The calming effect of a new wearable device during the anticipation of public speech

Abstract

We assessed the calming effect of doppel, a wearable device that delivers heartbeat-like tactile stimulation on the wrist. We tested whether the use of doppel would have a calming effect on physiological arousal and subjective reports of state anxiety during the anticipation of public speech, a validated experimental task that is known to induce anxiety. Two groups of participants were tested in a single-blind design. Both groups wore the device on their wrist during the anticipation of public speech, and were given the cover story that the device was measuring blood pressure. For only one group, the device was turned on and delivered a slow heartbeat-like vibration. Participants in the doppel active condition displayed lower increases in skin conductance responses relative to baseline and reported lower anxiety levels compared to the control group. Therefore, the presence, as opposed to its absence, of a slow rhythm, which in the present study was instantiated as an auxiliary slow heartbeat delivered through doppel, had a significant calming effect on physiological arousal and subjective experience during a socially stressful situation. This finding is discussed in relation to past research on responses and entrainment to rhythms, and their effects on arousal and mood.

Full text

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Scientific RepoRts | 7: 2285 | DOI:10.1038/s41598-017-02274-2
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The calming eect of a new
wearable device during the
anticipation of public speech
Ruben T. Azevedo1, Nell Bennett2, Andreas Bilicki2, Jack Hooper2, Fotini Markopoulou2 &
Manos Tsakiris1
We assessed the calming eect of doppel, a wearable device that delivers heartbeat-like tactile
stimulation on the wrist. We tested whether the use of doppel would have a calming eect on
physiological arousal and subjective reports of state anxiety during the anticipation of public speech, a
validated experimental task that is known to induce anxiety. Two groups of participants were tested in a
single-blind design. Both groups wore the device on their wrist during the anticipation of public speech,
and were given the cover story that the device was measuring blood pressure. For only one group, the
device was turned on and delivered a slow heartbeat-like vibration. Participants in the doppel active
condition displayed lower increases in skin conductance responses relative to baseline and reported
lower anxiety levels compared to the control group. Therefore, the presence, as opposed to its absence,
of a slow rhythm, which in the present study was instantiated as an auxiliary slow heartbeat delivered
through doppel, had a signicant calming eect on physiological arousal and subjective experience
during a socially stressful situation. This nding is discussed in relation to past research on responses
and entrainment to rhythms, and their eects on arousal and mood.
Wearable devices are becoming ubiquitous in everyday life, serving a range of functions, from measuring phys-
ical activity and a range of physiological variables to providing feedback on emotional states. Across most such
instantiations of wearable technologies, the overarching aim seems to be the quantication of the self1. However,
as recent studies suggest, the eects of such tracking devices are debatable2, seem to be short-lived, and con-
sumers oen stop using them aer a short period of time3. As a result, questions about what would be a more
intuitive wearable device that can assist people in their everyday life have motivated the development and design
of a new wearable device by Team Turquoise Ltd (http://www.doppel.london/). e doppel device, rather than
measuring physiological variables, aims at providing a sensory experience to help people manage the pressures of
time and stress in their daily lives by modulating the users’ physiological and potentially emotional and cognitive
states during a wide range of everyday life tasks. e doppel delivers an on-demand, discrete, user-controlled,
heartbeat-like vibration applied through a wristband. In the final product, the wristband is connected via
Bluetooth to a smart phone app where the user measures their resting heart rate and chooses their preferred
speed and intensity of tactile stimulation in relation to their own heartrate.
e design of doppel was inspired by several research strands that show how humans respond to and possibly
entrain to dierent rhythms. Entrainment is a broadly used term that, in the context of human behavior and phys-
iology, reects the voluntary or involuntary synchronization of our brains and bodies to the environment4. For
example, the tempo of a song can naturally alter our breathing rate and heart rate5. As a real-life example, choir
singers not only harmonise their voices, they can also synchronise their heartbeats6. Vickho and colleagues6
monitored the heart rates of singers and found that as the members sang in unison, their pulses began to speed
up and slow down at the same rate. Beyond music, several studies highlight entrainment eects in responses to
biological rhythms, and the heartbeat is perhaps the most ubiquitous biological rhythm in nature. e mother’s
own heartbeat is a particular salient multisensory signal that accompanies the development of the foetus and, not
surprisingly, has been shown to have benecial eects for the infant’s development. For example, the perception
of the maternal heartbeat in the womb provides the foetus with an important rhythmic experience7 that is thought
to facilitate the formation of the neural basis for entrainment and synchrony skills necessary for a wide range of
1Lab of Action & Body, Department of Psychology, Royal Holloway, University of London, Egham, TW20 0EX, UK.
2Team Turquoise Ltd, 1 Bermondsey Square, London, SE1 3UN, UK. Correspondence and requests for materials
should be addressed to M.T. (email: manos.tsakiris@rhul.ac.uk)
Received: 15 December 2016
Accepted: 18 April 2017
Published: xx xx xxxx
OPEN

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cognitive processes that underpin vocal, gestural, and gaze communication during mother–infant interactions8.
Such entrainment eects to physiological rhythms are evidenced in a wide range of contexts in later life. For
example, the heartbeats of a mother and baby will synchronise with one another when they interact closely9, and
similar eects have been observed in couples10.
Beyond specic entrainment eects, more general, our brains and bodies also respond naturally to rhythm.
In music, tempo has been consistently shown to play an important role in mood induction and physiological
changes11–14. For example, listening to slower tempo results in lower arousal and subjective states of positive or
calm emotional states12, 15–17, see ref. 18 for review. Conversely, fast rhythms are associated with high arousal
and positive and/or arousing emotional states such as joy, excitement, surprise, fear or anger12, 18. Beyond the
perception of tempo in music, the physiological importance of faster and slower heart rate as well as of high and
low heart rate variability for physical and mental health is well-documented, as well as their role for experienced
arousal and cognitive processing in general19. Not only high arousal is physiologically correlated with increased
heart rate, and calmness with lower heart rate, as we also intuitively associate higher and lower heart rate with
anxiety or high arousal and calmness, respectively. Based on the aforementioned lines of research about the
importance of heartbeats as pervasive physiological signals involved in emotional regulation and social interac-
tions, and the eects of slow rhythms on mood, doppel was designed to embed on the users’ body, the ubiquitous
biological rhythm of a beating heart as a means of using the felt faster or slower rhythm to modulate levels of
arousal and calmness. To that end, the present study was designed to test whether the use of doppel, as opposed
to its absence, could have a calming eect on physiological arousal and subjective reports of experienced anxiety
during a stressful situation.
Stressful situations are typically associated with increases in physiological arousal and negative affect.
However, stressful contexts dier from one another in character. For example, a mental arithmetic challenge dif-
fers from a respiratory challenge, which both dier from a social stress challenge. Socially stressful situations may
involve the threat of negative social evaluation (e.g., public speaking challenge) or may be accompanied by nega-
tive social evaluation resulting in social rejection (e.g., social exclusion manipulation). Given the signicance of
interoception in cognitive-aective processing20–22, potential changes in interoceptive signals (i.e. signals originat-
ing from visceral organs such as the heart) in stressful, negative and aective situations may inuence emotional
experience, emotion regulation and decision making in these contexts. In such situations, the ability to regulate
one’s physiological arousal and emotions may be important for lowering anxiety and for successful performance.
A classic task that has been used in controlled psychological experiments to elicit an ecologically valid and
socially stressful situation, is the anticipation of public speech task. Across a large number of studies, it has been
shown that anticipation of public speaking is particularly eective at inducing social anxiety with concomitant
increases in physiological arousal23–26. erefore, the current study utilized the speech anticipation manipulation
to examine how the use of doppel could enable participants to cope better with their anxiety while they were
preparing to deliver a speech to a group of people. Moreover, given the intended use of the product, we were
particularly interested in testing the ecacy of its use against a condition where participants were not using it.
Importantly, for the purposes of this study, participants were unaware of the true function of doppel as we wanted
to minimize expectations and potential confounds. To that end, participants were told that doppel was a device
designed to measure their blood pressure. Two groups of participants were tested. Both groups wore the device
on their wrist, but only for one group doppel was turned on and vibrated during the anticipation period. Doppel
was set to vibrate with a frequency ~20% slower than the participant’s heartbeats, as measured at rest, because
previous research has shown that slower rhythms tend to be associated with low arousal and subjective states of
calmness/serenity, sadness or boredom18. Before instructions were given and throughout the anticipatory period,
levels of physiological arousal were measured through continuous recordings of skin conductance and heart
rate. In addition, we collected psychometric data to quantify state anxiety levels before and aer the anticipation
of public speech task. It was hypothesized, that the doppel device active group would display lower increases in
physiological arousal and report lower levels of state anxiety. It should be noted that the method adopted here
with doppel diers from biofeedback or false feedback techniques27–29 in which exteroceptive stimulation reects
ongoing cardiac activity and participants are encouraged to pay attention and/or regulate it. Instead, we tested
whether periodic vibrotactile stimulation unrelated to participant’s ongoing heartbeats, as opposed to the absence
of such stimulation, could have a positive calming eect.
Methods
Participants. A total of 52 (20 Male; mean age = 26.4, s.d. = 5.7) volunteers took part in the study. Twenty
five participants (9 Male; mean age = 25.9, s.d. = 5.2) were assigned to the experimental group (i.e. doppel
active condition) and 27 (11 Male; mean age = 26.8, s.d. = 6.1) to the control group (i.e. doppel turned o con-
dition). Participants were randomly assigned to each group prior to study start. All participants provided writ-
ten informed consent to take part in this study, which was approved by the College Ethics Committee of Royal
Holloway University of London research ethics committee, and all methods were performed in accordance with
the relevant guidelines and regulations of the College Ethics Committee.
Procedure. A graphical illustration of the study’s procedure and timeline can be seen in Fig.1. Participants
were comfortably sat in an armchair, given written information about the study and asked to sign a consent form.
Skin conductance Ag/AgCl electrodes (MLT117F) with 0.5%-NaCl electrode gel were attached to the phalanges
of the middle and ring ngers of the participant’s non-dominant hand. e signal was recorded using a Powerlab
8/35 (https://www.adinstruments.com/), a GSR Amp unit (22 mV constant voltage at 75HZ) and LabChart (v 8.1)
soware with a recording range of 40 µS and a sampling rate of 1 kHz. A pulse transducer (TN1012/ST; https://
www.adinstruments.com/) was also attached to the thumb of non-dominant hand to monitor cardiac activity.

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e doppel device (see Fig.1A) was tted to the participant’s non-dominant wrist, in a rm but not tight posi-
tion, and remained o until the period preceding task instructions. e device sits on the inside of the wrist where
users expect to feel their pulse. e unit is 38 mm in diameter & 9 mm thick, held in place with a silicon strap.
e device provides a double heartbeat-like rhythm tactile sensation. e main casing has a steep metal base and
a plastic cover. e casing houses the electronic components: a coin vibration motor that delivers the stimulus, a
low energy Bluetooth chip that communicates with an app or computer to upload new rhythms to the device, and
a lithium ion battery that powers the device.
For the purposes of this study, participants were told that it was a new generation device to monitor blood
pressure, and none of the participants expressed any suspicion about the purpose of the device at any point
throughout the entire duration of the study. A single-blind protocol was adopted as necessary to provide the
experimenter with appropriate control over doppel (i.e. switch o to those assigned to the control group) and to
prevent participants from using cognitive strategies during the task related to the study’s goals.
At the beginning of the experiment, participants were instructed to rest for 5 minutes while sitting still, with
the purpose of measuring baseline levels of physiological activity. Average heart rate and skin conductance levels
during this period were taken as indices of pre-task physiological activity. Aer this rest period, the experimenter
told participants “I am going to change the settings of the device you have on the wrist to start measuring blood
pressure. You might feel some vibration. If you do, don’t worry it’s normal”. e device was then turned on in
all cases but switched o aer 10 seconds if the participant had been assigned to the control group. e device’s
vibration frequency was individually tailored to a frequency ~20% slower (mean = 58.2, s.d. = 6.3) than the par-
ticipant’s baseline HR (mean = 75.8, s.d. = 12.3), as measured during the rest period. However, upper (65 bpm)
and lower (40 bpm) frequency limits were imposed to prevent vibrations to be perceived as fast or unnaturally
slow, respectively. In the experimental group, the lower limit was applied to one participant (rest HR = 44.7) and
the upper limit to 9 participants (mean rest HR = 88.1, s.d. = 5.5). e average absolute adjustment to lower and
upper limits was of 4.4 bpm (s.d. = 3.9). Next, task instructions were provided verbally by the experimenter: “You
should now prepare a speech about the use of animals for research. You may present both the pros and cons of
using animals in research or give your personal point of view on this issue. You can use this pen and paper to take
notes if you wish to. You have 5 minutes to prepare it. Aer that we will move to the room next door where you
should give the speech to 3 or 4 colleagues of mine. e speech should last for 5 minutes”.
At the end of the study, to assess the success of our manipulation, participants were invited, in a
semi-structured way, to share their subjective experiences during task. First they were asked “how were you feel-
ing about giving a speech to unfamiliar people”? en the experimenter directly enquired if participants believed
they would actually give the speech. All participants, but one, were convinced they would give the speech.
Subjective Measures. Participants were asked to complete the STAI-Y-130 twice to measure self-reported
anxiety levels before the delivery of task instructions and aer the task completion. e STAI-Y-1 questionnaire
is composed of 20 items (e.g. “I am tense”; “I feel secure”) assessing state anxiety. Each item is rated on a 4-point
scale ranging from “not at all” to “very much so”. High scores reect high anxiety levels. To control for possible
dierences between groups in trait apprehension about other’s evaluations, participants were asked to complete
the Brief Fear of Negative Evaluation questionnaire (bFNE)31. e bFNE is composed of 12 items (e.g. “I am
afraid others will not approve of me”) scored on a 5-point scale ranging from “not at all characteristic of me” to
“extremely characteristic of me”. High scores reect high concern about others’ evaluation. To control for pos-
sible between-group dierences in participants’ general disposition towards public speaking and self-reported
trait social anxiety, participants were asked to state their agreement, on 8-point likert scales, on the following
sentences: “I like to speak in public” and “I can easily become anxious in social situations” (1- strongly disa-
gree; 8 – strongly agree). ese questions and the bFNE were only asked aer task completion to avoid inducing
task anticipation anxiety or evaluation concerns during baseline physiological recordings. Finally, they rated on
7-point likert scales, their experience during the task according to the dimensions: from relaxing (1) to stressful
(7); and from unpleasant (1) to pleasant (7). e questionnaire assessing self-reported social anxiety, attitudes
towards public speaking and subjective ratings of participants’ experience during the task was not administered
to the rst 6 participants (Experimental group: n = 2; Control group: n = 4) due to an experimental error.
Figure 1. e doppel device (A) and the timeline of the experimental procedure (B).

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Analyses of psychophysiological data. Non-specic-SCR or spontaneous uctuations in skin conduct-
ance (NS-SCRs) analyses were carried out using the SCRalyze b2.18 soware (http://pspm.sourceforge.net/ 32)
according to a convolution model to estimate the area and the curve (AUC), or skin-conductance level-corrected
time integral. e AUC is closely related to the conventional methods of estimation of the number and amplitude
of NS-SCRs (for further details see ref. 32). is method has been shown to be a better predictor of autonomic
arousal than conventional analysis, and has the advantages of not requiring subjective evaluations as well as being
computationally inexpensive32. HR was estimated with the HRV function implemented in Labchart (v 8.1). Visual
inspection and manual correction was carried out to correct unidentied or misidentied peaks. Data from three
participants (control group) were discarded from HR analyses due to technical failure during pulse recording.
e entire ve-minute periods during rest and speech preparation were analysed to estimate baseline and task
NS-SCRs and HR levels, respectively. Skin conductance levels and HR were entered into separate repeated meas-
ures ANOVAs with Time (Baseline; Task) and Group (Experimental; Control) as within- and between-subjects
factors, respectively.
Results
Psychophysiological Data. e analysis of NS-SCRs levels revealed a signicant main eect of Time (F(1,
50) = 36.69, p < 0.001, ƞ2 = 0.42) conrming, as expected, that speech anticipation resulted in an overall increase
in physiological arousal (see Fig.2A), providing a proof that the task was successful in eliciting arousal. e
main eect of Group was not signicant (F(1, 50) = 3.21, p = 0.079, ƞ2 = 0.060). Crucially, the critical Time x
Group device (F(1, 50) = 5.23, p = 0.027, ƞ2 = 0.095) interaction was signicant. Follow-up independent t-tests
conrmed lower skin conductance levels in the Experimental group than in Control group during the task (t(1,
50) = 2.24, p = 0.029, Hedges’ g = 0.54) but no dierence at baseline (t(1, 50) = 0.271, p = 0.79, Hedges’ g = 0.074).
We then investigated changes in average Heart Rate. While the main eect of Time (F(1, 47) = 30.02, p < 0.001,
ƞ2 = 0.39) on HR was signicant because HR increased during anticipation relative to baseline, the Time x Group
interaction (F(1, 47) = 0.47, p = 0.50, ƞ2 = 0.010) was not signicantly dierent. Furthermore, the main eect of
Group was not signicant (F(1, 47) = 0.67, p = 0.42, ƞ2 = 0.014).
Subjective measures. To assess dierences in self-reported anxiety at baseline and aer speech preparation,
pre and post STAI scores (see Table1) were entered into a repeated measures ANOVA with Time (baseline and
post-task) and Group (Experimental; Control) as within- and between-subjects factors, respectively. Results con-
rmed that speech preparation successfully induced anxiety in the participants, as revealed by the main eect of
Time (F(1, 50) = 53.91, p < 0.001, ƞ2 = 0.52). e interaction Time x Group (F(1, 50) = 4.14, p = 0.047, ƞ2 = 0.077,
see Fig.2B) and the main eect of Group (F(1, 50) = 6.75, p = 0.012, ƞ2 = 0.12) were also signicant. Independent
t-tests revealed no group dierences in anxiety at baseline (t(1, 50) = 1.34, p = 0.19, Hedges’ g = 0.36) but lower
levels of anxiety in the Experimental group aer speech preparation (t(1, 50) = 2.79, p = 0.007, Hedges’ g = 0.77).
We also carried out independent t-tests on the participants’ ratings on the task experience as relaxing/stressful
and unpleasant/pleasant. Results showed that participants in the Experimental group rated the experience as less
stressful than those in the control group (t(1, 44) = 2.35, p = 0.023, Hedges’ g = 0.68). Ratings on the pleasant-
ness question did not reach statistical signicance (t(1, 44) = 1.94, p = 0.059, Hedges’ g = 0.56). Control analy-
ses revealed no dierences between groups on the obtained trait measures: (i) fear of negative evaluation (t(1,
Figure 2. Average Skin Conductance levels across conditions and groups (A), and average state anxiety scores
(B). Error bars indicate S.E.M.
STAI pre STAI Post *bFNE Social
anxiety Public
speaking Pleasantness Stressfulness*
Experimental Group 30.2 (8.0) 38.1 (12.6) 36.1 (9.8) 5.00 (2.2) 3.90 (2.2) 5.36 (1.2) 2.96 (1.5)
Control Group 33.1 (7.5) 47.0 (10.3) 37.0 (10.2) 5.09 (1.8) 3.65 (1.9) 4.39 (1.8) 4.09 (1.7)
Table 1. Average (s.d.) scores on each questionnaire in the Experimental and Control groups. *p < 0.05.

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50) = 0.30, p = 0.76, Hedges’ g = 0.082); (ii) social anxiety (t(1, 44) = 0.15, p = 0.88, Hedges’ g = 0.044); (iii) and
attitude towards public speaking (t(1, 44) = 0.43, p = 0.67, Hedges’ g = 0.12).
Discussion
We tested the ecacy of a new wearable device on calmness using a task that typically induces high anxiety,
namely, the preparation and anticipation of giving a short public speech to an unfamiliar audience. doppel gives an
on-demand, discrete, user-controlled, heartbeat-like vibration applied through a wristband and it aims at mod-
ulating the alertness or calmness of the user by adjusting the frequency of the “tactile heartbeat”. In the present
experiment, we hypothesized that a slow heart-rate, as opposed to the absence of any vibro-tactile stimulation,
would enable participants to remain calmer during the anticipation of public speech. To that end, we told partici-
pants that doppel was a blood pressure monitoring device, and only for one of the two groups we turned on doppel
to deliver its tactile vibrations during the anticipation of public speech. Additionally, subsequent oral debrieng
conrmed that participants believed that they would actually give the speech and thought that, indeed, doppel
monitored blood pressure.
Even though, at the beginning of the experiment, the two groups displayed comparable levels of arousal (as
measured by Skin Conductance) and of state anxiety, participants in the doppel active condition showed a signif-
icantly smaller increase in arousal compared to the control group. Similarly, at the end of their speech prepara-
tion, and before they were debriefed, participants in the doppel active condition reported a signicantly smaller
increase in their state anxiety compared to the control group. No signicant dierences in average heart rate were
found as a result of doppel use. Finally, participants in the doppel active condition found the task signicantly less
stressful than participants in the control condition. Taken together, the results highlight that the use of doppel had
a clear and signicant calming eect in both physiological measures of arousal and subjective reports of anxiety
during a task that is eective in inducing social stress, suggesting that doppel enabled participants to stay calmer
and less anxious, as compared with the condition where the device was worn but was not performing its intended
function.
Previous studies have used pharmacological means to study anxiolytic-like eects during anticipation of
public speech or during simulated public speaking33. For example, de Oliveira and colleagues33 used intranasal
administration of oxytocin, a neuropeptide that is known to be involved in anxiety, as well as cardiovascular and
hormonal regulation, and showed that the oxytocin, but not the placebo, group had lower skin-conductance levels
during anticipation and actual speech. Biofeedback techniques have also been used to down-regulate anxiety and
physiological reactions during emotional situations27, 28. In particular, autonomic regulation training through bio-
feedback has been shown to reduce subjective and physiological arousal during public speaking27. Here, we add
to this literature by showing that the use of heartbeat-like vibrotactile stimulation, as opposed to its absence, can
also have an anxiolytic eect. ese two techniques (i.e. biofeedback and doppel use), however, dier considerably
in terms of the expectations and attention given to the exteroceptive stimuli. Unlike in biofeedback or false feed-
back approaches, in our active doppel condition, participants were not instructed to regulate their heart rate as a
function of these vibrations. Rather than feedback, doppel stimulation is thought to be related to physiological
entrainment mechanisms that are not dependent on direct attention or appraisals of interoceptive-exteroceptive
matching.
Numerous past studies have also shown how our bodies, including physiological cycles such as the respiratory
and cardiac cycles, entrain to dierent rhythms and how such responses may inuence mood11–14, 34. Reviewing a
large body of relevant research, Phillips-Silver and colleagues35 show that the ability to perceive and synchronize
to a beat is possible across dierent sensory modalities. e authors suggest a general model of entrainment that
builds upon pre-existing adaptations that allow us to perceive and produce rhythmic stimuli, as well as inte-
grate their production and perception with sensory feedback. Extending the eects of rhythms on mood, beyond
entrainment per se, Tajadura-Jiménez, Väljamäe and Väställ36 reported that heartbeat sounds and their rhythm
signicantly aected participants’ physiological reactions as well as the emotional judgments of pictures, and
their recall. In that study, listening to heartbeat sounds resulted in a small but signicant increase in participants’
heart rate with respect to the silence condition, and the sounds signicantly inuenced emotional responses to
aective visual stimuli. In particular, a fast-rate heartbeat (e.g. 110 bpm) sound resulted in higher arousal ratings
and enhanced pictures’ memorability during a free-recall task. It is noteworthy that in the present study we did
not nd any evidence of signicant modulations of heart rate, other than the overall increase of heart rate during
the anticipation period. is is not surprising given that typically entrainment eects on heart rate are relatively
small11, 12, 36, and in the present study we employed a task (i.e., anticipation of public speaking) that is meant to
increase heart rate. Entrainment eects on physiological activity have been mostly studied in response to musical
stimuli11–14. However, tempo-related entrainment eects on heart rate are less consistent than in other physiolog-
ical indices, such as skin conductance and respiration frequency, especially when entraining to slow tempo stim-
uli11, 12, 37, 38. It is possible that this might be related to the non-linear dynamics of cardiac responses to stressors or
emotional stimuli. e continuous uctuations of heart rate due to excitatory and inhibitory regulation processes
may explain why average heart rate, like the one reported here, is a less sensitive index to entrainment eects.
Unlike past studies that often use auditory feedback of heartbeats29, 36, 39, 40, instead of sounds, we used
heartbeat-like tactile stimulation to examine the eects of a calming “heartbeat” rate on anxiety. While no signif-
icant dierences were observed in participants’ heartrate, the consistent patterns of changes in skin conductance
levels and subjective anxiety reports support the hypothesis that the presence of a slow rhythm, which in the
present study was instantiated as an auxiliary slow heartbeat delivered through doppel, can inuence physiolog-
ical arousal and mood. We used slower frequencies from the participants’ own heart rate because, as previous
research has suggested, slower rhythms tend to be associated with low arousal and subjective states of positive
or calm emotional states12, 18. However, it remains to be tested whether faster or equivalent frequencies to the
participant’s heart rate can have similar eects. It is possible that anxiolytic eects can be observed to a range of

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heart-like vibrotactile stimulation frequencies and even that the “ideal” frequency varies from person to person.
Importantly, while we here show the calming eects for slower frequencies, doppel users can select the vibrating
frequency that corresponds better with their state and possible the one that seems to be more ecient for their
own needs and lifestyles.
While the precise underlying neurophysiological mechanism by which doppel elicits such eects was not
directly investigated in the present study, we suggest that the calming eect may be mediated by neural responses
to the rhythmic tactile input that the device delivers, especially neural responses in areas that are involved in
somatosensation and interoception such as the somatosensory cortex and the insula41,42 and in emotion and
rhythm processing such as the basal ganglia43. Future studies must specically investigate such neural responses
in parallel with the attenuated changes in skin conductance to complement the signicant and converging phys-
iological and subjective measures of reduced arousal and anxiety obtained through the use of doppel, as reported
here.
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Acknowledgements
The study was commissioned and funded by Team Turquoise Ltd. Team Turquoise Ltd provided the direct
research expenses related to the reimbursement of the participating volunteers and the salary costs for RA.
Author Contributions
M.T. and R.A. designed the study. R.A. collected the data, M.T. and R.A. analyzed the data and co-authored the
manuscript. F.T., A.B., N.B. & J.H. contributed to the authorship of the manuscript.
Additional Information
Competing Interests: N.B., A.B., J.H. and F.T. co-own Team Turquoise Ltd. M.T. is an independent consultant
for Team Turquoise Ltd.
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