Warm Ear Stroke to Make
Sounds More Pleasant and Sleepy
Yuta Goto

Shogo Okamoto

Tokyo Metropolitan Univeristy
Hino, JapanTokyo Metropolitan Univeristy
Hino, JapanAbstract—We investigated the effect of stroking stimulationnear the external auditory meatus, where vagus nerves exist, onemotions while listening to sounds to induce pleasant feelings. In
our previous study, we demonstrated that such stimuli ampliﬁed
the pleasant and arousing feelings evoked by pleasant sounds.
This study additionally investigated the effects of warming
stroking contactor. In a user study involving ten participants, acomparison of stroking stimuli with and without warming showedthat the warm stimulation increased subjectively reported pleasantness and sleepiness, and decreased arousal. These ﬁndings help
develop emotionally-appealing products in consumer electronics.
Index Terms—emotion, vagus verves, relaxation

I. I NTRODUCTION
Simultaneous presentation of audiovisual contents, such as
movies and music, and haptic stimuli to the body enhances theparticipant’s emotional experiences (e.g. [1]–[5]). For example, when an upper body vibration was applied while viewing
a horror scene, the participants felt greater fear than when novibration was applied [1]. Vibration stimuli tend to make theemotions evoked by audiovisual contents more arousing andunpleasant. In contrast, stroking stimuli to auditory meatusenhance pleasant and joyful feelings caused by pleasant audio
stimuli including the sounds of rain and winds [6]. In order
to induce less arousing or more sleepy feelings, in this study,
we investigate the effect of warm stroking stimuli to auditory
meatus.
Warm temperature stimuli to the human body, such asneck, decrease subjective and physiological arousal, leading
to relaxation [7]. There are many examples of combining
audiovisual and thermal stimuli to manipulate feelings evokedby audiovisual stimuli (e.g., [8], [9]). In many previous studies,
pleasant feelings were enhanced by warm stimuli. In somecases [8], [9], warm stimuli enhanced arousal during video
and image viewing.
This gap of the effects of warm stimuli on arousal between
earlier studies may originate from the differences in body parts
warmed in those studies. In some studies such as [8], [9],the warm stimuli were presented to the palm or abdomen.
Warming of the ear may have the same effects as warming of
the neck, i.e., causing relaxation.
In this study, we compare subjectively reported feelings
including pleasantness and sleepiness between with and without warming when pleasant sounds such as rain, winds, andshampoo are played with auditory stroking stimuli. Thus far,979-8-3503-4017-4/23/$31.00 ©2023 IEEE

Fig. 1. Experimental apparatus. Left) Experimental scene. Middle) Tactile
stimulator for ear. Right) Rod retained in temperature-controlled water.

the effects of warm stroking contactor for auditory meatus has
not been investigated, and this study will add a positive aspect
to the literature in consumer electronics.
II. METHODS
A. Apparatus
Fig. 1 shows the experimental apparatus. A similar apparatus was used in a previous research [6]. A 3D-printed plastic
rod was used as a contactor for presenting frictional stimuli tothe external auditory meatus. The tip of the rod was spherical(12 mm in diameter) with a smaller hemisphere, of whichdiameter was 8 mm. The plastic rod was ﬁxed to a DC geared
motor with a reduction ratio of 50. The speed of the DC motor
was controlled to be proportional to the transient volume ofthe sound by using a motor controller (SyRen 10, Dimension
Engineering Llc., OH). Two cups ﬁlled with water of different
temperatures were used to control the temperature of the rod.
In one cup, the water temperature was the room level ranging
20–25o C. In another cup, the water was warmed at 42–43o C.
A temperature controller (TXN-200AL, As One Corp., Japan)
was used to retain this range. The rod was immersed in thecup for more than 1 min long.
Along with the tactile stimuli, sound stimuli were presented to the participants through bone-conduction earphones(Aeropex, Shokz, TX). This type of earphones did not plug up
ears, and allowed the participants to contact the rod at theirauditory meatus.

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determine whether the frequencies of the three options differedfrom chance levels (0.33).
III. R ESULTS
Fig. 2 shows the proportions of three options selected in thequestionnaire for each of the eight emotions. For awake, theproportions of the three conditions were unequal (χ2 = 15.0,p < 0.001) and the room temperature condition was selected
most. For pleasant (χ2 = 20.6, p < 0.001) and sleepy(χ2 = 10.4, p < 0.05), the proportions were also unequal,
and the warm condition was selected most. For afraid, themost participants answered that the two conditions were notdifferent (χ2 = 12.8, p < 0.01). For the other adjective
attributes, we did not ﬁnd any differences in the proportions
among the three options.
Fig. 2. Proportion of participants who selected each of the three options asmost suitable for each adjective. *, **, and *** mean that three proportions
are unequal to the chance, i.e., 0.33 with Bonferroni adjustment of factor
eight, at p < 0.05, 0.01, and 0.001. The down arrow exhibits the largest
residuals among the three options.

B. Procedures and tasks
Before the main experiments, the participant adjusted aforce to contact the stimulator to the external auditory meatus
such that the motion of the rod could be recognized. During
the adjustment, the motor was continuously revolved.
In the main session, the participant experienced two temperature conditions for each of the three sounds that were thesounds of rain, winds, and shampoo. In one condition, therod was immersed in water at room temperature. In the othercondition, the rod was immersed in water at 42–43o C. For agiven sound, participants experienced both conditions for 30s each with the interval of 45 s. The order of the audio clips
and temperature conditions were randomized. The participants
closed their eyes during the presentation of the stimuli.
After the participant listened to each sound with the stroking
stimuli at the auditory meatus under the two temperature
conditions, for each of the eight quesionnaire items, they
selected a suitable one among three options: the room temperature condition, warm condition, or no difference between
two conditions. The questionnaire items were awake, sleepy,
joyful, derpressed, pleasant, unpleasant, relaxed, and afraidreferring to Russell’s circumplex model [10].

IV. D ISCUSSION
The participants judged the warm stimuli as more sleepy
and the room-temperature stimuli as more awake. Sleepy andawake or arousing feelings are considered as opposite [10].
Hence, the thermal stimuli suppressed arousal feelings.
In terms of pleasant, the warm condition was selected most,suggesting that the warm stimuli enhanced the pleasantness ofthe sounds. For unpleasant, which is the opposite of pleasant,the two types of stimuli were not felt differently. This may be
because the sounds used in this study were largely pleasant,and the use of the tactile stimuli did not affect unpleasantness.
V. C ONCLUSION
We focused on the effects of stroking stimuli to the external auditory meatus using a warm ear contactor, whereasthe effect of auditory stroking stimuli were demonstrated inan earlier study [6]. Further, most earlier studies employedvibratory stimuli to torsi and hands. The use of warm contactor
made pleasant sounds feel more pleasant and sleepy (or lessarousing) than that at the room temperature. In the future, wewill investigate the most effective temperature of the rod andinstall a temperature control function to the stroking rod.

C. Participants
Ten university students (seven males and three females)
unaware of the study objectives participated in the experiment
after providing a written informed consent.
D. Data analysis
Participants’ answers for all the sounds were pooled and theproportions of selection for each option, i.e., warm temperature, room temperature, and no difference, were calculated.
For each of the eight emotions, a chi-square test for goodnessof-ﬁt with Bonferroni correction of factor eight was used to639

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