Over the past years self-tracking of physiological parameters has become increasingly common: more and more people are keeping track of aspects of their physiological state (e.g., heart rate, blood sugar, and blood pressure). To shed light on the possible effects of self-tracking of physiology, a study was conducted to test whether physiology feedback has acute effects on self-reported stress and the extent to which self-reported stress corresponds to physiological stress. In this study, participants executed several short tasks, while they were either shown visual feedback about their heart rate or not. Results show that self-reported stress is more in sync with heart rate for participants who received physiology feedback. Interactions between two personality factors (neuroticism and anxiety sensitivity) and feedback on the level of self-reported stress were found, indicating that while physiology feedback may be beneficial for individuals high in neuroticism, it may be detrimental for those high in anxiety sensitivity. Additional work is needed to establish how the results of this study may extend beyond immediate effects in a controlled lab setting, but our results do provide a first indication of how self-tracking of physiology may lead to better body awareness and how personality characteristics can help us predict which individuals are most likely to benefit from self-tracking of physiology.
Recent developments in mobile sensors and wearable devices allow for ubiquitous 24/7 tracking of individual activity and physiological states. Although these technologies are already well-known in specific application areas of mobile health (see, for example [
Many existing mind-body practices involve a component of body awareness [
Biofeedback is a special case in the world of mind-body medicine when it comes to body awareness. Biofeedback, including biofeedback-assisted relaxation, has been found to be efficacious in treating problems ranging from headaches, anxiety, and motion sickness to attention deficit hyperactivity disorder (ADHD) and epilepsy (see [
As things stand, it is unclear what the effects of exposure to one’s own physiological measurements are. There is evidence that other interventions that promote body awareness have positive effects, but there are important differences between those interventions and self-tracking of physiology that make it difficult to determine whether the positive effects found will generalize to self-tracking of physiology. As a first step toward investigating the effects of self-tracking, we focus on the acute effects of physiology feedback. We have therefore performed a study where some participants were given feedback about their heart rate while performing several small tasks, while other participants performed the same tasks, but they were not given physiology feedback.
We hypothesize that participants may (consciously or otherwise) use physiology feedback to inform (reports about) their subjective experience of the tasks. To investigate this possibility, we collected momentary self-reported stress levels after each task. Stress was chosen here for several reasons: firstly, there is an intuitive connection between stress and heart rate. Secondly, (long-term) stress is an important factor in psychosomatic illness and is believed to be the cause of many health complaints. As such, stress is seen as an aspect of wellness that is of significant societal importance, and the significance of stress is intuitively understood by most.
In addition to momentary reports of stress, retrospective reports of the same are of interest here since retrospective self-report normally tends to deviate from momentary self-report, the latter often being more closely related to physiological measures [
Finally, we hypothesize that the effects of physiology feedback may not be the same for all individuals but may be moderated by certain personality variables. Two personality variables were selected as possible moderators. The first is neuroticism, which represents emotional instability, or the tendency to experience negative emotions [
Besides the actual content of the feedback, the interpretation of that information may also play a role in the effect of the feedback. Some terms or parameters may be easier for participants to interpret. For instance, the significance of a high stress score is probably more easily understood by most than a low heart rate variability (even though this is also considered an indicator of stress [
A 3 by 20 mixed design was used, comprising 20 different tasks as a within-subjects factor and 3 feedback types as a between-subjects factor.
Participants performed 20 brief (1 minute) tasks. For descriptions of the tasks, see Table
Brief descriptions of all 20 tasks used in the experiments. The time limit of tasks was restricted to one minute, sometimes by the length of the stimulus (e.g., sound or video clips) and sometimes by sounding a bell after 1 minute and having the software automatically continue with the next step of the experiment.
Number | Category | Task description |
---|---|---|
1 | Stressful | Mental arithmetic: calculate the result of 1149 minus 17, subtract 17 again from the result, etc. |
2 | Stressful | Read a scenario about standing in traffic, illustrated with a video. |
3 | Stressful | Play a computer game under time pressure, where falling cards need to be caught before they reach the bottom of the screen. |
4 | Stressful | Memorize a list of common English words (memory for the words is not tested afterward). |
5 | Stressful | Listen to a sound clip containing silence randomly interspersed with sharp bursts of noise. |
6 | Stressful | Count the red cars passing by in a video clip of a busy intersection. |
7 | Stressful | Relive a self-chosen memory that evokes frustration or anger. |
8 | Stressful | Make a to-do list. |
9 | Stressful | Watch a video clip of a throng of people getting pushed and pulled at a crowded subway station. |
10 | Stressful | Record a voicemail message for a job application. |
11 | Relaxing | Self-relaxation with eyes open. |
12 | Relaxing | Watch a video clip showing a quiet beach. |
13 | Relaxing | Play a simple computer game, where two cards with the same number need to be matched. |
14 | Relaxing | Watch a video of smooth, sparse traffic. |
15 | Relaxing | Read an article about “perfect summer weather.” |
16 | Relaxing | Watch a video clip showing a forest. |
17 | Relaxing | Read a scenario about taking a relaxing road trip, illustrated with a video. |
18 | Relaxing | Do a guided breathing exercise. |
19 | Relaxing | Relive a memory that evokes happiness or relaxation. |
20 | Relaxing | Listen to a sound clip containing some smooth jazz. |
To better understand what aspect of physiology feedback affects participants, we divided our participants into three groups: a “stress-feedback” group, who were told the physiology feedback reflected their stress level; a “HR-feedback” group, who were told the physiology feedback reflected their heart rate; and a “measurement-only” group, who wore ECG devices, but did not get physiology feedback.
The experiment was conducted in accordance with the Declaration of Helsinki (1964). All participants were informed in full about the experiment prior to participation and gave their informed consent. Participants were allowed to withdraw at any time during the experiment, without any adverse consequences. The experiment was approved by the local ethics committee at Eindhoven University of Technology, Human-Technology Interaction Group.
A total of 74 participants participated in the experiment (38 male, 36 female). The age of participants ranged from 18 to 67 years (average 27 years). Participants were recruited from a local participant database. People with a history of cardiac disease and/or mental illness were excluded from participation, by noting this point in both the invitation to participate and the informed consent. Participants were instructed beforehand not to smoke, engage in rigorous exercise, or drink caffeinated or alcoholic beverages in the 2 hours preceding the experiment. At the end of the experiment they were asked if they had indeed refrained from doing these things.
Descriptions of the tasks used in the experiment can be found in Table
For the physiology feedback, a custom application was used consisting of two parts (see Figure
Screenshot of the physiology feedback window.
Both physiological data and subjective data were gathered during the experiment.
For collection of ECG data, three Kendall H124SG ECG electrodes were used in the standard lead-II placement: the ground on top of the collar bone near the left shoulder, one electrode under the collar bone near the right shoulder, and one electrode underneath the ribs on the left side of the torso. A sampling frequency of 1024 Hz was used. From the raw ECG data, RR intervals were extracted and the average heart rate was subsequently calculated for each task.
After each task, subjects responded to four custom items about their experience of that task (see Table
The four statements posed after every task. Responses were given on a 7-point Likert scale ranging from “disagree completely” (1) to “agree completely” (7).
Number | Statement |
---|---|
1 | I felt stressed during this task. |
2 | I felt calm during this task. |
3 | I felt relaxed during this task. |
4 | I felt tense during this task. |
After subjects completed all tasks, they again rated all tasks on stressfulness, but this time in a retrospective and comparative way. The scale here ranged from 0 (“not at all stressful”) to 100 (“very stressful”) and participants added the tasks to the scale one by one, while the placement of earlier tasks remained visible to facilitate comparison of the tasks and consistent use of the scale. See Figure
Screenshot of the task stress rating, which was administered after all tasks were completed. Each task was presented with a brief description. The participant could then place the task on the scale by sliding the relevant marker up or down. Once the participant proceeded to placement of the next task, placement of the previous task was fixed and could no longer be altered.
After the tasks and rating task were completed, participants filled out two personality-related questionnaires: firstly, the 8 items on neuroticism from the Big Five Personality Inventory [
Overall scores for neuroticism and ASI were calculated for each participant, as the average of individual item scores of the relevant questionnaire (with reverse coding for the appropriate items in the neuroticism questionnaire). The neuroticism questionnaire showed a high reliability in our sample (Cronbach’s
To assess whether the feedback type manipulation had worked, participants who received physiology feedback during the experiment were asked at the end of the experiment how often they had looked at the feedback, on a scale from 1 (“not at all”) to 7 (“very much”).
When participants came into the lab, an informed consent was administered. After signing the informed consent, participants first performed a practice task at a computer, where they were instructed to relax as much as possible, while keeping their eyes open (the same as task 11 from the main experiment). The practice task was followed by the same four stress self-report items as the tasks in the main experiment.
Participants were then asked to apply the necessary electrodes for the ECG measurement. The ECG recording software was started, and for the HR-feedback and stress-feedback groups the feedback application was started as well. The HR-feedback group were told the feedback application would show their heart rate, while the stress-feedback group were told the application would show their stress level.
The 20 tasks were then presented to all participants via a computer program, each followed by the stress self-report items. After all 20 tasks were completed, participants filled out the postquestionnaires (task stressfulness ratings, neuroticism and anxiety sensitivity scales, and manipulation check). Finally, all participants were paid and thanked for their participation.
In our analyses, we tested the effects of feedback type on several dependent variables. Firstly, does feedback type affect the self-reported level of momentary and retrospective stress? Secondly, does feedback type affect the extent to which momentary and retrospective stress self-report are aligned? And thirdly, does feedback type affect the extent to which (momentary or retrospective) self-reported stress is in line with heart rate?
The last two dependent variables are both related to a “match” between two different measures of stress. We have devised two different measures to operationalize this concept of a match between two variables. The first measure is calculated on the individual level and consists of taking, for each participant, the correlation between the two relevant variables (i.e., momentary and retrospective stress, or heart rate and momentary stress, or heart rate and retrospective stress). An intrapersonal correlation is used here, as individual differences may exist in both baseline and variability on the different measures of stress.
The second measure is calculated on the task level. To this end we converted the raw heart rate and stress scores to a more comparable form by transforming them into
Data from a total of 8 participants had to be excluded for a number of reasons. For two participants, the ECG data could not be preprocessed, likely due to an electrode being faulty or not properly connected. One participant seemed to have misunderstood the intended use of the retrospective stressfulness scale, simply leaving the markers for all tasks at the place they were initially presented. One participant showed an exceptionally low (>4 standard deviations below the mean) correlation between momentary and retrospective stress (a parameter that is to be used in one of our analyses). Finally, 4 additional participants reported having exercised or consumed caffeine before the experiment. All data from these 8 participants was excluded from further analysis. This brought the total number of participants in the data set used for analysis to 66.
Results from the manipulation check show that the manipulation was successful: on average, participants in the feedback groups reported that they had looked at the physiology feedback quite often (an average of 5.27 on a scale from 1, not at all, to 7, very often). No one claimed never to have looked at the feedback.
To analyze the effect of feedback type on the levels of momentary and retrospective self-reported stress, a series of multilevel models was used. The data we have is hierarchical in nature: there are 3 feedback type groups, each containing several participants, each of whom performed 20 tasks. Multilevel models are aimed at modeling these different levels of the hierarchy. Separate models were estimated for momentary stress and retrospective stress. The initial model included “feedback type” as a fixed factor and “task” as a repeated measure. This model showed no significant main effect of feedback type on momentary stress for either momentary (
In a second iteration, two interaction terms (“neuroticism
Parameter estimates, 95% confidence intervals and significance levels for the different levels of the interactions of feedback type and personality factors on momentary self-reported stress.
Parameter | Estimate | 95% CI | Sig. |
---|---|---|---|
Measurement-only * ASI | 0.05 | −0.12–0.21 | 0.598 |
HR-feedback * ASI | 0.09 | −0.12–0.29 | 0.406 |
Stress-feedback * ASI | 0.25 | 0.08–0.42 | 0.004* |
Measurement-only * neuroticism | 0.15 | 0.01–0.28 | 0.030* |
HR-feedback * neuroticism | 0.11 | −0.04–0.25 | 0.143 |
Stress-feedback * neuroticism | −0.05 | −0.25–0.16 | 0.649 |
Dependent variable: momentary stress.
*Significant at
Parameter estimates, 95% confidence intervals and significance levels for the different levels of the interactions of feedback type and personality factors on retrospective self-reported stress.
Parameter | Estimate | 95% CI | Sig. |
---|---|---|---|
Measurement-only * ASI | −1.57 | −4.99–1.85 | 0.368 |
HR-feedback * ASI | 2.79 | −1.35–6.92 | 0.186 |
Stress-feedback * ASI | 3.58 | 0.15–7.01 | 0.041* |
Measurement-only * neuroticism | 3.07 | 0.36–5.79 | 0.027* |
HR-feedback * neuroticism | 2.11 | −0.78–5.00 | 0.151 |
Stress-feedback * neuroticism | −1.70 | −5.84–2.45 | 0.422 |
Dependent variable: retrospective stress.
*Significant at
To test how feedback type affects the extent to which participants’ subjective stress levels are in line with their heart rate and how well participants remember their self-reported stress levels, a MANOVA was used. In this analysis, feedback type was the independent variable and the correlation coefficients between each combination of two stress measures were dependent variables (see the beginning of Section
Average correlations (left) and difference scores (right) between different variables for the different feedback types. A higher correlation means a stronger match between two variables, while the reverse is true for the difference scores. For the sake of readability, feedback types are coded as 1 = measurement-only, 2 = HR-feedback, and 3 = stress-feedback.
Correlation between heart rate and momentary stress
Difference score for heart rate and momentary stress
Correlation between heart rate and retrospective stress
Difference score for heart rate and retrospective stress
Correlation between momentary and retrospective stress
Difference score for momentary and retrospective stress
The analysis showed that the average intrapersonal correlation between heart rate and both momentary and retrospective stress was significantly different for different feedback types (
The downside of the analysis described above is that, by collapsing the data into correlation coefficients per person, an aspect of the data is lost: the variability between tasks. As mentioned before, multilevel models can be used to model the different levels in our hierarchical data. For these multilevel models, a measure similar to the correlations used above is needed that can be calculated at the level of individual tasks for each person. The difference scores described in the beginning of Section
To reestablish the significant results obtained in the MANOVA for the correlations between both momentary and retrospective stress and heart rate, a simple model ignoring the hierarchical nature of the data was first tested. This model included only “feedback type” as a fixed factor. Separate analyses were performed for the HR versus momentary stress difference score and the HR versus retrospective stress difference score. As expected, the “feedback type” factor had a highly significant effect on both the HR versus momentary stress difference score (
In a second iteration, “task” was added to the model as a repeated measure. This addition significantly improved the fit of the overall model, as indicated by the change in −2 Log Likelihood (
In a third iteration, the personality factors were included in the model by adding two interaction terms (“neuroticism
The goal of this study was to assess some of the acute effects of physiology feedback, to better understand the effects self-tracking of physiology might have. Specifically, we investigated to what extent physiology feedback would affect the match between participants’ physiological stress and their self-reported stress. In addition, the effect of physiology feedback on participants’ memory for self-reported stress (i.e., the match between momentary and retrospective stress) was investigated. Finally, we examined whether physiology feedback might affect the self-reported stress level itself and explored the role of two personality variables (neuroticism and anxiety sensitivity) in this respect.
Our results show that when participants are given feedback about their heart rate, their estimates of their stress level become more in tune with their heart rate: when their heart rate is high, they report a high stress level, and when their heart rate is low, they report a low stress level. The effect seems to be stronger in the stress-feedback group compared to the HR-feedback group (although the effect was only marginally significant), suggesting that the instructions given about how to interpret the feedback might be important.
There are at least two explanations for the fact that physiology feedback resulted in a better match between stress self-report and heart rate. The first is that the physiology feedback helps people to become more aware of their body and that this heightened awareness then informs their subjective stress reports. Alternatively, people may see the feedback as a more objective and more accurate source of information about their stress level than their own experience. This might mean that when their subjective experience does not match the feedback, they use the feedback rather than their own experience to inform their reports about stress. The current study cannot provide conclusive evidence either way, but a follow-up study using false heart rate feedback might: if the second explanation is true, false heart rate feedback should cause self-report to become more in tune with the false feedback; if the first explanation is true, false heart rate feedback either might have no effect (if false feedback is not effective at triggering body awareness) or might cause stress self-report to become more in tune with one’s own heart rate.
Physiology feedback was found not to affect the extent to which retrospective self-reported stress matches momentary self-reported stress. This implies that although physiology feedback made subjective reports of stress more in tune with heart rate, it did not help participants to better remember their stress levels. Although this finding may well represent a true effect, it may also have been caused by a ceiling effect: the correlation between momentary and retrospective stress self-report was already quite high (
Our results did not show an effect of physiology feedback on self-reported stress, indicating that, on average, physiology feedback did not cause participants to become more or less stressed. The interaction between neuroticism and feedback on self-reported stress levels, however, was significant. Specifically, it was found that, in the measurement-only condition, a higher score on neuroticism predicted higher stress levels, while this effect was not present in the feedback conditions. Most items in the neuroticism questionnaire are related to whether participants see themselves as tense, nervous, or easily upset. Those who score high on this scale presumably believe they experience relatively high levels of stress. This might explain why those who score high on neuroticism report higher stress levels than low-neuroticism individuals in the measurement-only condition. For individuals with a high score on neuroticism, the physiology feedback may provide good news, in the sense that their objective, physiological stress response may be less strong than they expected. This might explain why the difference in self-reported stress between higher- and lower-neuroticism individuals disappears in the HR-feedback and stress-feedback conditions.
The interaction between anxiety sensitivity and feedback on self-reported stress was also found to be significant. In the stress-feedback group, individuals who scored higher on anxiety sensitivity were shown to report higher levels of stress. Individuals with a high level of anxiety sensitivity tend to experience anxiety when they detect anxiety-related body sensations [
On a general note, there are several differences between our lab setting and self-tracking in the field that limit the generalizability of our results: firstly, the pervasive feedback used in this study is different from the physiology feedback obtained in self-tracking, which is generally available on demand, rather than being presented constantly. Secondly, self-tracking of physiology involves other interactions with one’s data besides the real-time physiology feedback used in this study (e.g., feedback after the fact, viewing data aggregated over longer periods of time). Finally, this study only assessed acute effects of physiology feedback, precluding any conclusions about longer-term effects. Still, even though this study does not yet paint a complete picture of the effects of self-tracking of physiology, it does provide insight into how self-tracking of physiology may lead to better body awareness and how individual differences in personality characteristics may moderate the effects of self-tracking on stress.
A study was conducted to test whether physiology feedback has acute effects on self-reported stress and the extent to which it is in sync with physiological stress. In this study, participants executed several short tasks, while they were either shown visual feedback about their current and past heart rate or not. The group who received feedback was further subdivided into a group who were told the feedback represented their heart rate and a group who were told the feedback represented their stress level.
Results show that self-reported stress is more in sync with heart rate for participants who received physiology feedback. This implies that either the feedback helps these participants to better detect their own physiological stress or they use the external feedback to inform their reports of experienced stress. Either way, these results suggest that physiology feedback increases body awareness on a subjective—if short-term—level.
Physiology feedback was found not to affect participants’ stress levels. However, interactions between two personality factors and feedback on stress levels were found. Firstly, participants with a high score on neuroticism were found to report more stress than those with a low score on neuroticism when no physiology feedback was given, but this difference disappeared when physiology feedback was provided. This may reflect a belief-based bias, as neuroticism reflects the degree to which people believe they are prone to episodes of stress, tension, and upset. This in turn suggests that physiology feedback may be effective at reducing self-reported stress when it gives “good news.” Secondly, individuals high in anxiety sensitivity were found to report higher levels of stress in the condition where physiology feedback about stress was given, suggesting that self-tracking of physiology may be less suitable for these individuals.
The results found in this study are based on experiences in a lab setting which, although well-controlled, lacks the longitudinal nature and richness of interaction of real-world self-tracking. How the results of this study translate to long-term effects of self-tracking on general health and well-being is therefore a matter that will require additional work. Nevertheless, our findings give a first indication of how self-tracking of physiology may lead to better body awareness and how personality characteristics can help us predict which individuals are most likely to benefit from self-tracking of physiology.
The authors declare that there is no conflict of interests regarding the publication of this paper.