Colorful Tactile Stimuli. Association
Between Colors and Tactile-Display
Stimuli on Russell’s Psychological Plane
Hikaru Hasegawa, Ken Itoh, Shogo Okamoto, Hatem Elfekeyand Yoji Yamada

Abstract Supplementing the presentation of colors with tactile displays has yet to
be developed. This study used Russell’s aﬀective plane to investigate the association
between the rainbow colors and vibrotactile and variable-friction stimuli presented
as tactile displays. A user study indicated that high-frequency and rhythmical tactile
stimuli that were perceived as arousing were suitable for presenting the warm colors
such as red, orange, and yellow. In contrast, low-frequency and slow tactile stimuli
that were perceived as less arousing were suitable for the cold colors. Furthermore,
unpleasant tactile stimuli that involved ﬁne but strong frictional texture could belinked with purple and with unpleasant psychological images. Our ﬁndings indicatethat tactile displays can be used to assist the user’s perception of hue.
Keywords Hue ⋅ Vibrotactile ⋅ Friction ⋅ Electrostatic

1 Introduction
One of the roles of tactile displays is to compensate or complement visual information; however, the presentation of colors is challenging in this respect. The relationships between temperature stimuli and colors are well known [1–3]. Furthermore,
Ludwig and Simner reported psychological relationships between the lightness,
chroma, and surface roughness of materials [4]. However, the association between
hue and vibrotactile and frictional stimuli has yet to be clariﬁed. Our ultimate goal isto establish a stimulus set for expressing each of the rainbow colors. For this purpose,
we associated the tactile-display stimuli with color hues. As described in Sect. 2,
we ﬁrst attempted ﬁnd associations between color wave-length and the ﬁneness ofvibrotactile and frictional stimuli. However, we were unsuccessful because of thediscrepancy between psychological images for colors and those for tactile stimuli.
We then mapped hue and tactile stimuli via psychological images.
H. Hasegawa (✉) ⋅ K. Itoh ⋅ S. Okamoto ⋅ H. Elfekey ⋅ Y. Yamada
Department of Mechanical Science and Engineering, Nagoya University,
Furo-cho, Chikusa-ku, Nagoya, Japane-mail: hasegawa.hikaru@c.mbox.nagoya-u.ac.jp© Springer Nature Singapore Pte Ltd. 2018
S. Hasegawa et al. (eds.), Haptic Interaction, Lecture Notes
in Electrical Engineering 432, DOI 10.1007/978-981-10-4157-0_847

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2 Design Principles for Color-Tactile Association
2.1 Associations Based on Physical Color Elements
A color is typically decomposed into hue, luminance, and chroma. We consideredassociation of each of these three types of color element with independent tactile
stimuli. This idea is supported by a ﬁndings that texture roughness is correlated withthe chroma of a color [4], and a vibrotactile texture display can present textures withvarious levels of roughness [5]. Furthermore, because hue depends on the frequencyof light, intuitive color-tactile associations using vibrotactile stimuli with varying
frequencies appear plausible. For example, low-frequency vibrotactile stimuli may
correspond to colors such as red and yellow, and high-frequency stimuli may correspond to colors such as blue and purple. We tested such color-tactile associations
based on frequency by using a vibrotactile display. Unfortunately, we failed to ﬁndfrequency-based associations. This was because the impressions provided by colors
and vibrotactile stimuli did not match. For example, our impression of warm colors,
such as red, orange, and yellow, is energetic. In contrast, low-frequency vibrotactile
stimuli that were potentially linked with the warm colors evoked impressions such as
calmness and stillness. Hence, the psychological images associated with colors andvibrotactile stimuli are inconsistent, and hue-tactile associations based on frequency
may be inconsistent with an intuitive user-experience.

2.2 Associations Based on Aﬀective Responses
Colors can be associated with emotions [6]. Furthermore, vibrotactile stimuli canevoke aﬀective responses [7]. These ﬁndings led us to use psychological images toconnect tactile stimuli and colors. We adopted Russell’s psychological plane [8],which is a two-dimensional plane composed of arousal and pleasantness axes. We
designed nine tactile stimuli that mapped on Russell’s psychological plane, using
the vibrotactile and frictional stimuli to present stimuli that varied along arousal andpleasantness axes, respectively (Fig. 1).
Based on prior reports [7], we used attenuating sinusoidal vibrotactile stimuli,
and generated diﬀerent stimuli by changing the frequency of the sinusoidal wave
and the tempo of additional signal periodicities, as shown in Fig. 1. High frequency
and rhythmical vibrotactile stimuli were arousing, and low frequency and slow vibrotactile stimuli were sleepy. We used the electrostatic friction display to present stimuli that varied along the pleasant-unpleasant axis. We switched friction on and oﬀ
with switching frequencies of 30–100 Hz, with larger magnitudes for the fasterswitching frequencies. Strong and high-frequency friction stimuli were intended toevoke unpleasant user experiences, whereas weak and low-frequency stimuli wereintended to be relatively pleasant.

ElectrostaƟc fricƟon sƟmuli

Weak andcoarse fricƟonal
textureFig. 1 Nine types of tactile
stimuli using vibrotactile andelectrostatic frictioncomponents. S, N, and W
indicate the level offrictional stimuli. Underline
and overline indicate thelevel of vibrotactile stimuli

Strong andfine fricƟonal
textureColorful Tactile Stimuli. Association Between Colors . . .

49SSNNWWVibrotacƟle sƟmuliSlow and lowfrequency

Rhythmical andhigh frequency

3 Experimental System: Tactile Display for Vibrotactileand Electrostatic Frictional Stimuli
We used a tactile display that could present vibrotactile and variable-friction stimuli.
The same equipment has been used in another study by the authors [9]. The wholesystem was computer-controlled at 1 kHz. As shown in Fig. 2, the vibrotactile stimuli
were produced by four voice coil actuators (X-1741, Neomax Engineering Co. Ltd.,
Japan), each of which was located at each corner of the top panel. The four actuators were synchronously driven by a current ampliﬁer (ADS 50/5, Maxon motor,Switzerland) and delivered mechanical vibratory stimuli to the ﬁnger pad on the toppanel. The frictional stimuli were produced via the electrostatic force induced by thevoltage between an aluminum pad and an ITO panel. An insulator (Kimotect PA8X,
KIMOTO Co. Ltd., Japan) was located between the ITO panel and aluminum pad.
The induced voltage was operated by a high-ﬁdelity voltage ampliﬁer (HJOPS-1B20,
Matsusada Precision Inc., Japan).

Fig. 2 Tactile texture display for the presentation of vibrotactile and variable-friction stimuli. Left
Schematic side-view. Right Photo of apparatus

50H. Hasegawa et al.

4 Experiment
We performed two experiments to investigate the association between colors andpsychological images and between the tactile stimuli noted above and psychologicalimages. Three student volunteers who were unaware of the objectives of the study
participated in the two experiments in a counterbalanced manner.
In experiment 1, the participant experienced each of the nine types of tactile stimuli and mapped each stimulus on Russell’s psychological plane which was drawn on
a sheet of paper. The participant moved their ﬁnger on the panel and experienced
the tactile stimulus as long as they wanted, but typically each trial lasted several seconds. From this experiment, we assessed whether the designed tactile stimuli wereclearly located within Russell’s psychological plane. The nine types of stimuli werepresented in randomized order.
In experiment 2, the participants placed each of the rainbow colors, namely red,orange, yellow, green, blue, indigo, and purple, on Russell’s psychological plane.
Each color was tested only once for each participant. We did not show printed colors
to the participant; he/she imagined each color.

5 Results
Figure 3 shows the results of experiment 1. The tactile stimuli generally diﬀered intheir psychological, aﬀective components. Speciﬁcally, stimulus S was perceived tobe arousing, and stimulus W was perceived to be less arousing for every participant. Meanwhile, the responses toward S, S, N, and W were inconsistent among theparticipants.

Fig. 3 Tactile stimuli placed on Russell’s psychological planeColorful Tactile Stimuli. Association Between Colors . . .

51

Fig. 4 Colors placed on Russell’s psychological plane

Figure 4 shows the results of experiment 2. Note that locations of red, yellow, blue,and indigo only diﬀered slightly among individuals along the arousal-sleepiness axis.
Similarly, red, orange, green, and blue only diﬀered slightly among individuals along
the pleasure-misery axis. Moreover, most of the colors were assigned to the positiveside of the pleasure-misery axis except for purple, which seems to be an unpleasantcolor. We also note that the warm colors were considered arousing, and the cold
colors were placed in less arousing areas of the space.

6 Discussion and Conclusions
According to experiment 2, individual diﬀerences in the psychological associationsof colors are small. This indicates that it is possible to present a hue supported bytactile sensory input if we control the arousal and pleasantness of the tactile stimuli.
In particular, the warm colors are likely to be consistent with arousing stimuli, andthe cold colors are likely to be presented by less arousing stimuli. Among the tactile
stimuli tested above, S and W may be eﬀective for pairing with the warm and cold
colors, respectively.
We also note that changing the pleasantness of stimuli is not appropriate for presenting them in conjunction with colors. This is because all rainbow colors except
for purple are associated with pleasant or neutral perceptions. Only purple has thepossibility of being presented with unpleasant stimuli, such as S or N in our study.
To summarize, before the current study, no attempts had been made to ﬁnd
associations between the hue of colors and vibrotactile or variable-friction stimuli.
We found that a frequency modulation approach, in which high-frequency tactile

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stimuli were matched with colors with short wave lengths, was not intuitive forusers. Instead, we considered aﬀective responses toward colors and tactile stimuli.
Consequently, we found that warm colors can be linked with rhythmical and highfrequency tactile stimuli that evoke arousing responses. Furthermore, cold colors canbe linked with slow and low-frequency stimuli that evoke less arousing responses.
Since most of the rainbow colors mapped onto positive or neutral regions along thepleasure-misery axis, pleasantness may not be eﬀectively used to classify the colors. Nonetheless, purple can be associated with unpleasant stimuli, namely strong
and ﬁne frictional stimuli such as S and N. Because the number of participants wassmall, we cannot conclusively propose associations between color and tactile stimuli;
however, this study highlighted that such associations may exist.
Acknowledgements This study was in part supported by JSPS Kakenhi (15H-05923) and SCOPE(142106003).

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