A Perceptual Model-Based Approach to Plausible Authoring of Vibration for the Haptic Metaverse.

Haptic virtual reality is often misunderstood as being solely a physically identical copy of real environments. Thus, a perfect recording and reproduction of vibration that is indistinguishable in an A:B comparison is often the aim. However, in most virtual reality applications the real environment is not available for direct comparison. Instead, when judging the plausibility of a presented scene, the user compares the vibration to his expectations shaped by the audiovisual context. Therefore, it should be sufficient to find any vibration that the user expects to potentially occur in the given context. Such a vibration needs to elicit a perceptual profile with a minimal distance to an expected profile in the sensory tactile perceptual space. Building onto this formalization, this paper demonstrates a novel generative model-based approach to authoring vibrations. First, users quantify expectations as tactile profiles consisting of ratings of six sensory tactile attributes without the presence of vibrations. Subsequently, the model predicts vibration parameters from such profiles. This ensures the fulfillment of user expectations and thus high plausibility. Furthermore, it eliminates the necessity of recordings, infeasible for scenes with no real counterpart and opens the door to crowdsourcing the authoring process with laypersons for the haptic metaverse.

Phantom Illusion based Vibrotactile Rendering of Affective Touch Patterns.

Physically accurate (authentic) reproduction of affective touch patterns on the forearm is limited by actuator technology. However, in most VR applications a direct comparison with actual touch is not possible. Here, the plausibility is only compared to the user's expectation. Focusing on the approach of plausible instead of authentic touch reproduction enables new rendering techniques, like the utilization of the phantom illusion to create the sensation of moving vibrations. Following this idea, a haptic armband array (4x2 vibrational actuators) was built to investigate the possibilities of recreating plausible affective touch patterns with vibration. The novel aspect of this work is the approach of touch reproduction with a parameterized rendering strategy, enabling the integration in VR. A first user study evaluates suitable parameter ranges for vibrational touch rendering. Duration of vibration and signal shape influence plausibility the most. A second user study found high plausibility ratings in a multimodal scenario and confirmed the expressiveness of the system. Rendering device and strategy are suitable for a various stroking patterns and applicable for emerging research on social affective touch reproduction.

Perceptual Substitution Based Haptic Texture Rendering for Narrow-Band Reproduction.

Recorded high-resolution texture vibration contains perceptually redundant spectral information due to tactile limitations of human skin. Also, accurate reproduction of recorded texture vibration is often infeasible for widely available haptic reproduction systems at mobile devices. Usually, haptic actuators can only reproduce narrow-bandwidth vibration. With the exception of research setups, rendering strategies need to be developed, that utilize the limited capabilities of various actuator systems and tactile receptors while minimizing a negative impact on perceived quality of reproduction. Therefore, the aim of this study is to substitute recorded texture vibrations with perceptually sufficient simple vibrations. Accordingly, similarity of band-limited noise, single sinusoid and amplitude-modulated signals on display are rated compared to real textures. Considering that low and high frequency bands of noise signals might be implausible and redundant, different combinations of cut-off frequencies are applied to noise vibrations. Moreover, suitability of amplitude-modulation signals are tested for coarse textures in addition to single sinusoids because of their capability of creating pulse-like roughness sensation without too low frequencies. With the set of experiments, narrowest band noise vibration with frequencies between 90 Hz to 400 Hz is determined according to the fine textures. Furthermore, AM vibrations are found to be more congruent than single sinusoids to reproduce too coarse textures.

Congruence-based contextual plausibility modulates cortical activity during vibrotactile perception in virtual multisensory environments.

How congruence cues and congruence-based expectations may together shape perception in virtual reality (VR) still need to be unravelled. We linked the concept of plausibility used in VR research with congruence-based modulation by assessing brain responses while participants experienced vehicle riding experiences in VR scenarios. Perceptual plausibility was manipulated by sensory congruence, with multisensory stimulations confirming with common expectations of road scenes being plausible. We hypothesized that plausible scenarios would elicit greater cortical responses. The results showed that: (i) vibrotactile stimulations at expected intensities, given embedded audio-visual information, engaged greater cortical activities in frontal and sensorimotor regions; (ii) weaker plausible stimulations resulted in greater responses in the sensorimotor cortex than stronger but implausible stimulations; (iii) frontal activities under plausible scenarios negatively correlated with plausibility violation costs in the sensorimotor cortex. These results potentially indicate frontal regulation of sensory processing and extend previous evidence of contextual modulation to the tactile sense.

Deliberate Practice and Motor Learning Principles to Underpin the Design of Training Interventions for Improving Lifting Movement in the Occupational Sector: A Perspective and a Pilot Study on the Role of Augmented Feedback.

Spine posture during repetitive lifting is one of the main risk factors for low-back injuries in the occupational sector. It is thus critical to design appropriate intervention strategies for training workers to improve their posture, reducing load on the spine during lifting. The main approach to train safe lifting to workers has been educational; however, systematic reviews and meta-analyses have shown that this approach does not improve lifting movement nor reduces the risk of low back injury. One of the main limitations of this approach lies in the amount, quality and context of practice of the lifting movement. In this article, first we argue for integrating psychologically-grounded perspectives of practice design in the development of training interventions for safe lifting. Principles from deliberate practice and motor learning are combined and integrated. Given the complexity of lifting, a training intervention should occur in the workplace and invite workers to repeatedly practice/perform the lifting movement with the clear goal of improving their lifting-related body posture. Augmented feedback has a central role in creating the suitable condition for achieving such intervention. Second, we focus on spine bending as risk factor and present a pilot study examining the benefits and boundary conditions of different feedback modalities for reducing bending during lifting. The results showed how feedback modalities meet differently key requirements of deliberate practice conditions, i.e., feedback has to be informative, individualized and actionable. Following the proposed approach, psychology will gain an active role in the development of training interventions, contributing to finding solutions for a reduction of risk factors for workers.

Mapping the Sensory-Perceptual Space of Vibration for User-Centered Intuitive Tactile Design.

In vibrotactile design, it can be beneficial to communicate with potential users about the desired properties of a product. However, such users' expectations would need to be translated into physical vibration parameters. In everyday life, humans are frequently exposed to seat vibration. Humans have learned to intuitively associate specific labels (e.g., "tingling") with specific vibrations. Thus, the aim of this article is to identify the most common sensory-perceptual attributes and their relationships to vibration parameters. First, we generalized everyday-life seat vibration into sinusoidal, amplitude-modulated sinusoidal, white Gaussian noise and impulse-like vibrations. Subsequently, the (peak) level, (center/carrier) frequency, bandwidth, modulation frequency and exponential decay rate parameters of these vibrations were systematically varied depending on the signal type. A free association task was conducted to reveal the most common sensory-perceptual attributes for each vibration. After aggregating similar attributes, the 21 most frequently occurring attributes were utilized in a second experiment to rate their suitability for describing each vibration stimulus. Principal component analysis guided the selection of six attribute groups, which can be represented by "up and down," "tingling," "weak," "repetitive," "uniform" and "fading." The observed relationships between vibration parameters and attribute ratings are suitable for future model building.