Information from time-varying vibrotactile stimuli

"Can You Feel It": An Early Experience with Simulated Vibration to Recreate Glenoid Reaming

When developing educational simulators, meaningful haptic feedback is important. To our knowledge, no shoulder arthroplasty surgical simulator exists. This study focuses on simulating vibration haptics of glenoid reaming for shoulder arthroplasty using a novel glenoid reaming simulator.

Methods

We validated a novel custom simulator constructed using a vibration transducer transmitting simulated reaming vibrations to a powered nonwearing reamer tip through a 3D-printed glenoid. Validation and system fidelity were evaluated by 9 fellowship-trained shoulder surgeon experts performing a series of simulated reamings. We then completed the validation process through a questionnaire focused on experts' experience with the simulator.

Results

Experts correctly identified 52% ± 8% of surface profiles and 69% ± 21% of cartilage layers. Experts identified the vibration interface between simulated cartilage and subchondral bone (77% ± 23% of the time), indicating high fidelity for the system. An interclass correlation coefficient for experts' reaming to the subchondral plate was 0.682 (confidence interval 0.262-0.908). On a general questionnaire, the perceived utility of the simulator as a teaching tool was highly ranked (4/5), and experts scored "ease of instrument manipulation" (4.19/5) and "realism of the simulator" (4.11/5) the highest. The mean global evaluation score was 6.8/10 (range 5-10).

Conclusions

We examined a simulated glenoid reamer and feasibility of haptic vibrational feedback for training. Experts validated simulated vibration feedback for glenoid simulation reaming, and the results suggested that this may be a useful additional training adjuvant.

Level of Evidence

Level II, prospective study.

Driving with hemianopia VIII: Effects of a vibro-tactile assistance system on safety and gaze behavior in pedestrian crossing situations

People with homonymous visual field defects (HVFDs), the loss of vision in the same half of the visual field in both eyes, are permitted to drive in some jurisdictions. However, the HVFD may cause difficulties in detecting hazards approaching on the side of the field loss (the blind side). An advanced driver assistance system (ADAS) could assist with hazard detection, but little research has been conducted to evaluate the potential benefits of an ADAS for visually impaired drivers. We developed a prototype vibro-tactile assistance system for drivers with HVFDs and conducted a proof-of-concept driving simulation study to evaluate the system. Given that pedestrian accidents are the second most frequent cause of death in road traffic and most of those accidents occur in urban scenarios, we evaluated the potential of the assistance system to improve responses to pedestrian hazards in a city environment. Sixteen participants, of which eight had HVFDs and eight had normal vision, took part. Our analyses evaluated the effects of the driver assistance system, crossing direction and pedestrian behavior on the safety of pedestrian events and the participant's gaze behavior at each of the 256 crossing situations. Generalized linear mixed effects models were used to assess binomial outcome variables. Despite the limited sample size, the results suggest that the vibro-tactile directional warnings were effective in directing the drivers' gaze so that they were looking in the necessary direction before a potential hazard occurred. More time was spent fixating pedestrians on the blind side when the ADAS was engaged and as a result, the safety of street crossings from the blind side improved. The effect of the ADAS was greater on responses to pedestrians from the blind than the seeing side. With an activated ADAS, crossings from the participants' blind sides were as safe as from their seeing sides, and as safe as the crossings when normally-sighted participants were driving. The results suggest that the vibro-tactile ADAS is a promising approach to improve the safety of drivers with HVFD and surrounding traffic.

Vibrotactile Display of Patterned Surface Textures With Kinesthetic Haptic Devices Using Balanced Impulses

Kinesthetic haptic devices are designed primarily to display quasistatic and low-bandwidth forces and moments. Existing methods for vibrotactile display sometimes introduce haptic and/or audio artifacts. In this article, we propose a method to display vibrotactile stimulus signals of moderate to high frequency (20-500 Hz) using kinesthetic haptic devices with a standard 1 kHz haptic update rate. Our method combines symmetric square-wave signals whose periods are even multiples of the haptic update period with asymmetric square-wave signals whose periods are odd multiples of the haptic update period, while ensuring that the positive and negative impulses are balanced in both cases, and utilizing the just noticeable difference in frequency discrimination to avoid the need to display other frequencies. For frequencies at which the above method is insufficient, corresponding to a small band near 400 Hz for a 1 kHz update rate, we utilize a signal-mixing method. Our complete method is then extended to render haptic gratings by measuring scanning velocity, converting the local spatial frequency to its equivalent instantaneous temporal frequency, and displaying a single full-period vibration event. In a series of human-subject studies, we showed that our proposed method is preferred over existing methods for vibrotactile display of signals with relatively high-frequency content.

Perceptual Quality Assessment of Compressed Vibrotactile Signals Through Comparative Judgment

In this article, we present a comprehensive scheme for the quality assessment of compressed vibrotactile signals with human assessors. Inspired by the multiple stimulus test with hidden reference and anchors (MUSHRA) from the audio domain, we designed a method in which each compressed signal is compared to its original signal and rated on a numerical scale. For each signal tested, the hidden reference and two anchor signals are used to validate the results and provide assessor screening criteria. Differing from previous approaches, our method is hierarchically structured and strictly timed in a sequential manner to avoid experimental confounds and provide precise psychophysical assessments. We validated our method in an experiment with 20 human participants in which we compared two state-of-the-art lossy codecs. The results show that, with our approach, the performance of different codecs can be compared effectively. Furthermore, the method also provides a measure of subjective quality at different data compression rates. The proposed procedure can be easily adapted to evaluate other vibrotactile codecs.

Vibro-Tactile Enhancement of Speech Intelligibility in Multi-talker Noise for Simulated Cochlear Implant Listening

Many cochlear implant (CI) users achieve excellent speech understanding in acoustically quiet conditions but most perform poorly in the presence of background noise. An important contributor to this poor speech-in-noise performance is the limited transmission of low-frequency sound information through CIs. Recent work has suggested that tactile presentation of this low-frequency sound information could be used to improve speech-in-noise performance for CI users. Building on this work, we investigated whether vibro-tactile stimulation can improve speech intelligibility in multi-talker noise. The signal used for tactile stimulation was derived from the speech-in-noise using a computationally inexpensive algorithm. Eight normal-hearing participants listened to CI simulated speech-in-noise both with and without concurrent tactile stimulation of their fingertip. Participants' speech recognition performance was assessed before and after a training regime, which took place over 3 consecutive days and totaled around 30 min of exposure to CI-simulated speech-in-noise with concurrent tactile stimulation. Tactile stimulation was found to improve the intelligibility of speech in multi-talker noise, and this improvement was found to increase in size after training. Presentation of such tactile stimulation could be achieved by a compact, portable device and offer an inexpensive and noninvasive means for improving speech-in-noise performance in CI users.

Effect of Waveform on Tactile Perception by Electrovibration Displayed on Touch Screens

In this study, we investigated the effect of input voltage waveform on our haptic 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 the subjects moving on the screen with a constant speed. We analyzed the collected data in the frequency domain using the human vibrotactile sensitivity curve. The results suggested that Pacinian channel was the primary psychophysical channel in the detection of the electrovibration stimuli caused by all the square-wave inputs tested in this study. We also observed that the measured force and acceleration data were affected by finger speed in a complex manner suggesting that it may also affect our haptic perception accordingly.

Discriminating speech rhythms in audition, vision, and touch

We investigated the extent to which people can discriminate between languages on the basis of their characteristic temporal, rhythmic information, and the extent to which this ability generalizes across sensory modalities. We used rhythmical patterns derived from the alternation of vowels and consonants in English and Japanese, presented in audition, vision, both audition and vision at the same time, or touch. Experiment 1 confirmed that discrimination is possible on the basis of auditory rhythmic patterns, and extended it to the case of vision, using 'aperture-close' mouth movements of a schematic face. In Experiment 2, language discrimination was demonstrated using visual and auditory materials that did not resemble spoken articulation. In a combined analysis including data from Experiments 1 and 2, a beneficial effect was also found when the auditory rhythmic information was available to participants. Despite the fact that discrimination could be achieved using vision alone, auditory performance was nevertheless better. In a final experiment, we demonstrate that the rhythm of speech can also be discriminated successfully by means of vibrotactile patterns delivered to the fingertip. The results of the present study therefore demonstrate that discrimination between language's syllabic rhythmic patterns is possible on the basis of visual and tactile displays.

Evaluating vibrotactile dimensions for the design of tactons

Vibrotactile stimuli are defined in terms of their amplitude, frequency, waveform and temporal profile all of which have been varied to create tactons. A number of approaches have been adopted to design tactons including multidimensional scaling, iterative empirical methods and using perceptual processing models. The objective of the present set of experiments was to create sets of tactons based on the properties of the dimensions of vibrotactile stimuli. An absolute identification paradigm was used in which each of nine tactons was presented eight times using a tactor mounted on either the index finger or forearm. It was found that tactons created by varying the frequency, amplitude and temporal profile of the vibrotactile stimuli were correctly identified on 73-83 percent of the trials, with a mean information transfer of 2.41 bits. The latter metric indicates that for these sets of nine tactons between five and six could be reliably identified. The vibrotactile stimuli delivered in the experiments were identified as consistently on the forearm as the hand and the IT values were similar at the two locations. This suggests that sites other than the hand can be used effectively in tactile communication systems and that it is channel capacity that ultimately determines performance on this type of task.

Optimum Information Transfer Rates for Communication through Haptic and Other Sensory Modalities

This paper is concerned with investigating the factors that contribute to optimizing information transfer (IT) rate in humans. With an increasing interest in designing complex haptic signals for a wide variety of applications, there is a need for a better understanding of how information can be displayed in an optimal way. Based on the results of several early studies from the 1950s, a general "rule of thumb" has arisen in the literature which suggests that IT rate is dependent primarily on the stimulus delivery rate and is optimized for presentation rates of 2-3 items/s. Thus, the key to maximizing IT rate is to maximize the information in the stimulus set. Recent data obtained with multidimensional tactual signals, however, appear to contradict these conclusions. In particular, these current results suggest that optimal delivery rate varies with stimulus information to yield a constant peak IT rate that depends on the degree of familiarity and training with a particular stimulus set. We discuss factors that may be responsible for the discrepancies in results across studies including procedural differences, training issues, and stimulus-response compatibility. These factors should be taken into account when designing haptic signals to yield optimal IT rates for communication devices.

Congenital blindness leads to enhanced vibrotactile perception

Previous studies have shown that in comparison with the sighted, blind individuals display superior non-visual perceptual abilities and differ in brain organisation. In this study, we investigated the performance of blind and sighted participants on a vibrotactile discrimination task. Thirty-three blind participants were classified into one of three groups (congenital, early, late), depending on the age at which they became blind. Consistent with previous neuroimaging data, individuals blinded after late childhood (14 years) showed no advantage over sighted participants. Both the congenitally- and early-blind participants were better than the sighted. The congenitally blind participants were even more accurate than the early-blind participants; a distinction that has not been drawn previously. Duration of blindness did not predict task performance and the effect of onset age persisted after duration of daily Braille reading was accounted for. We conclude that complete visual deprivation early in life leads to heightened tactile acuity.

Vibrotactile Pattern Recognition on the Arm and Back

A series of experiments was conducted to evaluate the effectiveness with which a tactile display mounted on either the forearm or the back can be used to communicate simple instructions and commands. In the first two sets of experiments, participants identified a vibrotactile pattern using a visual template that represented the pattern of activation. For the patterns displayed on the forearm, accuracy depended on the specific set of patterns presented and ranged from 30% to 96% correct for the individual patterns. In a second series of experiments, seven hand-and-arm signals that are used to communicate in military contexts were converted into tactile representations that were displayed on the back. These were identified accurately (98% correct) and, when only the picture of the hand signal was available, participants achieved a recognition rate of 75% correct. A further study with these seven patterns indicated that participants were still able to identify the patterns accurately (92% correct) when they were engaged in a concurrent physical or cognitive task. The results indicate the importance of evaluating tactile communication in the context of the specific patterns or messages that will be conveyed, and that with the judicious selection of tactile patterns both the arm and back provide a functional substrate for tactile communication.

Tactile displays: guidance for their design and application

OBJECTIVE

This article provides an overview of tactile displays. Its goal is to assist human factors practitioners in deciding when and how to employ the sense of touch for the purpose of information representation. The article also identifies important research needs in this area.

BACKGROUND

First attempts to utilize the sense of touch as a medium for communication date back to the late 1950s. For the next 35 years progress in this area was relatively slow, but recent years have seen a surge in the interest and development of tactile displays and the integration of tactile signals in multimodal interfaces. A thorough understanding of the properties of this sensory channel and its interaction with other modalities is needed to ensure the effective and robust use of tactile displays.

METHODS

First, an overview of vibrotactile perception is provided. Next, the design of tactile displays is discussed with respect to available technologies. The potential benefit of including tactile cues in multimodal interfaces is discussed. Finally, research needs in the area of tactile information presentation are highlighted.

RESULTS

This review provides human factors researchers and interface designers with the requisite knowledge for creating effective tactile interfaces. It describes both potential benefits and limitations of this approach to information presentation.

CONCLUSION

The sense of touch represents a promising means of supporting communication and coordination in human-human and human-machine systems.

APPLICATION

Tactile interfaces can support numerous functions, including spatial orientation and guidance, attention management, and sensory substitution, in a wide range of domains.

Frequency and amplitude discrimination along the kinestheticcutaneous continuum in the presence of masking stimuli

Frequency and amplitude discrimination thresholds along the kinesthetic to cutaneous continuum were evaluated on the left index fingerpad using a multifinger tactual display. Target stimuli were presented either in isolation (no-masker condition) or in the presence of masking stimuli (one- or two-masker conditions). Six reference target signals in the frequency range 2-300 Hz (two each from low-, medium-, and high-frequency regions) and at an amplitude of either 20 or 35 dB sensation levels (SL) were used. In the no-masker condition, the range of frequency Weber fraction was 0.13-0.38 and 0.14-0.28, and the range of amplitude discrimination threshold was 1.82-2.98 dB and 1.65-2.71 dB, at 20 and 35 dB SL, respectively. In the masking conditions, average frequency Weber fractions rose to 0.60 and 0.46, and average amplitude thresholds rose to 3.63 and 3.72 dB, at 20 and 35 dB SL, respectively. In general, thresholds were largest in the two-masker condition and lowest in the no-masker condition. Although the frequency and amplitude thresholds generally increased in the presence of masking stimuli, there was some indication of channel independence for low- and high-frequency target stimuli. The implications of the results for tactual communication of speech are discussed.

Tactile information transfer: a comparison of two stimulation sites

Two experiments on the discrimination of time-varying tactile stimuli were performed, with comparison of stimulus delivery to the distal pad of the right index finger and to the right wrist (palmar surface). Subjects were required to perceive differences in short sequences of computer-generated stimulus elements (experiment 1) or differences in short tactile stimuli derived from a speech signal (experiment 2). The pulse-train stimuli were distinguished by differences in frequency (i.e., pulse repetition rate) and amplitude, and by the presence/absence of gaps (approximately 100-ms duration). Stimulation levels were 10 dB higher at the wrist than at the fingertip, to compensate for the lower vibration sensitivity at the wrist. Results indicate similar gap detection at wrist and fingertip and similar perception of frequency differences. However, perception of amplitude differences was found to be better at the wrist than at the fingertip. Maximum information transfer rates for the stimuli in experiment 1 were estimated at 7 bits s(-1) at the wrist and 5 bits s(-1) at the fingertip.

Information transmission with a multifinger tactual display

In this work, the tactual information transmission capabilities of a tactual display designed to provide stimulation along a continuum from kinesthetic movements to cutaneous vibrations are assessed. The display is capable of delivering arbitrary waveforms to three digits (thumb, index, and middle finger) within an amplitude range from absolute detection threshold to about 50 dB sensation level and a frequency range from dc to above 300 Hz. Stimulus sets were designed at each of three signal durations (125, 250, and 500 msec) by combining salient attributes, such as frequency (further divided into low, middle, and high regions), amplitude, direction of motion, and finger location. Estimated static information transfer (IT) was 6.5 bits at 500 msec, 6.4 bits at 250 msec, and 5.6 bits at 125 msec. Estimates of IT rate were derived from identification experiments in which the subject's task was to identify the middle stimulus in a sequence of three stimuli randomly selected from a given stimulus set. On the basis of the extrapolations from these IT measurements to continuous streams, the IT rate was estimated to be about 12 bits/sec, which is roughly the same as that achieved by Tadoma users in tactual speech communication.