Many devices, such as smart phones, implement vibration motors for tactile feedback. When multiple vibration motors are placed on, for instance, the backrest of a chair it is possible to trace shapes on the back of a person by sequentially switching motors on and off. Social Haptic Communication (SHC) is a tactile mode of communication for persons with deafblindness that makes use of tracing shapes or other types of spatiotemporal patterns with the hand on the back of another person. This could be emulated using vibrotactile patterns. Here we investigated whether SHC users with deafblindness would recognize the vibrotactile patterns as SHC signs (Haptices). In several cases the participants immediately linked a vibrotactile patterns to the Haptice that is was meant to imitate. Together with the participants we improved and expanded the set of vibrotactile patterns.

Social Haptic Communication (SHC) is one of the many tactile modes of communication used by persons with deafblindness to access information about their surroundings. SHC usually involves an interpreter executing finger and hand signs on the back of a person with multi-sensory disabilities. Learning SHC, however, can become challenging and time-consuming, particularly to those who experience deafblindness later in life. In this work, we present PatRec: a mobile game for learning SHC concepts. PatRec is a multiple-choice quiz game connected to a chair interface that contains a 3x3 array of vibration motors emulating different SHC signs. Players collect scores and badges whenever they guess the right SHC vibration pattern, leading to continuous engagement and a better position on a leaderboard. The game is also meant for family members to learn SHC. We report the technical implementation of PatRec and the findings from a user evaluation.

Vibrotactile Morse code provides a way to convey words using the sense of touch with vibrations. This can be useful in applications for users with a visual and/or auditory impairment. The advantage of using vibrotactile Morse code is that it is technically easy to accomplish. The usefulness of tactile Morse code also depends on how easy it is to learn to use without providing a visual representation of the code. Here we investigated learning of the vibrotactile the Morse code alphabet without any visual representation of the code and whether the learned letters can immediately be used to recognize words. Two vibration motors were used: one was attached to the left arm (dots) and the other to the right arm (dashes). We gave the participants a learning session of 30 minutes and determined how many letters they had learned. All participants managed to learn at least 15 letters in this time. Directly afterward, they were presented with 2-, 3-, 4-, or 5-letter words consisting of only the letters they had learned. Participants were able to identify words, but correct rates decreased rapidly with word length. We can conclude that it is possible to learn vibrotactile Morse code using only a vibrotactile representation (15 to 24 letters in 30 minutes). After the learning session, it was possible to recognise words, but to increase the recognition rates extra training would be beneficial.

When we touch an object, we can obtain tactile information through our skin. Thus it is important to reveal the relationship between the subjective sensation and objective quantities like the skin vibration elicited on our skin. In this paper, we focus on roughness perception, one of the main tactile sensations of materials. We measured skin vibration and contact force in natural active roughness perception for a large set of different materials, of which the physical roughness could be expressed in various industrial roughness measures like Ra. The results showed that there was no relationship between contact force and subjective roughness, so apparently humans do not control contact forces intentionally in a roughness estimation task. Power functions were fitted to each relationship between the other objective parameters and estimated roughness. The goodness-of-fit value of skin vibration was significantly better than any of the other parameters. Thus, the main conclusion is that these results suggest that skin vibration plays a determining role in roughness perception.

In controlling teleoperation systems subject to communication delays, unstable behavior is often prevented by injecting damping. A proper perception of hardness is required to efficiently interact with an object, but it is unknown if and how this injected damping influences the perceived hardness of objects. To investigate the effect of damping on the perceived hardness of an object, 12 participants compared the hardnesses of lightly and heavily damped objects in a two-alternative forced choice experiment. Two tasks were investigated: an in-contact and a contact-transition task. For each task, 3 reference stiffnesses were used. Both force and position data were recorded. The results show that adding damping increases the perceived hardness of an object for an in-contact task, while it decreases perceived hardness for a contact-transition task. Movement and force data show that object indentation, mean and maximum velocity and adjusted rate-hardness, a new parameter defined in this paper, correlate with perceived object hardness. From a fundamental perspective, the results show that perceived hardness is influenced by damping in a task-specific way. Moreover, for designers of teleoperation systems the results provide insights for tuning and designing control architectures that properly reflect the desired hardness.

Active movement of the hand and fingers enables dynamic exploration of objects. Lederman and Klatzky [1987] have proposed a set of stereotyped movement patterns called Exploratory Procedures (EPs) that are linked to the acquisition of knowledge concerning specific object properties. For example, lateral motion is the optimal EP for acquiring roughness information and compliance is best estimated by employing pressure.

Although the existence of haptic size aftereffects has been known for quite some time, e.g. [1, 8, 10, 16], almost all of these studies investigated length and not volume as a measure of size. As the haptic aftereffect of three-dimensional volumes has so far only been observed qualitatively, we investigated the significance of this haptic size aftereffect in more detail by means of a size bisection task. The results are straightforward: after grasping a large sphere for a while, a subsequently grasped smaller test sphere feels even smaller. Likewise, adaptation to a small sphere results in perceiving larger spheres as even larger. The difference in perceived size in these two conditions is on average 24 %. An additional result is that in the haptic size bisection task with spheres as stimuli, participants use volume and not surface area or diameter as a measure of size, as might have been expected on the basis of a haptic volume discrimination task [5].

In the present study, blindfolded subjects had to explore differently shaped objects with two hands and to judge their volume. The results showed a significant effect of the shape of objects on their perceived volume. Additional analysis showed that this effect could not be explained by the subjects' tendency to base the volume judgment on a specific object dimension other than the volume itself. This contrasts with the results from previous studies, which used cylindrical objects or objects that could fit in one hand, in which the effect of shape on volume perception could be explained by the height/width ratio or the surface area of objects, respectively.

Inspired by the work of Yarbus on eye movements, we investigated the dependence of hand movements on “scene” and question about the scene. Our haptic scenes consisted of arrays of 3×3 samples of materials that could differ in material properties or orientation of texture. Questions we asked our participants were, for example, “Describe the relief” or “Which sample is warmest?”. Our results show that different questions lead to very distinctive movement patterns, such as a series of “static touches” or local “back and forth movements”. Interestingly, different participants produce remarkably similar movement patterns.

Salient features help identify objects. However, they can also influence subsequent comparison between objects. In this study, we investigate the influence of edges on perception of the shape of 3D objects. We tested two conditions in which subjects were asked to indicate the orientation of a block by exploring it either statically without touching the edges or freely. When edges were excluded, the threshold to determine the orientation of a block was an aspect ratio of 1.030. When the edges were explored, the threshold was 1.045. We conclude that edges disrupt the precision at which 3D objects can be perceived.

Movement strategies were investigated in a haptic search task where participants indicated whether a target was present among a varying number of items. Hand movements were classified according to two criteria into three movement types. Results indicated that an easy search was performed with a parallel strategy, while in a more difficult search a serial movement strategy is used. Short, fluent movements were made in the easy search, whereas the difficult search showed more detailed movements and this amount increased when more items were to be searched. These differences between the search tasks remained when corrected for travelled distance, while path length could partly explain dissimilarities between trials with a target present and absent. Overall, these results indicate that movement strategies are adjusted primarily to the search condition and the salience of the target, and less to the presence of a target and set size.

Discrimination thresholds for tactually perceived traversed distance were measured in three conditions: cutaneous-only, kinaesthetic-only and combined information. The results were 25 mm (32 %) in the first and 11 mm (14 %) in the latter two conditions. Although cutaneous length perception was shown to be possible, perception in the combined condition was found to be mainly based on kinaesthetic information. The maximum-likelihood estimation model of cue combination was not supported.

Specularities on surfaces with tangential hairs or grooves are readily observable in nature. Examples of such phenomena are the arched or looped highlights observed on horses and on human heads and the linear or curved specularities observed on parts of industrial machinery that have tangential grooves. We investigate the geometry of curvilinear specularities on surfaces of different curvature with tangential hairs or grooves of different orientation, under controlled lighting and viewing conditions. First the nature of these specularities is investigated qualitatively. Then specularities on parametric surfaces and hair or groove orientations are calculated for some specific cares. Explicit calculations of specularities on some special surfaces, cylinders, cones, and spheres, are verified by photographs of the reflections. Aspects of the work are applicable to computer graphics and can be utilized for the image interpretation of surface specularities.

REALISE was designed to extract from sequences of images, acquired with a moving camera, the information necessary for determining the 3D (CAD-like) structure of a real-life scene together with information about the radiometric signatures of surfaces bounding the extracted 3D objects (e.g. reflectance behaviour). The retrieved information is then integrated in a virtual reality (VR) software environment. The R&D work is been performed principally in the following areas of computer vision and computer graphics: structure from motion, recovery of geometries, recovery of photometric and texture information, highly realistic rendering on the basis of empirically-based reflectance models, and the design and development of improved rendering processes together with a new VR system. Beside this innovative R&D work another key aspect of REALISE is to have computer vision & computer graphics cooperate to produce realistic 3D data efficiently.