Publications
Vibrations effectively transmit information from objects, surfaces or events to the human skin through the cutaneous sense. However, due to the diverse densities of receptive fields and mechanoreceptor populations vibrotactile sensitivity differs across body parts. Hardware that utilizes vibrotactile information should consider such differences. Here, we examined perceived intensity of vibrotactile stimuli applied to the front and back of the human torso. Participants wore a vibrotactile vest. They had to judge if a vibration from the back side of the vest was larger or smaller than a fixed vibration given from the front side; the intensity of the stimulus at the back was adapted using staircase methods. We found that, stimuli at the back had to be physically more intense by 12.3% than stimuli at the front to be perceived equally intense: Presentation of vibrotactile information through wearables could equalize for differential sensitivity, e.g., to equalize attention-capturing effects.
Celebi, B., Cavdan, M., Drewing, K. (2022). Vibrotactile Stimuli are Perceived More Intense at the Front than at the Back of the Torso. In: , et al. Haptics: Science, Technology, Applications. EuroHaptics 2022. Lecture Notes in Computer Science, vol 13235. Springer, Cham. https://doi.org/10.1007/978-3-031-06249-0_7
Perceiving mechanical properties of objects, i.e., how they react to physical forces, is a crucial ability in many aspects of life, from choosing an avocado to picking your clothes. There is, a wide variety of materials that differ substantially in their mechanical properties. For example, both, silk and sand deform and change shape in response to exploration forces, but each does so in very different ways. Studies show that the haptic perceptual space has multiple dimensions corresponding to the physical properties of textures, however in these experiments the range of materials or exploratory movements were restricted. Here we investigate the perceptual dimensionality in a large set of real materials in a free haptic exploration task. Thirty‑two participants actively explored deformable and non‑deformable materials with their hands and rated them on several attributes. Using the semantic differential technique, video analysis and linear classification, we found four haptic dimensions, each associated with a distinct set of hand and finger movements during active exploration. Taken together our findings suggest that the physical, particularly the mechanical, properties of a material systematically affect how it is explored on a much more fine‑grained level than originally thought. Dövencioǧlu, D.N., Üstün, F.S., Doerschner, K. et al. Hand explorations are determined by the characteristics of the perceptual space of real-world materials from silk to sand. Sci Rep 12, 14785 (2022). https://doi.org/10.1038/s41598-022-18901-6
When humans explore objects haptically, they seem to use prior as well as sensory information to adapt their exploratory behavior. For texture discrimination, it was shown that participants adapted the direction of their exploratory movement to be orthogonal to the orientation of textures with a defined direction. That is, they adapted the exploratory direction based on the sensory information gathered over the course of an exploration, and this behavior improved their perceptual precision. In the present study we examined if prior visual information that indicates a texture orientation produces a similar adjustment of exploratory movement direction. We expected an increase of orthogonal initial exploration movements with higher qualities of prior information. In each trial, participants explored two grating textures with equal amplitude, only differing in their spatial period. They had to report the stimulus with the higher spatial frequency. Grating stimuli were given in six different orientations relative to the observer. Prior visual information on grating orientation was given in five different qualities: 50% (excellent information), 35%, 25%, 15% and 0% (none). We analyzed movement directions of the first, middle and last strokes over the textures of each trial. The results show an increase in the amount of initial orthogonal strokes and a decrease in variability of movement directions with higher qualities of prior visual information. Jeschke, M., Zöller, A.C., Drewing, K. (2022). Influence of Prior Visual Information on Exploratory Movement Direction in Texture Perception. In: , et al. Haptics: Science, Technology, Applications. EuroHaptics 2022. Lecture Notes in Computer Science, vol 13235. Springer, Cham. https://doi.org/10.1007/978-3-031-06249-0_4
Haptic perception of objects’ softness plays an important role in the identification and interaction with objects. How softness is represented in the brain is yet not clear. Here we investigated whether there is a neutral point in the perceptual representation of haptically perceived softness relative to which the objects are represented as being “soft” or “hard”. We created a wide range of softness stimuli, varying from very hard (ceramic) to very soft foam with differently soft foam and silicone stimuli in between. Participants were assigned to one of three different stimulus set conditions: full set (18 stimuli), soft set (13 softest stimuli) or the hard set (13 hardest stimuli). They categorized each stimulus as “hard” or “soft” and we estimated the neutral point as the point of subjectively equal categorization as “hard” or “soft”. We found that neutral points were different from the middle stimulus of each set. Furthermore, during the course of the experiment neutral points rather moved away from the middle of the stimulus set than towards it. Our results indicate that there might be a neutral point in the representation of haptically perceived softness, however range effects may play a role. Metzger, A., Lotz, A., Drewing, K. (2022). Neutral Point in Haptic Perception of Softness. In: , et al. Haptics: Science, Technology, Applications. EuroHaptics 2022. Lecture Notes in Computer Science, vol 13235. Springer, Cham. https://doi.org/10.1007/978-3-031-06249-0_7
Fingertip friction and the related shear of skin are key mechanical mechanisms in tactile perception, but the perception of friction itself is rarely explored except for the flat surfaces of tactile displays. We investigated the perception of friction for tactile exploration of a unique set of samples whose fabric-like surfaces are equipped with regular arrays of flexible micropillars. The measured fingertip friction increases with decreasing bending stiffness, where the latter is controlled by radius (20–75 µm) and aspect ratio of the micropillars. In forced-choice tasks, participants noticed relative differences in friction as small as 0.2, and even smaller when a sample with less than 100 µm distance between pillars is omitted from the analysis. In an affective ranking of samples upon active touch, the perception of pleasantness is anticorrelated with the measured friction. Our results offer insights towards a rational design of materials with well-controlled surface microstructure which elicit a dedicated tactile appeal. Fehlberg, M., Kim, KS., Drewing, K., Hensel, R., Bennewitz, R. (2022). Perception of Friction in Tactile Exploration of Micro-structured Rubber Samples. In: , et al. Haptics: Science, Technology, Applications. EuroHaptics 2022. Lecture Notes in Computer Science, vol 13235. Springer, Cham. https://doi.org/10.1007/978-3-031-06249-0_3
In the flash lag effect (FLE), a moving object is seen to be ahead of a brief flash that is presented at the same spatial location; a haptic analogue of the FLE has also been observed [1, 2]. Some accounts of the FLE relate the effect to temporal delays in the processing of the stationary stimulus as compared to that of the moving stimulus [3–5]. We tested for movement-related processing effects in haptics. People judged the temporal order of two vibrotactile stimuli at the two hands: One hand was stationary, the other hand was executing a fast, medium, or slow hand movement. Stimuli at the moving hand had to be presented around 36 ms later, to be perceived to be simultaneous with stimuli at the stationary hand. In a control condition, where both hands were stationary, perceived simultaneity corresponded to physical simultaneity. We conclude that the processing of haptic stimuli at moving hands is accelerated as compared to stationary ones–in line with assumptions derived from the FLE. Drewing, K., Vroomen, J. (2022). Moving Hands Feel Stimuli Before Stationary Hands. In: , et al. Haptics: Science, Technology, Applications. EuroHaptics 2022. Lecture Notes in Computer Science, vol 13235. Springer, Cham. https://doi.org/10.1007/978-3-031-06249-0_2
We interact with different types of soft materials on a daily basis such as salt, hand cream, etc. Recently we have shown that soft materials can be described using four perceptual dimensions which are deformability, granularity, viscosity, and surface softness [1]. Here, we investigated whether humans can actually perceive systematic differences in materials that selectively vary along one of these four dimensions as well as how judgments on the different dimensions are correlated to softness judgments. We selected at least two material classes per dimension (e.g., hair gel and hand cream for viscosity) and varied the corresponding feature (e.g., the viscosity of hair gel). Participants ordered four to ten materials from each material class according to their corresponding main feature, and in addition, according to their softness. Rank orders of materials according to the main feature were consistent across participants and repetitions. Rank orders according to softness were correlated either positively or negatively with the judgments along the associated four perceptual dimensions. These findings support our notion of multiple softness dimensions and demonstrate that people can reliably discriminate materials which are artificially varied along each of these softness dimensions. Cavdan, M., Doerschner, K., Drewing, K. (2022). Haptic Discrimination of Different Types of Soft Materials. In: , et al. Haptics: Science, Technology, Applications. EuroHaptics 2022. Lecture Notes in Computer Science, vol 13235. Springer, Cham. https://doi.org/10.1007/978-3-031-06249-0_1
We recorded vibratory patterns elicited by free haptic exploration of a large set of natural textures with a steel tool tip. Vision and audio signals during the exploration were excluded. After the exploration of each sample, participants provided judgments about its perceptual attributes and material category. We found that vibratory signals can be approximated by a single parameter in the temporal frequency domain, in a similar way as we can describe the spatial frequency spectrum of natural images. This parameter varies systematically between material categories and correlates with human perceptual judgements. It provides an estimate of the spectral composition of the power spectra which is highly correlated with the differential activity of the Rapidly Adapting (RA) and Pacinian Corpuscle (PC) afferents. Toscani, M., Metzger. A. (2022). A Database of Vibratory Signals from Free Haptic Exploration of Natural Material Textures and Perceptual Judgments (ViPer): Analysis of Spectral Statistics. In: , et al. Haptics: Science, Technology, Applications. EuroHaptics 2022. Lecture Notes in Computer Science, vol 13235. Springer, Cham. https://doi.org/10.1007/978-3-031-06249-0_36
The ability to sample sensory information with our hands is crucial for smooth and efficient interactions with the world. Despite this important role of touch, tactile sensations on a moving hand are perceived weaker than when presented on the same but stationary hand. This phenomenon of tactile suppression has been explained by predictive mechanisms, such as internal forward models, that estimate future sensory states of the body on the basis of the motor command and suppress the associated predicted sensory feedback. The origins of tactile suppression have sparked a lot of debate, with contemporary accounts claiming that suppression is independent of sensorimotor predictions and is instead due to an unspecific mechanism. Here, we target this debate and provide evidence for specific tactile suppression due to precise sensorimotor predictions. Participants stroked with their finger over textured objects that caused predictable vibrotactile feedback signals on that finger. Shortly before touching the texture, we probed tactile suppression by applying external vibrotactile probes on the moving finger that either matched or mismatched the frequency generated by the stroking movement along the texture. We found stronger suppression of the probes that matched the predicted sensory feedback. These results show that tactile suppression is specifically tuned to the predicted sensory states of a movement . Führer, E., Voudouris, D., Lezkan, A., Drewing, K., & Fiehler, K. (2021). Tactile suppression stems from sensation-specific sensorimotor predictions. Proceedings of the National Academy of Sciences (2022). https://doi.org/10.1073/pnas.2118445119
Creativity has traditionally been associated with high independence and low conformity. The present study investigated the moderating role of collectivist (conformity) and individualist (self-direction) values in the link between self-construals and creativity in a collectivist cultural context. We hypothesized that (1) creativity would be related to both independent and interdependent self, and (2) creativity would be higher when individual values fit with cultural norms. We also investigated whether a bicultural self, characterized by high independence coupled with high interdependence, benefits creativity more than nonbicultural combinations and whether values moderate these relations. The task-specific perceived and actual creativity scores of 201 undergraduate students in Turkey showed expected relations with self-construals and values: First, both independence and interdependence were positively related to higher creativity. Second, high interdependence benefitted creativity more when coupled with high conformity or low self-direction. Finally, people with a bicultural self were more creative, especially when they were also high on conformity. Overall, our study provides first evidence for the interplay between self-construals, values, and the larger cultural context in affording or limiting individuals’ creativity. The results were discussed in terms of the implications for cultivating creativity in educational and intercultural settings. Güngör, D., Yildiz, G.Y. & Cavdan, M. Values Moderate the Relations Between Self-Construals and Creativity: The Role of Cultural Fit. Psychol Stud (2022). https://doi.org/10.1007/s12646-022-00651-0
When touching the surface of an object, its spatial structure translates into a vibration on the skin. The perceptual system evolved to translate this pattern into a representation that allows to distinguish between different materials. Here, we show that perceptual haptic representation of materials emerges from efficient encoding of vibratory patterns elicited by the interaction with materials. We trained a deep neural network with unsupervised learning (Autoencoder) to reconstruct vibratory patterns elicited by human haptic exploration of different materials. The learned compressed representation (i.e., latent space) allows for classification of material categories (i.e., plastic, stone, wood, fabric, leather/wool, paper, and metal). More importantly, classification performance is higher with perceptual category labels as compared to ground truth ones, and distances between categories in the latent space resemble perceptual distances, suggesting a similar coding. Crucially, the classification performance and the similarity between the perceptual and the latent space decrease with decreasing compression level. We could further show that the temporal tuning of the emergent latent dimensions is similar to properties of human tactile receptors. Metzger, A., & Toscani, M. (2022). Unsupervised learning of haptic material properties. eLife, 11, e64876. https://doi.org/10.3758/s13414-021-02427-6
The Approximate Number System (ANS) is conceptualized as an innate cognitive system that allows humans to perceive numbers of objects or events (>4) in a fuzzy, imprecise manner. The representation of numbers is assumed to be abstract and not bound to a particular sense. In the present study, we test the assumption of a shared cross-sensory system. We investigated approximate number processing in the haptic modality and compared performance to that of the visual modality. We used a dot comparison task (DCT), in which participants compare two dot arrays and decide which one contains more dots. In the haptic DCT, 67 participants had to compare two simultaneously presented dot arrays with the palms of their hands; in the visual DCT, participants inspected and compared dot arrays on a screen. Tested ratios ranged from 2.0 (larger/smaller number) to 1.1. As expected, in both the haptic and the visual DCT responses similarly depended on the ratio of the numbers of dots in the two arrays. However, on an individual level, we found evidence against medium or stronger positive correlations between “ANS acuity” in the visual and haptic DCTs. A regression model furthermore revealed that besides number, spacing-related features of dot patterns (e.g., the pattern’s convex hull) contribute to the percept of numerosity in both modalities. Our results contradict the strong theory of the ANS solely processing number and being independent of a modality. According to our regression and response prediction model, our results rather point towards a modality-specific integration of number and number-related features. Ziegler, M., Drewing, K. Get in touch with numbers – an approximate number comparison task in the haptic modality. Atten Percept Psychophys (2022). https://doi.org/10.3758/s13414-021-02427-6