ISASE 2023

Stroking Stimuli to Ear Induces Pleasant Feelings
while Listening to Sounds
Yuta GOTO* and Shogo OKAMOTO** Tokyo Metropolitan University, 6-6 Asahigaoka, Hino-shi, Tokyo 191-0065, Japan

Abstract: We investigated whether stroking stimuli near the external auditory meatus while listening to sounds enhances pleasantfeelings. Previous studies have demonstrated that vibratory stimuli manipulate emotions evoked by watching videos or listening tosounds; however, none have investigated the effects of stroking stimuli near the external auditory meatus through which vagus nerves
extend. Participants were exposed to three types of sounds with and without the stroking stimuli to their ears, and selected one stimulus
condition that induced intense feelings. When the sound stimuli were presented with the stroking stimuli to the ear, joyful and pleasantfeelings were intensified, whereas depressing feelings weakened. Stroking stimulation of the outer ears in combination with soundstimulation was suggested to induce positive feelings.
Keywords: Emotion, Natural sounds, Shampoo, Stroke

1. INTRODUCTION

rotated by DC motors and presented stroking stimuli whenparticipants were listening to sounds that could induce
emotions. These included sounds of rain, storms, andshampooing. The findings of the present study will
provide a basis for new emotional haptic interface designs.

Emotional changes induced by sound and videos may
influence the judgment of their values. Haptic stimuli tohuman bodies affect humans’ emotions while
experiencing audiovisual contents [1–10]. For example,
vibrotactile stimuli, which are delivered through chairs totorsos are synchronized with movie soundtracks to
improve emotional impressions [6, 7]. Vibratory stimuli
are typically applied to torsos and the stimulation of ears
is expected to cause effects similar to that of torsos [10].
Extant studies adopted vibratory stimuli which gave riseto arousing or unpleasant feelings [1–10]. Vibratory
stimuli alone may not effectively induce pleasant and nonarousing feelings. Further, most studies selected torsos orhands to be stimulated but few studies investigated theexternal ears [10]. Vagus nerves that send the informationof organs’ states to the brain are also found in the outerears. Thus, stimulation to the outer ears is linked to various
physiological responses [11]. Hence, ear stimulation may
become an alternative to torso stimulation and induce
some emotional effects.
This study investigates the emotional effects of stroking
stimulus to the external ear while listening to sounds. We
adopted stroking stimuli unlike earlier studies. Stroking
stimuli cause pleasant feelings when presented to arms[12], unlike vibratory stimuli. Hence, the stroking andvibratory stimuli to ears may have different emotional
effects, which has yet to be studied. In the present
experiment, a plastic tactile contactor placed at the ear was

2. METHODS
2.1 Apparatus
Figure 1 shows the appearance of the experimental
apparatus. As a tactile stimulator, a resin rod fabricated by
a 3D printer was used to stroke near the external acousticmeatus. The tip of the rod was spherical (12 mm indiameter) with a hemisphere (8 mm in diameter) attached
to it. The shape and size were determined such that theexternal acoustic meatus could be stimulated without

Figure 1: Experimental apparatus. Left) Experimental scene. Middle) Tactile stimulator for ear.
Right) Tip of the ear stimulator.

12.2 Sound stimuli
We used the sounds of shampoo [13], rain [14], andwinds in a storm [15] to evoke pleasant feelings. Thesesounds are expected to produce positive feelings including
relaxation and stress-relief [16–18]. Each audio clip was 3
min long with a sampling frequency of 44100 Hz.
2.3 Stroking stimuli to ear
The plastic rod attached to the DC motor was rotated in
response to the sound. Voltage commands to the DC motor
were generated from the waveform of audio stimuli by thefollowing process (Figure 3). First, the audio channel
corresponding to the ear to be stroked was extracted fromthe two channels of the stereo audio. Second, the negative
output voltage from a phone jack was removed and set to
0. Finally, the envelope of the waveform was extractedusing the envelope function in Matlab (Mathworks, USA)with a peak mode of 1000. This peak interval value
determines the smoothness of the envelope. When thisvalue is small, the DC motor trembles slightly. When thepeak interval is large, the DC motor rotates smoothly. This
study did not aim to optimize the stroking stimulation, andthe peak interval value was adjusted by the authors suchthat the stimulus felt comfortable.

Figure 2: Configuration of apparatus

Figure 3: Voltage/speed instruction to DC motor
generated from sound waves.

2.4 Participants
Seven healthy participants (five males and two females)in their early 20s participated in the experiment. All
participants had never experienced the apparatus and did
not know the purpose of the experiment.

damaging it. The resin rod was connected to a DC gearedmotor (TG-47G-SG, Tsukasa Denko, Japan, reduction
ratio: 50) via a coupling (Capricon MRG-20-6-8, Nabeya
Bi-tech, Japan). The DC motor was given a speedcommand via a motor controller (SyRen 10, Dimension
Engineering, USA).
Figure 2 shows the configuration of the apparatus. The
command value to the DC motor was output from theearphone jack of the personal computer. It then passed
through a non-inverting amplifier circuit using anoperational amplifier and was input to the motor controller.
The motor controller applied a pulse-width-modulation
signal of up to 12 V to the DC motor. The voltage input tothe DC motor was generated based on the waveform of thesound, as described in Section 2.3.
In addition to the tactile stimuli, the participants werepresented with the sound stimuli. The sound stimuli werepresented through bone-conducting earphones (Aeropex,Shokz, USA) via Bluetooth connection. We did not use
inner ear or canal-type earphones because they would
block the external acoustic meatus, where the stroking
stimulus was applied.

2.5 Procedures and tasks
Participants experienced two conditions in succession
for each of the three types of sounds: In the first condition,
only the sound was played; in the second condition, boththe sound and tactile stimulus were played. For a givensound, the sound was first played for 3 min in one of theconditions, and after a 2 min interval, the sound wasplayed for 3 min under the other condition. The order inwhich the two conditions and three types of sounds werepresented were randomized. Participants were asked toclose their eyes during the presentation of audio stimuli.
After experiencing an audio stimulus under the twoconditions, participants chose the more applicable of thetwo conditions for eight emotional items (two-alternativetask). The items measured were arousing, sleepy, joyful,depressing, pleasant, unpleasant, relaxing, and scary thatwere adapted from Russell’s circumplex affect model [19].
2.6 Data analysis

2arousing and unpleasant feeling.
In the field of emotional haptics, researchers often use
vibration stimuli, with which arousing and unpleasantemotions are induced [1–10]. In contrast, the use ofstroking stimuli in the present study led to arousing andpleasant feelings, suggesting that vibratory and stroking
stimuli give rise to different types of feelings. In this study,
we used only one type of tactile contactor and stimulus
generation algorithm. In the future, we will optimize thesefactors to effectively evoke pleasant feelings. In addition,
we used sounds that could induce pleasant feelings. It will
be interesting to investigate how the stroking stimulus
affects feelings evoked by unpleasant sounds.
5. CONCLUSION
Earlier researchers established the emotional effects ofvibration stimuli presented to the torsos of human bodies.
In contrast, we investigated the emotional effects ofstroking stimuli presented to the external acoustic meatus
while listening to sounds. The user study involving sevenparticipants suggested that the stroking stimuli elicited
positive feelings including joyful and pleasant, andsuppressed negative feelings such as depression.
Optimization and generalization of the stroking stimuli tothe ear remain to be studied.

Figure 4: Proportion at which audio + tactile
condition was selected as more suitable to each of
the eight emotional words. * and ** mean that theproportions are significantly different from 0.5(50%) at 𝑝 < 0.05 and 0.01 with Bonferroni
correction.

For each of the eight emotions, we calculated thepercentage of participants who selected the audio-tactile
stimulus condition. A binomial test was used to determine
if each of the eight types of proportions was significantly
different from the chance, i.e., 0.5 with Bonferroni
correction of factor eight.

REFFERENCES[1] I. Tara, S. Okamoto, Y. Akiyama, and H. Ozeki;
Timing of vibratory stimuli to the upper body forenhancing fear and excitement of audio-visualcontent, International Journal of Affective
Engineering, vol. 22, 2023.
[2] I. Tara, S. Okamoto, Y. Akiyama and Y. Yamada;
How important is the timing of vibrotactile stimuli
for the excitation of an emotional response foraudio-visual content?, IEEE Global Conference onConsumer Electronics, pp. 157–159, 2021.
[3] I. Tara, S. Okamoto, Y. Akiyama and Y. Yamada;Heightening fear response to horror video scenes byapplying vibratory stimuli to upper bodies ofviewers, IEEE 4th Global Conference on Life
Sciences and Technologies, pp. 250–252, 2022.
[4] G. Karafotias, A. Teranishi, G. Korres, F. Eyssel, S.
Copti and M. Eid; Intensifying Emotional
Reactions via Tactile Gestures in Immersive Films,
ACM Transactions on Multimedia Computing,Communications, and Applications, 13(3), pp. 1–17, 2017.

3. RESULTS
Figure 4 shows the proportions at which the audiotactile condition was selected as more suitable for eachfeeling. For joyful, the audio-tactile condition was selected
at 0.81 (𝑝 < 0.05). For pleasant, this proportion was 0.81
(𝑝 < 0.05). Conversely, the proportion for depressing was0.10 (𝑝 < 0.01), suggesting that the audio-only condition
felt more depressing. For other types of feelings, there
were no significant differences between the twoconditions.
4. DISCUSSION
Stroking near the external acoustic meatus resulted instronger positive emotions such as joyful and pleasant andweaker negative emotions such as depressing compared tosimply listening to the audio. Returning to Russell’s
circumplex model [19], joyful is an arousing and pleasantfeeling in the circumplex model and depressing is a non-3

[5] S. Sakurai, T. Katsumura, T. Narumi, T. Tanikawa
and M. Hirose; Evoking emotions in a story usingtactile sensations as pseudo-body responses withcontextual cues, International Conference on
Human Interface and the Management ofInformation, pp. 241–250, 2014.
[6] F. Giroux, J. Boasen, S. Sénécal, M. Fredette, A.
Tchanou, J. Ménard, M. Paquette and P. Léger;Haptic stimulation with high fidelity vibro-kinetic
technology psychophysiologically enhances seatedactive music listening experience, Proceedings inIEEE World Haptics Conference, pp. 151–156,
2019.
[7] S. Merchel and M. Altinsoy; The Influence ofVibrations on Musical Experience, Journal of the
Audio Engineering Society, 62(4), pp. 220–234,
2014.
[8] T. Makioka, S. Okamoto and I. Tara; Fearmagnified by vibratory stimuli to the upper-body at
predictive horror scenes, Proceedings of IEEE
Global Conference on Consumer Electronics, 2022.
[9] H. Hasegawa, S. Okamoto, K. Ito and Y. Yamada;
Affective vibrotactile stimuli: Relation between
vibrotactile parameters and affective responses,
International Journal of Affective Engineering,18(4), pp. 171–180, 2019.
[10] S. Fukushima, K. Amou, A. Nakata and H.
Kajimoto; Emotional Vibration: Enhancement ofemotion using a Combination of Sound and Skin
Sensation to the Pinna, The Virtual Reality Societyof Japan, 19(4), pp. 467–476, 2014.
[11] A. R. Murray, L. Atkinson, M. K. Mahadi, S. A.
Deuchars and J. Deuchars; The strange case of theear and the heart: The auricular vagus nerve and its
influence on cardiac control, Autonomic
Neuroscience, 199, pp. 48–53, 2016.
[12] G. K. Essick, F. McGlone, C. Dancer, D. Fabricant,Y. Ragin, N. Phillips, T. Jones and S. Guest;
Quantitative assessment of pleasant touch,
Neuroscience & Biobehavioral Reviews, 34(2), pp.
192–203, 2010.
[13] https://www.youtube.com/watch?v=RCT8hGGnTjw[14] https://www.youtube.com/watch?v=NNLIC0bMdP
E[15] https://www.youtube.com/watch?v=sGkh1W5cbH4[16] M. Annerstedt, P. Jönsson, M. Wallergård, G.
Johansson, B. Karlson, P. Grahn, Å. Hansen and P.
Währborg; Inducing physiological stress recovery
with sounds of nature in a virtual reality forest—

Results from a pilot study, Physiology & Behavior,
118, pp. 240–250, 2013.
[17] R. S. Ulrich, R. F. Simons, B. D. Losito, E. Fiorito,
M. A. Miles and M. Zelson; Stress recovery duringexposure to natural and urban environments,
Journal of Environmental Psychology, 11(3), pp.
201–230, 1991.
[18] P. McGeoch and R. Romke; How everyday sounds
can trigger strong emotions: ASMR, misophonia
and the feeling of wellbeing, Bioessays, 42(12), no.
2000099, 2020.
[19] A. Tseng, R. Bansal, J. Liu, A. J. Gerber, S. Goh, J.
Posner, T. Colibazzi, M. Algermissen, I. Chiang, J.
A. Russell, and B. S. Peterson; Using thecircumplex model of affect to study valence andarousal ratings of emotional faces by children andadults with autism spectrum disorders, Journal ofAutism and Developmental Disorders, 44, pp.
1332–1346, 2014.

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