Context effects in haptic perception of roughness

Roughness integration across fingers within compared with across the hands

Feeling a texture typically involves sliding the fingers of a hand across that surface or rubbing the surface between the thumb and another digit. Texture signals appear to be integrated across the digits of a hand with perceived roughness at one finger swayed in the direction of texture touched by another finger of the same hand. To date, one study has reported similar integrative effects when the pairs of digits belong to different hands. This contrasts with observations from studies of tactile detection and tactile attention where the patterns of interactions between the digits depend on whether the digits belong to the same hand or not. The present experiments revisit the question of hand identity on multidigit roughness perception using two interval forced choice (2IFC) discrimination and single interval absolute magnitude estimation (AME). Pairs of tactile gratings were actively touched using the thumb and index fingers from the same or different hands. Attention was directed towards roughness at the thumb and index finger sensations were to be ignored. For both discrimination and ratings tasks, roughness perceived at the thumb varied with the textures touched by the index finger suggesting integration of roughness cues from the two digits. This integration occurred despite differences in the two tasks such as working memory requirements. Notably, roughness signals were integrated when originating in pairs of digits on the same hand but not when from different hands. These findings add to a body of evidence based on experiments using different stimuli and tasks, suggesting that hand identity affects interactions across the digits.

Tactile information affects alternating visual percepts during binocular rivalry using naturalistic objects

INTRODUCTION

Past studies have provided evidence that the effects of tactile stimulation on binocular rivalry are mediated by primitive features (orientation and spatial frequency) common in vision and touch. In this study, we examined whether such effects on binocular rivalry can be obtained through the roughness of naturalistic objects. In three experiments, the total dominant time of visual percepts of two objects was measured under binocular rivalry when participants touched one of the objects.

RESULT

In Experiment 1, the total dominant time for the image of artificial turf and bathmat was prolonged by congruent tactile stimulation and shortened by incongruent tactile stimulation. In Experiment 2, we used the same stimuli but rotated their visual images in opposite directions. The dominant time for either image was prolonged by congruent tactile stimulation. In Experiment 3, we used different types of stimuli, smooth marble and rough fabric, and noted significant effects of the congruent and incongruent tactile stimulation on the dominant time of visual percepts.

CONCLUSION

These three experiments demonstrated that visuo-tactile interaction on binocular rivalry can be mediated by roughness.

Feeling Illusory Textures Through a Hole: Rotating Frame At Skin-Object Interface Modifies Perceived Tactile Texture

Modulating tactile texture perception for the surface of real objects is a promising way to artificially present various tactile textures. Here, we propose a simple method of modulating tactile textures for various materials, which is named the rotating-frame method. In the method, one touches an arbitrary material's surface through a hole in a cardboard frame. When the frame is rotated between the hand and material, the tactile texture of the material is perceived as if it has turned into another material. We investigated the qualitative and quantitative characteristics of the illusory modulation created by the method in a series of psychophysical experiments. We found that the method altered the tactile textures of the surfaces of touched materials such as glass and carpet to seem softer, smoother, slipperier, and warmer than they actually are. The illusory texture change occurred robustly when the method was applied with different categories of materials. Our method paves the way for the development of simple techniques for texture augmentation that can be applied to a wide range of materials and do not disrupt stable direct contact between the hand and the materials.

Describing the Sensation of the 'Velvet Hand Illusion' in Terms of Common Materials

When sandwiching two moving parallel metallic wires between both hands, one often experiences an unexpected tactile sensation known as the "velvet hand illusion" (VHI). Researchers have revealed the optimal conditions for inducing VHI, while the subjective nature of VHI remains obscure. In this article, we conducted a psychophysical experiment to investigate the quality and magnitude of the illusory sensation felt during VHI. Participants were asked to evaluate the tactile sensation of moving wires by giving tactile adjective and intensity ratings of the illusory sensation. In the same experiment, for the sake of comparison, participants also rated the sensation for various common materials one may encounter in daily life. We found that, as the intensity of the illusory sensation increased, the tactile sensation became softer, wetter, warmer, and more favorable. We also found that, when a strong illusion was reported, the sensation was similar to those for leather and fabrics rather than metallic wire, which suggests that the illusion indeed changes the perceived material category. These findings provide a better characterization of VHI as well as a better understanding of tactile texture perception.

Tactile aesthetics: Textures that we like or hate to touch

Considering object identification and recognition as well as human interaction with objects, texture as a surface property plays a crucial role. A deeper understanding of tactile aesthetics can be useful in the applied field such as in product designs that appeal more to our senses and that are more effective in eliciting certain emotional responses from a potential consumer. In the present study, behavioral experiments were performed using unfamiliar custom-made dot pattern stimuli under two complementary questionings. The first question focused on the tactile perceptive attributes related to topographical characteristics of the textures exhibited by the material surfaces. The second question focused on the texture pleasantness related both to the perceptive attributes and to the topographical characteristics of the textures. The perspective of this work opens on complementary fields of research such as neurosciences to determine the brain mechanisms in the processing of the pleasantness of tactile stimuli.

A Theoretical Framework of Haptic Processing in Automotive User Interfaces and Its Implications on Design and Engineering

Driving a car is a highly visual task. Despite the trend towards increased driver assistance and autonomous vehicles, drivers still need to interact with the car for both driving and non-driving relevant tasks, at times simultaneously. The often-resulting high cognitive load is a safety issue, which can be addressed by providing the driver with alternative feedback modalities, such as haptics. Recent trends in the automotive industry are moving towards the seamless integration of control elements through touch-sensitive surfaces. Psychological knowledge on optimally utilizing haptic technologies remains limited. The literature on automotive haptic feedback consists mainly of singular findings without putting them into a broader user context with respect to haptic design of interfaces. Moreover, haptic feedback has primarily been limited to the confirmation of control actions rather than the searching or finding of control elements, the latter of which becomes particularly important considering the current trends. This paper presents an integrated framework on haptic processing in automotive user interfaces and provides guidelines for haptic design of user interfaces in car interiors.

Effect of Visual Information on Active Touch During Mirror Visual Feedback

Several studies have demonstrated that observation of a dummy or mirror-reflected hand being stroked or moving at the same time as the hidden hand evokes a feeling that the dummy hand is one’s own, such as the rubber hand illusion (RHI) and mirror visual feedback (MVF). Under these conditions, participants also report sensing the tactile stimulation applied to the fake hands, suggesting that tactile perception is modulated by visual information during the RHI and MVF. Previous studies have utilized passive stimulation conditions; however, active touch is more common in real-world settings. Therefore, we investigated whether active touch is also modulated by visual information during an MVF scenario. Twenty-three participants (13 men and 10 women; mean age ± SD: 21.6 ± 2.0 years) were required to touch a polyurethane pad with both hands synchronously, and estimate the hardness of the pad while observing the mirror reflection. When participants observed the mirror reflection of the other hand pushing a softer or harder pad, perceived hardness estimates were significantly biased toward softer or harder, respectively, even though the physical hardness of the pad remained constant. Furthermore, perceived hardness exhibited a strong correlation with finger displacement of the mirrored, but not hidden, hand. The modulatory effects on perceived hardness diminished when participants touched the pad with both hands asynchronously or with their eyes closed. Moreover, participants experienced ownership of the mirrored hand when they touched the pad with both hands synchronously but not asynchronously. These results indicate that hardness estimates were modulated by observation of the mirrored hand during synchronous touch conditions. The present study demonstrates that, similar to passive touch, active touch is also modulated by visual input.

Integration of vibrotactile frequency information beyond the mechanoreceptor channel and somatotopy

A wide variety of tactile sensations arise from the activation of several types of mechanoreceptor-afferent channels scattered all over the body, and their projections create a somatotopic map in the somatosensory cortex. Recent findings challenge the traditional view that tactile signals from different mechanoreceptor-channels/locations are independently processed in the brain, though the contribution of signal integration to perception remains obscure. Here we show that vibrotactile frequency perception is functionally enriched by signal integration across different mechanoreceptor channels and separate skin locations. When participants touched two sinusoidal vibrations of far-different frequency, which dominantly activated separate channels with the neighboring fingers or the different hand and judged the frequency of one vibration, the perceived frequency shifted toward the other (assimilation effect). Furthermore, when the participants judged the frequency of the pair as a whole, they consistently reported an intensity-based interpolation of the two vibrations (averaging effect). Both effects were similar in magnitude between the same and different hand conditions and significantly diminished by asynchronous presentation of the vibration pair. These findings indicate that human tactile processing is global and flexible in that it can estimate the ensemble property of a large-scale tactile event sensed by various receptors distributed over the body.

Human roughness perception and possible factors effecting roughness sensation

Surface texture sensation is significant for business success, in particular for solid surfaces for most of the materials; including foods. Mechanisms of roughness perception are still unknown, especially under different conditions such as lubricants with varying viscosities, different temperatures, or under different force loads during the observation of the surface. This work aims to determine the effect of those unknown factors, with applied sensory tests on 62 healthy participants. Roughness sensation of fingertip was tested under different lubricants including water and diluted syrup solutions at room temperature (25C) and body temperature (37C) by using simple pair-wise comparison to observe the just noticeable difference threshold and perception levels. Additionally, in this research applied force load during roughness observation was tested with pair-wise ranking method to illustrate its possible effect on human sensation. Obtained results showed that human's capability of roughness discrimination reduces with increased viscosity of the lubricant, where the influence of the temperature was not found to be significant. Moreover, the increase in the applied force load showed an increase in the sensitivity of roughness discrimination. Observed effects of the applied factors were also used for estimating the oral sensation of texture during eating. These findings are significant for our fundamental understanding to texture perception, and for the development of new food products with controlled textural features.

PRACTICAL APPLICATIONS

Texture discrimination ability, more specifically roughness discrimination capability, is a significant factor for preference and appreciation for a wide range of materials, including food, furniture, or fabric. To explore the mechanism of sensation capability through tactile senses, it is necessary to identify the relevant factors and define characteristics that dominate the process involved. The results that will be obtained under these principles will be helpful for the industry in the development and optimization of new products, especially for the individuals' with special needs. With this exploratory study, we illustrate differential thresholds of tactile senses under changing conditions of surface lubrication and applied force load. Also, the tests were carried out under different temperatures to understand the oral sensation capability. The results and correlations may provide useful information about texture sensitivity and also methodologies could be applied to general sensory studies.

Too fat to fit through the door: first evidence for disturbed body-scaled action in anorexia nervosa during locomotion

To date, research on the disturbed experience of body size in Anorexia Nervosa (AN) mainly focused on the conscious perceptual level (i.e. body image). Here we investigated whether these disturbances extend to body schema: an unconscious, action-related representation of the body. AN patients (n = 19) and healthy controls (HC; n = 20) were compared on body-scaled action. Participants walked through door-like openings varying in width while performing a diversion task. AN patients and HC differed in the largest opening width for which they started rotating their shoulders to fit through. AN patients started rotating for openings 40% wider than their own shoulders, while HC started rotating for apertures only 25% wider than their shoulders. The results imply abnormalities in AN even at the level of the unconscious, action oriented body schema. Body representation disturbances in AN are thus more pervasive than previously assumed: They do not only affect (conscious) cognition and perception, but (unconscious) actions as well.

Haptic perception

Fueled by novel applications, interest in haptic perception is growing. This paper provides an overview of the state of the art of a number of important aspects of haptic perception. By means of touch we can not only perceive quite different material properties, such as roughness, compliance, friction, coldness and slipperiness, but we can also perceive spatial properties, such as shape, curvature, size and orientation. Moreover, the number of objects we have in our hand can be determined, either by counting or subitizing. All these aspects will be presented and discussed in this paper. Although our intuition tells us that touch provides us with veridical information about our environment, the existence of prominent haptic illusions will show otherwise. Knowledge about haptic perception is interesting from a fundamental viewpoint, but it also is of eminent importance in the technological development of haptic devices. At the end of this paper, a few recent applications will be presented. WIREs Cogn Sci 2013, 4:357-374. DOI: 10.1002/wcs.1238 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

Roughness perception of unfamiliar dot pattern textures

Both vision and touch yield comparable results in terms of roughness estimation of familiar textures as was shown in earlier studies. To our knowledge, no research has been conducted on the effect of sensory familiarity with the stimulus material on roughness estimation of unfamiliar textures. The influence of sensory modality and familiarity on roughness perception of dot pattern textures was investigated in a series of five experiments. Participants estimated the roughness of textures varying in mean center-to-center dot spacing in experimental conditions providing visual, haptic and visual-haptic combined information. The findings indicate that roughness perception of unfamiliar dot pattern textures is well described by a bi-exponential function of inter-dot spacing, regardless of the sensory modality used. However, sensory modality appears to affect the maximum of the psychophysical roughness function, with visually perceived roughness peaking for a smaller inter-dot spacing than haptic roughness. We propose that this might be due to the better spatial acuity of the visual modality. Individuals appeared to use different visual roughness estimation strategies depending on their first sensory experience (visual vs. haptic) with the stimulus material, primarily in an experimental context which required the combination of visual and haptic information in a single bimodal roughness estimate. Furthermore, the similarity of findings in experimental settings using real and virtual visual textures indicates the suitability of the experimental setup for neuroimaging studies, creating a more direct link between behavioral and neuroimaging results.

Length and Roughness Perception in a Moving-Plateau Touch Display

We have proposed a tactile geometry display technique based on active finger movement. The technique uses a perceptual feature that, during finger movement, the length of a touched object is perceived to increase when the object is moved in the same direction as the finger movement or to decrease when it is moved in the opposite direction. With this display technique, a wide range of tactile shapes can be presented with realistic rigid edges and continuous surfaces. In this work, to further develop our technique, we performed psychophysical experiments to study perceptions of length and roughness under this presentation technique. The results indicated that the elongation (shrinkage) of the object can be observed regardless of the roughness of the touched object and that the perceived roughness of the object slightly changes but the changes are much smaller than those theoretically expected.

The role of somatotopy and body posture in the integration of texture across the fingers

In two experiments, we investigated the automatic integration of touch across the fingers. Participants made judgments about the roughness of sequences of textures presented to one finger while simultaneously feeling textures of varying roughness with another finger (the distractor digit) on the same hand. Integration across digits was evident when the thumb and index finger were used together, whereas there was a general disruption of attention when the thumb and little finger were used together. In addition, interference was greater when the distractor digit was above the touched surface than when it was below the touched surface. These results suggest that there is integration of information across fingers when people feel textures, but that this integration pattern does not conform to a spread of activation across somatosensory maps.