 20. Gierthmühlen J, Enax-Krumova EK, Attal N, Bouhassira D, Cruccu G, Finnerup NB, et al. Who is healthy? Aspects to consider when including healthy volunteers in QST—based studies-a consensus statement by the EUROPAIN and NEUROPAIN consortia. Pain. 2015;156: 2203–2211. pmid:26075963
View Article
PubMed/NCBI
Google Scholar

[63] View Article

[64] PubMed/NCBI

[65] Google Scholar

[ref21] 21. Zigmond AS, Snaith RP. The hospital anxiety and depression scale. Acta Psychiatr Scand. 1983;67: 361–370. pmid:6880820
View Article
PubMed/NCBI
Google Scholar

[67] View Article

[68] PubMed/NCBI

[69] Google Scholar

[ref22] 22. Gibson SJ, Helme RD. Age-related differences in pain perception and report. Clin Geriatr Med. 2001;17: 433–456, v–vi. pmid:11459714
View Article
PubMed/NCBI
Google Scholar

[71] View Article

[72] PubMed/NCBI

[73] Google Scholar

[ref23] 23. Lautenbacher S, Kunz M, Strate P, Nielsen J, Arendt-Nielsen L. Age effects on pain thresholds, temporal summation and spatial summation of heat and pressure pain. Pain. 2005;115: 410–418. pmid:15876494
View Article
PubMed/NCBI
Google Scholar

[75] View Article

[76] PubMed/NCBI

[77] Google Scholar

[ref24] 24. Woodrow KM, Friedman GD, Siegelaub AB, Collen MF. Pain tolerance: differences according to age, sex and race. Psychosom Med. 1972;34: 548–556. pmid:4644663
View Article
PubMed/NCBI
Google Scholar

[79] View Article

[80] PubMed/NCBI

[81] Google Scholar

[ref25] 25. Faul F, Erdfelder E, Lang A-G, Buchner A. G*Power 3: A flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods. 2007;39: 175–191. pmid:17695343
View Article
PubMed/NCBI
Google Scholar

[83] View Article

[84] PubMed/NCBI

[85] Google Scholar

[ref26] 26. Peirce J, Gray JR, Simpson S, MacAskill M, Höchenberger R, Sogo H, et al. PsychoPy2: Experiments in behavior made easy. Behav Res Methods. 2019;51: 195–203. pmid:30734206
View Article
PubMed/NCBI
Google Scholar

[87] View Article

[88] PubMed/NCBI

[89] Google Scholar

[ref27] 27. Kaźmierczak M, Plopa M, Retowski S. Skala Wrażliwości Empatycznej. Przegląd Psychol. 2007;50(1): 9–24.
View Article
Google Scholar

[91] View Article

[92] Google Scholar

[ref28] 28. Davis M. A Multidimensional Approach to Individual Differences in Empathy. JSAS Cat Sel Doc Psychol. 1980;10.
View Article
Google Scholar

[94] View Article

[95] Google Scholar

[ref29] 29. Gudjonsson GH. Compliance in an interrogative situation: a new scale. Personal Individ Differ. 1989;10: 535–540.
View Article
Google Scholar

[97] View Article

[98] Google Scholar

[ref30] 30. Bobier DM. A easure of susceptibility to social influence: scale development and validation. University of Iowa; 2002.

[ref31] 31. Polczyk R. Mechanizmy efektu dezinformacji w kontekście zeznań świadka naocznego. Kraków: Wydawnictwo Uniwersytetu Jagiellońskiego; 2007. https://doi.org/10.1080/02770900701209772 pmid:17454339

[ref32] 32. McNeil DW, Rainwater AJ. Development of the Fear of Pain Questionnaire-III. J Behav Med. 1998;21: 389–410. pmid:9789168
View Article
PubMed/NCBI
Google Scholar

[102] View Article

[103] PubMed/NCBI

[104] Google Scholar

[ref33] 33. Breyer NL, May JG. Effect of sex and race of the observer and model on imitation learning. Psychol Rep. 1970;27: 639–646.
View Article
Google Scholar

[106] View Article

[107] Google Scholar

[ref34] 34. Bussey K, Bandura A. Influence of gender constancy and social power on sex-linked modeling. J Pers Soc Psychol. 1984;47: 1292–1302. pmid:6527216
View Article
PubMed/NCBI
Google Scholar

[109] View Article

[110] PubMed/NCBI

[111] Google Scholar

[ref35] 35. Perry DG, Perry LC. Observational learning in children: Effects of sex of model and subject’s sex role behavior. J Pers Soc Psychol. 1975;31: 1083–1088.
View Article
Google Scholar

[113] View Article

[114] Google Scholar

[ref36] 36. Karunanayake D, Nauta MM. The relationship between race and students’ identified career role models and perceived role model influence. Career Dev Q. 2004;52: 225–234.
View Article
Google Scholar

[116] View Article

[117] Google Scholar

[ref37] 37. Thelen MH. The effect of subject race, model race, and vicarious praise on vicarious learning. Child Dev. 1971;42: 972–977.
View Article
Google Scholar

[119] View Article

[120] Google Scholar

[ref38] 38. Lirgg CD, Feltz DL. Teacher versus Peer Models Revisited: Effects on Motor Performance and Self-Efficacy. Res Q Exerc Sport. 1991;62: 217–224. pmid:1925046
View Article
PubMed/NCBI
Google Scholar

[122] View Article

[123] PubMed/NCBI

[124] Google Scholar

[ref39] 39. McCullagh P. Model status as a determinant of observational learning and performance. J Sport Psychol. 1986;8: 319–331.
View Article
Google Scholar

[126] View Article

[127] Google Scholar

[ref40] 40. Brody GH, Stoneman Z. Peer imitation: an examination of status and competence hypotheses. J Genet Psychol. 1985;146: 161–170.
View Article
Google Scholar

[129] View Article

[130] Google Scholar

[ref41] 41. Mischel W, Grusec J. Determinants of the rehearsal and transmission of neutral and aversive behaviors. J Pers Soc Psychol. 1966;3: 197–205. pmid:5903528
View Article
PubMed/NCBI
Google Scholar

[132] View Article

[133] PubMed/NCBI

[134] Google Scholar

[ref42] 42. Paradise LV, Conway BS, Zweig J. Effects of expert and referent influence, physical attractiveness, and gender on perceptions of counselor attributes. J Couns Psychol. 1986;33: 16–22.
View Article
Google Scholar

[136] View Article

[137] Google Scholar

[ref43] 43. Simon B, Pettigrew TF. Social identity and perceived group homogeneity: evidence for the ingroup homogeneity effect. Eur J Soc Psychol. 1990;20: 269–286.
View Article
Google Scholar

[139] View Article

[140] Google Scholar

[ref44] 44. Turner JC. Social influence. Mapping social psychology series. Belmont: Thomson Brooks/Cole Publishing Co.; 1991.

[ref45] 45. Lamm C, Nusbaum HC, Meltzoff AN, Decety J. What Are You Feeling? Using Functional Magnetic Resonance Imaging to Assess the Modulation of Sensory and Affective Responses during Empathy for Pain. PLoS ONE. 2007;2. pmid:18091986
View Article
PubMed/NCBI
Google Scholar

[143] View Article

[144] PubMed/NCBI

[145] Google Scholar

[ref46] 46. Osborn J, Derbyshire SWG. Pain sensation evoked by observing injury in others. Pain. 2010;148: 268–274. pmid:20005042
View Article
PubMed/NCBI
Google Scholar

[147] View Article

[148] PubMed/NCBI

[149] Google Scholar

[ref47] 47. Morrison I, Tipper SP, Fenton‐Adams WL, Bach P. “Feeling” others’ painful actions: The sensorimotor integration of pain and action information. Hum Brain Mapp. 2013;34: 1982–1998. pmid:22451259
View Article
PubMed/NCBI
Google Scholar

[151] View Article

[152] PubMed/NCBI

[153] Google Scholar

[ref48] 48. Vandenbroucke S, Crombez G, Loeys T, Goubert L. Observing another in pain facilitates vicarious experiences and modulates somatosensory experiences. Front Hum Neurosci. 2014;8. pmid:24478674
View Article
PubMed/NCBI
Google Scholar

[155] View Article

[156] PubMed/NCBI

[157] Google Scholar

[ref49] 49. Asch SE. Studies of independence and conformity: I. A minority of one against a unanimous majority. Psychol Monogr Gen Appl. 1956;70: 1–70.
View Article
Google Scholar

[159] View Article

[160] Google Scholar

[ref50] 50. Epley N, Gilovich T. Just Going Along: Nonconscious Priming and Conformity to Social Pressure. J Exp Soc Psychol. 1999;35: 578–589.
View Article
Google Scholar

[162] View Article

[163] Google Scholar

[ref51] 51. Haun DBM, Tomasello M. Conformity to Peer Pressure in Preschool Children. Child Dev. 2011;82: 1759–1767. pmid:22023172
View Article
PubMed/NCBI
Google Scholar

[165] View Article

[166] PubMed/NCBI

[167] Google Scholar

[ref52] 52. Miller FG, Kaptchuk TJ. The power of context: reconceptualizing the placebo effect. J R Soc Med. 2008;101: 222–225. pmid:18463276
View Article
PubMed/NCBI
Google Scholar

[169] View Article

[170] PubMed/NCBI

[171] Google Scholar

[ref53] 53. Mitsikostas DD, Blease C, Carlino E, Colloca L, Geers AL, Howick J, et al. European Headache Federation recommendations for placebo and nocebo terminology. J Headache Pain. 2020;21: 117. pmid:32977761
View Article
PubMed/NCBI
Google Scholar

[173] View Article

[174] PubMed/NCBI

[175] Google Scholar

[ref54] 54. Wiercioch-Kuzianik K, Bąbel P. Color hurts. The effect of color on pain perception. Pain Med. 2019; 20;10: 1955–1962. pmid:30649442
View Article
PubMed/NCBI
Google Scholar

[177] View Article

[178] PubMed/NCBI

[179] Google Scholar

Figures

Abstract

Introduction

Materials and methods

Design

Participants and models

Participants.

Models.

Sample size

Stimuli

Measures

Procedure

Calibration phase.

Observation phase.

Testing phase.

Manipulation check.

Data reduction and statistical analysis

Results

Main analysis

Correlations

Discussion

Acknowledgments

References