https://iopscience.iop.org/article/10.1088/1361-665X/ab675b/pdf

Bidirectional tactile display driven by electrostatic dielectric elastomer actuator

As smart textiles are becoming more present in our lives, investigating and designing textile interfaces has started getting more and more attention. Still, very little research has been done on how to design interactive elements for non-wearable textile interfaces for the best recognition, perception, and interaction. In this paper, we present initial assumptions for designing such interfaces, which we derived from working intensively with our partners from the industry. These have been further explored with experts from the field during interviews, and finally tested in a user study. As a conclusion of the study, we define five design recommendations for textile interfaces and present several prototypes that demonstrate them in practice. Our recommendations cover tactile contrast between textures, heights, and shapes; minimal recognizable size of elements; perception of concave and convex shapes as interactive elements; indication of interaction through shape; and recognition of tactile symbols.

Design Investigation of Embroidered Interactive Elements on Non-Wearable Textile Interfaces

The human perception of square ultrasonic modulation of the finger-surface friction was investigated during active tactile exploration by using short frictional cues of varying duration and sharpness. In a first experiment, we asked participants to discriminate the transition time and duration of short square ultrasonic reductions of friction. They proved very sensitive to discriminate millisecond differences in these two parameters with the average psychophysical thresholds being 2.3–2.4 ms for both parameters. A second experiment focused on the perception of square friction reductions with variable transition times and durations. We found that for durations of the stimulation larger than 90 ms, participants often perceived three or four edges when only two stimulations were presented while they consistently felt two edges for signals shorter than 50 ms. A subsequent analysis of the contact forces induced by these ultrasonic stimulations during slow and fast active exploration showed that two identical consecutive ultrasonic pulses can induce significantly different frictional dynamics especially during fast motion of the finger. These results confirm the human sensitivity to transient frictional cues and suggest that the human perception of square reductions of friction can depend on their sharpness and duration as well as on the speed of exploration.

/pdf/the-perception-of-ultrasonic-square-reductions-of-friction-4qzgan2wec.pdf

The Perception of Ultrasonic Square Reductions of Friction With Variable Sharpness and Duration

We study users' perception of simultaneous tactile textures in ultrasonic devices. We investigate how relevant is providing the user with different complementary and simultaneous textures with respect to the different fingers that can be used to touch the surface. We show through a controlled experiment that users are able to distinguish the number of different textures independently of using fingers from one or two hands. However, our findings indicate that users are not able to differentiate between two different textures, that is to correctly identify each of them, when using fingers from the same hand. Based on our findings, we are then able to outline three relevant guidelines to assist multi-finger tactile feedback ergonomic and devices design.

/pdf/understanding-users-perception-of-simultaneous-tactile-qhqgsbriel.pdf

Understanding users' perception of simultaneous tactile textures

Tactile discrimination and roughness perception of real textures are extensively studied and underlying perceptual mechanisms are relatively well-established. However, tactile perception of virtual textures rendered by friction modulation techniques on touch surfaces has not been investigated in detail yet. In this article, we investigated our ability to discriminate two consecutive step changes in friction (called edges), followed by discrimination and roughness perception of multiple edges (called periodic gratings). The results showed that discrimination of two consecutive edges was significantly influenced by edge sequence: a step fall in friction ( $FF$ ) followed by a step rise in friction ( $RF$ ) was discriminated more easily than the reverse order. On the other hand, periodic gratings displayed by consecutive sequences of $FF$ followed by $RF$ were perceived with the same acuity as compared to vice versa. Independent of the edge sequence, we found that a relative difference of 14% in spatial period was required to discriminate two periodic gratings. Moreover, the roughness perception of periodic gratings decreased with increasing spatial period for the range that we have investigated (spatial period $>$ 2 mm), despite the lack of spatial cues on grating height. We also observed that rate of change in friction coefficient was better correlated with the roughness perception than the friction coefficient itself. These results will further help to understand and design virtual textures for touch surfaces.

/pdf/tactile-perception-of-virtual-edges-and-gratings-displayed-11m7q0nsn0.pdf

Tactile Perception of Virtual Edges and Gratings Displayed by Friction Modulation via Ultrasonic Actuation

Tactile devices with ultrasonic vibrations (based on squeeze film effect) using piezoelectric actuators are one of the existing haptic feedback technologies. In this study we have performed two psychophysical experiments on an ultrasonic haptic tablet, in order to find the minimum size of a tactile element on which all the users are able to perfectly identify different types of textures. Our results show that the spatial resolution of the tactile element on haptic touchscreen actually varies, depending on the number and types of tactile feedback information. A first experiment exhibits three different tactile textures, chosen as being easily recognized by users. We use these textures in a second experiment, and evaluate minimal spatial area on which the chosen set of textures can be recognized. Among other, we find the minimal size depends on the texture nature.

/pdf/finding-the-minimum-perceivable-size-of-a-tactile-element-on-2yhsjafe6m.pdf

Finding the Minimum Perceivable Size of a Tactile Element on an Ultrasonic Based Haptic Tablet

Alongside questions of how to create haptic effects on displays via alternative hardware, recent work has explored rendering options with respect to haptic effects, i.e. when and where to provide haptic feedback. In particular, recent work by Zhang and Harrison for electrostatic haptic feedback noted that the optimal technique for haptic feedback during interaction is the Fill technique, where haptic effects are rendered at all times when a user's finger is within the bounds of the target. In this paper, we explore whether this result generalizes to an alternative haptic rendering technology that uses ultrasonic vibrations to create haptic sensations, a technique called the “Squeeze Film Effect”. In contrast to prior work, our results indicate that positioning the haptic feedback as a discrete linear stimulus centred on the target provides an optimal trade-off between speed, accuracy, and user preference. We highlight the implications of this work to the generalizability of haptic feedback: Haptic feedback can improve time, errors, and user satisfaction during interaction, but only if the correct form of feedback is used for the specific haptic effect generated by the hardware.

https://hal.inria.fr/hal-01734927/document

Determining the haptic feedback position for optimizing the targeting performance on ultrasonic tactile displays

In the recent years, a great interest has emerged to utilize tactile interfaces for musical interactions. These interfaces can be enhanced with tactile feedback on the user’s fingertip through various technologies, including programmable friction techniques. In this study, we use a qualitative approach to investigate the potential influence of these tactile feedback interfaces on user’s musical interaction. We have experimented three different mappings between the sound parameters and the tactile feedback in order to study the users’ experiences of a given task. Our preliminary findings suggest that friction-based tactile feedback is a useful tool to enrich musical interactions and learning.

/pdf/enriching-musical-interaction-on-tactile-feedback-surfaces-4znz6433w6.pdf

Enriching Musical Interaction on Tactile Feedback Surfaces with Programmable Friction

Recent research in haptic feedback is motivated by the crucial role that tactile perception plays in everyday touch interactions. In this paper, we describe psychophysical experiments to investigate the perceptual threshold of individual fingers on both the right and left hand of right-handed participants using active dynamic touch for spatial period discrimination of both sinusoidal and square-wave gratings on ultrasonic haptic touchscreens. Both one-finger and multi-finger touch were studied and compared. Our results indicate that users’ finger identity (index finger, middle finger, etc.) significantly affect the perception of both gratings in the case of one-finger exploration. We show that index finger and thumb are the most sensitive in all conditions whereas little finger followed by ring are the least sensitive for haptic perception. For multi-finger exploration, the right hand was found to be more sensitive than the left hand for both gratings. Our findings also demonstrate similar perception sensitivity between multi-finger exploration and the index finger of users’ right hands (i.e. dominant hand in our study), while significant difference was found between single and multi-finger perception sensitivity for the left hand.

/pdf/exploring-fingers-limitation-of-texture-density-perception-3cuqd5gnux.pdf

Farzan Kalantari

Papers

Finding the Minimum Perceivable Size of a Tactile Element on an Ultrasonic Based Haptic Tablet

Determining the haptic feedback position for optimizing the targeting performance on ultrasonic tactile displays

Enriching Musical Interaction on Tactile Feedback Surfaces with Programmable Friction

Exploring Fingers’ Limitation of Texture Density Perception on Ultrasonic Haptic Displays