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ElectroCalm: Investigating User Experience and Physiological Responses to Multi-Node Transcutaneous Electrical Stimulation for Stress Modulation
Yoon Kyung Shon, Pablo E. Paredes
TL;DR
TES stress research has focused on vagal stimulation, leaving user experience at the sensitive neck and the stress effects of electrotactile feedback underexplored. The paper studies an 8-node array at the neck and arm during a 2-back task, finding comparable comfort but placement-specific physiological responses. Only neck TES produced cortical and autonomic changes consistent with stress modulation; arm TES did not differ from inactive stimulation.
Problem
TES research has focused on clinical efficacy and vagal mechanisms, leaving the user experience of electrotactile sensation and its potential role in stress modulation less studied.
Source: §1 · p. 2, §2.1 · p. 3Method
The authors applied an 8-node TES array to the neck and arm during a 2-back task, assessing user experience and physiological responses in usability and controlled active-versus-inactive studies.
Source: §1 · p. 2, §5 · p. 13Results
Neck TES produced cortical and autonomic changes consistent with stress modulation, whereas arm TES did not differ from inactive conditions.
Source: §1 · p. 2, §9 · p. 20Takeaways & Limitations
Neck TES was comparably comfortable and acceptable to arm TES, while physiological changes differed by placement under the tested configuration.
Source: §1 · p. 2, §9 · p. 20Stimulation blocks lasted 2 minutes, and larger samples could provide more precise estimates of the smaller autonomic effects.
Source: §8 · p. 19
Abstract
from arXiv · showhide
Transcutaneous Electrical Stimulation (TES) for stress modulation has largely focused on vagus nerve stimulation at the neck, yet two questions remain underexplored: how users experience electrotactile sensations at this sensitive site, and whether electrotactile feedback itself can function as a haptic stress intervention. To investigate this gap, we applied an 8-node TES array to two body sites during a cognitively demanding 2-back task: the neck, a site used in prior vagal TES research for its anatomical proximity to the cervical vagus nerve, and the arm, the most common haptic wearable site, which primarily provides cutaneous electrotactile sensation without vagal access. In a usability study, both sites were rated as comparably comfortable without disrupting task performance, though the same stimulation was interpreted differently across sites. A second study assessing the physiological effects of active versus inactive stimulation under identical electrode attachment revealed that only neck TES produced cortical and autonomic changes consistent with stress modulation, while arm TES did not differ from inactive conditions. These findings suggest that neck TES can be acceptable despite the site's sensitivity, and that both the physiological effects and the sensory experience of TES depend on placement.
1 INTRODUCTION
The paper asks whether users can accept TES at the sensitive neck and whether electrotactile stimulation without vagal access can modulate physiological stress. Across two studies, neck stimulation was comparably comfortable to arm stimulation and produced physiological changes consistent with stress modulation, unlike arm stimulation.
1 INTRODUCTION
- The paper addresses limited evidence on whether users tolerate electrotactile stimulation at the sensitive neck and whether its tactile component can modulate stress without vagal access.TES research has focused on clinical efficacy and vagal mechanisms rather than the experience and physiological role of its tactile component.Source: §1 · p. 2
- An 8-node array was applied to the neck and arm to assess user experience and placement-dependent physiological responses during a demanding task.The neck was the physiologically targeted site; the arm primarily provided cutaneous electrotactile sensation.Source: §1 · p. 2
- Neck TES produced cortical and autonomic changes consistent with stress modulation, whereas arm TES did not differ from inactive stimulation.Participants rated both sites comparably comfortable, and task performance remained stable.Source: §1 · p. 2
2 RELATED WORK
Prior TES stress research emphasizes vagal and physiological effects, while user experience and electrotactile effects remain less studied. The related work positions TES among haptic approaches and highlights the limited evidence on sensitive body placements.
2.1 TES for Stress Modulation
- TES stress research has focused on physiological efficacy and vagal mechanisms, while the comfort and acceptability of its electrotactile sensation have received less attention.Wearable use depends both on physiological efficacy and on whether stimulation is comfortable enough for repeated wear.Source: §2.1 · p. 3
2.2 TES as Electrotactile Feedback
- TES predominantly recruits cutaneous Aβ afferents for touch sensations, but whether electrotactile feedback is comfortable during stress or can influence stress states remains little known.Electrotactile sensations vary across users and sites, and can range from pleasant tapping to uncomfortable prickling or shocking.Source: §2.2 · pp. 3–4
2.3 Haptic Interventions for Stress Modulation
- Haptic stress interventions trade off physiological efficacy, comfort, and deployment; TES offers placement-dependent autonomic access and a thin, silent form, while neck placements remain rarely studied.A review found the forearm, wrist, and hand accounted for roughly two-thirds of placements, leaving limited evidence on sensitive sites such as the neck.Source: §2.3 · pp. 4–5, Table 1 · p. 4
3 TES SYSTEM DESIGN
The system uses a compact, voltage-controlled multi-node TES device and a distributed stimulation pattern intended to produce comfortable electrotactile sensations.
3.1 Multi-Node TES Device
- The voltage-controlled, 8-channel device was chosen for a compact, low-power wearable architecture, with per-participant and per-site intensity calibration and short stimulation blocks.Current control was considered more robust to impedance variation but would require additional sensing and feedback circuitry.Source: §3.1 · p. 5
3.2 Spatiotemporal TES Pattern
- Eight electrodes in a 2 × 4 array activate sequentially with crossfading to distribute stimulation, reduce localized discomfort, and create a moving electrotactile sensation.The pattern combines spatial distribution with individually calibrated just-perceptible intensity to target comfortable or pleasant sensations.Source: §3.2 · pp. 5–6
4 Study 1: Usability Study with Exploratory Physiological Assessment
Study 1 evaluated the multi-node TES system at the neck and arm during a cognitively demanding task, using a device-free control and exploratory physiological measures. The study recruited 24 eligible participants and calibrated stimulation separately by site.
4 Study 1: Usability Study with Exploratory Physiological Assessment
- The usability study assessed TES at the neck and arm during a cognitively demanding task, with exploratory physiological measures and a device-free control condition.The control omitted electrode attachment to establish an unencumbered baseline.Source: §4 · p. 6, §4.1 · p. 6
4.1 Conditions
- Neck electrodes were placed on the left lateral cervical region, while arm electrodes were placed on the forearm to provide electrotactile sensation primarily through somatosensory pathways.The left neck placement followed clinical practice to minimize potential cardiac risks; arm stimulation was used to examine electrotactile input without expected direct vagal targeting.Source: §4.1 · p. 6
4.2 Participants
- The study recruited 24 eligible participants from the local community, screened for TES contraindications, and calibrated each site to a just-perceivable intensity.The study setup used a 2-back task with an EEG headset and HRV chest strap.Source: §4.2 · pp. 6–7, §4.1 · p. 6, Figure 2 · p. 7
4.3 Apparatus
The study setup combined EEG and heart-rate-variability recording while participants completed a cognitively demanding task.
4.3 Apparatus
- Participants wore an Emotiv EPOC X EEG headset and a Polar H10 chest strap to record physiological responses.The chest strap was worn underneath their clothes, and EEG signal quality was verified.Source: §4.3 · p. 7
4.4 Task & Procedure
Participants completed a counterbalanced within-session comparison of control, neck TES, and arm TES during a 2-back task. Each condition included a rest period before the task and physiological recording.
4.4 Task & Procedure
- The 2-back task served as a stressor that elicits measurable stress responses while remaining manageable throughout the session.Participants practiced the task before the main study, which began with a 2-minute baseline nature video and stress-and-affect questionnaire.Source: §4.4 · p. 7
- The three conditions—control, neck, and arm—were fully counterbalanced across participants to address order effects.Participants completed stress and affect questionnaires after each condition and experience ratings after the TES conditions.Source: §4.4 · pp. 7–8
- Each condition block included TES calibration when applicable, a 5-minute rest, and a 2-minute 2-back task with continuous physiological recording.The session began with baseline recording and ended with a semi-structured interview.Source: Figure 3 · p. 8
4.5 Measures
The study combined self-reports, task performance, EEG, and heart-rate measures to assess experience and physiological responses during TES.
4.5 Measures
- Participants rated stress, valence, and arousal after each condition, with measures baseline-corrected to assess condition-related changes.Stress used a 0–10 scale; valence and arousal used 1–9 scales.Source: §4.5.1 · p. 8
- After each TES placement, participants rated pleasantness, tactile comfort, subtlety, task focus, extended wearability, and willingness for future use.They also answered open-ended questions, followed by a recorded semi-structured interview analyzed with reflexive thematic analysis.Source: §4.5.1 · p. 8
- Task performance was assessed using 2-back accuracy and response time, with accuracy based on correct responses and response time on correct target hits.Accuracy included hits and correct rejections; response time was the mean reaction time for hits.Source: §4.5.2 · pp. 8–9
- The study monitored EEG and HRV relative to each participant’s baseline; EDA was excluded because keyboard motion artifacts confounded its signal.The baseline was recorded during the video-watching phase.Source: §4.5.3 · p. 9
- EEG analysis focused on frontal alpha and beta band power, using baseline-corrected spectral power from 2-second epochs.Alpha covered 8–13 Hz and beta 13–30 Hz; EEG data were filtered, artifact-rejected, and analyzed with Welch’s method.Source: §4.5.3 · p. 9
- Heart activity was assessed with RMSSD and heart rate from ECG, with participant values baseline-corrected and z-scored.RMSSD indexes parasympathetic activity, while higher heart rate indicates increased stress.Source: §4.5.3 · p. 9
4.6 Findings
In this study, neck and arm TES produced distinct user experiences, while task performance and subjective stress ratings showed no clear condition differences. Exploratory physiological measures varied by condition, with cortical patterns generally stronger at the neck and autonomic changes observed at both sites.
4.6 Findings
- All participants completed all three conditions without adverse events or early termination.Source: §4.6 · p. 9
4.6.1 User Experience.
- Arm stimulation was often described with familiar tactile terms, while neck sensations elicited more varied metaphors and reports of social presence occurred more often for the arm.Participants described the neck with images such as raindrops or butterflies, while some described arm stimulation as someone holding or reassuring them.Source: §4.6.1 · pp. 9–10
- Arm and neck comfort ratings were similar, but participants more often described the neck as intrusive or vulnerable and the arm as natural and familiar.Neck comfort averaged 5.17 and arm comfort 5.33; arm wearability ratings were also higher than neck ratings.Source: §4.6.1 · pp. 10–11
- Arm was rated slightly more subtle and more wearable, while willingness for future use was nearly identical across sites and overall site preference was divided.Arm was preferred by 13 of 24 participants and neck by 11 of 24; future-use ratings were 5.00 for arm and 4.96 for neck.Source: §4.6.1 · pp. 10–11
- Both sites were often experienced as subtle, but participants differed on which placement was easier to ignore, and focus ratings were identical on average.Mean focus ratings were 3.96 for both arm and neck; some participants reported distraction, while others found stimulation supportive of focus.Source: §4.6.1 · p. 11
4.6.2 Task Performance and Subjective Response.
- Condition had no significant effect on 2-back accuracy or response time, and self-reported stress, valence, and arousal were descriptively comparable across conditions.The authors reported that TES produced no clear additional subjective benefits over control.Source: §4.6.2 · p. 11
4.6.3 Exploratory Physiology Assessment.
- Both arm and neck TES increased frontal alpha and beta power relative to control, with larger increases at the neck; the patterns were compatible with reduced stress cortical activity and increased cognitive engagement, respectively.Alpha increased versus control for arm (r = 0.53) and neck (r = 0.78); beta increased versus control for arm (r = 0.63) and neck (r = 0.79).Source: §4.6.3 · pp. 12–13, Figure 5 · p. 12
- Both TES sites increased RMSSD and reduced heart rate relative to control, with no significant arm–neck differences for either measure.The authors noted that these exploratory patterns could not distinguish active stimulation effects from electrode presence or expectancy.Source: Figure 5 · p. 12, §4.6.3 · p. 13
5 Study 2: Physiological Assessment of Active Stimulation
Study 2 compared active and inactive TES at the arm and neck with electrode attachment held constant, testing whether stimulation had site-dependent physiological effects. Neck stimulation produced cortical and autonomic changes relative to inactive stimulation, while arm stimulation and task performance showed no significant condition differences.
5 Study 2: Physiological Assessment of Active Stimulation
- Study 2 followed Study 1 because its device-free control could not separate active-stimulation effects from electrode-presence effects.The follow-up matched electrode attachment across active and inactive conditions to isolate stimulation-related physiological changes.Source: §5 · p. 13
5.1 Conditions
- The within-subject design compared arm-active, arm-inactive, neck-active, and neck-inactive conditions, with pads attached in every condition and stimulation delivered only in active conditions.The 24 participants completed counterbalanced site blocks; each block included a baseline video and two 2-minute 2-back conditions separated by a 5-minute rest.Source: §5.1 · p. 13, §5.2 · p. 13, §5.3 · p. 14
5.4 Measures
- EEG and HRV were recorded during baseline videos and the 2-back task, while perceived stress, stimulation intensity, and awareness were assessed after conditions.Physiological measures were baseline-corrected within each block; the study used repeated-measures ANOVAs and corrected post-hoc tests.Source: §5.4 · p. 15, §5.5.1 · p. 15
5.5 Findings
- NA produced greater frontal alpha and beta power than NI, while AA and AI did not differ significantly on either measure.The site × stimulation interaction was significant for alpha (F(1, 23) = 9.74, p = .005) and beta (F(1, 23) = 16.74, p < .001).Source: §5.5.1 · p. 15, Figure 8 · p. 16
- Alpha topographies showed widespread increases for NA, comparable task-related suppression for AI and NI, and a nonsignificant focal increase for AA.Figure 9 maps baseline-relative alpha power across 14 channels; blue indicates decreases and red increases.Source: §5.5.1 · p. 15, Figure 9 · p. 16
- NA increased RMSSD and reduced HR relative to NI, whereas AA and AI did not differ significantly on either measure.The RMSSD interaction was F(1, 23) = 4.67, p = .041; the HR interaction was F(1, 23) = 6.19, p = .020.Source: §5.5.1 · p. 15, Figure 8 · p. 16
- No condition effects were significant for 2-back accuracy or response time across AA, AI, NA, and NI.Mean accuracy exceeded 90% across conditions.Source: §5.5.2 · p. 15
- Participants reported neutral or below-neutral expectations, and perceived stress was descriptively similar between active and inactive conditions at both sites.Inactive conditions nevertheless had non-negligible intensity and awareness ratings, indicating that pad presence was perceptible to some extent.Source: §5.5.3 · pp. 16–17
6 DISCUSSION
The discussion interprets neck TES as acceptable despite site sensitivity, with physiological effects beyond inactive stimulation observed at the neck but not the arm. These physiological changes were not accompanied by perceived-stress changes, and performance remained stable during the brief 2-back task.
6.1 Neck TES Was Acceptable Despite Site Sensitivity
- Neck TES was rated comfortable and acceptable despite sensitivity and visibility, with future-use intentions comparable to the arm.Participants described arm sensations as tapping or buzzing and neck sensations through varied natural and bodily-rhythm metaphors.Source: §6.1 · p. 17
6.2 Physiological Stress Modulation Depended on Placement
- Under matched electrode attachment, neck-active TES produced cortical and autonomic changes relative to neck-inactive TES, whereas arm-active did not differ from arm-inactive TES.The authors note that vagal engagement was not directly measured, so the changes cannot be attributed specifically to vagal activation; tactile experience may also have contributed.Source: §6.2 · pp. 17–18
6.3 Physiological Changes Did Not Translate Into Subjective Awareness
- Physiological stress modulation at the neck was not accompanied by perceived-stress changes; cognitive load, retrospective ratings, and low-salience stimulation are proposed as possible explanations.The authors suggest visible measures such as HRV trends or progress indicators could help users notice physiological improvements while retaining low-salience operation.Source: §6.3 · p. 18
6.4 TES Did Not Interfere with Cognitive Performance
- Performance remained stable across conditions during the brief 2-minute task, and reported divided attention or enhanced focus did not translate into measurable performance changes.The authors frame maintained performance alongside reduced physiological load at the neck as evidence consistent with stress reduction without a performance cost.Source: §6.4 · pp. 18–19
7 IMPLICATIONS
The implications distinguish physiological relevance from tactile acceptability in TES design. They also call for considering sensitive sites and body-site differences in how stimulation patterns are interpreted.
Separate physiological efficacy from tactile comfort
- Evaluate TES placement separately for physiological relevance and tactile acceptability; comfort alone does not establish physiological stress modulation.Both sites were rated comfortable and acceptable, but effects beyond inactive stimulation emerged only at the neck.Source: §7 · p. 19
Design for acceptability at sensitive body sites
- Do not dismiss the neck solely for sensitivity or social visibility; participants rated it comparably acceptable to the arm and expressed comparable willingness for future use.Skin-tone-matched patches, collar-integrated designs, and jewelry-like wearables are suggested ways to reduce visibility while preserving access to relevant sites.Source: §7 · p. 19
Consider body-site differences in sensory interpretation
- Account for placement when designing patterns: participants interpreted neck stimulation through natural or bodily-rhythm metaphors and arm stimulation through familiar tactile experiences.The same spatiotemporal pattern may be perceived differently across body sites.Source: §7 · p. 19
8 LIMITATIONS & FUTURE WORK
The findings are bounded by brief stimulation blocks, a narrow intensity and pattern design, and testing only in cognitive-stress contexts. The authors call for longer and larger studies, broader stimulation comparisons, and testing across other stressors and settings.
8 LIMITATIONS & FUTURE WORK
- Autonomic effects were smaller and estimated with wider confidence intervals, so larger samples could provide more precise estimates.The study used 2-minute blocks as a conservative safety measure; future work should use longer measurement periods and consider pupil dilation.Source: §8 · p. 19
- Testing only comfortable, individually calibrated just-perceptible stimulation leaves effects across subliminal, perceptible, and salient intensities unresolved.The voltage-controlled approach may be less robust to impedance changes than current control; per-participant, per-site calibration mitigated baseline impedance differences in this setting.Source: §8 · p. 19
- A fixed spatiotemporal pattern leaves open how pattern design shapes the cognitive interpretation of electrotactile feedback.Future work could vary speed, direction, and rhythm to examine comfort and social presence.Source: §8 · pp. 19–20
- The findings are limited to cognitive stress contexts, and TES effectiveness may vary across social, environmental, or physical stressors and intensities.The authors propose testing in more naturalistic settings and comparing TES with vibrotactile, pressure-based, and thermal feedback.Source: §8 · p. 20
9 CONCLUSION
Neck TES produced cortical and autonomic changes consistent with stress modulation, while arm TES did not differ from inactive conditions. Neck stimulation was comparably comfortable and acceptable to the arm, but participants did not report corresponding changes in perceived stress.
9 CONCLUSION
- Neck TES produced cortical and autonomic changes consistent with stress modulation, whereas arm TES did not differ from inactive conditions on any physiological measure.The comparison used identical electrode attachment in active and inactive conditions.Source: §9 · p. 20
- Participants rated neck stimulation as comparably comfortable and acceptable to the arm, despite the neck site's sensitivity.Task performance remained stable across conditions in both studies during the brief cognitive task.Source: §9 · p. 20
- Participants did not report corresponding changes in perceived stress despite physiological stress modulation.The authors suggest that physiological effects of low-salience TES may not be consciously perceived.Source: §9 · p. 20