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## Über dieses Buch

The two-volume set LNCS 10893 and 10894 constitutes the refereed proceedings of the 11th International Conference EuroHaptics 2018, held in Pisa, Italy, in June 2018.
The 95 papers (40 oral presentations and554 poster presentations) presented were carefully reviewed and selected from 138 submissions. These proceedings reflect the multidisciplinary nature of EuroHaptics and cover all aspects of haptics, including neuroscience, psychophysics, perception, engineering, computing, interaction, virtual reality and arts.

## Inhaltsverzeichnis

### Effect of Dual Tasking on Vibrotactile Feedback Guided Reaching – A Pilot Study

Valay A. Shah, Nicoletta Risi, Giulia Ballardini, Leigh Ann Mrotek, Maura Casadio, Robert A. Scheidt

### Is Cross-Modal Matching Necessary? A Bayesian Analysis of Individual Reference Cues

The number of research activities on multi-modal feedback cues and their potential to enhance the performance of human operators during teleoperation tasks is growing. Yet, it is still unclear how stimulus intensities of cues in different modalities should be matched when investigating the effects of feedback modality on task performance. Previous work has shown a high within- and between-subject variability of multi-modal intensity adjustments. The source of this variability is not yet clear. In this study, we investigate the individual perception of the cues by setting individual reference intensities for cross-modal matching. In addition to traditional frequentist models, Bayesian models are used for data analysis. The results suggest that haptic as well as auditory cue intensity adjustments are not influenced by modality when combining it with a visual reference. Thus, it seems sufficient to let subjects adjust the intensity for haptic and auditory cues individually prior to investigating the effectiveness of haptic-auditory cues. In contrast, with a 99% probability, visual cues are adjusted to lower intensities by subjects if combined with haptic or auditory cues, which points to the importance of individual cross-modal matching when investigating the effects of visual-haptic or visual-auditory feedback cues.

Tobias Michael Benz, Verena Nitsch

### Differences in Beta Oscillation of the Middle Frontal Cortex with or Without Tactile Stimulation in Active Touch Task

Tactile sensation is a valuable feedback for shaping human perception, for instance when using a mobile device or a touch screen. Most studies have used subjective assessments and focused on passive touch. This paper investigates the role of tactile stimulation objectively and quantitatively in active touch task just like real human computer interaction on a tablet device. In this study, participants performed an active touch task to touch virtual guitar lines on a tactile display device. We investigated the difference of neural activities with or without tactile stimulation and found a difference in beta oscillation in the middle frontal area at the late period (from 650 ms to 1000 ms) of the active touch task period. It is assumed that the tactile stimulation felt by the participants’ fingertip further induces cognitive processing than the absence of tactile stimulation case. This study provides objective and quantitative evidence that tactile stimulation is able to affect the cognitive processing and top-down control.

Wanjoo Park, Mohamad Eid

### Optimization of the Hanger Reflex (I): Examining the Correlation Between Skin Deformation and Illusion Intensity

One method of presenting a pseudo-force sensation is based on a phenomenon called the hanger reflex, in which placement of a wire hanger on the head induces involuntary head rotation. The main cause of this phenomenon is considered to be a pseudo-force sensation generated by lateral displacement of the skin via skin compression. However, the relationship between the physical amount of skin displacement and the strength of the illusion has not been thoroughly investigated, impeding optimization of a device that elicits the hanger reflex. As a first step towards developing an optimized hanger reflex device, we describe a method for measuring the amount of skin deformation during the occurrence of the hanger reflex, by using optically observable artificial skin. We report the correlation between deformation of the artificial skin and head rotation angle, which had previously been reported only qualitatively.

Masahiro Miyakami, Yuki Kon, Takuto Nakamura, Hiroyuki Kajimoto

### A Case of Perceptual Completion in Spatio-Temporal Tactile Space

We reproduced a perceptual phenomenon where a tactile stimulus moving on the fingertip jumps instantly over a gap but is felt as if the space of the gap was perceptually obliterated. This phenomenon was recently demonstrated on the forearm using brushes. On the fingertip, we elicited this effect using virtual edges and measured psychometric response curves obtained by varying the time taken by the moving edge to traverse the gap between the first and the third portion of the stimulus. Most people failed to detect 2 mm gaps when the traversal time fell below 0.2 s. The gaps were consistently detected when they were traversed at same the speed as that of the moving edge in the first and third portion of the stimulus. We discuss the implications of these findings.

Seitaro Kaneko, Hiroyuki Kajimoto, Vincent Hayward

### How Visual Images and Tactile Durations Affect the Emotional Ratings of the Cutaneous-Rabbit Illusion

We studied affective tactile stimulation utilizing cutaneous rabbit illusion associated with images of saltatorial animals. The emotional ratings were clearly affected by the pleasantness of the animal displayed on the screen. The modulation of the tactile stimulation itself (short or long) was affected by how many times an animal appears on the screen. Our study suggests that fewer images resulted in higher emotional ratings affecting, therefore, shorter and longer durations differently based on the nature of the visual stimulus. This study is the first step in a long investigation to understand the visual-tactile emotional association for better implementation in the future.

Mounia Ziat, Kimberly Snell, Chatrine Johannessen, Roope Raisamo

### Simon Effect for the Design of Tactile Stimulation

Tactile stimulation appears to be useful in a noisy or demanding environment to alert or notify the user as it provides a direct and private communication channel. In such cases, the user has to respond fast and accurately to the stimulation. This requires an optimal detection and response to the signal. The current study focused on the layout of tactile stimulation interfaces to be used for alert or notification with regard to the user’s position in space. We investigated the well-known Simon Effect in a tactile modality. The Simon Effect refers to a cognitive interference due to the spatial incongruence induced by a signal when it originates from the side opposite to the user’s response. In addition, we studied the influence of the amplitude of the signal and explored the effect of the location and amplitude of the previous signal. Results showed that the Simon Effect was observed with Linear Resonant Actuators, over user fingertips and user’s response delivered on push button pedals. Besides, the findings show that participants responded faster when two consecutives signals were congruent and with equal intensity. These results are discussed to provide guidelines for designing tactile stimulation systems for alert or notification.

Alix Pérusseau-Lambert, Margarita Anastassova, Mehdi Boukallel, Mohamed Chetouani, Ouriel Grynszpan

### Parameters that Affect Subjective Hardness in the Acceleration Response of a Stylus when Hitting an Object

We can hit an object with a stylus held in our hand to judge the hardness of the object. In order to realize this motion with a teleoperation system, it is necessary to clarify the factors that affect subjective hardness when hitting an object with a stylus. Therefore, we conducted a perceptual experiment to compare subjective hardness and a collision experiment to measure the acceleration response when hitting a block with a stylus. We confirmed that subjective hardness when hitting an object with low stiffness is related to Young’s modulus, which largely agrees with intuitive understanding. In contrast, we also confirmed that the subjective hardness when hitting an object with high stiffness varied depending on the material of the stylus and in some case objects with high stiffness may be perceived softer. This was caused by the double-strike phenomenon of the stylus, and we found that the subjective hardness changed according to the strength of the stimulation due to the double-strike phenomenon. Consequently, we found that the double striking phenomenon appearing in the acceleration response of the stylus can be one a measure for assessing subjective hardness.

Yasuyuki Saito, Kotaro Tadano

### Correlation Between Electrovibration Perception Magnitude and the Normal Force Applied by Finger

Electrovibration has been used to render the surface texture on tactile devices. To understand how the rendering performance is related to the normal force applied to the surface of the device by a finger, we investigated the influence of the applied normal force on electrovibration perception magnitude. We conducted a magnitude estimation experiment to observe how the electrovibration perception relates to the applied normal force ranging from 0.5 to 5 N. We measured the frictional force on a finger together with the normal force and calculated the friction induced by the electrostatic force. We found that the electrovibration perception magnitude increased with the increased applied normal force. Similarly, the friction induced by the electrostatic force increased with the applied normal force. This study demonstrates that the applied normal force has a large influence on the electrovibration perception, which needs to be considered in virtual texture rendering on electrovibration-based tactile devices.

Xingwei Guo, Yuru Zhang, Dangxiao Wang, Lei Lu, Jian Jiao, Weiliang Xu

### Haptic Texture Perception on 3D-Printed Surfaces Transcribed from Visual Natural Textures

Humans have a sophisticated ability to discriminate surface textures by touch, which is valuable for discriminating materials. Conventional studies have investigated this ability by using stimuli with simple (lower-order) statistical structures. Nevertheless, the structure of natural textures can be much more complex, and the human brain can encode complex (higher-order) spatial structures at least when they are processed by the visual system. To see how much the tactile system can encode complex surface patterns, we 3D-printed textured surfaces based on visual images of natural scenes including leaves and stones and conducted a haptic texture discrimination experiment. The mean surface carving depths were equated among the patterns. The participants touched the patterns in three modes: passive scan, static touch, and vibration only. The results showed that the “photo” patterns, which were visually very different from one another, were nearly indiscriminable by touch regardless of the touching mode. This suggests that though human touch may be good at discriminating differences in simple spatial structures such as statistics about the amplitude spectrum, it is relatively insensitive to more complex spatial structures, possibly due to spatial and temporal summation of local signals. Although further investigation is necessary to fully understand spatial statistics relevant to tactile texture perception, directly comparing touch with vision by using the 3D printing technology is a promising research strategy.

Scinob Kuroki, Masataka Sawayama, Shin’ya Nishida

### Identification and Evaluation of Perceptual Attributes for Periodic Whole-Body and Hand-Arm Vibration

When a systematic tactile design of a product is to be conducted, it is necessary to understand important perceptual properties of vibration from a user perspective. In everyday life humans are exposed to whole-body and hand-arm vibration, e.g. when driving a vehicle. Vibration of the steering wheel and seat is transmitted to the driver and conveys information about the condition of the road and vehicle. Depending on the spectral and temporal properties of the vibration signal certain attributes are elicited in the driver, e.g., “bumpy”. Such verbaliseable attributes describe the vibration from a perceptual perspective. In this study periodic whole-body and hand-arm vibration were presented to test subjects. The most common tactile attributes were collected using a free interview. Afterwards, these attributes were rated for their suitability to characterize the signal patterns. The results show a systematic relationship between physical parameters (level, carrier frequency and modulation frequency) and this suitability.

Robert Rosenkranz, Sebastian Gruschwitz, Martin Wilberg, M. Ercan Altinsoy, Sebastian Merchel

### Influence of Shape Elements on Performance During Haptic Rotation

In this work, we investigate how local shape elements of a grasped object affect performance of haptic rotation. Blindfolded participants were asked to grasp a rotary knob using thumb and index finger and to rotate it 90$$^\circ$$∘ counterclockwise around its own axis. The knobs exhibited a suitably distributed “grasp conform” combination of local shape elements (edged, flat or round). We tested all possible scenarios where both fingers had to grasp one of the three shape elements, resulting in a total of nine experimental conditions. Based on the rotation angle, determined with a novel apparatus named Twister, we evaluated the variable and signed errors. The results imply that a round rotary knob is the hardest to rotate by a correct goal angle, while other local shape elements can benefit the performance. Independent of the experimental condition, we found a bias towards rotating too far.

Kathrin Krieger, Alexandra Moringen, Astrid M. L. Kappers, Helge Ritter

### Effects of Chai3D Texture Rendering Parameters on Texture Perception

Touching objects in a virtual environment is a challenge that has yet to be addressed convincingly, in part because haptic technology and, in particular, low-cost haptic technology have strong limitations. This work aimed at assessing the impact of Chai3D texture rendering parameters on texture perception. We used Multidimensional Scaling techniques to build psychological scales for the texture level, stiffness, dynamic friction and several texture patterns. Two perceptual dimensions were in general necessary to fully account for the one-dimensional parameter change. The scales for the texture level, dynamic friction and texture pattern parameters were markedly larger than the stiffness scale, indicating the potential of these parameters to generate well differentiated textures.

Nicolo Balzarotti, Gabriel Baud-Bovy

### Effect of Control Movement Scale on Visual Haptic Interactions

Although the human hand is a complex system which can perform multiple actions, when the kinaesthetic actions are scaled in a system, the applications are limitless. In this paper, we examine the effect of control movement scale on user’s kinaesthetic actions. We use the Fitts’ Law for quantifying the user’s performance on different scales and to verify if higher control movement scale, in general, can be better than natural movements in tasks which require extended accuracy. The experiment consists of a Wacom™ tablet as an input device connected to a system. The tablet provides means for scaling the kinaesthetic input movement of a user. The experiment is a modified version of the classical multi-directional tapping task. It was performed on 16 healthy participants with ages between 20 to 48 years. The Fitts’ regressions were visualised and the Z-scores were computed. It was found that the performance of the participants increases with the scale and has an optimum scale at 1:3.3 before reducing rapidly. Future works include experiments involving 3D models and other haptic input devices.

Joseph H. R. Isaac, Arun Krishnadas, Natesan Damodaran, Manivannan Muniyandi

### Tactile Apparent Motion Through Human-Human Physical Touch

We investigate the effects of vibrotactile feedback from a hand of a partner as a medium of vibration propagation. By controlling the vibrotactile feedback provided on wrists, a tactile apparent motion can be induced between hands of a pair holding each other. Two experiments were conducted to demonstrate the tactile apparent motion. In the first experiment, we measured intensity of the vibration propagated from a bracelet device on the wrist to the hand. The result shows that the vibration on one hand is perceivable by the other person. In the second experiment, we measured the range of stimulus onset asynchrony (SOA) that induces a continuous motion between the hands under a constant duration of vibration (d). The psychophysical experiment shows that the tactile apparent motion is observed when (d, SOA) is around either (120, 80) or (240, 120) milliseconds. The paper discusses the present results in a context of augmenting awareness of touch communication describing our future direction of the research.

Taku Hachisu, Kenji Suzuki

### Preliminary Stiffness Perception Assessment for a Tele-palpation Haptic Interface

Palpation of patients is a common type of examination that is carried out by physicians for the early diagnosis of abnormalities in abdomens. In the ReMeDi project, a system for tele-palpation is developed. The system includes a diagnostician haptic interface which renders the abdomen of the remote patient. For the design of such a haptic interface, we investigate how the stiffness of a tissue layer is perceived by a human when mediated by a high-performance haptic interface acting in a simulated teleoperation loop. In our setup, the participants interacted with a haptic interface that displayed on their hands a force proportional to the stiffness of two layers that were compressed. The participants had to discriminate whether they were pushing on one or two layers of tissue. The stiffness of the first layer ($$k_1$$k1) was used as a baseline, whereas the stiffness of the second layer ($$k_2$$k2) varied. We investigated the just noticeable difference (JND) in the tissues stiffness that the participants could perceive. The stiffness JND was investigated by varying the thickness and the stiffness of the first layer. Moreover, we simulated the teleoperation loop by including a delay and damping in the interaction of the user with the virtual tissues. The preliminary results show that the estimated JND is higher with respect to direct interaction with real objects. Our study is in line with the finding that delay is detrimental to stiffness detection. Moreover, we found that higher baseline stiffness, as well as a thicker first tissue layer, help the stiffness discrimination. From this study, we hypothesize that enhancing the feedback to the doctors is crucial to help them making correct diagnoses.

Juan Manuel Jacinto, Alessandro Filippeschi, Carlo Alberto Avizzano, Emanuele Ruffaldi

### Passive Probing Perception: Effect of Latency in Visual-Haptic Feedback

Latency is detrimental to haptic systems, specifically in networked telepresence systems. Although the latency effect on stiffness is well studied in the literature, it is not very clear if the latency effects on the stiffness perception are due to the displacement perception or the force perception. In this study, we propose passive probing which involves force perception alone, without any displacement of the finger, for studying latency effects. A psychophysical experiment is conducted with a set of artificially induced latencies which provides a quantitative measure of the effect of these latencies on three parameters: Just Noticeable Difference (JND), the time taken to reach the reference forces and the maximum overshoot. The results showed that the latency has a significant effect on the user ability in task performance after 185.5 ms. From the observation, the latency effect on JND in passive probing is similar to that of the stiffness perception (active probing) task which shows that the effect is significantly higher on the force perception rather than on the displacement perception.

Ravali Gourishetti, Joseph Hosanna Raj Isaac, M. Manivannan

### Perceived Frequency of Aperiodic Vibrotactile Stimuli Depends on Temporal Encoding

Mechanical transients and events arising during dexterous manipulation are detected by tactile afferents. Naturally occurring vibrotactile stimuli have a mix of frequencies, which creates complex afferent discharge patterns. Psychophysical correlates of these complex discharge patterns could be useful tools to gain greater insights into tactile coding and the principles of signal processing in the nervous system. In a previous study, we discovered that frequency perception of periodic bursting stimuli depended on the duration of the silent gap between spike bursts. Here, we investigated the perceived frequency of aperiodic vibrotactile stimuli. We found that perceived frequency was lower than the mean discharge rate of the afferents. This supports a hypothesis stemming from our previous work, that within spike trains consisting of mixed length inter-spike intervals, the contribution of a given interval to perceived frequency is weighted by its length. Thus, the present study reveals that frequency perception of both periodic and aperiodic stimuli is encoded by sophisticated processing of individual inter-spike intervals, rather than based on detection of periodicity or spike counting.

Kevin K. W. Ng, Ingvars Birznieks, Ian T. H. Tse, Josefin Andersen, Sara Nilsson, Richard M. Vickery

### Haptic Tracing of Midair Linear Trajectories Presented by Ultrasound Bessel Beams

This paper verifies the ability of human subjects with no audiovisual clues to trace their hands along an invisible vibrotactile line in three-dimensional space created by an ultrasound Bessel beam. A narrow, long, and stationary Bessel beam that passes through a target position is generated. The beam produces midair vibrotactile stimuli on the subjects’ hands. The subjects are required to perceive the beam location and direction actively to trace the presented linear trajectory. With our method, no real-time hand tracking is necessary, which guarantees no latency in presenting the vibrotactile stimuli. We experimentally verified that the subjects were able to trace the beam over 50 cm in its stretching direction with their hands. The average deviation from the beam center was less than 6 cm. Unlike conventional wearable-based motion guidance, the proposed technique requires no devices to be worn by the users in practical situations.

Shun Suzuki, Keisuke Hasegawa, Yasutoshi Makino, Hiroyuki Shinoda

### Asymmetric Cooling and Heating Perception

A series of experiments have been conducted to evaluate human thermal response to asymmetric thermal stimulation. It has been validated in previous studies that asymmetric thermal stimuli can create perceptions of heating or cooling while maintaining a constant average temperature applied to the skin. In this study we implemented three experimental procedures on the ventral forearm to evaluate asymmetric thermal stimulation. These experiments also examined several ways to collect perceptual thermal responses from subjects. Constant and asymmetric thermal pattern average temperatures were adjusted based on multiple aspects of thermal perception theories. Temporally optimized thermal patterns were implemented and resulted in counter-intuitive thermal perceptions. These results also demonstrated that the perceptual neutral point differs from the thermally neutral point on the skin.

Mehdi Hojatmadani, Kyle Reed

### Haptic Scene Analysis: Mechanical Property Separation Despite Parasitic Dynamics

The physical mass and damping of a haptic device contribute features that can be considered parasitic in that they potentially mask the virtual environment the user is intended to feel. On the other hand, users are generally able to adapt to the mechanical properties of physical tools and concentrate on the dynamics of task objects in the environment. It would be unsurprising, then, if humans were also able to ignore parasitic effects and focus on the mechanical properties of interest within a rendered environment. In this work, we explore a particular parasitic effect (damping) and its impact on the perception of stiffness. We examine the various perceptual impacts of predictable or unpredictable levels of damping. We find that, overall, humans are quite capable of ignoring damping to focus on stiffness, but that this ability may be hampered in the presence of unpredictable damping.

Emma Treadway, Steven Cutlip, R. Brent Gillespie

### Influence of Scanning Velocity on Skin Vibration for Coarse Texture

Tactile information can be obtained from the skin vibration elicited by the mechanical interaction between human fingertip and an object. Here, the skin vibration can be changed depending on exploratory movements. We herein investigated the influence of scanning velocity on the skin vibration for coarse textures. We used non-periodic coarse textures and measured the skin vibration under three different velocities. The results showed that the intensity of skin vibration is not significantly influenced by the velocity. However, the median frequency of the power spectrum significantly increased with the increase in velocity, whereas it did not have a proportional relation to the velocity and the particle size as on periodic textures. In addition, the median frequency had a tendency of slightly decreasing as the particle size became larger. A possible reason was discussed based on both the frequency response of the human fingertip and the object pattern.

Kohei Kimura, Makiko Natsume, Yoshihiro Tanaka

### Judged Roughness as a Function of Groove Frequency and Groove Width in 3D-Printed Gratings

For different types of textures judged roughness has been shown to be an inverted U-shaped function of inter-element spacing when texture amplitude is low [1, 2]. This may be due to an interplay of two “components” that contribute to the skin’s spatial deformation, and thus to a spatial-intensive code to roughness [1, 3, 4]: (1) deformation increases with the depth of the finger’s intrusion between elements, which increases with inter-element spacing until the finger contacts the ground; and (2) skin deformation decreases with a decreasing number of inter-element gaps being simultaneously under the skin, i.e. with the texture’s spatial frequency (which is negatively correlated with inter-element spacing). The present study systematically tested these ideas. We presented participants different series of 3D-printed rectangular grating stimuli, in which the width of the grating’s grooves varied and the spatial frequency of grooves was constant, or vice versa. Participants touched the stimuli without lateral movement and judged roughness using magnitude estimation. As predicted and previously observed, judged roughness increased with groove width and groove frequency. However, the predicted increase with groove frequency, was only found for frequencies below about 0.5 mm−1. For larger frequencies, roughness decreased with increasing frequency. The decrease is at odds with findings from earlier studies that used aluminum rather than plastic gratings [5]. The results corroborate the assumption that the area of skin deformation plays a crucial role for roughness, but at the same time, point to the influence of subtle differences between materials that should be investigated in the future.

Knut Drewing

### Using Spatiotemporal Modulation to Draw Tactile Patterns in Mid-Air

One way to create mid-air haptics is to use an ultrasonic phased-array, whose elements may be controlled to focus acoustic pressure to points in space (referred to as focal points). At these focal points the pressure can then deflect off the skin and induce a tactile sensation. Furthermore, by rapidly and repeatedly updating the position of a focal point over a given trajectory, ultrasound phased-array can draw two dimensional curves (referred to as patterns) on a users’ palms. While producing these patterns, there are three major parameters at play: the rate at which the pattern is repeated, the pattern length, and the focal point speed. Due to the interdependence between these parameters, only the repetition rate (frequency) or the speed can be set for a tactile pattern of a given length. In the current study, we investigate which approach (frequency or speed) is most effective at maximising the tactile sensation. We first carried out a vibrometry study to show that optimising the speed can maximise the skin deflection caused by a focal point following circular patterns. A further user study was undertaken to show that optimising the speed consequently maximises the perceived intensity of the tactile pattern. In both studies, the optimal speed result is shown to be equivalent to the speed at which surface waves propagate from the skin deflection effected by the focal point. Overall, our investigations highlight the importance of the speed of stimulation movement in the design of tactile patterns.

William Frier, Damien Ablart, Jamie Chilles, Benjamin Long, Marcello Giordano, Marianna Obrist, Sriram Subramanian

### Discovering Articulations by Touch: A Human Study for Robotics Applications

Getting robots to manipulate arbitrary objects in unstructured, human-centric environments is an open problem. Typical assumptions for engineering-based solutions to this problem are that the object can be recognized, that it is nearly rigid, and that its pose can be estimated. Even under these stringent assumptions, autonomous performance of such tasks has remained primitive over decades of research and development. The reasons for the slow pace of advancement are generally unknown, though careful engineering of robotic systems to perform such tasks continues. This paper attempts to investigate why by examining human manipulation performance on a task that appears heavily dependent upon tactile feedback, a known deficiency in current robotic manipulation technology. Current contact sensors are noisy, bulky (preventing precisely localized contact sensing), wear out, or—commonly—some combination of the three. This paper presents the result of a human study to understand the importance of haptic kinesthetic feedback to discover articulations upon encountering a novel mechanism. The findings of the study indicate a decrease in performance of a complex manipulation task when haptic feedback—as the primary sensory input—is desensitized.

Roxana Leontie, Evan Drumwright

### A Multimodal Illusion of Force Improves Control Perception in Above-Surface Gesture: Elastic Zed-Zoom

Emerging above-surface technology is an opportunity to exploit interaction spaces above a device’s surface; however, the resulting loss of the proprioceptive feedback available from on-surface interactions degrades the user’s sense of control and precision. We asked whether a pseudohaptic illusion (PHI) could help: a sense of force in the absence of actual contact, induced by manipulating the relation of body motion to graphical and auditory cues.To examine the value of above-surface PHIs, we used a zooming microtask, because finger occlusion impedes current implementations on small displays such as smartwatches. In a qualitative study (N = 12), we were able to trigger a physical illusion most often described as elasticity in 92% of participants through physical control/graphical display (C/D) manipulation, and that audio cues significantly strengthened the illusion. Participants experiencing this PHI reported improved sense of control when zooming, and found the interaction’s physicality natural.

Dilan Ustek, Kevin Chow, Haihua Zhang, Karon MacLean

### Pseudohaptic Feedback for Teleoperated Gripping Interactions

We present a proof-of-concept for pseudohaptic feedback in gripping interactions. This paper includes a review about known applications of pseudohaptic feedback in virtual reality and teleoperation as well as the results of an identification experiment in a gripping task. In this experiment, 16 subjects identified five stimuli with different compliances. Independent factors were the visual condition (side or top view of the gripper) and the compliance of the human-machine-interface (stiff or compliant). A mean information transfer of $$1.09 \pm 0.25\,\text {bit}$$1.09±0.25bit (mean and standard deviation) in 60 trials was achieved by the participants. However, a large and significant habituation effect was found. It leads to an increased information transfer of $$1.47\pm 0.29\,\text {bit}$$1.47±0.29bit in the last 15 trials of the experiment. The visual condition exhibits a small effect with a mean difference of 0.14 bit for all trials, no effect was found for the compliance of the HMI.

Sarah Anna Wojcik, Carsten Neupert, Johannes Bilz, Roland Werthschützky, Mario Kupnik, Christian Hatzfeld

### A Pilot Study: Introduction of Time-Domain Segment to Intensity-Based Perception Model of High-Frequency Vibration

The intensity of a high-frequency vibration is the primary cue to convey vibrotactile information perceived by the Pacinian system. However, the conventional intensity-based spectral power model is not sufficient to interpret a relatively slow time-variant pattern of vibration such as amplitude-modulated (AM) vibrations. This paper introduced a time-domain segment to the intensity-based model such that a long-term vibration pattern is divided into multiple short-term sinusoidal vibrations that maintain the same energy. We expected that such short-term segmentation could deliver the similar perception if the energy of each segment of the reproduced vibration is the same as the original waveform even though the time-segmented reproduced waveform has a step-wise envelope shape. We conducted a pilot psychophysical experiment in which the participants discriminated between the original AM vibrations and the time-segmented vibrations by changing the segment size from 1/6 to 1/2 of the AM period. The experiment is conducted under different combinations of the carrier frequencies (300 Hz and 600 Hz) and envelope frequencies (15 Hz, 30 Hz, and 45 Hz) frequencies. The results showed that the participants had low discrimination ratios (the mean values are less than 0.6) at the segment size from 1/6 to 1/3 of the AM period and the participants could discriminate easily between the flat sinusoidal vibration and the original AM vibration (the mean discrimination ratios are larger than 0.90) even if the energies of the two vibrations were maintained. The results suggest that the time-segmented intensity-based model could reproduce perceptually-similar vibrations for AM vibrations at the segment size from 1/6 to 1/3 of the AM period.

Nan Cao, Hikaru Nagano, Masashi Konyo, Shogo Okamoto, Satoshi Tadokoro

### Haptic Human-Human Interaction Through a Compliant Connection Does Not Improve Motor Learning in a Force Field

Humans have a natural ability to haptically interact with other humans, for instance while physically assisting a child to learn how to ride a bicycle. A recent study has shown that haptic human-human interaction can improve individual motor performance and motor learning rate while learning to track a continuously moving target with a visuomotor rotation. In this work we investigated whether these benefits of haptic interaction on motor learning generalize to a task in which the interacting partners track a target while they learn novel dynamics, represented by a force field. Pairs performed the tracking task and were intermittently connected to each other through a virtual spring. Motor learning was assessed by comparing each partner’s individual performance during trials in which they were not connected to the performance of participants who learned the task alone. We found that haptic interaction through a compliant spring does not lead to improved individual motor performance or an increase in motor learning rate. Performance during interaction was significantly better than when the partners were not interacting, even when connected to a worse partner.

Niek Beckers, Arvid Keemink, Edwin van Asseldonk, Herman van der Kooij

### Relative Sensation of Wetness of Different Materials

Previous studies have already shown that an illusion of wetness can be elicited by touching a dry cold object. Both metal and cloth are materials that can cause this illusion. This paper investigated the relative sensation of wetness caused by some other materials at the same low temperature. Participants were presented with stimulus pairs of different materials such as metal, PVC, acrylic and paper, and they had to judge which of the two felt wetter. From the results we obtained a scale of relative wetness sensation. Subsequently, several physical properties of the materials were measured. We conclude that materials that cause the human skin to cool quickly, cause the stimulus to feel relatively wet. Interestingly, also stickiness can lead to a sensation of relative wetness, even when presented at room temperature.

Mai Shibahara, Katsunari Sato, Astrid M. L. Kappers

### Exploring Fingers’ Limitation of Texture Density Perception on Ultrasonic Haptic Displays

Recent research in haptic feedback is motivated by the crucial role that tactile perception plays in everyday touch interactions. In this paper, we describe psychophysical experiments to investigate the perceptual threshold of individual fingers on both the right and left hand of right-handed participants using active dynamic touch for spatial period discrimination of both sinusoidal and square-wave gratings on ultrasonic haptic touchscreens. Both one-finger and multi-finger touch were studied and compared. Our results indicate that users’ finger identity (index finger, middle finger, etc.) significantly affect the perception of both gratings in the case of one-finger exploration. We show that index finger and thumb are the most sensitive in all conditions whereas little finger followed by ring are the least sensitive for haptic perception. For multi-finger exploration, the right hand was found to be more sensitive than the left hand for both gratings. Our findings also demonstrate similar perception sensitivity between multi-finger exploration and the index finger of users’ right hands (i.e. dominant hand in our study), while significant difference was found between single and multi-finger perception sensitivity for the left hand.

Farzan Kalantari, David Gueorguiev, Edward Lank, Nicolas Bremard, Laurent Grisoni

### Hardness Perception Through Tapping: Peak and Impulse of the Reaction Force Reflect the Subjective Hardness

Humans can judge the hardness of an object by tapping its surface. To investigate physical indicators for estimating subjective hardness, we analyzed the short-time reaction force caused by tapping various types of objects. We focused on five indicators in the time domain, including the peak force value, peak time, duration, maximum increase rate, and impulse of the reaction force. A strong correlation was observed between the peak force value, peak time, duration, and maximum increase rate. We found that subjective hardness can be predicted by combining the peak force value and impulse of the reaction force. Results suggest that the hardness involving stiffness and damping factor of objects can be estimated from the reaction force caused by tapping objects. Especially, the former and latter are, respectively, associated with the peak force value and impulse of the reaction force.

Kosuke Higashi, Shogo Okamoto, Yoji Yamada, Hikaru Nagano, Masashi Konyo

### Analysis of Ultrasound Radiation and Proposal of Design Criteria in Ultrasonic Haptic Display for Practical Applications

This paper describes a technology to reduce ultrasound radiation which is caused by normal mode vibration of an ultrasonic haptics display. Reduction and analysis of ultrasonic acoustic radiation from the display were implemented for safety use and coexistence with other devices. The focus on solving the problem of ultrasound radiation is based on the investigation of constructive interference conditions of acoustic waves on the top panel. We successfully demonstrated a practical sound pressure level on the prototype. To reduce radiation, it is necessary to reduce the thickness or the lower stiffness-to-density ratio E/ρ. A thickness of 0.3 mm has practical stiffness in the case of glass and the maximum pressure is 110 dB or less at 30 kHz for the usual size of smartphone. This means that raising the “coincident frequency” higher than the driving frequency by reducing the thickness and lowering the E/ρ, causes sound radiation to be sharply reduced.

Kiyoshi Taninaka, Akinori Miyamoto, Yuichi Kamata, Yasuhiro Endo, Yoshihiro Mizuno

### Haptic Saliency Model for Rigid Textured Surfaces

When touching an object, we focus more on some of its parts rather than touching the whole object’s surface, i.e. some parts are more salient than others. Here we investigated how different physical properties of rigid, plastic, relieved textures determine haptic exploratory behavior. We produced haptic stimuli whose textures were locally defined by random distributions of four independent features: amplitude, spatial frequency, orientation and isotropy. Participants explored two stimuli one after the other and in order to promote exploration we asked them to judge their similarity. We used a linear regression model to relate the features and their gradients to the exploratory behavior (spatial distribution of touch duration). The model predicts human behavior significantly better than chance, suggesting that exploratory movements are to some extent driven by the low level features we investigated. Remarkably, the contribution of each predictor changed as a function of the spatial scale in which it was defined, showing that haptic exploration preferences are spatially tuned, i.e. specific features are most salient at different spatial scales.

Anna Metzger, Matteo Toscani, Matteo Valsecchi, Knut Drewing

### Vibrotactile Pattern Identification in a Multisensory Display

In multisensory cutaneous displays in which both tactile and thermal signals are presented, it is important to understand the perceptual interactions that can occur between the two modalities. Phenomena such as masking, facilitation and inhibition may occur that influence how multisensory inputs are processed. In the present experiment participants were required to identify vibrotactile patterns that varied in intensity and pulse duration while the skin was warmed, cooled or remained at a neutral temperature. The results indicate that the temperature of the skin influences the ability to identify vibrotactile patterns that are well above threshold. This thermal-tactile interaction occurred when the skin was warmed and assisted in the identification of vibrotactile stimuli that varied in intensity. In contrast, warming the skin appeared to impede identification of patterns whose pulse duration varied. These results suggest that the enhanced activity of cutaneous thermoreceptors during warming may facilitate the processing of amplitude-related properties of incoming signals from cutaneous mechanoreceptors.

Lynette A. Jones, Anshul Singhal

### Influence of Different Types of Prior Knowledge on Haptic Exploration of Soft Objects

When estimating the softness of an object by active touch, humans typically indent the object’s surface several times with their finger, applying higher peak indentation forces when they expect to explore harder as compared to softer stimuli [1]. Here, we compared how different types of prior knowledge differentially influence exploratory forces in softness discrimination. On each trial, participants successively explored two silicone rubber stimuli which were either both relatively soft or both relatively hard, and judged which of the two were softer. We measured peak forces of the first indentation. In the control condition, participants obtained no information about whether the upcoming stimulus pair would be from the hard or the soft category. In three test conditions, participants received implicit (pairs from the same category were blocked), semantic (the words soft and hard), or visual prior knowledge about the softness category. Visual information was provided by displaying the rendering of a compliant object deformed by a probe. Given implicit information, participants again used significantly more force in their first touch when exploring harder as compared to softer objects. Surprisingly, when given visual information, participants used significantly less force in the first touch when exploring harder objects. There was no effect when participants were given semantic information. We conclude that different types of prior knowledge influence the exploration behavior in very different ways. Thus, the mechanisms through which prior knowledge is integrated in the exploration process might be more complex than expected.

Aaron Cedric Zöller, Alexandra Lezkan, Vivian C. Paulun, Roland W. Fleming, Knut Drewing

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### Globales Erdungssystem in urbanen Kabelnetzen

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