Yasemin Vardar - Academia.edu (original) (raw)

Papers by Yasemin Vardar

PLOS ONE, 2022

Pressing the fingertips into surfaces causes skin deformations that enable humans to grip objects... more Pressing the fingertips into surfaces causes skin deformations that enable humans to grip objects and sense their physical properties. This process involves intricate finger geometry, non-uniform tissue properties, and moisture, complicating the underlying contact mechanics. Here we explore the initial contact evolution of dry and hydrated fingers to isolate the roles of governing physical factors. Two participants gradually pressed an index finger on a glass surface under three moisture conditions: dry, water-hydrated, and glycerin-hydrated. Gross and real contact area were optically measured over time, revealing that glycerin hydration produced strikingly higher real contact area, while gross contact area was similar for all conditions. To elucidate the causes for this phenomenon, we investigated the combined effects of tissue elasticity, skin-surface friction, and fingerprint ridges on contact area using simulation. Our analyses show the dominant influence of elastic modulus over friction and an unusual contact phenomenon, which we call friction-induced hinging.

Frontiers in Neuroscience, Apr 15, 2020

One may notice a relatively wide range of tactile sensations even when touching the same hard, fl... more One may notice a relatively wide range of tactile sensations even when touching the same hard, flat surface in similar ways. Little is known about the reasons for this variability, so we decided to investigate how the perceptual intensity of light stickiness relates to the physical interaction between the skin and the surface. We conducted a psychophysical experiment in which nine participants actively pressed their finger on a flat glass plate with a normal force close to 1.5 N and detached it after a few seconds. A custom-designed apparatus recorded the contact force vector and the finger contact area during each interaction as well as pre-and post-trial finger moisture. After detaching their finger, participants judged the stickiness of the glass using a nine-point scale. We explored how sixteen physical variables derived from the recorded data correlate with each other and with the stickiness judgments of each participant. These analyses indicate that stickiness perception mainly depends on the pre-detachment pressing duration, the time taken for the finger to detach, and the impulse in the normal direction after the normal force changes sign; finger-surface adhesion seems to build with pressing time, causing a larger normal impulse during detachment and thus a more intense stickiness sensation. We additionally found a strong between-subjects correlation between maximum real contact area and peak pull-off force, as well as between finger moisture and impulse.

In Proceedings of the IEEE World Haptics Conference, 2017

In this study, we have investigated the human roughness perception of periodical textures on an e... more In this study, we have investigated the human roughness perception of periodical textures on an electrostatic display by conducting psychophysical experiments with 10 subjects. To generate virtual textures, we used low-frequency unipolar pulse waves in different waveform (sinusoidal, square, saw-tooth, triangle), and spacing. We modulated these waves with a 3kHz high frequency sinusoidal carrier signal to minimize perceptional differences due to the electrical filtering of human finger and eliminate low-frequency distortions. The subjects were asked to rate 40 different macro textures on a Likert scale of 1-7. We also collected the normal and tangential forces acting on the fingers of subjects during the experiment. The results of our user study showed that subjects perceived the square wave as the roughest while they perceived the other waveforms equally rough. The perceived roughness followed an inverted U-shaped curve as a function of groove width, but the peak point shifted to t...

Springer Series on Touch and Haptic Systems

Springer Series on Touch and Haptic Systems, 2020

In this chapter, we investigated the effect of input voltage waveform on our tactile perception o... more In this chapter, we investigated the effect of input voltage waveform on our tactile perception of electrovibration on touch screens. Through psychophysical experiments performed with eight subjects, we first measured the detection thresholds of electrovibration stimuli generated by sinusoidal and square voltages at various fundamental frequencies. We observed that the subjects were more sensitive to stimuli generated by square wave voltage than sinusoidal one for frequencies lower than 60 Hz. Using Matlab simulations, we showed that the sensation difference of waveforms in low fundamental frequencies occurred due to the frequency-dependent electrical properties of human skin and human tactile sensitivity. To validate our simulations, we conducted a second experiment with another group of eight subjects. We first actuated the touch screen at the threshold voltages estimated in the first experiment and then measured the contact force and acceleration acting on the index fingers of th...

Springer Series on Touch and Haptic Systems, 2020

Generating realistic texture feelings on tactile displays using data-driven methods has attracted... more Generating realistic texture feelings on tactile displays using data-driven methods has attracted a lot of interest in the last decade. However, the need for large data storage and transmission rates complicates the use of these methods for the future commercial displays. In this chapter, we proposed a new texture rendering approach which can compress the texture data significantly for electrostatic displays. Using three sample surfaces, we first explained how to record, analyze and compress the texture data, and render them on a touchscreen. Then, through psychophysical experiments conducted with nineteen participants, we showed that the textures can be reproduced by a significantly less number of frequency components than the ones in the original signal without inducing perceptual degradation. Moreover, our results indicated that the possible degree of compression is affected by the surface properties.

Springer Series on Touch and Haptic Systems, 2020

In this chapter, we have investigated the human roughness perception of periodical textures on an... more In this chapter, we have investigated the human roughness perception of periodical textures on an electrostatic display by conducting psychophysical experiments with 10 subjects. To generate virtual textures, we used low frequency unipolar pulse waves in different waveform (sinusoidal, square, saw-tooth, triangle), and spacing. We modulated these waves with a 3 kHz high frequency sinusoidal carrier signal to minimize perceptional differences due to the electrical filtering of human finger and eliminate low-frequency distortions. The subjects were asked to rate 40 different macro textures on a Likert scale of 1–7. We also collected the normal and tangential forces acting on the fingers of subjects during the experiment. The results of our user study showed that subjects perceived the square wave as the roughest while they perceived the other waveforms equally rough. The perceived roughness followed an inverted U-shaped curve as a function of groove width, but the peak point shifted t...

Wearable tactile displays can create the illusion of touching real textures by applying vibration... more Wearable tactile displays can create the illusion of touching real textures by applying vibrations to the finger as it moves across a virtual surface. There are many possible methods of modulating this vibratory content with finger movement, each potentially best suited to different texture length scales. Using a vibrotactile haptic ring paired with finger position tracking, here we explore the advantages of three vibration modulation schemes that scale the frequency or amplitude of applied vibrations as a function of finger velocity. Ongoing psychophysical experiments will characterize trade-offs between ease of control and perceived texture realism for frequencies associated with both coarse and fine textures.

Generating realistic texture feelings on tactile displays using data- driven methods has attracte... more Generating realistic texture feelings on tactile displays using data- driven methods has attracted a lot of interest in the last decade. However, the need for large data storages and transmission rates complicates the use of these methods for the future commercial displays. In this paper, we propose a new texture rendering approach which can compress the texture data significantly for electrostatic displays. Using three sample surfaces, we first explain how to record, analyze and compress the texture data, and render them on a touchscreen. Then, through psychophysical experiments conducted with nineteen participants, we show that the textures can be reproduced by a significantly less number of frequency components than the ones in the original signal without inducing perceptual degradation. Moreover, our results indicate that the possible degree of compression is affected by the surface properties.

Springer Series on Touch and Haptic Systems

One approach to generating realistic haptic feedback on touch screens is electrovibration. In thi... more One approach to generating realistic haptic feedback on touch screens is electrovibration. In this technique, the friction force is altered via electrostatic forces, which are generated by applying an alternating voltage signal to the conductive layer of a capacitive touchscreen. Although the technology for rendering haptic effects on touch surfaces using electrovibration is already in place, our knowledge of the perception mechanisms behind these effects is limited. This thesis aims to explore the

Journal of the Royal Society Interface, 2021

Electrovibration holds great potential for creating vivid and realistic haptic sensations on touc... more Electrovibration holds great potential for creating vivid and realistic haptic sensations on touchscreens. Ideally, a designer should be able to control what users feel independent of the number of fingers they use, the movements they make, and how hard they press. We sought to understand the perception and physics of such interactions by determining the smallest 125 Hz electrovibration voltage that 15 participants could reliably feel when performing four different touch interactions at two normal forces. The results proved for the first time that both finger motion and contact by a second finger significantly affect what the user feels. At a given voltage, a single moving finger experiences much larger fluctuating electrovibration forces than a single stationary finger, making electrovibration much easier to feel during interactions involving finger movement. Indeed, only about 30% of participants could detect the stimulus without motion. Part of this difference comes from the fact...

IEEE World Haptics Conference, 2019

Masking has been used to study human perception of tactile stimuli, including those created on ha... more Masking has been used to study human perception of tactile stimuli, including those created on haptic touch screens. Earlier studies have investigated the effect of in-site masking on tactile perception of electrovibration. In this study, we investigated whether it is possible to change the detection threshold of electrovibration at fingertip of index finger via remote masking, i.e. by applying a (mechanical) vibrotactile stimulus on the proximal phalanx of the same finger. The masking stimuli were generated by a voice coil (Haptuator). For eight participants, we first measured the detection thresholds for electrovibration at the fingertip and for vibrotactile stimuli at the proximal phalanx. Then, the vibrations on the skin were measured at four different locations on the index finger of subjects to investigate how the mechanical masking stimulus propagated as the masking level was varied. Finally, electrovibration thresholds were measured in the presence of vibrotactile masking stimuli. Our results show that vibrotactile masking stimuli generated sub-threshold vibrations around fingertip and, hence, probably did not mechanically interfere with the electrovibration stimulus. However, there was a clear psychophysical masking effect due to central neural processes. Electrovibration absolute threshold increased approximately 0.19 dB for each dB increase in the masking level.

IEEE World Haptics Conference, 2019

Both vision and touch contribute to the perception of real surfaces. Although there have been man... more Both vision and touch contribute to the perception of real surfaces. Although there have been many studies on the individual contributions of each sense, it is still unclear how each modality's information is processed and integrated. To fill this gap, we investigated the similarity of visual and haptic perceptual spaces, as well as how well they each correlate with fingertip interaction metrics. Twenty participants interacted with ten different real surfaces from the Penn Haptic Texture Toolkit by either looking at or touching them and judged their similarity in pairs. By analyzing the resulting similarity ratings using non-metric multi-dimensional scaling (NMDS), we found that surfaces are similarly organized within the three-dimensional perceptual spaces of both modalities. Also, between-participant correlations were significantly higher in the haptic condition. In a separate experiment, we obtained the contact forces and accelerations acting on one finger interacting with each surface in a controlled way. We analyzed the collected fingertip interaction data in both the time and frequency domains. Our results suggest that the three perceptual dimensions for each modality can be represented by roughness/smoothness, hardness/softness, and friction, and that these dimensions can be estimated by surface vibration power, tap spectral centroid, and kinetic friction coefficient, respectively.

International Workshop on Haptic and Audio Interaction Design, 2019

Generating realistic texture feelings on tactile displays using data-driven methods has attracted... more Generating realistic texture feelings on tactile displays using data-driven
methods has attracted a lot of interest in the last decade.
However, the need for large data storage and transmission rates
complicates the use of these methods for future commercial
displays. In this paper, we propose a new texture rendering approach
that can compress the texture data signifcantly for electrostatic
displays. Using three sample surfaces, we first explain
how to record, analyze and compress the texture data, and render
them on a touchscreen. Then, through psychophysical experiments
conducted with nineteen participants, we show that the textures can
be reproduced by a significantly less number of frequency components
than the ones in the original signal without inducing perceptual
degradation. Moreover, our results indicate that the possible
degree of compression is affected by the surface properties.

6th IFAC Symposium on Mechatronic Systems, 2013

Abstract In high-precision motion systems, set-point tracking often comes with the problem of ove... more Abstract In high-precision motion systems, set-point tracking often comes with the problem of overshoot, hence poor settling behavior. To avoid overshoot, PD control (thus without using an integrator) is preferred over PID control. However, PD control gives rise to steady-state error in view of the constant disturbances acting on the system. To deal with both overshoot and steady-state error, a sliding mode controller with saturated integrator is studied. For large servo signals the controller is switched to PD mode as to constrain the integrator buffer and therefore the overshoot. For small servo signals the controller switches to PID mode as to avoid steady-state error. The tuning of the switching parameters will be done automatically with the aim to optimize the settling behavior. The sliding mode controller will be tested on a high-precision motion system.

IEEE Transactions on Haptics, 2019

Realistic display of tactile textures on touch screens is a big step forward for haptic technolog... more Realistic display of tactile textures on touch screens is a big step forward for haptic technology to reach a wide range of consumers utilizing electronic devices on a daily basis. Since the texture topography cannot be rendered explicitly by electrovibration on touch screens, it is important to understand how we perceive the virtual textures displayed by friction modulation via electrovibration. We investigated the roughness perception of real gratings made of plexiglass and virtual gratings displayed by electrovibration through a touch screen for comparison. In particular, we conducted two psychophysical experiments with 10 participants to investigate the effect of spatial period and the normal force applied by finger on roughness perception of real and virtual gratings in macro size. We also recorded the contact forces acting on the participants' finger during the experiments. The results showed that the roughness perception of real and virtual gratings are different. We argue that this difference can be explained by the amount of fingerpad penetration into the gratings. For real gratings, penetration increased tangential forces acting on the finger, whereas for virtual ones where skin penetration is absent, tangential forces decreased with spatial period. Supporting our claim, we also found that increasing normal force increases the perceived roughness of real gratings while it causes an opposite effect for the virtual gratings. These results are consistent with the tangential force profiles recorded for both real and virtual gratings. In particular, the rate of change in tangential force (dFt/dt) as a function of spatial period and normal force followed trends similar to those obtained for the roughness estimates of real and virtual gratings, suggesting that it is a better indicator of the perceived roughness than the tangential force magnitude.

IEEE Transactions on Haptics, 2018

Future touch screen applications will include multiple tactile stimuli displayed simultaneously o... more Future touch screen applications will include multiple tactile stimuli displayed simultaneously or consecutively to single finger or multiple fingers. These applications should be designed by considering human tactile masking mechanism since it is known that presenting one stimulus may interfere with the perception of the other. In this study, we investigate the effect of masking on the tactile perception of electrovibration displayed on touch screens. Through conducting psychophysical experiments with nine participants, we measured the masked thresholds of sinusoidal electrovibration bursts (125 Hz) under two masking conditions: simultaneous and pedestal. The masking signals were noise bursts, applied at five different sensation levels varying from 2 to 22 dB SL, also presented by electrovibration. For each participant, the thresholds were elevated as linear functions of masking levels for both masking types. We observed that the masking effectiveness was larger with pedestal masking than simultaneous masking. Moreover, in order to investigate the effect of tactile masking on our haptic perception of edge sharpness, we compared the perceived sharpness of edges separating two textured regions displayed with and without various types of masking stimuli. Our results suggest that sharpness perception depends on the local contrast between background and foreground stimuli, which varies as a function of masking amplitude and activation levels of frequency-dependent psychophysical channels.

In Proceedings of the IEEE World Haptics Conference, 2017

Frontiers in Neuroscience, 2020

One may notice a relatively wide range of tactile sensations even when touching the same hard, fl... more One may notice a relatively wide range of tactile sensations even when touching the same hard, flat surface in similar ways. Little is known about the reasons for this variability, so we decided to investigate how the perceptual intensity of light stickiness relates to the physical interaction between the skin and the surface. We conducted a psychophysical experiment in which nine participants actively pressed their finger on a flat glass plate with a normal force close to 1.5 N and detached it after a few seconds. A custom-designed apparatus recorded the contact force vector and the finger contact area during each interaction as well as pre- and post-trial finger moisture. After detaching their finger, participants judged the stickiness of the glass using a nine-point scale. We explored how sixteen physical variables derived from the recorded data correlate with each other and with the stickiness judgments of each participant. These analyses indicate that stickiness perception mainly depends on the pre-detachment pressing duration, the time taken for the finger to detach, and the impulse in the normal direction after the normal force changes sign; finger-surface adhesion seems to build with pressing time, causing a larger normal impulse during detachment and thus a more intense stickiness sensation. We additionally found a strong between-subjects correlation between maximum real contact area and peak pull-off force, as well as between finger moisture and impulse.

PLOS ONE, 2022

Frontiers in Neuroscience, Apr 15, 2020

In Proceedings of the IEEE World Haptics Conference, 2017

Springer Series on Touch and Haptic Systems

Springer Series on Touch and Haptic Systems, 2020

Springer Series on Touch and Haptic Systems

Journal of the Royal Society Interface, 2021

IEEE World Haptics Conference, 2019

International Workshop on Haptic and Audio Interaction Design, 2019

Generating realistic texture feelings on tactile displays using data-driven methods has attracted... more Generating realistic texture feelings on tactile displays using data-driven
methods has attracted a lot of interest in the last decade.
However, the need for large data storage and transmission rates
complicates the use of these methods for future commercial
displays. In this paper, we propose a new texture rendering approach
that can compress the texture data signifcantly for electrostatic
displays. Using three sample surfaces, we first explain
how to record, analyze and compress the texture data, and render
them on a touchscreen. Then, through psychophysical experiments
conducted with nineteen participants, we show that the textures can
be reproduced by a significantly less number of frequency components
than the ones in the original signal without inducing perceptual
degradation. Moreover, our results indicate that the possible
degree of compression is affected by the surface properties.

6th IFAC Symposium on Mechatronic Systems, 2013

IEEE Transactions on Haptics, 2019

IEEE Transactions on Haptics, 2018

In Proceedings of the IEEE World Haptics Conference, 2017

Frontiers in Neuroscience, 2020

One may notice a relatively wide range of tactile sensations even when touching the same hard, fl... more One may notice a relatively wide range of tactile sensations even when touching the same hard, flat surface in similar ways. Little is known about the reasons for this variability, so we decided to investigate how the perceptual intensity of light stickiness relates to the physical interaction between the skin and the surface. We conducted a psychophysical experiment in which nine participants actively pressed their finger on a flat glass plate with a normal force close to 1.5 N and detached it after a few seconds. A custom-designed apparatus recorded the contact force vector and the finger contact area during each interaction as well as pre- and post-trial finger moisture. After detaching their finger, participants judged the stickiness of the glass using a nine-point scale. We explored how sixteen physical variables derived from the recorded data correlate with each other and with the stickiness judgments of each participant. These analyses indicate that stickiness perception mainly depends on the pre-detachment pressing duration, the time taken for the finger to detach, and the impulse in the normal direction after the normal force changes sign; finger-surface adhesion seems to build with pressing time, causing a larger normal impulse during detachment and thus a more intense stickiness sensation. We additionally found a strong between-subjects correlation between maximum real contact area and peak pull-off force, as well as between finger moisture and impulse.