**1. Introduction**

Haptic stimulation yields diverse sensations such as pressure, softness and hardness, vibration, and roughness of surface (Katz, 1989). These sensations originate from the sensory process through mechanoreceptors on the skin, such as Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini corpuscles (Fig. 1.). The mechanoreceptors work interactively to build up haptics as an elaborate sensory system. Thus far, a number of studies have investigated the characteristics of the mechanoreceptors, yet the mechanisms have not been fully understood. Instead, these studies have exposed the complexity of the haptic sensory process.

Apart from the mechanoreceptors and the sensory system, cognitive scientists have investigated perceptual processing for haptic stimulation. They have revealed how haptic

Fig. 1. Schematic illustration of 3 levels of haptic information process.

Although we developed a simple haptic display (Fig. 2.) that is suitable for examining abstract feeling emerging from haptic stimulation, the purpose of these studies **was not** to develop a haptic device to enable users to experience abstract feelings. Instead, we aimed at understanding the human cognitive process in relation to the abstract feelings emerging from haptic stimulation and their impact on human behavior and experience, and also providing useful and basic insights to design a user-friendly haptic device that is able to present abstract

Abstract Feelings Emerging from Haptic Stimulation 99

Humans can perceive animacy even from inanimate visual objects. This feeling of the animacy of inanimate objects has been well investigated in the context of animacy perception (Blakemore et al., 2003; Gao et al., 2010; Gao & Scholl, 2011; Heider & Simmel, 1944; Scholl & Tremoulet, 2000). In animacy perception, given the mutually interactive motion of multiple visual objects, human observers sense intention or sociality in artificial visual objects (Fukuda & Ueda, 2010; Gao et al., 2009; Santos et al., 2008). Furthermore, recent studies have reported that a particular motion pattern of a single visual object could induce animacy perception (Tremoulet & Feldman, 2000), which implies that apparently higher cognitive appreciation of complex properties such as animacy may originate from low-level sensory processes. Along with these studies, cognitive neuroscientific studies using functional magnetic resonance imaging (fMRI) have shown that the neural activities in primary visual areas, as well as in higher brain areas that are related to the cognitive function (Santos et al., 2010), such as the mirror system (Rizzolatti, 2005) or the theory of mind (Gallese & Goldman, 1998), might be related to animacy perception (Morito et al., 2009). Thus, the emergence of animacy perception of inanimate objects may originate not only from the top-down cognitive processes of intention or sociality but also partially from the bottom-up processes of primitive sensations

As in the fisherman's case, haptic stimulation that induces feelings of animacy in daily life is composed of dynamic and complex patterns. However, given the possibility that primitive sensations might induce feelings of animacy in a bottom-up manner, one challenging question concerns what the lower limit of haptic stimulation is that induces feelings of animacy. To answer this question, Takahashi et al. (2011a) developed a haptic display device and investigated whether simple and cyclic haptic vibratory stimulation can induce feelings of animacy and pleasantness, and if so, what would determine the strength of these feelings.

In order to investigate the abstract feelings for haptic sensation, we developed a haptic display device that is suitable for presenting a soft haptic sensation (Takahashi et al., 2011a) (Fig. 2.). The device can present only vibratory pressure stimulation. However, since the pressure was determined by impressed voltage, and because the impressed voltage was programmable, the

The device was composed of an operator personal computer, an amplifier, and a stimulator. The amplifier was attached to a digital-to-analog converter connected to the operator PC. The stimulator comprised (a) an actuator, (b) a medium, (c) a chassis, and (d) a contact plate (Fig. 2B.). The actuator can be one that changes in size by impressed voltage. Any incompressible fluid may work as the medium. The chassis must be a rigid body, be filled with liquid, and be completely enclosed. We chose a piezoelectric vibrator for the actuator (diameter was 54.5 mm), water for the medium, an acrylic resin and polyurethane-tube (inner and outer

**2. Feelings of animacy for vibratory haptic stimulation**

such as vibration, softness, and warmth.

device could present arbitrary pressure changes.

**2.1 Haptic device**

feelings efficiently.

inputs are processed in the perceptual system for spatial and temporal perception, object and texture recognition, attention, and memory (Fig. 1.). Here again, haptic perception was revealed to be complex since the haptic perception is built on interaction with other cognitive functions such as action (e.g., active touch) (Gibson, 1962), and other sensory modalities (e.g., proprioceptive, vision and audition).

In addition to these sensory and perceptual systems, and although this aspect is often downplayed, we experience abstract feelings from haptic stimulation, such as feelings of animacy, pleasantness, presence, and intimacy (Fig. 1.). For example, a fisherman can sense the movement of an animate object on his rod when a fish is caught on the hook without seeing or hearing the fish. When we hold hands with a lover, we sense her or his presence through the hands and develop a feeling of pleasure. Hence, there is no doubt that haptic stimulation and these abstract feelings (i.e., feelings of animacy, pleasantness, or presence) are strongly related (Knapp & Hall, 1992; Morris, 1971; Richmond et al., 2007). Since the haptic system has no receptor that is directly associated with animacy or pleasantness, however, these abstract feelings would emerge from dynamic spatial-temporal patterns of haptic stimulation to the mechanoreceptors and from the perceptual process thereof.

In daily experience, the abstract feelings emerging from haptic stimulation seem not to be trivial. Rather, most haptic experience seems to involve these kinds of abstract feelings to some degree. In fact, haptic sensation is one of the essential channels of interpersonal communication (Richmond et al., 2007). When we communicate with others in daily life, physical contact involving haptic sensation is the most primitive communication channel, as may be widely observed in human infants and animals (Knapp & Hall, 1992; Richmond et al., 2007). Certainly, the purpose of haptic communication is not to inspect, for example, the stiffness or texture of another person's skin. The purpose of haptic communication would be to feel animacy or the presence of the other and to develop a feeling of pleasure.

The abstract feelings emerging from haptic stimulation are not limited to situations of interpersonal communication. As in the case of the fisherman, we sometimes feel strong and vivid animacy from haptic stimulation. Although the vivid animacy of haptic stimulation would originate from the sensory and perceptual system, we are not usually conscious of the perceptual aspects of haptic stimulation (e.g., stiffness, softness, and frequency). Rather, in most cases we cannot explicitly describe the perceptual aspects of haptic stimulation that lead to animacy. We directly feel the animacy of the object. In other words, such abstract feelings seem to be dominant in our consciousness.

Although the abstract feelings emerging from haptic stimulation can be widely seen and, hence, would be worthwhile to examine empirically, our knowledge thereof is very poor. What types of haptic stimulation yield which kinds of abstract feelings? How do such abstract feelings affect our experience, for example, in interpersonal communication? Do abstract feelings emerging from haptic stimulation interact with the process in the sensory modalities other than with regard to haptics? All these questions are still open.

In this chapter, we review 3 psychological studies recently conducted in our laboratory. All these studies were aimed at understanding how abstract feelings emerge from haptics sensation and, at the same time, how such feelings affect our behavior and experience. The first study investigated the characteristics of haptic stimulation associated with abstract feelings, especially focusing on the animacy of haptic stimulation. The second study investigated the effect of abstract feelings on experience and behavior in interpersonal haptic communication. The third study investigated haptic modulation on abstract feeling in the sensory modalities other than haptics.

2 Will-be-set-by-IN-TECH

inputs are processed in the perceptual system for spatial and temporal perception, object and texture recognition, attention, and memory (Fig. 1.). Here again, haptic perception was revealed to be complex since the haptic perception is built on interaction with other cognitive functions such as action (e.g., active touch) (Gibson, 1962), and other sensory modalities (e.g.,

In addition to these sensory and perceptual systems, and although this aspect is often downplayed, we experience abstract feelings from haptic stimulation, such as feelings of animacy, pleasantness, presence, and intimacy (Fig. 1.). For example, a fisherman can sense the movement of an animate object on his rod when a fish is caught on the hook without seeing or hearing the fish. When we hold hands with a lover, we sense her or his presence through the hands and develop a feeling of pleasure. Hence, there is no doubt that haptic stimulation and these abstract feelings (i.e., feelings of animacy, pleasantness, or presence) are strongly related (Knapp & Hall, 1992; Morris, 1971; Richmond et al., 2007). Since the haptic system has no receptor that is directly associated with animacy or pleasantness, however, these abstract feelings would emerge from dynamic spatial-temporal patterns of haptic stimulation to the

In daily experience, the abstract feelings emerging from haptic stimulation seem not to be trivial. Rather, most haptic experience seems to involve these kinds of abstract feelings to some degree. In fact, haptic sensation is one of the essential channels of interpersonal communication (Richmond et al., 2007). When we communicate with others in daily life, physical contact involving haptic sensation is the most primitive communication channel, as may be widely observed in human infants and animals (Knapp & Hall, 1992; Richmond et al., 2007). Certainly, the purpose of haptic communication is not to inspect, for example, the stiffness or texture of another person's skin. The purpose of haptic communication would be

The abstract feelings emerging from haptic stimulation are not limited to situations of interpersonal communication. As in the case of the fisherman, we sometimes feel strong and vivid animacy from haptic stimulation. Although the vivid animacy of haptic stimulation would originate from the sensory and perceptual system, we are not usually conscious of the perceptual aspects of haptic stimulation (e.g., stiffness, softness, and frequency). Rather, in most cases we cannot explicitly describe the perceptual aspects of haptic stimulation that lead to animacy. We directly feel the animacy of the object. In other words, such abstract feelings

Although the abstract feelings emerging from haptic stimulation can be widely seen and, hence, would be worthwhile to examine empirically, our knowledge thereof is very poor. What types of haptic stimulation yield which kinds of abstract feelings? How do such abstract feelings affect our experience, for example, in interpersonal communication? Do abstract feelings emerging from haptic stimulation interact with the process in the sensory modalities

In this chapter, we review 3 psychological studies recently conducted in our laboratory. All these studies were aimed at understanding how abstract feelings emerge from haptics sensation and, at the same time, how such feelings affect our behavior and experience. The first study investigated the characteristics of haptic stimulation associated with abstract feelings, especially focusing on the animacy of haptic stimulation. The second study investigated the effect of abstract feelings on experience and behavior in interpersonal haptic communication. The third study investigated haptic modulation on abstract feeling in the

to feel animacy or the presence of the other and to develop a feeling of pleasure.

other than with regard to haptics? All these questions are still open.

proprioceptive, vision and audition).

mechanoreceptors and from the perceptual process thereof.

seem to be dominant in our consciousness.

sensory modalities other than haptics.

Although we developed a simple haptic display (Fig. 2.) that is suitable for examining abstract feeling emerging from haptic stimulation, the purpose of these studies **was not** to develop a haptic device to enable users to experience abstract feelings. Instead, we aimed at understanding the human cognitive process in relation to the abstract feelings emerging from haptic stimulation and their impact on human behavior and experience, and also providing useful and basic insights to design a user-friendly haptic device that is able to present abstract feelings efficiently.

#### **2. Feelings of animacy for vibratory haptic stimulation**

Humans can perceive animacy even from inanimate visual objects. This feeling of the animacy of inanimate objects has been well investigated in the context of animacy perception (Blakemore et al., 2003; Gao et al., 2010; Gao & Scholl, 2011; Heider & Simmel, 1944; Scholl & Tremoulet, 2000). In animacy perception, given the mutually interactive motion of multiple visual objects, human observers sense intention or sociality in artificial visual objects (Fukuda & Ueda, 2010; Gao et al., 2009; Santos et al., 2008). Furthermore, recent studies have reported that a particular motion pattern of a single visual object could induce animacy perception (Tremoulet & Feldman, 2000), which implies that apparently higher cognitive appreciation of complex properties such as animacy may originate from low-level sensory processes. Along with these studies, cognitive neuroscientific studies using functional magnetic resonance imaging (fMRI) have shown that the neural activities in primary visual areas, as well as in higher brain areas that are related to the cognitive function (Santos et al., 2010), such as the mirror system (Rizzolatti, 2005) or the theory of mind (Gallese & Goldman, 1998), might be related to animacy perception (Morito et al., 2009). Thus, the emergence of animacy perception of inanimate objects may originate not only from the top-down cognitive processes of intention or sociality but also partially from the bottom-up processes of primitive sensations such as vibration, softness, and warmth.

As in the fisherman's case, haptic stimulation that induces feelings of animacy in daily life is composed of dynamic and complex patterns. However, given the possibility that primitive sensations might induce feelings of animacy in a bottom-up manner, one challenging question concerns what the lower limit of haptic stimulation is that induces feelings of animacy. To answer this question, Takahashi et al. (2011a) developed a haptic display device and investigated whether simple and cyclic haptic vibratory stimulation can induce feelings of animacy and pleasantness, and if so, what would determine the strength of these feelings.

#### **2.1 Haptic device**

In order to investigate the abstract feelings for haptic sensation, we developed a haptic display device that is suitable for presenting a soft haptic sensation (Takahashi et al., 2011a) (Fig. 2.). The device can present only vibratory pressure stimulation. However, since the pressure was determined by impressed voltage, and because the impressed voltage was programmable, the device could present arbitrary pressure changes.

The device was composed of an operator personal computer, an amplifier, and a stimulator. The amplifier was attached to a digital-to-analog converter connected to the operator PC. The stimulator comprised (a) an actuator, (b) a medium, (c) a chassis, and (d) a contact plate (Fig. 2B.). The actuator can be one that changes in size by impressed voltage. Any incompressible fluid may work as the medium. The chassis must be a rigid body, be filled with liquid, and be completely enclosed. We chose a piezoelectric vibrator for the actuator (diameter was 54.5 mm), water for the medium, an acrylic resin and polyurethane-tube (inner and outer

**2.2 Animacy and pleasantness emerges from haptic sensation**

Finger

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The figures were modified from Takahashi et al. (2011a).

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pleasantness of the haptic stimuli on a 7-point scale.

and pleasantness.

25, and 50 Hz.

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Using the haptic display device, Takahashi et al. (2011a) conducted a psychological experiment to investigate the effects of the frequency of vibratory stimulation on felt animacy

Abstract Feelings Emerging from Haptic Stimulation 101

Six volunteers participated in the experiment. In each trial, haptic stimuli were presented for 3 s after a 1 s blank period, which was followed by an evaluation display on a touch panel screen. The participants were instructed to evaluate the strength of felt animacy and the

They conducted two conditions according to the body parts where the haptic stimuli were presented—finger condition and wrist condition. In the finger condition, the haptic stimuli were presented to the pad of the right index finger. The participants were instructed to softly touch the contact plate by their right index finger. In the wrist condition, the haptic stimuli were presented to the inner side of the right wrist. The component, including the contact plate, was fixed to the right wrist using a band. A haptic stimulus was sinusoidal vibratory stimulation with variable frequency. The frequency was randomly chosen from 0.5, 1, 2, 5, 10,

Wrist

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Fig. 3. Mean scores of feelings of animacy (top) and pleasantness (bottom) as a function of stimulus frequency and sensed body part. Error bars indicate the standard errors of means.

Fig. 3. shows the felt animacy and pleasantness as a function of the stimulus frequency and body parts. A statistical test (two-way repeated measures ANOVA) revealed that the stimulus frequency significantly affects felt animacy (F(6,30) = 13.1, p < .01), whereas the body parts did not significantly affect felt animacy (F(1,5) = 2.98, p = .15). Thus, the effects of the

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Fig. 2. Haptic device. **A**. Working principle of the device. **B**. Appearance and structure of the haptic stimulator used in the experiment. The figures were modified from Takahashi et al. (2011a).

diameters were 4 mm and 6 mm, respectively) for the chassis, and silicon rubber for the contact plate (the diameter was 16 mm, and the size of the box, including contact plate, was 30 mm × 30 mm × 12 mm).

The working principle of the stimulator was as follows (Fig. 2.). The waveform of pressure change was defined using the operator PC and sent to the stimulator through the DA converter and the amplifier. The input terminal of the actuator of the stimulator was attached to the output terminal of the amplifier. After a start signal was sent to the DA converter, actual voltage was conveyed to the stimulator through the amplifier, which induced the vibration of the actuator. The actuator and contact plate parts were connected with a polyurethane-tube, which was also water-filled. The vibration of the actuator was conveyed to the contact plate through the medium, leading to the production of haptic stimulation at the contact plate. A significant feature of the device we developed is as follows:

#### **1. Flexibility of the material of the contact plate**

Although we chose silicon rubber for the contact plate because we wanted to create a limp sensation, one can choose a hard or textured material (e.g., harsh, scratchy) as required.

#### **2. Flexibility of the placement of the contact plate**

In our device, the actuator and contact plate were not solidly attached but were connected by a flexible material (i.e., the polyurethane-tube), and the component, including the contact plate, was small and lightweight. The mobility of the components enables the stimulation of any part of the body surface, and hence enables one to compare the haptic stimulation among the different body parts using identical stimuli.

#### **3. Dynamic range of pressure displacement**

The device can present a wide range of pressure displacement. The ratio of the size of the actuator and contact plate determines the amplitude of the displacement of the contact plate; a smaller contact plate and a larger actuator lead to a larger amplitude. The larger amplitudes of the displacement lead to a larger pressure change in the haptic sensation.

#### **4. Programmable pressure change**

Since the pressure change is defined as the change of impressed voltage and because the impressed voltage is fully programmable, the device can present any temporal profile of pressure change.

4 Will-be-set-by-IN-TECH

Fig. 2. Haptic device. **A**. Working principle of the device. **B**. Appearance and structure of the haptic stimulator used in the experiment. The figures were modified from Takahashi et al.

diameters were 4 mm and 6 mm, respectively) for the chassis, and silicon rubber for the contact plate (the diameter was 16 mm, and the size of the box, including contact plate, was

The working principle of the stimulator was as follows (Fig. 2.). The waveform of pressure change was defined using the operator PC and sent to the stimulator through the DA converter and the amplifier. The input terminal of the actuator of the stimulator was attached to the output terminal of the amplifier. After a start signal was sent to the DA converter, actual voltage was conveyed to the stimulator through the amplifier, which induced the vibration of the actuator. The actuator and contact plate parts were connected with a polyurethane-tube, which was also water-filled. The vibration of the actuator was conveyed to the contact plate through the medium, leading to the production of haptic stimulation at the contact plate.

Although we chose silicon rubber for the contact plate because we wanted to create a limp sensation, one can choose a hard or textured material (e.g., harsh, scratchy) as required.

In our device, the actuator and contact plate were not solidly attached but were connected by a flexible material (i.e., the polyurethane-tube), and the component, including the contact plate, was small and lightweight. The mobility of the components enables the stimulation of any part of the body surface, and hence enables one to compare the haptic

The device can present a wide range of pressure displacement. The ratio of the size of the actuator and contact plate determines the amplitude of the displacement of the contact plate; a smaller contact plate and a larger actuator lead to a larger amplitude. The larger amplitudes of the displacement lead to a larger pressure change in the haptic sensation.

Since the pressure change is defined as the change of impressed voltage and because the impressed voltage is fully programmable, the device can present any temporal profile of

B

Contact plate

Polyurethane-tube

Acrylic resin

Actuator

Amplier

Medium (water) (inside the chassis)

Actuator

30 mm × 30 mm × 12 mm).

Superimposed voltage (AC)

A significant feature of the device we developed is as follows:

stimulation among the different body parts using identical stimuli.

**1. Flexibility of the material of the contact plate**

**2. Flexibility of the placement of the contact plate**

**3. Dynamic range of pressure displacement**

**4. Programmable pressure change**

pressure change.

Medium (water)

A

(2011a).

Contact plate

#### **2.2 Animacy and pleasantness emerges from haptic sensation**

Using the haptic display device, Takahashi et al. (2011a) conducted a psychological experiment to investigate the effects of the frequency of vibratory stimulation on felt animacy and pleasantness.

Six volunteers participated in the experiment. In each trial, haptic stimuli were presented for 3 s after a 1 s blank period, which was followed by an evaluation display on a touch panel screen. The participants were instructed to evaluate the strength of felt animacy and the pleasantness of the haptic stimuli on a 7-point scale.

They conducted two conditions according to the body parts where the haptic stimuli were presented—finger condition and wrist condition. In the finger condition, the haptic stimuli were presented to the pad of the right index finger. The participants were instructed to softly touch the contact plate by their right index finger. In the wrist condition, the haptic stimuli were presented to the inner side of the right wrist. The component, including the contact plate, was fixed to the right wrist using a band. A haptic stimulus was sinusoidal vibratory stimulation with variable frequency. The frequency was randomly chosen from 0.5, 1, 2, 5, 10, 25, and 50 Hz.

Fig. 3. Mean scores of feelings of animacy (top) and pleasantness (bottom) as a function of stimulus frequency and sensed body part. Error bars indicate the standard errors of means. The figures were modified from Takahashi et al. (2011a).

Fig. 3. shows the felt animacy and pleasantness as a function of the stimulus frequency and body parts. A statistical test (two-way repeated measures ANOVA) revealed that the stimulus frequency significantly affects felt animacy (F(6,30) = 13.1, p < .01), whereas the body parts did not significantly affect felt animacy (F(1,5) = 2.98, p = .15). Thus, the effects of the

Finger vs. Wrist

Abstract Feelings Emerging from Haptic Stimulation 103

Pleasantness

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**2.3 Summary**

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Animacy

Fig. 4. **Top:** Scatter plot of finger and wrist sensations of animacy and pleasantness. **Bottom:** Scatter plot of feeling of animacy and pleasantness in the finger and wrist conditions. In both panels, each point indicates individual participants. The dark gray curve indicates the Lowess (locally weighted scatter plot smoothing) regression curve (degree of smoothing = 0.75, degree of polynomials = 2). The light gray area indicates the standard error of the

the feeling of animacy for haptic stimulation was susceptible to the pressure as well as to the

Takahashi et al. (2011a) showed that the stimulus frequency strongly influenced the feeling of animacy vibratory stimulation, with the lower frequency (1–2 Hz) inducing stronger feelings of animacy than the higher frequency (25–50 Hz). The frequency dependence was consistent among different participants. The animacy for haptic stimulation would partially

How do human observers come to feel animacy from the simple vibratory stimulation of an inanimate object? Two accounts, which are not mutually exclusive, would be possible. First, humans may intrinsically feel animacy from low-frequency haptic stimulation. Second,

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Lowess regression. The figures were modified from Takahashi et al. (2011a).

but intrinsically originate from temporal patterns of haptic stimulation.

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stimulus frequency on animacy perception were qualitatively similar between finger and wrist stimulation, although they were quantitatively different. At first glance, the low-frequency stimulation (from 0.5 to 5 Hz) appeared to induce stronger feelings of animacy than the high-frequency stimulation (from 10 to 50 Hz) in both the finger and wrist conditions. The peak rating of animacy was around 1 to 2 Hz in both conditions, but the peak looked more prominent in the finger condition than in the wrist condition. The felt animacy in the finger condition was significantly, or marginally significantly, stronger at 1 Hz (F(1,5) = 7.08, p < .05) and 2 Hz (F(1,5) = 4.27, p < .10) and significantly weaker at 25 Hz (F(1,5) = 7.79, p < .05) than that in the wrist condition. These results imply that the finger was more sensitive to the frequency difference of haptic stimulation than the wrist in feeling animacy. Note that the patterns of frequency dependence were consistent among different participants.

With regard to the feeling of pleasantness, neither the stimulus frequency nor the body parts affected the pleasantness of the haptic stimuli, although a visual inspection of the data would suggest that the high-frequency stimulation induced stronger feelings of pleasantness than the low-frequency stimulation.

Fig. 4. shows the scatter plot of the finger condition vs. wrist condition (top) and that of the animacy rating vs. pleasantness rating (bottom). Each data point indicates the data from individual participants. There were strong correlations between the finger and wrist sensations in both the animacy (r = 0.83, t(40) = 9.40, p < .01) and pleasantness (r = 0.71, t(40) = 6.34, p < .01) evaluations. These results supported the theory that feelings of pleasantness and animacy were qualitatively similar between the finger and wrist stimulation.

On the other hand, the feelings of animacy and pleasantness did not correlate in both finger conditions (r = -0.13, t(40) = 0.80, p = .43) and wrist (r = 0.04, t(40) = 0.25, p = .80). However, the pattern of results would not support the theory that the two evaluations were independent. A visual inspection, as well as the Lowess regression of the scatter plot, exhibited an inverse V shape, especially in the finger condition. These results suggest that the moderate strength of animacy is associated with higher pleasantness.

Thus, the experimental study in Takahashi et al. (2011a) suggested the following:


In another series of studies, Takahashi, Mitsuhashi, Norieda, Murata & Watanabe (2010) showed that the patterns of frequency dependence were partially different between finger and wrist stimulation. Takahashi, Mitsuhashi, Norieda, Murata & Watanabe (2010) showed a V-shaped curve for animacy evaluation as a function of the stimulus frequency in the wrist stimulation: the felt animacy was stronger for 1–2 Hz stimulus frequency, weak for 5–10 Hz frequency, and stronger again for 25 Hz frequency. The main difference between Takahashi, Mitsuhashi, Norieda, Murata & Watanabe (2010) and Takahashi et al. (2011a) was the pressure of water inside the haptic stimulator (Fig. 2A.). In Takahashi et al. (2011a), the chassis was filled with water to the maximum, while this was not the case in Takahashi, Mitsuhashi, Norieda, Murata & Watanabe (2010). Although further examinations are warranted, this difference in pressure might lead to the different patterns of frequency dependence. Perhaps 6 Will-be-set-by-IN-TECH

stimulus frequency on animacy perception were qualitatively similar between finger and wrist stimulation, although they were quantitatively different. At first glance, the low-frequency stimulation (from 0.5 to 5 Hz) appeared to induce stronger feelings of animacy than the high-frequency stimulation (from 10 to 50 Hz) in both the finger and wrist conditions. The peak rating of animacy was around 1 to 2 Hz in both conditions, but the peak looked more prominent in the finger condition than in the wrist condition. The felt animacy in the finger condition was significantly, or marginally significantly, stronger at 1 Hz (F(1,5) = 7.08, p < .05) and 2 Hz (F(1,5) = 4.27, p < .10) and significantly weaker at 25 Hz (F(1,5) = 7.79, p < .05) than that in the wrist condition. These results imply that the finger was more sensitive to the frequency difference of haptic stimulation than the wrist in feeling animacy. Note that the

With regard to the feeling of pleasantness, neither the stimulus frequency nor the body parts affected the pleasantness of the haptic stimuli, although a visual inspection of the data would suggest that the high-frequency stimulation induced stronger feelings of pleasantness than

Fig. 4. shows the scatter plot of the finger condition vs. wrist condition (top) and that of the animacy rating vs. pleasantness rating (bottom). Each data point indicates the data from individual participants. There were strong correlations between the finger and wrist sensations in both the animacy (r = 0.83, t(40) = 9.40, p < .01) and pleasantness (r = 0.71, t(40) = 6.34, p < .01) evaluations. These results supported the theory that feelings of pleasantness

On the other hand, the feelings of animacy and pleasantness did not correlate in both finger conditions (r = -0.13, t(40) = 0.80, p = .43) and wrist (r = 0.04, t(40) = 0.25, p = .80). However, the pattern of results would not support the theory that the two evaluations were independent. A visual inspection, as well as the Lowess regression of the scatter plot, exhibited an inverse V shape, especially in the finger condition. These results suggest that the moderate strength

1. The stimulus frequency systematically affects felt animacy. The lower stimulus frequency around 1–2 Hz induced the strongest feeling of animacy compared with the higher

2. The effect of the stimulus frequency on animacy and pleasantness were comparable

3. The moderate level of animacy of haptic sensation was associated with higher

In another series of studies, Takahashi, Mitsuhashi, Norieda, Murata & Watanabe (2010) showed that the patterns of frequency dependence were partially different between finger and wrist stimulation. Takahashi, Mitsuhashi, Norieda, Murata & Watanabe (2010) showed a V-shaped curve for animacy evaluation as a function of the stimulus frequency in the wrist stimulation: the felt animacy was stronger for 1–2 Hz stimulus frequency, weak for 5–10 Hz frequency, and stronger again for 25 Hz frequency. The main difference between Takahashi, Mitsuhashi, Norieda, Murata & Watanabe (2010) and Takahashi et al. (2011a) was the pressure of water inside the haptic stimulator (Fig. 2A.). In Takahashi et al. (2011a), the chassis was filled with water to the maximum, while this was not the case in Takahashi, Mitsuhashi, Norieda, Murata & Watanabe (2010). Although further examinations are warranted, this difference in pressure might lead to the different patterns of frequency dependence. Perhaps

patterns of frequency dependence were consistent among different participants.

and animacy were qualitatively similar between the finger and wrist stimulation.

Thus, the experimental study in Takahashi et al. (2011a) suggested the following:

the low-frequency stimulation.

stimulus frequency.

pleasantness.

of animacy is associated with higher pleasantness.

between different body parts—finger and wrist.

Fig. 4. **Top:** Scatter plot of finger and wrist sensations of animacy and pleasantness. **Bottom:** Scatter plot of feeling of animacy and pleasantness in the finger and wrist conditions. In both panels, each point indicates individual participants. The dark gray curve indicates the Lowess (locally weighted scatter plot smoothing) regression curve (degree of smoothing = 0.75, degree of polynomials = 2). The light gray area indicates the standard error of the Lowess regression. The figures were modified from Takahashi et al. (2011a).

the feeling of animacy for haptic stimulation was susceptible to the pressure as well as to the stimulus frequency.

#### **2.3 Summary**

Takahashi et al. (2011a) showed that the stimulus frequency strongly influenced the feeling of animacy vibratory stimulation, with the lower frequency (1–2 Hz) inducing stronger feelings of animacy than the higher frequency (25–50 Hz). The frequency dependence was consistent among different participants. The animacy for haptic stimulation would partially but intrinsically originate from temporal patterns of haptic stimulation.

How do human observers come to feel animacy from the simple vibratory stimulation of an inanimate object? Two accounts, which are not mutually exclusive, would be possible. First, humans may intrinsically feel animacy from low-frequency haptic stimulation. Second,

so, how. To examine this question, Takahashi et al. (2011b) conducted an experimental study investigating the effects of haptic communication on the quality of participants' experiences,

Abstract Feelings Emerging from Haptic Stimulation 105

In a series of psychological surveys, Takahashi, Mitsuhashi, Norieda, Sendoda, Murata & Watanabe (2010) and Takahashi et al. (2011c) investigated how people experience

Takahashi, Mitsuhashi, Norieda, Sendoda, Murata & Watanabe (2010) presented observers with pictures depicting two persons performing either positive (e.g., hugging, shaking hands) or negative (e.g., grappling) haptic communication. The observers were asked to make a subjective evaluation of the depicted communication concerning its desirability, frequency of experience, and impressiveness. All these evaluations had a positive correlation (R > 0.59, p < .001), suggesting that the haptic communication that was more frequently experienced and that made a stronger impression tended to be evaluated as more desirable. Although these correlations cannot reveal a causal relationship, one possibility may be related to the widely known psychological phenomenon of "mere exposure effect" (Zajonc, 1968), and the other is

The observers were also asked to identify the person who was imagined to be involved in the communication depicted in the picture. The persons associated with the desirable communication were a spouse, a child, a mother, a son or a daughter, a father, and a grandparent. Thus, haptic communications that recall family members are more desirable. Takahashi et al. (2011c) asked their observers to evaluate two types of haptic communication, tapping and padding, by using adjectives, and examined what factors reside in haptic communication. Table 1 shows the results of the factorial analysis. The results suggested that two factors represent interpersonal haptic communication. One factor affected the evaluation of lightsome, pleasant, comfortable, and warm feelings, and the other factor affected the evaluation of strong, rough, and active feelings. Thus, the first factor was associated with the abstract feelings of haptic communication, while the second factor was relevant to the characteristics of motion. These structures were common between the two types of haptic communications. Furthermore, the first factor strongly affected the desirability of the haptic communications when compared with the second factor, suggesting that the abstract feeling emerging from the communication, not the motion itself, strongly influenced the desirability

Tapping Patting

Adjective Factor 1 Factor 2 Factor 1 Factor 2 Lightsome 0.87 0.01 0.80 0.07 Pleasant 0.86 0.05 0.83 0.09 Comfortable 0.86 -0.07 0.70 -0.26 Warm 0.83 -0.13 0.79 -0.25 Soft 0.46 -0.51 0.59 -0.44 Strong -0.06 0.90 0.19 0.67 Rough -0.22 0.80 -0.18 0.73 Active 0.47 0.61 0.69 0.35 Table 1. First and second component score of each adjective for describing two types (tapping and patting) of haptic interpersonal communication. Data were from Takahashi et al. (2011c).

as well as on their impression of the person with whom they communicated.

**3.1 Psychological survey on interpersonal haptic communication**

interpersonal haptic communication in their daily activity.

related to "directional forgetting" (Golding & Macleod, 1998).

of the haptic communication.

animacy perception may emerge as a result of the frequent experience of touching animate objects such as animals. While the stimulation from these animate objects would involve more complex patterns than those noted in Takahashi et al. (2011a), the frequency of stimulation might be the major factor that induces the feeling of animacy. Therefore, it would be intriguing to survey the frequencies of haptic stimulation from these animate objects in the real world and to compare them to the results of the experimental study in Takahashi et al. (2011a).
