Haptics: Perception, Devices, Control, and Applications

A human can perceive the hardness of an object by tapping its surface. We compared the ranked subjective hardness values and physical properties of objects, including their stiffness, viscosity, density, and Shore hardness, and the frequencies and time constants of the natural vibrations caused by tapping. The stiffness, frequency, and viscosity exhibited a relatively strong positive correlation with the perceived hardness. The results show that the viscosity influences the hardness perceived by tapping, as well as the stiffness, whereas the stiffness and elasticity are considered to be major factors in the hardness perceived by pinching or pushing.

On July 28th 2014, 23:47 UTC, the European Space Agency launched the Haptics-1 Kit to the International Space Station (ISS) on its last Automated Transfer Vehicle ATV-5. The Kit reached the station two weeks later, marking the first haptic master device to enter the ISS. The first force-feedback and human perceptual motor performance tests started to take place on December 30th 2014, and are the first of their kind in the history of spaceflight. Three astronauts participated in the Haptics-1 experiment until November 2015, allowing the investigation of the effects of microgravity on various psycho-motor performance metrics related with the usage of haptic feedback. Experiments are conducted following full adaptation to the space environment (after 3 months in space). This paper introduces the Haptics-1 experiment and associated hardware. Detailed experimental results are reported from a first stiffness just noticeable difference (JND) experimental study in space, carried out on the ISS and pre-flight on ground with 3 astronauts. The first findings from the experiment show no major alterations in-flight, when compared to on-ground data, if the manipulandum is secured in flight against a sufficiently stiff reference structure.

Past sensory experience can influence present perception. We studied the effect of adaptation in haptic softness perception. Participants compared two silicon rubber stimuli, a reference and a comparison stimulus, by indenting them simultaneously with the index fingers of their two hands and decided which one felt softer. In adaptation conditions the index finger that explored the reference stimulus had previously been adapted to another rubber stimulus. The adaptation stimulus was indented 5 times with a force of >15 N, thus the two index fingers had a different sensory past. In baseline conditions there was no previous adaptation. We measured the Points of Subjective Equality (PSEs) of one reference stimulus to a set of comparison stimuli. We used four different adaptation stimuli, one was harder, two were softer and one had approximately the same compliance as compared to the reference stimulus. PSEs shifted as a function of the compliance of the adaptation stimulus: the reference was perceived to be softer when the finger had been adapted to a harder stimulus and it was perceived to be harder after adaptation to a softer stimulus. We conclude that recent sensory experience causes a shift of haptically perceived softness away from the softness of the adaptation stimulus. The finding that perceived softness is susceptible to adaptation suggests that there might be neural channels tuned to different softness values and softness is an independent primary perceptual quality.

The aim of this paper is to investigate the recovery time of human-fingertip’s mechanical properties after indentations cycles. To determine the influencing parameters, three indentation velocities, five recovery times and three subjects were tested. During each experiment, the fingertip of participant was driven against a flat surface, while indentation displacement and velocity were controlled. The results show not only the indentation forces values increase depending on the indentation velocity increment, but also they decrease depending on the number of cycles. While the fingertip recovery depends on the time, but not on the indentation velocity. Finally the recovery time was determined: in 5 min the fingertip restored 99.6 % of the initial mechanical properties.

The present study presents a new rendering algorithm for a moving tactile stroke on the palm of the hand placed on a sparse 2D tactor array. Our algorithm utilizes the relation between signal duration and signal onset asynchrony previously proposed for “tactile brush” [1], but extends it by applying 3-actuator phantom sensations and adjusting the sampling rate. We compare our proposed algorithm to the tactile brush algorithm for their similarity in target trajectories and uniformity of tactile stroke motions. The results show that the participants judge the tactile strokes with our algorithm to move significantly closer to target motions and with more uniform velocity than the “tactile brush.” The effect of our algorithm is more significant for experimental stimuli with longer travel time and length.

We fabricated a midair tactile display using a 70 kHz airborne ultrasound. The spatial resolution of the display was improved 1.75 times compared with the conventional 40 kHz ultrasound tactile display. Since the focal spot diameter was smaller than a finger pad, the user could perceive a localized spot on the finger pad. In the experiment determining the physical properties, we found that the ultrasound attenuation at 70 kHz was comparable to that at 40 kHz. The small focal spot was successfully created as expected using the theory. The psychophysical experimental results showed that the minimum perceivable radiation force for the focal spot of 70 kHz was smaller than that for the 40 kHz case in average under 40 or 100 Hz modulations, and the smaller focal spot was easier to perceive. We also conducted a comparison test of the perceived force area with real contacts.

Mid-air ultrasound can remotely invoke tactile sensation to bare hand. However, it is difficult to control it precisely because the hand itself scatters ultrasound. In this paper, a scattering model, which can be solved in real-time, is proposed and, this model can create a stronger focal point as compared to the conventional model. The proposed algorithm is based on the boundary element method and is a natural extension of the previously proposed phased array synthesis algorithms. Numerical analysis shows the relationship between the error of the surface model, computation time, and focusing performance. Psychophysical experiment shows that the internal tactile intensity of the focused ultrasound is significantly improved using the proposed adaptive focusing method. The proposed method can be used for mid-air ultrasound as a test bench of precise weak force haptic interaction.

Traditional haptic interfaces require physical contact between the haptic device and the user. An elegant and novel solution is to provide contactless tactile stimulation via airborne acoustic radiation pressure. However, the characteristics of contactless tactile displays are not well studied in the literature. In this paper, we study the characteristics of the ultrasonic tactile display as a haptic interface. In particular, we examine the effects of increasing the number of ultrasound transducers on four characteristics, namely the maximum producible force, the workspace, the workspace resolution, and the robustness of the simulation. Three rectangular-shaped 2D array configurations are considered: single-tile (10$$\,\times \,$$10 transducers), two-tiles (10$$\,\times \,$$20 transducers), and four-tiles (20$$\,\times \,$$20 transducers). Results show that the maximum producible force remains almost constant as the number of tiles increases, whereas the elevation at which these maxima are generated increases. The workspace increases along the xy-plane as the number of tiles increase almost linearly, however, the elevation of the workspace remains almost the same. Finally, we found that the robustness of tactile display decreases as the number of tiles increases.

For optimal control of wearable lower limb exoskeletons the sensory information flow should also be (partly) restored, especially when the users are Spinal Cord Injury subjects. Several methods, like electrotactile or electromechanical vibrotactile stimulation, to provide artificial sensory feedback have been studied thoroughly and showed promising results. Pneumatic tactile stimulation might be an alternative to these methods, because the stimulation amplitudes can be larger and in cases of force feedback, the modality of stimulation and sensing can be matched. In this study we have developed a setup that can provide pneumatic feedback with four feedback levels via three stimulation modalities: (1) amplitude modulation, (2) position modulation and (3) frequency modulation. The differences in subject stimulus perception between these three stimulation modalities were evaluated through a magnitude estimation task performed with 10 healthy subjects. Percentages correctly identified feedback levels were significantly higher for frequency modulation than the other two stimulation modalities. Also through questionnaires the subjects indicated that feedback through frequency modulation was the most intuitive and the only method where addition of an extra feedback level was indicated as possible. The results of this study show that pneumatic feedback is feasible, can provide high percentages of feedback level discrimination that are at least comparable to vibrotactile stimulation and therefore encourages further research to optimize the pneumatic setup.

This paper presents an inexpensive, versatile and easy-to-install robotic haptic stimulator, capable of delivering computer-controlled innocuous and noxious mechanical stimuli. The system can be coupled with robotic interfaces typically employed to investigate human motor control and learning, and synchronized with the acquisition of relevant physiological measures. The design is based on a modified commercial rotative servomotor that actuates a 1-DOF parallel guiding mechanism connected to an end-effector that applies forces against a subject’s target body area. The position of the end-effector and the interaction force with the skin, as well as sensor readings of the subject’s movements, can be used by a microcontroller to control the stimulator. The results of experiments to test the stimulator’s control and subjects’ psychophysical responses show that the device provides robust and consistent mechanical stimulation, which elicits perceptual ratings compatible with previous relevant psychophysical studies. The presented system is the first to allow investigating the effects of painful versus innocuous stimulation on human motor control and learning.

The effects of extra arm weight and weightlessness on sensorimotor performance were investigated in three studies. In all studies, subjects performed two-dimensional tracking tasks with a joystick. Results indicated that extra arm weight did not decrease tracking performance, but decreased acceleration variance. In weightlessness, tracking performance decreased and the control of movement impulses was deteriorated. This result pattern was found during water immersion as well as during spaceflight. The sensorimotor performance losses in weightlessness could be compensated by providing additional haptic cues with the input device.

According to between arms position matching assessments, more than 50 % of individuals with stroke may have moderate to severe proprioceptive deficits. This study is the first of a series of studies designed to investigate the reason for observed between arms position matching deficits. In this work, we quantified the ability of five participants with chronic hemiparetic stroke (participants with stroke) and five age-matched participants without neurological impairments (controls) to match forearm positions within a single arm. According to the revised Nottingham Sensory Assessment, the participants with stroke all had impaired forearm position sense and unimpaired forearm movement direction sense, while the controls had unimpaired forearm position and movement direction sense. A custom robotic device was used to quantify each participant’s task performance during active movements when performing a single arm memory matching task. Participants were asked to match the location of the forearm with a remembered target location. Results show that the participants with stroke identified the target location just as well as the controls. Based on our findings, we suggest that our participants with chronic hemiparetic stroke, who have deficits in matching forearm positions across both arms, may not have impaired forearm position sense within a single arm, and we suggest that the position matching deficits may arise for non-sensory related reasons. Future work will continue to use such behavioral studies to investigate possible central neural mechanisms that may be contributing to the observed between arms position matching deficits.

We have investigated spontaneous haptic search in a scenario in which both the search target and the search field are represented by a random composition of different primitive shapes. In our experiment, blindfolded sighted individuals were asked, firstly, to learn a complex search target and, secondly, to find this search target embedded in a larger, encompassing search field. Our goal was to examine, how different shape characteristics of the complex search target influenced the overall search behaviour.We have evaluated data of eight participants by correlating the features, representing the search behaviour, with the features, representing the target object. This approach showed that the number of vertices, the curvature and the height of the target may have a global impact on the hand posture, velocity and pressure during the haptic search.

Dynamic tactile exploration enables humans to seamlessly estimate the shape of objects and distinguish them from one another in the complete absence of visual information. Such a blind tactile exploration allows integrating information of the hand pose and contacts on the skin to form a coherent representation of the object shape. A principled way to understand the underlying neural computations of human haptic perception is through normative modelling. We propose a Bayesian perceptual model for recursive integration of noisy proprioceptive hand pose with noisy skin–object contacts. The model simultaneously forms an optimal estimate of the true hand pose and a representation of the explored shape in an object–centred coordinate system. A classification algorithm can, thus, be applied in order to distinguish among different objects solely based on the similarity of their representations. This enables the comparison, in real–time, of the shape of an object identified by human subjects with the shape of the same object predicted by our model using motion capture data. Therefore, our work provides a framework for a principled study of human haptic exploration of complex objects.

Movement of a limb substantially decreases the intensity and sensitivity with which tactile stimuli on that limb are perceived. This movement-related tactile suppression likely interferes with performance in motor tasks that require the precise evaluation of tactile feedback, such as the adjustment of grip forces during grasping. Therefore, we hypothesise that suppression might be stronger for stimuli that are irrelevant to successful performance in a given motor task. To test this hypothesis, we measured participants’ perception of tactile intensity while performing different motor tasks. We investigated perception of both supra-threshold stimuli (Exp. 1: intensity discrimination) and of stimuli close to the detection threshold (Exp. 2: detection). We compared tactile perception between two grasping conditions (active, tactile inputs relevant), a condition where participants pointed in the air (active, tactile inputs irrelevant) and a static condition (baseline). In both experiments, we observed tactile suppression in all three movement conditions but not the predicted attenuation of tactile suppression in the grasp conditions. Contrary to our hypothesis, there was even an amplification of tactile suppression in the grasping conditions of Exp. 1, which might be related to the movement velocity. In conclusion, we did not find evidence that motor tasks modulate the strength of tactile suppression. Our results further suggest that it is important to control for possibly confounding variables, such as movement velocity and laterality, in this line of research.

Current touchscreen technology makes for intuitive human-computer interactions but often lacks haptic feedback offered by conventional input methods. Typing text on a virtual keyboard is arguably the task in which the absence of tactile cues imparts performance and comfort the most. Here we investigated the feasibility of modulating friction via ultrasonic vibration as a function of the pressing force to simulate a tactile feedback similar to a keystroke. Ultrasonic vibration is generally used to modulate the sliding friction which occurs when a finger moves laterally on a surface. We found that this method is also effective when the exploratory motion is normal to the surface. Psychophysical experiments show that a mechanical detent is unambiguously perceived in the case of signals starting with a high level of friction and ending to a low friction level. A weaker effect is experienced when friction is increasing with the pressure exerted by the finger, which suggests that the mechanism involved is a release of the skin stretch accumulated during the high-friction state.

Skin stretch is a powerful haptic effect with a great potential as a feedback mechanism for digital gaming applications. For example, it has been shown to communicate directional information accurately to game players. However, the existing devices apply stretch to the tip of index finger except the Reactive Grip game controller by Tactical Haptics, which applies skin stretch to a user’s palm and finger pads. We have designed a compact hand-held haptic device that applies skin stretch to the palm via an actuated tactor. Compared to the fingertip, the palm is slightly less sensitive to skin stretch but affords larger stretch area. The stretch area of the palm enables us to control both tactor displacement and speeds for a broader range, resulting in richer haptic feedback. Using this device, we conduct experiments with 8 participants to investigate the effects of tactor displacement, speed, direction and hand orientation on perceived magnitude of skin stretch. The results of the study show that not only the tactor displacement but also the speed has a significant effect on the perceived intensity of skin stretch and the mapping function between them is nonlinear. Moreover, it appears that the tactile sensitivity of human palm to skin stretch is not homogeneous and stretch applied to the radial aspect of palm (towards the thumb) results in higher intensity than that of ulnar aspect.

The perceived intensity of electrovibration can be altered by modulating the amplitude, frequency, and waveform of the input voltage signal applied to the conductive layer of a touchscreen. Even though the effect of the first two has been already investigated for sinusoidal signals, we are not aware of any detailed study investigating the effect of the waveform on our haptic perception in the domain of electrovibration. This paper investigates how input voltage waveform affects our haptic perception of electrovibration on touchscreens. We conducted absolute detection experiments using square wave and sinusoidal input signals at seven fundamental frequencies (15, 30, 60, 120, 240, 480 and 1920 Hz). Experimental results depicted the well-known U-shaped tactile sensitivity across frequencies. However, the sensory thresholds were lower for the square wave than the sinusoidal wave at fundamental frequencies less than 60 Hz while they were similar at higher frequencies. Using an equivalent circuit model of a finger-touchscreen system, we show that the sensation difference between the waveforms at low fundamental frequencies can be explained by frequency-dependent electrical properties of human skin and the differential sensitivity of mechanoreceptor channels to individual frequency components in the electrostatic force. As a matter of fact, when the electrostatic force waveforms are analyzed in the frequency domain based on human vibrotactile sensitivity data from the literature [15], the electrovibration stimuli caused by square-wave input signals at all the tested frequencies in this study are found to be detected by the Pacinian psychophysical channel.

We investigated the perceived frequency elicited by two vibrating probes on the skin. Participants (n = 11) compared two probes vibrating in counter-phase (25 Hz), with comparison stimuli of in-phase vibration (18–54 Hz). They indicated which had the higher perceived frequency. Skin sites on the palm (glabrous) and arm (hairy) were tested with a range of probe separations (1–16 cm) and amplitudes (10–120 µm). Perceived frequency increased with decreasing separation of the probes (F_1,10 = 182.8, p < 0.001). The two skin sites did not significantly differ (F_1,10 = 3.6, p = 0.087). Perceived frequency was only minimally affected by amplitude changes between 40 and 120 μm (F_2,20 = 6.4, p = 0.007, $$ \eta_{G}^{2} = 0.06 $$). Both phase and spatial separation strongly influence vibrotactile interaction between two skin locations in a manner largely independent of changes in amplitude, and of skin type.

Many applications in the domain of haptics make use of vibrotactile rendering. One means for the delivery of the signals is employing voice coil actuators. However, existing control strategies for these exhibit limitations, for instance their dynamic characteristic is often not taken into account leading to output distortion. We propose two new control methods to improve vibrotactile rendering – once based on data-driven spline interpolation and once on following power spectral density. Both approaches rely on the idea of first decomposing a desired signal into a combination of harmonic components of different frequencies. For these, separate optimal gains are then employed to achieve a flat frequency response. The behavior of these controllers is examined in experiments and compared to a constant gain strategy. Both proposed methods result in improvements, such as lower spectral dissimilarity scores.

Achieving high stiffness, low inertia and friction is a big challenge in the design of a haptic device. Admittance display is a common solution to obtain high stiffness but is difficult to achieve low inertia and friction. We describe a new concept of co-actuation to overcome this difficulty. The co-actuation approach disconnects the actuators and joints of a haptic device, making the two components work cooperatively according to characteristics of simulated environment. In free space, the joints are tracked and followed by the actuators. Users can move the joints freely without feeling resistance from the actuators. In constraint space, physical constraints driven by the actuators apply impedance to the joints. By producing a direct physical contact between the joints and the physical constraints, users can feel a hard virtual surface. The paper describes the mechanical and control design and implementation of a one degree-of-freedom (DOF) co-actuation module. Stiffness of 40 N/mm and friction force of less than 0.3 N was achieved on the module. By effectively reducing inertia and friction, the proposed approach demonstrates its potential advantage over conventional admittance displays. The co-actuation approach can be applied to multi-DOF haptic devices to achieve high stiffness, low inertia and friction.

While feedback control can be used to cause a motorized device to render the dynamic behavior of a virtual environment, this capacity inevitably breaks down at high frequencies where the rendered impedance reverts to the impedance of the device hardware. This situation amounts to a disadvantage for admittance display, for which hardware impedance is high. Series elastic actuators offer an attractive alternative with lower impedance at high frequencies, though stability considerations impose limits on the stiffest virtual environment that may be rendered. In this paper we explore the tradeoffs between admittance control and series elastic actuation with the use of analytical comparisons in the frequency domain backed up by experiments and complemented with a passivity analysis that accounts for an excess of passivity contributed by human biomechanics.

Ultrasonic vibrations of a plate can modify the perception of the friction between a surface and a sliding finger. This principle, coupled with modern position sensing techniques, is able to reproduce textured materials. In this paper, an open loop control through model inversion of the friction force between the finger and the plate is presented. The device incorporating the control system is described, and two different reproduction strategies are formalized to address the reproduction of objects and textures. In the end, a psychophysical experiment evaluating the two control strategies is described.

This paper proposes a method to further enlarge the displayed stiffness range of the impedance-type haptic interfaces. Numerous studies have been done for a stable haptic interaction in a wide impedance range. However, most of the approaches sacrifice the actual displayed stiffness as a cost of stability. A novel approach, which successively increases the stiffness as the number of interaction cycle increase, is presented. The stiffness is sequentially modulated from a low value to a high value, close to the desired stiffness while maintaining stability. This sequential stiffness increment was possible because the proposed approach guarantees the convergence of the penetration distance and increases the feedback force with every successive interaction cycle. The main advantage of the proposed approach over conventional approaches is that this approach allows much larger actual displayed stiffness than any other approach, such as time-domain passivity approach, force bounding and energy bounding approach. Experiments with PHANToM Premium 1.5 evaluate the performance of the proposed approach, and compare the actual displayed stiffness with other approaches.

The present study aims to determine whether color has an impact on temperature perception, a paradigm known as the hue-heat hypothesis. Our results shows that a color-temperature association exists since the participants hold a hot vessel longer when associated with blue and similarly a cold vessel longer when paired with red. Participants’ ratings of the perceived temperature were also influenced by crossmodal interaction between color and temperature confirming the effect of color on temperature perception. These findings are consistent with previous studies and validates the hue-heat hypothesis that was first investigated almost a century ago.

When the hand makes contact with an object, the changes in skin temperature provide information about not only the object’s material composition but also its geometry. Consider, for example, the temperature difference felt when touching an aluminum block and a piece of aluminum foil. To study the thermal cues associated with material properties and object thickness, we measured the changes in skin temperature elicited when touching objects with varying material properties and geometries, and compared them to the theoretical predictions obtained from two thermal models, of which one assumes the object having an infinite thickness and the other takes into consideration the actual object thickness. The comparison results indicate that the former model is effective in capturing the rapid temperature changes at the moment of contact and the latter model is better at predicting the total change in skin temperature at the end of contact. These findings provide a knowledge basis for the development of thermal displays for material simulation and automatic object identification systems that identify an object’s material composition and thickness based on thermal feedback.

This experiment was focused on determining whether the spatial representation of thermal stimuli is influenced by the temporal parameters of stimulation as has been demonstrated for tactile stimuli. Four warm thermal pulses within the innocuous range of temperatures were presented on the forearm in varying spatial and temporal sequences. Participants indicated the perceived location of the first two pulses in the four-pulse sequence after each trial. The results indicate that the perceived position of the second pulse changed substantially in the direction of the third pulse when the interval between the pulses was brief (0.2 s). At longer intervals there was no change in perceived location. These results indicate that despite the limitations in the spatial and temporal processing of thermal stimuli, somatotopic information appears to be integrated similarly for tactile and thermal stimuli.

In this paper, we present a notable study to control occurrence of a phantom sensation by visual stimuli. A phantom sensation is one of tactile illusion caused by vibration stimuli. Some previous works employed vibration motors for a tactile display, and utilized a phantom sensation to present tactile stimuli in a large area with a few vibration motors. However, there are few studies to investigate the influence of visual stimuli on a phantom sensation. Our previous works showed that visual stimuli influenced localization of vibrotactile perception. From the results, we considered that visual stimuli also influence on a phantom sensation. We made a visual-tactile display, and conducted some experiments. The results showed that visual stimuli influenced a phantom sensation and it seemed to be possible to control the occurrence of a phantom sensation by changing visual stimuli.

In teleoperation systems, the master robot receives force feedback from the remote slave side. Thus, the human operator can perceive the contact between the slave robot and its environment. Application of a force sensor at the slave robot improves the performance of the telepresence system in terms of transparency. Still, so far no approach allowing measured force feedback in time delayed multilateral systems that allow the interaction of multiple agents can be found in literature. To this end, this paper presents a multilateral setup with passive measured force feedback based on the time domain passivity approach. Besides this solution to measured force feedback in multilateral systems, the presented approach promises improvements compared to other time invariant and model based approaches for measured force feedback also when applied to bilateral systems. Experiments are presented to allow for a performance analysis of the proposed system design.

This paper presents simulations of marine crane operations using a haptic device with force feedback. Safe and efficient marine crane operations are challenging under adverse environmental conditions. System testing and operation training on physical systems and prototypes are time-consuming and costly. The development of virtual simulators alleviates the shortcomings with physical systems by providing 3D visualization and force feedback to the operator. Currently, haptic technology has limited applications in heavy industries, due to the system stability and safety issues related to the remote control of large manipulators. As a result, a novel 6-DoF haptic device was developed for crane operations allowing for a larger workspace range and higher stiffness. The employment of the haptic device enlarges the interaction scope of the virtual simulator by sending feedback forces to the operator. In the case study, simulations of marine crane anti-sway control suggested that the load sway time and amplitude were reduced with force feedback. Using the haptic device, it also helps the crane operator to prevent problematic operations.

Haptic interaction is a new interactive function in human-computer interaction of mobile terminal. In this work, we present a novel haptic stylus for mobile terminal, which can achieve haptic display of visual image. The haptic stylus generates force feedback and tactile feedback through electromechanical structure and piezoelectric ceramics respectively. In order to obtain the haptic information of image, we adopt shape from shading (SFS) algorithm to extract height information of image, which is presented in the form of force feedback. And fractional differential method is used to extract edge information of image, which is expressed in the form of tactile feedback. The software system of haptic interaction is developed based on Android system. And the mode of communication is Bluetooth. Finally, the haptic perception experiment is conducted to investigate effect of perception with different haptic stylus and different mode of haptic interaction.

A texture rendering system relying on pseudo-haptic and audio feedback is presented in this paper. While the user touches the texture displayed on a tactile screen, the associated image is deformed according to the contact area and the rubbing motion to simulate pressure. Additionally audio feedback is synthesized in real-time to simulate friction. A novel example-based scheme takes advantage of recorded audio samples of friction between actual textures and a finger at several speeds to synthesize the final output sound. This system can be implemented on any existing tactile screen without any extra mechanical device.

This paper presents the DOVI (Device for Orientation of the Visually Impaired) system, a new inertial and RFID-based wearable navigation device for indoor environments providing vibrotactile feedback to visually impaired people for reaching a target place. The DOVI system is based on sensor fusion techniques, allowing a precise and global localization of the pedestrian thanks to inertial measurements from accelerometers and gyroscope and passive RFID tags. The pedestrian is provided a haptic feedback through a vibrotactile bracelet, that can guide him/her through the correct path toward the target. The DOVI system is complementary to both those systems allowing the detection of mobile obstacles along the path and to other aids, such as the white cane or the guide dog.

In order to create a device that produces the sensation of wet cloth, we have proposed a method to augment the wet sensation of dry cloth. This paper investigated whether controlling the surface temperature and softness of a cloth could reproduce the wet sensation or not. Participants scored their feelings after touching the cloth with different temperatures and softness. Results indicated a tendency to perceive a wet sensation equivalent to actual wet cloth by not only decreasing the temperature but also increasing softness of the cloth.

This study investigated how attention is allocated by the physical distinction between tactile 2D shape features: Part 1 tested whether certain shape feature distinctions are perceived efficiently (pre-attentively), as opposed to inefficiently (attention dependent). Part 2 explored what discrimination strategies are at use, and with what level of attention (from pre to focused).It was found (Part 1) that the straight line ↔ angle distinction and the curve ↔ straight line distinction are perceived pre-attentively; the angle ↔ curve distinction attention dependent. Furthermore (Part 2), three discrimination strategies were identified: The figure identity strategy has three levels of attention; it ranks a feature conjunction as the most important target-discriminating feature. The global characteristics strategy and the touch vision strategy have two levels of attention; both rank one separate feature as the most important target-discriminating feature. Despite this, they are equally fast, accurate, and after-decision certain.

We investigate the effect of procedure-specific parameters on the performance of three common psychophysical procedures. Methods considered include transformed-staircases, the $$\varPsi $$-method and the UML method, while performance is evaluated in terms of accuracy, efficiency, precision and robustness. Simple Yes/No- and three alternative forced choice response paradigms were considered. A Monte Carlo simulation was conducted for three different types of test persons and analyzed by analysis of variances. Results show a large effect of the test person on the performance, especially for staircase procedures. No parameter exhibited a relevant effect on accuracy for each analyzed methods, estimation precision can be increased with an increasing number of trials. Only for staircase procedures, efficiency can be influenced by the choice of the progression rule.

In the literature, haptic training has long been regarded as an effective means of acquiring skills that involve force feedback. This is relevant in the context of haptic virtual reality applications that argue that the addition of haptics increases the effectiveness of the training system. Here we describe an experimental investigation which examines whether haptic feedback increases people’s spatial knowledge of a simulation. In particular, we address the following question: Is visuo-haptic interaction a more effective way of learning spatial information than purely visual interaction? A comparison of two groups of participants (visual versus visuo-haptic) revealed no significant differences in their spatial knowledge of the simulation. The findings are discussed with reference to potential variables which may affect spatial learning such as cognitive load.

Vibrotactile stimuli are of growing interest for everyday interfaces, including car interfaces. For example they can be applied to lane departure warning, collision warning, notifications etc. Yet interfaces that are not directly in contact with the user’s skin must take clothing into account. This study investigates whether clothes have a significant effect on perceived intensity of simple vibrotactile stimuli or not, and therefore if they have to be taken into account in the setting of vibrotactile feedback. In this study, we considered a single actuator on the back of a car seat, which was covered by a thin layer of foam, a layer of clothes, and hidden by a black covering. Simple vibrations of 1 s with frequencies ranging from 100 Hz to 200 Hz and three different amplitude levels were triggered. The lowest of them were below several subjects’ detection thresholds. We asked 31 subjects to give a score from 0 to 10 to assess the intensity of the stimulus. Results showed that perceived intensity is adversely affected by a thick winter coat but seems to be lightly affected by several thin layers such as T-shirts. We concluded that designers do not have to consider all the variety of clothes to set the vibration parameters, but they must take winter coats into account if final users are expected to wear that type of clothing. Moreover, we demonstrated the ability of naive subjects to score their perception of intensity of simple vibrotactile stimuli.

Generation of high-amplitude high-frequency pure-tone mechanical vibrations over a wide frequency range is required in many applications, such as Vibrotactile (VT) stimulation, material testing and so on. This paper describes development of three different types of actuator systems, pneumatic, electromagnetic and piezoelectric, towards the objective of conducting VT psychophysical experiment above 1 kHz starting from few hundreds of Hz. While the piezoelectric system offers compactness, the 120 W electromagnetic system offers wider bandwidth and is capable of generating suprathreshold stimulus even above 2 kHz. Design and response of the piezoelectric actuator system, including the custom built LVDT coupled with the actuator are detailed in this paper. The frequency response of the tested configuration remains flat over a wide bandwidth till 4 kHz, even at high level of excitation, while generating bursts of 100 µm amplitude sine waves. The developed linear charge-drive is suitable for low-current application ~50 mA, maintaining low EMI and small size.

In haptic perception sensory signals depend on how we actively move our hands. For textures with periodically repeating grooves, movement direction can determine temporal cues to spatial frequency. Moving in line with texture orientation does not generate temporal cues. In contrast, moving orthogonally to texture orientation maximizes the temporal frequency of stimulation, and thus optimizes temporal cues. Participants performed a spatial frequency discrimination task between stimuli of two types. The first type showed the described relationship between movement direction and temporal cues, the second stimulus type did not. We expected that when temporal cues can be optimized by moving in a certain direction, movements will be adjusted to this direction. However, movement adjustments were assumed to be based on sensory information, which accumulates over the exploration process. We analyzed 3 individual segments of the exploration process. As expected, participants only adjusted movement directions in the final exploration segment and only for the stimulus type, in which movement direction influenced temporal cues. We conclude that sensory signals on the texture orientation are used online during exploration in order to adjust subsequent movements. Once sufficient sensory evidence on the texture orientation was accumulated, movements were directed to optimize temporal cues.

Attention training using virtual environments is a promising way to treat mental disorders such as attention-deficit hyperactivity disorder (ADHD). Interactive haptic tasks combined with immersive visual display provide a potential solution for attention modulation and training. In this paper, we introduced a visuo-haptic game consisting of stimulus-response tasks using fingertip pressure control with immersive visual display using the Oculus Rift. Users were required to press a force sensor using either the index or middle finger from either hand. In each trial, users needed to maintain a constant force with an expected tolerance within an allowable response time. An adaptive strategy was proposed to tune the difficulty level of the task to match the force control skill of the user, which may produce an optimal success rate in each trial to maintain users’ interest and keep them motivated. Furthermore, a randomized algorithm was adopted to vary the target fingertip, target force magnitude and target tolerance between adjacent trials, which was designed to avoid the boring repetition and thus to keep the users’ curiosity on the task. Experimental results on six participants show that the proposed strategy was able to obtain different expected success rates, i.e. either 79.4 % or 50 %.

This paper introduces the first haptic interface to help blind and deaf-blind people to practice horse riding as a sportive, recreational and therapeutic activity. As a form of animal assisted therapy, horse riding has been shown to benefit people with various medical conditions. Among other benefits, horse riding can improve self-esteem and a sensation of independence. However, in the case of deaf-blind individuals a therapist or an interpreter must be present at all times to communicate with the rider by touch. We developed a novel interface which enables deaf-blind people to ride a horse while the therapist is observing and remotely providing cues to the rider, which improves his independence. Initial tests of the concept with an autistic deaf-blind individual received very positive feedback from the rider, his family and therapist.

The hanger reflex is a phenomenon that accompanies illusory force sensation and involuntary head rotation when the head is fastened with a wire hanger. This phenomenon is also observed on the wrist, and is expected to apply when using small and simple haptic feedback devices. However, issues of slow response and the requirement for large actuators still remain. Here, we discuss the discovery of a new phenomenon: the perceptual force from the hanger reflex is enhanced when a vibration is also presented. If we can control the strength of the perceptual force induced by vibration, a smaller, simpler, and higher response device might be achieved, because a vibrator can be controlled easily. This paper reports details of this phenomenon, and the effect of the frequency and amplitude of the vibration on the strength of the perceptual force. We observed that low frequency (50–100 Hz) vibrations efficiently enhanced the perceptual force, and that participants perceived a stronger perceptual force if the vibration of a greater amplitude was presented. These results suggest that the enhancement of the perceptual force is controllable and can be applied to construct a new type of wearable haptic device.

We propose a pocket-size device that enables users with no prior long-time trainings to intuitively read text letters using only their haptic sense. The device forces the user’s finger-tip to trace trajectories of lowercase roman alphabet characters. In displaying multistroke characters, vibrotactile stimuli are accordingly superposed on fingers so that users can distinguish writing strokes from transient movements of fingers between strokes. Our experiments showed that participants could recognize all alphabet characters. They were able to identify them with an accuracy rate of approximately 80 % when presented at an average rate of 1.4 s/letter. We also showed that the accuracy rate varied slightly depending on holding orientation of the device, and that these identification performances could be obtained after only five-minute training. These results suggest that the access to symbolic information via haptic modalities, which were conventionally considered to be of limited use among people with early blindness, would turn into practical mobile applications for people with late blindness or even people with normal vision.

In real world, we often come across with soft objects having spatially varying stiffness such as human palm or a wart on the skin. In this paper, we propose a novel approach to render thin, deformable objects having spatially varying stiffness (inhomogeneous material). We use the classical Kirchhoff thin plate theory to compute the deformation. In general, physics based rendering of an arbitrary 3D surface is complex and time consuming. Therefore, we approximate the 3D surface locally by a 2D plane using an area preserving mapping technique - Gall-Peters mapping. Once the deformation is computed by solving a fourth order partial differential equation, we project the points back onto the original object for proper haptic rendering. The method was validated through user experiments and was found to be realistic.

According to the laws of friction, in order to initiate a sliding motion between two objects, a tangential force larger than the maximum static friction force is required. This process is governed by a material constant called the coefficient of static friction. Therefore, it is of great utility for robots to know the coefficient of static friction between its gripper and the object being manipulated, especially when a stable and precise grip on an object is necessary. Furthermore, it is most useful if the robot can estimate the coefficient of static friction upon touching an object at the very beginning of a manipulation task, instead of having to further explore the object before it tries to move the object. Motivated by this issue, we have designed (and in this paper, further improved) a novel eight-legged tactile sensor to estimate the coefficient of static friction between a planar surface and the sensing components of the prototype sensor (which will also serve as the gripper). While the basic principle of the sensor is still unchanged, here we highlight some improvements to the sensor’s design and evaluation, including more robustly controlled frictional angles (vital for the accurate sensing) and the use of a programmable xyz-stage during evaluation. The coefficients of static friction between the sensor and nine different materials were estimated and compared to a measurement obtained via traditional methods as a reference. For all testing materials, the estimated ranges cover the corresponding reference values. Good conformance with the reference coefficients is also visually indicated from a least-square fitted line of the estimated coefficients, which has a gradient close to one and an r2 value greater than 0.9.

We developed a device that converts visual information on a tablet into tactile information on the fingertip. To achieve this we mount optical sensors and a tactile display on the fingertip. Our first prototype using a vibrator for each finger revealed that it was difficult to recognize the information of the display, mainly because of its low resolution. We addressed this limitation in our second prototype by using electro-tactile stimulation. From our preliminary experiment with a mechanical pin matrix, we decided to use a single index finger. In a subsequent alphabet recognition experiment, we confirmed that it is possible to recognize relatively complex shapes on a tablet with the device. Furthermore, we observed that the learning curve is quite steep, which implies the potential of the device.

This paper proposes a thermal display that can present a virtual thermal sensation to the finger pad using thermal stimuli on the finger side. The author developed the prototype device and evaluated the perceived strength of the thermal sensation on the finger pad after the pad makes contacts with an object. The results confirm that users perceive hot or cold sensation even if there are no thermal stimuli on the finger pad by presenting stimuli to the finger side. Furthermore, the proposed method successfully improves thermal sensation by applying the same thermal stimuli to the finger side as the sensation on the finger pad.

In this study, we develop and implement a method for superimposing two vibration modes in order to produce different tactile stimuli on two fingers located in different positions. The tactile stimulation is based on the squeeze film effect which decreases the friction between a fingertip and a vibrating plate.Experimental test have been conducted on a 1D tactile device. They show that it is possible to continuously control the friction on two fingers moving independently. Then, we developed the design of a 2D device based on the same principle, which gives rise to the design of a two-fingers tactile display. Evaluations were conducted using a modal analysis with experimental validation.