| Fragen |
| Mapping Scalars on vibrotactile Dimensions / single/multi |
| Balance Feedback select + extend |
| Continous VT feedback w/ complex stimuli |
| Year | Key | Authors | Title | Type | Goal / Hypothesis | Outcomes | Context | Contribution to Field | Connection to own research | Main Takeaways / Quotes | Location | Channels / Receptors | Stimuli | N | T | Future Work |
| 2007 | Mortimer2007 | Mortimer, Bruce J. P. Zets, Gary A. Cholewiak, Roger W. |
Vibrotactile transduction and transducers | review and actuator design | replacing ERMs: building a linear actuator; matching impedance/loading | - The body’s sense of touch is potentially a versatile channel for the conveyance of directional, spatial, command, and timing information. - In glabrous / smooth skin, Pacinian corpuscles PCs, Meissner’s corpuscles, Merkel’s disks, and Ruffini cylinders are the structures associated with the four psychophysically defined channels Bolanowski et al., 1988. Of these, the PCs are the most sensitive. At 250 Hz, the sensitivity of human glabrous skin to displacement is less than 1 µm. A similar set of channels have been proposed for hairy skin (Bolanowski et al., 1994) although the delineation is less precise. For example, rapidly adapting PC-like responses are obtained from hair follicles and field receptors (Greenspan and Bolanowski, 1996, pp. 42–43). Furthermore, the overall sensitivity is less: that of the PC-like channel is 20 dB less than in glabrous skin (about 1/10 as sensitive). - Hairy skin is about 20 dB less sensitive in the high-frequency range than the glabrous skin curve. It also has a slightly different shape, especially in the 100 Hz range - Selecting the transducer specifications for vibrotactile applications requires some careful consideration, especially in applications that require wearable transducers. The human tactile sensory response is limited in frequency response, temporal and spatial resolution. Tactile conveyance of infor- mation is more limited in bandwidth than the other senses. However, the body’s ability to discern some level of frequency, amplitude, spatial, and temporal information is well known, and this information can be enhanced by multilocation tactile stimuli or spatial cuing. It follows that reasonable transducer specifications should be equivalent or better than the human receptor system’s own response limitations. Reasonable technical requirements would include a frequency response to 300 Hz, a displacement output that exceeds 24 dB (to account for noise) above the threshold for sensi- tivity for a hairy skin body location and a rise time of less than 5 ms. |
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| 2018 | Mills2018 | Mills, Sean R Morioka, Miyuki Griffin, Michael J |
Limitations of Vibrotactile Thresholds | review | Sound and Vibration Research | Challenges the sufficiency of thresholds | - The physical interaction between the skin and a surface generates vibrations in a repeatable way (Bensmaia and Hollins, 2003). This information about the interaction is captured by neurons in the skin and processed so that the vibrations can be discriminated from one another on the basis of frequency (Cohen and Kirman, 1986) or waveform (Bensmaia and Hollins, 2000). - The complex and multi-faceted process of tactile perception can be described in a simple model of information processing (Gescheider et al., 2004) - two core approaches to looking at a perceptual system: function of physiological structures or look at behaviour of observers in response to stimuli, a psychophysical approach, looking at the system as a whole - combined by characterising the tactile system as a set of ‘Information Processing Channels’ (e.g. Verrillo, 1968) with independent neural substrates - There is a range of psychophysical measures that can be used to collect data. For example, observers can report feeling a vibration (‘Detection’), whether they can feel the difference between vibrations (‘Discrimination’) or match them to each other (‘Matching’), and how much of a particular perceptual property (e.g., intensity) they feel in the vibration (‘Magnitude Estimation’). The model of information processing in the tactile system has been focused on vibrotactile thresholds – the minimum amplitude of vibration that generates detection (Verrillo, 1985, 1963). This overview of the human tactile system concentrates on how psychophysical investigations of vibrotactile thresholds have been integrated with neurophysiology to provide a model of information processing in the tactile system. It is argued that expressing the properties of the tactile system in terms of vibrotactile thresholds is restrictive and ignores the full scope of observations from psychophysics and neurophysiology. It is concluded that the model of information processing based on this foundation is incomplete because it builds in a set of fundamental limitations. - Thresholds for the detection of vibration are not uniform across the frequency spectrum. Instead, detection is mediated by a set of overlapping broadband filters known as ‘information-processing channels’, which are selective for different frequency ranges. Originally conceptualised as a ‘duplex’ model of complementary low- and high-frequency selective channels (Verrillo, 1968; von Békésy, 1939), then ‘triplex’ (Capraro et al., 1979), there is now understood to be four independent systems in the glabrous skin of the hand which respond differently as a function of the frequency content of the vibration (Gescheider et al., 2010). This psychophysical work has usually labelled the channels as Pacinian (P) and non-Pacinian (NPI, NPII and NPIII). For clarity, however, these channels are referred to throughout this review by their neurophysiological labels: PC, RA, SAI and SAII, respectively. The channel organisation of vibrotaction has two fundamental properties: channels are independent and frequency selective. Psychophysical procedures that reveal the thresholds of particular channels have provided substantial evidence for these ideas. Adaptation (Hollins et al., 1990; Verrillo and Gescheider, 1977), and masking (Bolanowski et al., 1988; Gescheider, et al., 1978; Gescheider et al., 1983; Gescheider et al., 1985), have been shown to affect thresholds for perception within frequency ranges associated with particular channels, but not across them. See Gescheider and colleagues (2010) for a detailed review of the psychophysical evidence. - Over time, the information processing channels identified through psychophysical procedures became associated with distinct physiological structures. Each channel is now strongly associated with the properties of particular classes of mechanoreceptors and their afferent nerve fibres (Johansson, 1978; Johansson et al. 1982; Johansson and Vallbo, 1979; Johnson, 2001). - There is a difference between how the channels are defined and how they are typically expressed in an experimental setting. The channels are defined in terms of the frequency selectivity of their processing regardless of stimulus amplitude, but their properties are almost entirely expressed in terms of the lowest energy to which they are sensitive – their psychophysical threshold for perception of vibration as a function of frequency (Gescheider et al., 2001) - Mechanoreceptors are a dedicated class of nerve endings that transduce physical deformation of the skin into electrical impulses. Their precise structures, locations, and neural response characteristics vary substantially across mechanoreceptor types (Johansson et al., 1982) – this variability is what allows different classes of mechanoreceptors to respond selectively to different frequencies of vibration, giving rise to information processing channels that respond selectively to different vibratory inputs. - Based on the information-processing model, a psychophysical experiment allows inferences about which mechanoreceptors are responding to a particular stimulus. By assuming that the most sensitive channel mediates perception at the lowest amplitude of a particular vibratory stimulus (Gescheider et al., 2004), psychophysically determined vibrotactile thresholds identify the most sensitive mechanoreceptors in specific frequency ranges. Given the complex interacting factors that influence the firing of the afferents in the skin, however, this assumption may be simplistic. - … increasing probability of a yes response as the amplitude of the stimulus increases – resulting in a situation in which some missed targets are of higher amplitude than some observed targets. This probabilistic processing reflects the noise in any biological system. Detecting a low-energy target depends on differentiating between normal background activity (noise) and a very small increase in this signal generated by the presence of a weak stimulus (signal + noise)…. A measured vibrotactile threshold is not a constant value. Instead, it is the product of a particular participant, stimulus, experimental design, and response criterion. This is one reason for the intra- and inter-subject variability observed in vibrotactile thresholds (Aaserud et al., 1990). - The vibrations delivered during experiments on vibrotactile detection are not assessing the information content of the system, merely the presence or absence of any information. This abstraction of a single aspect of vibrotactile sensation has been useful for the identification of the ‘information-processing channels’, but limits the degree to which we can observe the function of the channel in the context of normal touch. The difference between the normal function of the channels and the abstracted isolation of their vibrotactile thresholds plays into a broader point about ecological validity – the extent to which experimental findings can be generalised to normal life. Tactile perception in the hand and fingers is arguably primarily discriminative; it is concerned with rich data extraction about the properties of objects rather than the detection of vibration. Natural tactile stimuli will to give rise to activity in several or all of the four channels, and perception will be the result of the integration of the information they have captured (e.g. Gescheider et al., 2010). - The glabrous skin of the hand can be considered to be performing a function analogous to the fovea in vision: it contains high relative receptor density compared to the periphery, hyper-acuity, high receptor diversity, over-representation in the brain, and demonstrates stereotyped information- seeking behaviours – exploratory procedures and eye movements respectively. - Although the information processing channels for tactile perception might be characterised by their selectivity for the frequency content of vibration, they also display marked selectivity to a wide variety of other stimulus parameters. These parameters include: the static force of the contactor (Brisben et al., 1999; Craig and Sherrick, 1969; Harada and Griffin, 1991; Lamoré and Keemink, 1988; Maeda and Griffin, 1994), contact area (Lamoré and Keemink, 1988; Maeda and Griffin, 1994; Verrillo, 1985), stimulus duration (Gescheider and Joelson, 1983; Verrillo, 1965), skin temperature (Bolanowski et al., 1988), skin indentation (Whitehouse and Griffin, 2002), active or passive movement (Yıldız et al., 2015), pressure distribution (Srinivasan and LaMotte, 1991) body location (Forta et al., 2012) and surface topography (Skedung et al., 2013). Untangling the effects of these factors on thresholds is challenging because they interact with one another. For example, introducing a surround limits the effective surface area of stimulation, but also alters factors like static force, skin indentation and pressure distribution (e.g. Verrillo, 1985). - Neurophysiological research has shown that the channels employ a range of codes to capture information about a stimulus (Bensmaia, 2008; Cohen and Vierk, 1993; Harvey et al., 2013; Hollins and Bensmaia, 2007; Weber et al., 2013). The PC and RA channels appear to code primarily temporally (Muniak et al., 2007), so a single channel’s spike pattern over time contains information about the frequency of the vibration. This activity interacts with amplitude, such that increases in amplitude will produce non-linear changes in the response of the neuron as a function of frequency. |
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| 2013 | Hwan2013 | Inwook Hwang, Jongman Seo, Myongchan Kim, Seungmoon Choi, |
Vibrotactile Perceived Intensity for Mobile Devices as a Function of Direction, Amplitude, and Frequency | 2 psychophysical studies, modelling | build a robust model for the perceived intensities of mobile device vibrations |
I: Only the vibration direction was found to be a statistically significant factor, showing the highest perceived intensities along the height direction of a mobile device. II: psychophysical magnitude function and equal sensation contours that clearly visualize the consequences of vibration parameter changes on the resulting perceptual strength + monotonic relationship between the physical power of vibration absorbed by the hand and the resulting perceived intensity. |
Mobile Phone VT | Modelled Influence of Weight, Direction, Frequency of perceptual magnitude of vibrating cell phone | - Frequencies on the Hand: Lower is more intense, because RA & Pacinian channel respond and its cummulative - Total Energy is key |
- measured amplitude & PD-controlled intenstity for controlled stimuli intensity across frequencies and grip intensity (I suppose) - XP1: 60/120/250 Hz: 60 seems most intense? - XP2: 60/80/120/180/250 Hz X 6 Amplitudes: Given the amplitude, the perceived intensities decreased with the frequency, with more salient effects in the low-frequency region (<100 Hz) - The equal sensation contours form a U-shaped curve at low perceived intensity levels less than 2 (approximately 0.4 G in acceleration amplitude). This is similar to the typical detection threshold curve of the PC channel, which has lower thresholds than the other Non-Pacinian (NP) channels in the frequency range tested in our experiment. At higher intensity levels, other NP channels such as the RA and SA1 channels also respond. For example, the detection threshold of the RA channel is approximately 0.1 G in acceleration for 125-Hz vibrations and increases with frequency [18]. In this range, each individual channel contributes to the intensity function [18], [19]. Our equal sensation curves were consistent with this general tendency. They monotonically increased with vibration frequency, sometimes including a flat region, similar to the equivalent comfort contours reported by Morioka and Griffin [7]. |
Hand / Cell Phone Mockup | RA/PC | 60/80/120/180/250 Hz X 6 Amplitudes | 24 |
| Year | Key | Authors | Title | Type | Goal / Hypothesis | Outcomes | Context | Contribution to Field | Connection to own research | Main Takeaways | Location | Channels / Receptors | Stimuli | N | T | Future Work |
| 2000 | Bensmaia2000 | Bensmaı̈a, Sliman J. Hollins, Mark |
Complex tactile waveform discrimination | perceptual study, model | investigate the ability of the vibrotactile system to discriminate among com- plex mechanical waveforms, consisting of two superimposed sinusoids differing only in the phase of the high-frequency component with respect to the low-frequency component |
- low-frequency waveforms were discriminable from one another while discrimination of the high-frequency vibrations was poor: subjects could not use Pacinian signals to discriminate between diharmonic stimuli that differed only in the phase angle of the high-frequency component with respect to the low-frequency component. - High-frequency adaptation did not impair discrimination of the low-frequency waveforms, suggesting that the RA channel mediated discrimination. Low-frequency adaptation impaired discrimination of the high-frequency stimuli, suggesting that the RA channel likewise mediated the modest level of performance observed in the absence of an adapting stimulus. The results indicate that this channel encodes complex waveforms temporally. - A simple model for low-frequency waveform discrimination is proposed. The results obtained with the high-frequency complex waveforms are compatible with the hypothesis that the PC channel integrates stimulus energy over time. |
Fingertip | RA, PC | Complex vibrotactile waveforms (10+30, 100+300 Hz), consisting of two superimposed sinusoids at varying phases | |||||||
| 2005 | Bensmaia2005 | Bensmaïa, Sliman Hollins, Mark Yau, Jeffrey |
Vibrotactile intensity and frequency information in the Pacinian system: A psychophysical model | perceptual study, model | characterize the Pacinian representation of stimulus waveform | - a model that characterizes the Pacinian rep- resentation of an arbitrary vibratory stimulus as a pattern of activity in a population of frequency-tuned minichan- nels has been shown to be an excellent predictor of the dis- criminability of high-frequency stimuli. - ...model... information about individual spectral components is conveyed in parallel and quasi-independently. By simulating the response of a population of Pacinian afferents to a polyharmonic stimulus, we demonstrated that such a population can simultaneously convey information about mul- tiple frequency components, despite having a homogeneous spectral profile. |
Fingertip | PC + NPC | Sinusoidal (100, 150, 200, 300) and diharmonic (100Hz+200Hz, 100Hz+300Hz, and 150Hz+300Hz), frequencies were chosen so that the stimuli vigorously stimulated the Pacinian system while eliciting little response in the RA system (Bensmaïa & Hollins, 2000) | 3 m 2 f, 22-31y |
long | Stimuli containing beats, interaction with stimulus amplitude |
| Year | Key | Authors | Title | Approach/Method/Strategy | Goal / Hypothesis / Aims / Objectives | Outcomes | Context | Contribution to Field | Connection to own research | Main Takeaways / Quotes | Location | Stimuli | N | Future Work | HW |
| 2010 | MacLean, Karon E. | Foundations of Transparency in Tactile Information Design |
review, design | HCI | Multifaceted Approach: Situated Observation (Qualitative) + Controlled User Studies (Quantitative) + Tool Building (Rapid Protoyping) Outlining design process questions for iterating towards transparent interfaces that use minimal cognitive resources: - Where and how will stimuli be useful (Utility)? - What should they be, and how should they be created? - How are Tactons most easily acquired, and what limits or constraints pertain? |
Justification of our thesis approach Driving stimuli design to perform in the periphery |
BG: - Through both taction and proprioception, the haptic channel has an important role to play in a new generation of transparent interfaces, which will convey information as it is needed or desired without overwhelming the user’s mental resources. Designing for transparency means considering the user’s reality of divided attention and multiple un- coordinated information sources. Displays must convey data abstractions haptically in a way that places little burden on sensory and cognitive resources, and requires a user’s attention only when appropriate; but must balance these needs with available display technology. - Taction is a practical place to enter the larger space of haptic information design: displays must be miniature, portable, and low power, and currently, this is harder to achieve when displaying forces. MULTIFACETED APPROACH: - 1. Situated observation. Qualitative and self-report methods capture user needs, coping mechanisms, and the uptake of the proposed technological interventions in realistic but loosely or uncontrolled situations. 2. Controlled user studies. Quantitative examination of specific human abilities are often triggered by questions revealed through the qualitative methods of situated observation. 3. Tool building. - Practicality demands streamlined mechanisms for creating perceptually and cogni- tively usable signals and integrating them into applications, such as those that exist for many audio and graphical areas. Controlled and observational user studies operate under different philosophies. The first are driven by statistically provable hypotheses, and the second by qualitative methods. The combination is powerful. Qualitative and well-simu- lated contextual research is essential both for framing relevant needs-driven quantitative issues and to highlight practical significance. RESOURCE EFFICIENCY VS CALM DESIGN: - As we reach the limits of other mental resources (e.g., when vision and audition are saturated or unavailable), touch is available for “offloading.” This view is enticing but risky. Sensory perception is just one step in the processing pipeline; downstream constrictions occur in attention, cognition, and response, with Multiple Resource Theory providing one model [60], - But is our need to supply more information or, rather, to supply it in a manner that leaves the user relaxed and in control? Very often, the problem is not insufficient display volume but, rather, the stress and inefficiency associated with too much and the need to continually and explicitly switch contexts in order to process it [33]. - Over a decade ago, Weiser and Brown [59] described a “calm technology” as one that “moves easily from the periphery of our attention, to the center, and back,” drawing on the premise that our brains have more capacity for peripheral than for central processing. We can attune to more things when they are in the periphery; if something in the periphery is easily moved to the center, we can more easily and transparently take control of it. Weiser envisioned interfaces that are “filled with details yet engage our pre- attentive periphery so we are never surprised ... . This connection to the world we call “locatedness”.” There is little evidence of calm technology today outside of human- computer interaction research laboratories. - Locatedness cannot occur without transparency (i.e., requiring only peripheral awareness). Low attentional demand may thus be a clue by which locatedness can be measured and hence designed for. Transparency is how the information is displayed, while locatedness is the gist or gestalt awareness that the perception produces. This brings us back to tactile display. While calming interfaces are clearly holistic and cannot be assembled one modality at a time, we can nevertheless progress by discovering how tactile display (alone) can help us to locate, with unintrusive accessible use of the periphery, and by exploring mechanisms for moving seamlessly between the periphery and the center—the possibilities afforded to a user EXAMPLE: Tactile cues could be in the background, whereas visual cues had to interrupt. Thus, users could process tactile cues with less mental effort, but visual cues could provide more informa- tion. Multimodal support was therefore valued, in the sense of different but complementary information available through the most suitable channel. CAPACITY/LEARNING: For tactile displays, we can assume that this limit will lie in the technological ability to accommodate human tactile acuity and learning mechanisms, and not in mental storage space. Processes and Heuristics for Icon Design: 1. stimulus set prototyping, 2. stimulus set perceptual optimization (see below), 3. meaning assignment, and 4. testing and further adjustment under realistic conditions CONCLUSIONS: - We have found constructive themes in the pursuit of the most useful information representations and creation of tools and processes that support efficient iterative design, by incorporating user data when open-loop design is not possible. Another recurrent thread is the trade-off between what the user needs and what today’s hardware can provide. - Our discussion was organized along the lines of potential utility, form, and learning. Following this, we summarize what we know now and what needs to come next. - Utility. The surveyed research shows that well-designed haptic icons do allow appropriate background processing— with low effort and intended level of attention—confirming their candidacy as conduits in calm design. Icons intended to be perceived in the background need to be well integrated with other modalities to support movement from perception to action—from the periphery to the center and back—when their own capabilities for communication or response have been exceeded. Scalability and learnability, topics of future work, will impact appropriate application. - Form and processes. Our analysis suggests that while representational approaches may be initially easier to learn, they do not scale well. It is currently unclear how the early advantage will persist as set sizes and ubiquity grows, as there is little data here. The ultimate capacity is likely indifferent to the representational approach, given exam- ples in other domains; it is presently limited by expressive capability of available displays. More work is needed to understand learning rates. In terms of process, there are already adequate tool- supported procedures (albeit with room to improve) for rapidly iterating/testing stimuli to form perceptually viable sets. We need heuristics for designing good matches and/or a better understanding of how much this matters as the design approach inevitably becomes more abstract in larger sets. - Learning. All of the results mentioned here need to be examined in the context of longer learning, realistic contexts, and larger sets. As sets grow, learning mechanisms will be more critical in terms of both effectiveness and user willingness, but conversely, as this medium becomes more commonplace we anticipate that tactile skill in some demographics may improve. It is often noted that learning to taste and verbalize subtleties of wine, for example, or to smell fragrances greatly increases awareness and sensitivity to nuances. - Of Braille, Morse code, and wine tasting, what do we keep and what should we discard? How haptic iconography is learned will have as much to do with this as what is being learned. |
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| 2010 | Soller2010 | Soller, Dario | Haptic Icon Prototyping | review | Media Informatics | Gives good overview on tactons and their prototyping | Entry point into the literature, stimuli ideas | - "Ivan Sutherland, a founding father of virtual reality, suggested that the ”human kinesthetic sense is as yet another independent channel to the brain, a channel whose information is as- similated quite subconsciously”[51]" - “The goal, inspired by the common use of audio icons in desktop interfaces and mobile telephony \cite{Brewster2004}, is to allow for the design and construction of specific and short abstract tactile messages that can easily be interpreted by users with minimal cognitive effort.“ \cite{Maclean2003} - On a closer view on the actual structure of the skin’s mechanoreceptors some limitation already become clear. Hale and Stanney \cite{Hale2004a} give a good overview about the different properties of the human skin: • the skin’s sensitivity depends on its size (large receptors have poor spatial resolution) • density (many receptors in a given area results in high spatial acuity) • frequency range (receptors don’t perceive signals outside their range) • nerve fiber branching (higher branching leads to spatial and temporal summation of signals) • the type of stimulation (skin motion or sustained pressure) affects the degree to which individual mechanoreceptors are activated - Duration: A certain number of meanings could easily be encoded in pulses of different durations alone \cite{Brown2005}. Investigations by Gunther \cite{Gunther2001} show that vibrotactile ”stimuli lasting less than 0.1 seconds were perceived as taps or jabs whereas stimuli of longer duration, when combined with gradual attacks and decays, may be perceived as smoothly flowing tactile phrases” \cite{Brewster2004}. Taps are experienced by sudden attacks, while a gradual attack is perceived as a rising pressure on the skin \cite{Brewster2004}. But in any case, stimuli must be at least 5.5ms apart to ensure that the cutaneous signals are perceived individually [50]. - Amplitude: The amplitude, pressure or intensity of a tactile stimuli is proposed by several scientists ([13] [17] [53]) as an useful parameter in tacton design, but only if certain thresholds are factored into the haptic icon design process. Gunther writes that the intensity range is felt from the level of detection till approximately 55dB. An intensity above 55dB is perceived as painful [28]. Pressure sensations are activated by forces greater than 0.06 to 0.2 N per cm [50]. As a further limitation this range has no linear or homogeneous resolution, as it deteriorates at a level of 28dB [49], which is proposed by Brewster to be a useful maximum level of intensity [13]. Although Gunther found out that the just noticeable difference (JND) in detecting intensities is carried out in steps from 0.4dB-3.2dB [29], it is suggested by Gill not to use more than four different amplitudes within a single context [27]. Sherrick describes the JND as a ”values range from 5 milligrams on a woman’s face to 355 mg on a man’s big toe”[50]. … The most suitable approach of designing with the amplitude parameter is certainly reported by Brown et al.[15], as they suggest to leave the control of actual intensities in the hand of the user. Having the possibility to customize the amplitudes of the tactile signals in a pre- defined range individually, will ensure the best general performances in terms of usability at the same time. - Frequency: Experiments by Tan showed that users could distinguish three categories of frequencies between DC and 300Hz \cite{Tan1999}. Frequencies below 100Hz are experienced as periodicity or buzzing whereas higher frequencies are felt smoother or diffuse [58]. For example Hoggan and Brewster did successfully use frequencies of ”6 Hz (slow motion, very rough), 70Hz (fluttering slightly faster motion, rough), and 250 Hz (smooth)” in their experiment \cite{Hoggan2007a}. Another discrepancy to the abilities of the human ear, is the identification of absolute frequencies. ”Making relative comparisons between stimuli is much easier than absolute identification” \cite{Brewster2004}. Therefore a maximum of nine different frequencies is suggested by Gill [27]. A similarity to the field of sound is that ”a change in amplitude leads to a change in the perception of frequency so this has an impact on the use of frequency as a cue” \cite{Brewster2004}. As a consequence of this strong affection of the different parameters, they all have to be taken into account simultaneously. - Waveforms: With waveforms one means a sine wave whose amplitude is modulated by a second frequency different to the first one \cite{Brown2005}. Users are even able to differentiate between sine and square waves \cite{Brewster2004}, but more subtle differences are critical to perceive clearly [29]….In practice, 250Hz sinusoids modulated by 50Hz or 30Hz frequencies have been proven positive application \cite{Brown2005} [32]. But ”since tactons should be as short as possible in order to communicate information quickly, it is important to choose higher modulation frequencies, so that shorter pulses can be used” \cite{Brown2005}. - Temperature: latency, cold-sensitive thermoreceptors exist ten times more often than warm-sensitive ones, a fast change from cold to hot can cause a paradoxical response to heat - According to Swindells et al.[54] an ideal set of HIP tools should support: • All haptic types (kinesthetic & tactile) and affected parameters • Interaction between all degrees-of-freedom (horizontal) and many levels-of-detail (vertical) • Rapid iterations between various static & dynamic behaviors and reactions • Completely representing the psychophysical capabilities of the user (ergonomics) via a standard set of mathematical relations • Having easy-to-understand mental mappings between the underlying mathematical representations, the interaction widgets, and the final haptic renderings • Providing usable interaction widgets for designers to effectively create and modify haptic renderings • Integrating seamlessly with other haptic development tools, and development tools for other sensory modalities (vision, hearing, smell and taste) |
how ”temporal information affects absolute identfication of tactile rhythm”[42] needs further scientific evidence. ”In addition, future studies could investigate the perception of more complex amplitude changes”(parabolic shapes), as much as, howother musical techniques like the (de-)crescendos can be applied to the field of hatpic icon design [17]. Identification of haptic icons encoded by roughness and containing short notes turned out dif- ficult, due to the short time to identify roughness. It will need future Work to define the minimum duration of notes at which a roughness parameter can still be identified, so ”rhythms could then be designed around these results”[15], even though roughness is not a suitable tac- ton parameter ”when using mobile phone vibration motors”[18]. | ||||||
| 2006 | Enriquez2006 | Enriquez, Mario MacLean, Karon Chita, Christian |
Haptic Phonemes: Basic Building Blocks of Haptic Communication | study | users can distinguish a set of phonemes | - A haptic phoneme represents the smallest unit of a constructed haptic signal to which a meaning can be assigned. These haptic phonemes can be combined serially or in parallel to form haptic words, or haptic icons, which can hold more elaborate meanings for their users. Here, we use phonemes which consist of brief (<2 seconds) haptic stimuli composed of a simple waveform at a constant frequency and amplitude…. users could consistently recall an arbitrary association between a haptic stimulus and its assigned arbitrary meaning in a 9-phoneme set, during a 45 minute test period following a reinforced learning stage. | Hand/Knob | - The ”number and complexity of required haptic syllables” is still questionable say Enriquez et al.[25]. They also assume that avoiding mid-values in hatpic phoneme sets would ”sufficiently improve identification performance to justify additional dimensions to increase set size”. It then would be easier for people to distinguish haptic icon sets with 3 dimensions with 2 values on each (23=8) rather than 2 dimensions with 3 values (32=9) [25]. | |||||||
| 2007 | Hoggan2007a | Hoggan, Eve Brewster, Stephen A. |
New parameters for tacton design | study | comparing synthesis techniques for tacton creation; rate „urgency“ 1. There will be a difference in participants’ ability to recognize three different levels of texture in cues using amplitude modulation, frequency, or wave- form. (accepted) 2. Participants will be able to distinguish between the three different textures created by the three differ- ent waveforms and three different frequency levels (over 90% correct identification) (partially accepted, except frequency) |
- recognition rates of 94% for waveform, 81% for frequency, and 61% for amplitude modulation, indicating that a more effective way to create Tactons using the texture parameter is to employ different waveforms to represent roughness. - „Tactons are structured vibrotactile messages which can be used to communicate information non-visually [2]. They are the tactile equivalent of audio Earcons [1] and visual icons, and can be used for communication in situations where vision is overloaded, restricted, or unavailable.“ - Frequency: There are conflicting views as to whether using differ- ent frequencies to create different textures is an appro- priate parameter for Tactons. On the one hand, because the frequency range of the skin is only from 10Hz to 400Hz, and the usable frequency range is further reduced by the limited bandwidth of standard actua- tors, frequency is unsuitable as a parameter in Tacton design [2]. However, on the other, studies have shown that frequency can still play a role in tactile texture as subjects in psychophysical experiments have reported a sensation of periodicity or buzzing at low frequencies (below 100Hz) while at higher frequencies a more dif- fuse, smooth sensation is perceived [8]. Furthermore, different frequencies have been used in experiments with multifinger tactual displays [7] where it was shown that participants could categorise frequencies into three perceptually distinct groups over the range of DC to 300Hz. - waveform: ...it has been shown by Miller [5] that it is better to have a small number of values for several attributes of a stimulus set as op- posed to having many values for one attribute of the stimuli. Furthermore, the vibrotactile range from pure sinethe vibrotatctile range from pure sine to noise is often described as continous transition from smoothness roughness to roughness \cite{Rovan2000} |
index finger of non-dominant hand | ~1s long 250 Hz (varying amplitude) 250*50 Hz, 250*30Hz 250 Hz/70 Hz/6 Hz sine, squaresawtooth, square |
9 | C2 | |||||
| 2018 | Ferguson2018a | Ferguson, Jamie Williamson, John Brewster, Stephen |
Evaluating mapping designs for conveying data through tactons | study | a magnitude estimation paradigm was used to map how the magnitudes of vibrotactile parameters like frequency and duration relate to the perception of the magnitude of conceptual data variables such as error, size and distance. The | - Touch is one of the earliest senses we develop- \cite{Field2014} speaks of early development after birth - "Tactons are structured vibrotactile messages which can be used to transmit information solely through the cutaneous sense. These are particularly useful in situations where visual or auditory displays are unavailable or inappropriate." - „The cutaneous sense is integral to human communication - it is one of the earliest developed senses [10] and is a power- ful tool for information transmission, both between people and between a user and a system.“ - „More expressive vibrotactile feedback can allow more information to be encoded within the vibration feedback itself, reducing the need to repeatedly visually attend to the device for information transmission.“ - „[often] vibrotactile feedback is simply used to attract attention […], however vibration has a number of properties, such as frequency, amplitude, rhythm and location on the body, that can be structured into messages or Tactons which can afford more complex information to be encoded in vibration. The advantage of Tactons is that they not only notify the user to information but also convey it. “ - Use Cases: Process Monitoring, Feedback in hazardous environments, feedback in loud environments - In Geldard’s 1957 paper Adventures in Tactile Literacy \cite{Geldard1957}, they presented a vibrotactile language Vibratese which three individuals learned in only 12 hours and could interpret a maximum of 38 words per minute. Vibratese shows vibration’s information transmission potential. - Most data:vibration mappings do not consider the user’s perceptions of the mappings being used, which can lead to confusion and Tactons which are difficult to interpret. To explore this issue, we conducted a magnitude estimation experiment to map how a number of vibrotactile parameters such as duration and frequency relate to the perceived magnitude of data variables that may be used in a real-world context such as error and danger. - Results from this study show that when tempo and duration are used to convey data, they are perceived in the same polarity, regardless of the type of data being conveyed. - „Although there have been a number of studies addressing the design of vibrotactile param- eters in Tactons [4, 6, 17, 24], there is very little experimental evidence to guide designers regarding what vibrotactile parameters are best suited to convey particular variables or data types. Research“ - „a mental model driven preference as found in data:sound displays may be a useful tool in establishing the optimum vibrotactile parameter to convey a particular data value.“ - comparison parameter mapping sonification: Ferguson & Brewster [8, 9] found that increasing an auditory parameter that is often considered "undesirable" (e.g. noise or roughness/disharmony) led to a perceived increase in the magnitude of an "undesirable" data concept (e.g. error, danger or stress). - Affect/Analogy: „For example, rougher patterns as well as stronger vibrations were perceived as more alarming [29] - analogously, a strong, rough vibration in the real-world may indicate an alarming event such as an earthquake. Furthermore, Hameed et al. [14] mapped a high importance cue designed to divert attention to a rapidly on/off fluctuating vibration which "equated to a rapid tapping of the skin" - this is similar to tapping someone rapidly on the shoulder to gain their attention“. Although these works indicate that there are associations made between vi- brotactile stimuli and various concepts and meanings such as roughness/intensity = alarming [29], "tapping" = interruption [14] or increasing intensity = unpleasantness [\cite{Yoo2015}, \cite{Wilson2017a}], there has not been any attempt to evaluate data:vibration parameter mappings. - Frequency Stimuli consisted of one-second long cues at 90, 200 and 300 Hz. Similarly to audible frequency [27], perception of frequency via the skin is also affected by the intensity of the stimulus [\cite{Geldard1957}, \cite{Verrillo1969}], therefore each frequency cue’s amplitude was adjusted such that intensity was equal across each stim- ulus - Results: Univariate results for every individual data:vibration mapping showed that manipulating duration and tempo had a significant effect on the perceived magnitude of the specific data concept being used. Only the accuracy, current and stress mappings reached statistical significance in the frequency conditions - and the frequency:accuracy mapping had more no polarities than positive or negative, suggesting that there was a lot of confusion among participants when choosing a polarity for this mapping….These results show that the polarity and perceived magnitude of data concepts varies considerably between participants (fre- quency), or it may be consistent across mappings (duration, tempo), further underlining the importance of understanding data:vibration mappings in vibrotactile feedback design. „ - DESIGN GUIDELINES Duration and tempo Tactons are not mapping dependent Longer vibrations resulted in an increase in perceived magnitude of all data concepts. Similarly, a faster tempo of a repeating vibration resulted in an increase in perceived magni- tude across all data concepts. This study investigated a small number of potential data variables, however they were selected in such a way as to attempt to cover a variety of potential uses. Further research needs to be carried out on more data:vibration mappings, however these results suggest that if using duration or tempo to convey a data variable through a Tacton, the perceived magnitude of the data variable will increase as duration or tempo increases. This may be of use when designers cannot fully investigate potential Tactons mappings - using Tacton du- ration or tempo to indicate the magnitude variable in a positive polarity, regardless of what the particular variable is. Semantically opposing concepts are not necessarily perceived in opposing polarities A priori expectations were that mappings for accuracy and error would generally be perceived in opposite polarities, for example in the conditions in which tempo was used to con- vey these concepts accuracy would be mostly perceived in a negative polarity and error would be perceived mostly in a positive polarity. However, the results for the duration and tempo mappings showed both accuracy and error polarity choices to be almost unanimous. This suggests that semantically oppos- ing variables may not necessarily be perceived in opposing vibrotactile polarities and more research needs to be carried out to further investigate this phenomena. However from these results it can be suggested that designers test their mappings when Tactons are used for similarly semantically opposing variables, to ensure that feedback is designed such that the user can understand the intended meaning of each Tacton. - Possible study design: ferguson, brewster 2017 magnitude estimation |
non-dominant palm | one-second long cues Frequency: 1s, 90, 200 and 300 Hz, equal intensity, based on \cite{Wilson2017} Roughness: 1s, 200 Hz sine wave modulated at 20 and 50 Hz, as well as an unmodulated waveform Duration: 200 Hz waveforms that were 100, 500 and 1000 ms in duration, also \cite{Wilson2017} Tempo: two-second long 200 Hz waveforms in which each cue rapidly fluctuated on and off at different frequencies. Each cue’s on period was 50 ms and the off periods were 15, 50 and 800 ms. |
18 | Tactile Labs Haptuator Mk II 1. This actuator was chosen based both on its high ac- celeration and bandwidth. The actuator was fixed to the inside wall of a cylindrical steel housing and the housing was filled with sound-proof foam to secure the actuator and reduce noise. The housing was then placed in vibration isolating foam to re- duce vibrating the surrounding equipment. Participants | |||||
| 2018 | Jones2018 | Jones, Lynette A. Singhal, Anshul |
Perceptual dimensions of vibrotactile actuators | study | determine how variations in the signals generated by three representative vibrotactile actuators are perceived and which features are judged as being distinctive | Fairly recent, reviews the field of tacton parameters and conducts MDS study on 3 levels of Frequency, Waveform and Intensity on C2/ERM/Haptuator. - The first dimension that emerged from the MDS represented a continuum associated with transitions in the amplitudes of the signals, with a smooth sine wave pattern contrasting with the more abrupt transitions in square waves. This may be considered a smooth-rough dimension. The second dimension extracted from the data was more difficult to characterize in that each of the two clusters along this dimension involved signals of varying waveform and frequency - At present, most tactile displays deliver simple vibrotactile inputs at single frequencies that are within the range of maximal sensitivity of the skin (i.e. 100 Hz - 300 Hz). Tactile displays can provide either static inputs as in refreshable Braille displays in which round-tipped pins indent the skin [5], or dynamic signals like the vibrations implemented in many consumer devices [8], [9]. The advantages of vibrotactile signals are that they vary along several dimensions namely frequency, waveform, intensity, and duration each of which can be used to create a range of inputs [10]. Such tactile stimuli are often referred to as tactons and represent the basic element of a tactile communication system [11-14]. Psychophysical studies provide a framework that assists in determining which stimulus dimensions and ranges of values are effective for designing tactons [15], [16]. - DIMENSIONS: - TEMPORAL: To date, variations in the temporal profile of stimuli and the location on the body stimulated have been used most frequently to generate different tactile patterns \cite{Jones2009}. The selection of these two parameters reflects the skin’s sensitivity to changes in the temporal properties of stimuli, which is inferior to that of the ear but superior to the eye \cite{Geldard1960}, and its capacity to encode the spatial coordinates of tactile stimulation accurately [19]. …. rhythm: \cite{Ternes2008} - WAVEFORM \cite{Summers1997a}! - ...variations in waveform are not readily distinguished at higher frequencies \cite{Summers1997a}. Whether such an effect occurs at lower vibrotactile frequencies is not known - frequency and amplitude of vibration are not orthogon al perceptually...The frequency and amplitude of vibration are not orthogonal perceptually, which means that when one changes, for example the frequency of vibration, so too does the other, namely its perceived amplitude \cite{Summers1997a} \cite{morley1990perceived}, - Previous work in which MDS techniques have been used to aid the design of haptic icons with one specific actuator \cite{Jones2008a}, [42], used waveform, frequency and force amplitude as the three primitives. For that stimulus set and sorting task, frequency which varied from 0.5 to 100 Hz was determined to be the strongest grouping variable, with waveform being the next most important [42]. In a further experiment when the frequency range was limited to between 3 and 25 Hz, it no longer dominated how participants grouped haptic stimuli. This clearly indicates that the specific range of values implemented for any parameter in a stimulus set can have a profound effect on perceptual distinctiveness. - perceived frequency of a constant vibration signal also varies at different locations on the body. In regions with higher densities of mechanoreceptors, like the fingertips, perceived frequency increases more rapidly with increasing frequency than in areas with lower innervation densities, such as the forearm [23], [24]. This means that the same vibrotactile stimulus may be perceived differently when presented on a device attached at different locations on the skin. GOOD JUSTIFICATION FOR BELT STUDY - SPATIAL cues about the environment can be conveyed very effectively using an array of vibrating motors mounted on the body – grid ref: studies have often been performed with a specific type of actuator, such as the C2 tactor (Engineering Acoustics, Inc) [25], [26], which has made it difficult to generalize findings across studies in which smaller, less robust actuators have been used (e.g. [27], \cite{Jones2008a} - TEXTURE When the amplitude of a base signal such as a 250 Hz sinusoid is modulated by a second sinusoid, the modulating frequency decreases from 50 to 20 Hz The creation of tactile textures based on waveform modulation provides a further dimension for use in tactile communication systems. - ACTUATOR TYPE: Variations in the mechanical signals generated by these various actuators could be exploited in designing multi-actuator tactile displays to provide inputs that are perceptually distinct and so readily recognized by users. Specific types of information, such as a subtle pressure cue delivered by an actuator with a limited bandwidth may be used to signal the passage of time, whereas a high frequency vibratory input could indicate a sense of urgency. - some of the organizational principles used to create vibrotactile libraries for gaming applications and digital media are relevant to the development of tactile signal libraries XP: Participants were required to judge the degree of similarity-dissimilarity between pairs of vibrotactile stimuli generated by these three actuators. These stimuli varied with respect to amplitude, waveform and frequency, the basic elements of such signals. In creating the set of stimuli, the objective was to have vibrotactile signals that were discriminable so that a judgment regarding their degree of similarity-dissimilarity could be made. At the same time, it was desirable to have stimuli that spanned a range of dimensions (e.g. different waveforms) to determine whether variations in these properties were perceptually relevant. Multi-dimensional scaling (MDS) techniques were used to determine the perceptual relations among the stimuli. It was anticipated that the MDS analysis would provide an indication of the most salient variables that people use to group vibrotactile signals. MDS has been successfully applied to understand the perceptual dimensions of tactile textures [39-41], and haptic icons [30], [42] ACTUATORS: The rotation of the eccentric mass results in an off-axis load on the contactor on the skin and the suspension restricts the lateral compliance of the motor mass. The vibration signal delivered is primarily perpendicular to the skin. The C3 tactor is a small linear moving-magnet actuator with a moving contactor that is lightly preloaded against the skin. When activated the contactor oscillates perpendicular to the skin while the surrounding area is shielded by passive housing. The Haptuator Mark II is an ungrounded moving magnet voice-coil type linear actuator with a cylindrical magnet suspended by two rubber membranes…. For the EMR tactor, there was no perceptible difference between a square wave and a triangular wave RESULTS - As the frequency increased above 25-30 Hz on all three tactors it became very difficult to distinguish between the waveforms of the signals, they all felt like a constant buzzing. - At the low frequencies implemented (15-30 Hz), participants grouped the stimuli along one dimension that perceptually went from “rougher” waveforms with abrupt amplitude transitions to smoother signals with more gradual transitions in amplitude. – app examples: navigation: . J.B.F. Van Erp, S. Brewster, R. Murray-Smith, "Tactile navigation display" in Haptic HCI 2000, Berlin:Springer-Verlag, pp. 165-173, 2001. Show Context CrossRef FindIt Google Scholar 32. J.B.F. Van Erp, "Presenting directions with a vibrotactile torso display", Ergonomics, vol. 48, pp. 302-313, 2005. Show Context CrossRef FindIt Google Scholar 33. J.B.F. Van Erp, A.H.C. Van Veen, C. Jansen, T. Dobbins, "Waypoint navigation with a vibrotactile waist belt", ACM Trans. Appl. Percept., vol. 2, pp. 106-117, 2005. |
Fingertip | 4s long cues, Haptuator/C2 Square/Sine/Triangle @ 20/15/30 Hz ERM Square/Sine @ 20/15 Hz |
10 | Haptuator mkII, EAI C2, EAI EMR |
| Year | Key | Authors | Title | Venue | Type | Sensor | Actuator | Mapping | Metrics | Goal / Hypothesis | Outcomes | Context | Contribution to Field | Connection to own research | Main Takeaways / Quotes | Location | Task | N | T | Future Work |
| 2001 | Wall2001 | Wall, Conrad III Weinberg, M S Schmidt, P B Krebs, D E |
Balance Prosthesis Based on Micromechanical Sensors Using Vibrotactile Feedback of Tilt |
IEEE transactions on bio-medical engineering | 2 Studies | On Head; Integrated Gyro, Accelerometer → Tilt Estimate | 16 Audiological Engineering Tactors VBW32=Tactaid | Tilt → Pulse Rate (1-5 Hz, 1-7 Tactors, 0.25° steps, 0.5° Deadzone train of 100-ms pulses (25 vibrational cycles/pulse) at a rate of 1, 3, or 5 pulses/s in a step-wise fashion. Larger values of head tilt correspond to higher pulse rates. Tactors |
Head-tilt angle (phi), fraction of time for which the head-tilt angle exceeded the 0.5 threshold for triggering the tactors, the fraction over threshold (FOT), The rms center of pressure displacement (rms CPD) | When compared with the no-aid condition, the shoulder tactors, side tactors, and light touch conditions all show a significant reductions in rms CPD. The difference between the shoulder tactor and side tactor rms CPD responses was not significant using the two-tailed matched pair test. As compared with the no-aid condition, the use of tactors significantly reduced rms . Light touch did not significantly reduce rms compared with the no-aid condition. From these tests, we can conclude that all aids significantly reduce rms CPD responses. We can also conclude that the tactor aids significantly reduce rms . VI. |
Shoulder vs Side; vs light touch / no support | Tandem Romberg Stance w/ Eyes Closed | 6 | |||||||
| 2003 | Kadkade2003 | Kadkade, Prajoy P. Benda, Brian J. Schmidt, Patricia B. Wall, Conrad |
Vibrotactile Display Coding for a Balance Prosthesis | IEEE Transactions on Neural Systems and Rehabilitation Engineering | Study | Joystick | 16 Tactors in one row | 4 Schemes compared: Pulse rate on 1 tactor vs. proportional activation on 3/4/7 tactors | critical lambda, when performance breaks down | Position significantly better than interval-based; roughly equivalent for the latter | Set the path to the column-based belt; vt introduces delay larger than visual | pulsing-rate not as effective as position? | - Providing information by changing the location of a continuously activated (250 Hz) tactor resulted in better performance than changing the pulse repetition rate (1–5 pulses/s) of tactor vibration at a single location. - However, magnitude information is not available until the second pulse of the train is sent. Thus, there is a delay in magnitude coding equal to the interval between two consecutive pulses (200–1000 ms in our experiments) that is inherent in this display scheme. The pulse repetition rates used in this study were chosen based on per- sonal communication with staff at the U.S. Navy Aeromedical Research Laboratory who collected empirical data while exper- imenting with similar tactile displays. One pulse per secondwas selected as the lowest rate that is practically useful and 5 pulses/s was selected because it was the highest rate having individually perceivable pulses. Above this rate, stimulation seemed to sub- jects to be a constant train of vibration. Three pulses per second is the mean of these limiting frequencies, and it is clearly differentiated from 1 and 5 pulses/s. - According toWeber et al. [13], two-point static discrimination is approximately 4 cm on the back. According to Kaczmarek, two-point dynamic discrimination is approximately 2 cm on the back [14]. A dynamic discrimination limit of 2 cm predicts that there would be a performance improvement from Scheme B (4.6-cm spacing) to Scheme C (2.6-cm spacing),... - The dramatic decrement in performance on the second-order task when velocity feedback was not provided indicates that for effective control of balance using a vibrotactile display, velocity information must be explicitly provided. Inferring velocity from change in position of the vibrotactile stimulus is not sufficiently effective for successful control of a second-order unstable system. - Response time to VT stimulus ca 30 ms |
waist / back (horizantal and vertical) | critical tracking task (CTT), operator attempts to control an increasingly unstable system using a joystick | 16 | ||||
| 2004 | Sienko2008 | Sienko, Kathleen H. Balkwill, M D Oddsson, Lars I E Wall, Conrad III |
Effects of multi-directional vibrotactile feedback on vestibular-deficient postural performance during continuous multi-directional support surface perturbations | Journal of Vestibular Research | motion platform study | on-belt IMU → tilt signal displayed to the subject for this study was the tilt estimate plus one half the tilt rate. This is a special case of a proportional–integral–derivative cotroller (PID controller); optotrack, force plate | 3x16 Tactors | Tactor row indicated tilt magnitude and tactor column indicated tilt direction, 250 Hz, constant amplitude. 3 levels of activation, 0.5°/33%/66% of per-subject limit of stability (LOS) | Root-mean-square trunk tilt, elliptical fits to trunk sway trajectory areas, percentage of time spent outside a no vibrotactile feedback zone, RMS center of pressure, and anchoring index parameters indicating intersegmental coordination | - Subjects had significantly reduced RMS trunk sway, significantly smaller elliptical fits of the trajectory area, and spent significantly less time outside of the no feedback zone in the tactors on versus the tactors off configuration. Among the displays evaluated in this study, there was not an optimal tactor column configuration for standing tasks involving continuous surface perturbations. Furthermore, subjects performed worse when erroneous information was displayed. Therefore, a spatial resolution of 90◦ (4 columns) seems to be as effective as a spatial resolution of 22.5◦ (16 columns) for control of standing. - This study is the first to demonstrate that subjects with vestibular loss can use vibrotactile feedback to control their body tilt during multi-directional planar continuous support surface perturbations. Subjects had significantly reduced RMS trunk sway, significantly smaller elliptical fits of the trajectory area, and spent significantly less time in the dead zone in the tactors on versus the tactors off configuration. To our knowledge, this is the first time that multi-directional vibrotactile feedback has been used to supplement body orientation information. - No improvement after one session after a month |
waist | Eight weakly compensated vestibulopathic subjects | ||||||||
| 2006 | Peterka2006 | Peterka, Robert J. Wall, Conrad Kentala, Erna |
Determining the effectiveness of a vibrotactile balance prosthesis | Journal of Vestibular Research: Equilibrium and Orientation | motion platform study | AP rotational position of the backboard with respect to the SS was measured by a potentiometer, rotational velocity by a rate sensor; also measured by a custom inertial sensor [16],used to drive the prosthesis | 12 AE tactors, in pairs (3 pairs anterior and 3 pairs posterior) | A step-wise coding scheme was used to activate pairs of tactors. Each pair of tactors was activated in an all-or-none manner with activation determined by the sum of the measured tilt and one half of the measured tilt velocity | comparing transfer function: method to determine effectiveness of vt feedback on sway angle/velocity | - We felt that it would simplify the subject’s task of generating a corrective response if the information pro-vided by the tactor array could be mapped directly into the torque required for postural corrections. Therefore, a combination of tilt and tilt velocity was used as an input signal to drive the tactor activation because it is well known that a control system designed to stabilize an inverted pendulum must generate corrective torque in proportion to a combination of both tilt and tilt ve-locity [5]. - Body sway levels were consistently and significantly reduced with the use of the balance prosthesis at all SS stimulus amplitudes for both normal and VL subjects. |
„vest“ | stand on motion plate | 6 healthy, 5 with severe vestibular disorders | |||||||
| 2009 | Goodworth2009 | Goodworth, Wall, Peterka | Influence of Feedback Parameters on Performance of a Vibrotactile Balance Prosthesis | IEEE Transactions on Neural Systems and Rehabilitation Engineering | motion platform study | micro-mechanical linear accelerometer and rate gyroscope (gyro) that was attached to the backboard about 35 cm above ankle height. | 12 AE tactors, in pairs (3 pairs anterior and 3 pairs posterior) | a step-wise coding scheme with activation determined in different Tactors ON conditions by different combinations of body sway angular position and velocity. | frequency-response functions were computed from power and cross-power spectra., Root-mean-square (RMS) and peak-to-peak values of body sway angle and angular velocity were measured from the mean body sway responses for each postural test, averaged over the last 5 stimulus cycles. | 1) identify the particular combination of position and velocity feedback provided by the vibrotactile prosthesis that would produce the greatest improvement in balance control 2) use a model-based interpretation of the experimental results to understand how orientation information from the prosthesis was combined with natural sensory information and used for postural control |
determining proportions of position/velocity; model that explains changes: bandwidth mismatch, only sensory addition not substitution |
- The 5 Tactors ON conditions each had a different combination of position and velocity feedback information given to the subjects through the vibrotactile interface. The 5 different feedback settings include position only feedback (P100V0), 75% position and 25% velocity feedback (P75V25), 50% position and 50% velocity feedback (P50V50), 25% position and 75% velocity feedback (P25V75), and velocity only feedback (P0V100). - 1): Results from measures of body sway and from model-identified prosthesis feedback gains showed that subjects generally were able to utilize position-dominated prosthesis feedback to a greater extent than velocity-dominated feedback. However, our analysis showed that all combinations of position and velocity feedback provided both desirable and undesirable postural effects such that a determination of the combination of feedback that is most effective depends on the frequency distribution of external perturbations or internal disturbances that evoke body sway. - 2): orientation information from the vibrotactile prosthesis is effectively heavily low-pass filtered and therefore is very different from the wide-bandwidth dynamic characteristics of the vestibular and proprioceptive systems. The dynamic mismatch between the wide-bandwidth orientation information from natural sensory systems and the low-pass filtered prosthesis information likely precludes a substitution of vibrotactile cues for natural sensory information. Rather, the modeling results indicate that vibrotactile information is incorporated into the existing postural system mainly through a sensory addition mechanism as opposed to a sensory substitution mechanism. - frequency-response function analysis showed that the sway reduction was due primarily to a reduction in sway below about 0.5 Hz, whereas there was actually an enhancement of sway above 0.6 Hz. |
waist | 8 healthy | ||||||
| 2010 | Wall2010b | Wall, Conrad III Kentala, E. |
Effect of displacement, velocity, and combined vibrotactile tilt feedback on postural control of vestibulopathic subjects | Journal of Vestibular Research: Equilibrium and Orientation | study | 2 tactors, A/P | step-wise, P vs D vs PD vs prediction | RMS of tilt estimate | PD display produces less tilt than P or D display alone. In sum, P alone, D alone, and PD all reduce tilt, but PD works best | - We believe that subjects did not show larger changes in tilt among different signal display modes because they spent the majority of their time during a test trial in the “dead zone” in which no tactors were activated. - We think that some residual vestibular information might have been avail- able for subjects to estimate bodymotion and thus avoid falling. Another plausible alternative from the senso- ry side is that extravestibular motion and graviception, perhaps fromsome of the body’s internal organs as sug- gested by the experiments of Mittelestaedt and others may also provide estimates of body motion which can be used to maintain postural stability |
SOT 5/6 | |||||||||
| 2011 | Goodworth2011 | Goodworth, Adam D. Wall, Conrad III Peterka, Robert J. |
A balance control model predicts how vestibular loss subjects benefit from a vibrotactile balance prosthesis | Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS | perturbed stance/motion platform study → model | 12 AE tactors, in pairs (3 pairs anterior and 3 pairs posterior) | model how subjects with a severe vestibular loss (VL) used vibrotactile information from a balance prosthesis to enhance balance control. |
vibrotactile feedback information reduced sway at frequencies below ~0.6 Hz, but vibrotactile feedback was less effective in reducing sway as stimulus amplitude increased. accurately predicted by the model, which was based on time-delayed sensory feedback control | model for eyes-closed stance balance w/ vt feedback | Model simulations predicted that: - the values chosen as impact on the tactor thresholds can have an important balance responses. - the prosthesis was relatively less effective at stimulus-evoked sway at larger compared to reducing smaller stimulus amplitudes - it is possible to select thresholds such that prosthesis becomes relatively more effective at reducing stimulus-evoked sway at larger compared to smaller stimulus amplitudes - if longer-term learning could take place, then despite the dynamic mismatch in bandwidth between vibrotactile information and in lower natural vestibular information, large reductions frequencies of sway are predicted by the model if subjects were able to increase their reliance of prosthesis feedback. |
5 w/ severe VL | |||||||||
| 2010 | Wall2010 | Wall, Conrad III | Application of vibrotactile feedback of body motion to improve rehabilitation in individuals with imbalance | Journal of neurologic physical therapy : JNPT | lit review, system description, study | 6 DOF Acc, Gyr | 3x16 Tactors | step-like activation | sway reduced, Dynamic Gait Index (DGI) improved | - feedback has minimal effects during the ballistic phase (body’s outbound trajectory in response to the perturbation), and the greatest effects during the recovery (return toward baseline) and steady state (post-recovery) phases, specifically, feedback significantly decreases the time required for the body tilt to return to baseline values and significantly increases the velocity of the body’s return to baseline values and significantly decreases root mean square roll and pitch sway and significantly increases the amount of time spent in the no feedback zone - no one tactor column configuration was optimal for standing tasks involving discrete surface perturbations. - Feedback produced larger effects on body tilt versus center of pressure parameters. - the subjects’ performance worsened when erroneous feedback was provided, suggesting that vibrotactile stimulation applied to the torso is actively processed and acted upon rather than being responsible for simply triggering a stiffening response. |
12 | stance: 12 with well compensated vestib. lesion; walk 10 with documented lesions | ||||||||
| 2011 | Wall2011 | Wall, Conrad III Lyford, N D Sienko, Kathleen H. Balkwill, M D |
The design and development of a production prototype balance belt | Engineering in Medicine and Biology Society, EMBC, 2011 Annual International Conference of the IEEE | Evolution Paper, Studies | 35K → 500$ IMU | tactaids → C2 | position-based coding, waveform-based coding |
SOT | position-based coding → waveform-baded coding, performed as well, 3→1 tactor/pos | Experimental results that enable device simplification: 1) Fewer tactile vibrators to signal tilt direction 2) Newer vibrators allow the use of fewer vibrators to signal tilt magnitude: Originally, 250 Hz only Tactaid, varying amplitude not effective; A second feedback scheme, waveform-based coding, was developed using a new tactile vibrator (EAI C2, tactor - unit cost: $200) that provides a wider variety of signals, enabling tilt magnitude to be signaled with just one C2 tactor by using carefully selected states: no signal; a 250 Hz sinusoid; and a signal that has several periodic components. 3) Simplified electronics test bed: PC104+35K$ IMU → 80 Mhz PIC32 + 500$ IMU w/ Bluetooth; 4 kg to 0.7 kg 4) Ergonomic belt design |
waist | ||||||||
| 2012 | Sienko2012 | Sienko, Kathleen H. David Balkwill, M. Wall, Conrad III |
Biofeedback improves postural control recovery from multi-axis discrete perturbations |
Journal of NeuroEngineering and Rehabilitation | perturbed stance/motion platform study | 3x16 Tactors | step-like activation, 4/8/16 columns | Torso kinematics (IMU) and center of pressure (force plate) | examine the effect of multidirectional vibrotactile biofeedback on postural stability during discrete multidirectional support surface perturbations | 4 colums as good as 16 | - The number of columns displayed was varied to determine the effect of spatial resolution upon subject response. - Transient and steady state postural responses - Based on laboratory-based pilot studies, response times to vibrotactile stimulation applied on the torso can range between 250 and 400 ms (unpublished observations) - Most of the parameters did not differ significantly from those obtained without vibrotactile feedback, and even the small differences were in the direction of poorer performance. - It has been shown that the hip is the primary means of controlling M/L sway while the ankles are predomin-antly used to control A/P sway [20]. |
6 VD | ||||||||
| 2012 | Wall2012 | Wrisley, Diane Oddsson, Lars I E Wall, Conrad III |
Vibrotactile feedback of mediolateral trunk tilt or foot pressure increases locomotor performance in healthy older adults - a pilot study | Engineering in Medicine and Biology Society (EMBC), 2012 Annual International Conference of the IEEE | mini studies w/o control | vest: tilt sensor sock: pressure sensors (FSRs) |
vest / sock: 3x16 VBW32=Tactaid | position-based coding | Dynamic Gait Index (DGI) | compare VT belt with VT socks | DGI increased for both devices, slightly | Predictions: In subjects with normal sensory function there will be better performance when either orientation or proprioceptive sensory substitution information is provided. There will be even further improvement with both modalities enhanced. In subjects with vestibulopathies and peripheral neuropathies there will be some performance improvement when information is added to the intact modality, but better performance when information is added to the missing modality. We would predict even further improvement when information is added to both missing and intact modalities. | waist, feet | |||||||
| 2012 | Lee2012 | Lee, Beom-Chan Kim, Jeonghee Chen, Shu Sienko, Kathleen H. |
Cell phone based balance trainer | Journal of neuroengineering and rehabilitation | comparative study | Accelerometer: LIS302DL in iPhone 3GS; xsens imu for reference | 2 ERMs | vibration when over limit | elliptical area, RMS, % time in dead zone | validate cheaper vt fb for in-home systems | results suggest that the real-time feedback provided by this system can be used to reduce body sway | - The system was capable of providing real-time vibrotactile cues that informed corrective postural responses. When feedback was available, both healthy subjects and those with vestibular deficits significantly reduced their A/P or M/L RMS sway (depending on the direction of feedback), had significantly smaller elliptical area fits to their sway trajectory, spent a significantly greater mean percentage time within the no feedback zone, and showed a significantly greater A/P or M/L mean power frequency. |
waist | eyes closed during Romberg, semi-tandem Romberg, and tandem Romberg stances | 5 healthy, 4 w/ vest def | |||||
| 2013 | Bechly2013 | Bechly, Kelli E. Carender, Wendy J. Myles, James D. Sienko, Kathleen H. |
Determining the preferred modality for real-time biofeedback during balance training | XSens | 4x C2 @ 250 Hz | visual ranked high, but not always possible, performance for simple task similar | - Both groups improved performance for each feedback modality compared to baseline, with no significant differences in performance observed among vibrotactile, discrete visual, or multimodal feedback for either group. Subjects with vestibular deficits performed best with continuous visual feedback and ranked it highest. Although the control subjects performed best with continuous visual feedback in terms of mean M/L tilt, they ranked it lowest. Despite the observed improvements, continuous visual feedback involves tracking a moving target, which was noted to induce dizziness in some subjects with vestibular deficits and cannot be used during exercises in which head position is actively changed or during eyes-closed conditions. | waist | eyes-open tandem Romberg stance trials with (vibrotactile, discrete visual, continuous visual, and multimodal) and without (baseline) feedback | Eight subjects (46.6 ± 10.6. years) with peripheral vestibular deficits and eight age-matched control subjects (45.3 ± 11.1. years) | ||||||||||
| 2013 | Sienko2013 | Sienko, Kathleen H. Balkwill, M David Oddsson, Lars I E Wall, Conrad III |
The effect of vibrotactile feedback on postural sway during locomotor activities |
Journal of neuroengineering and rehabilitation | position-based coding | root-mean-square (RMS) trunk tilt and percentage of time below the tilt thresholds | characterize the effects of two real-time feedback displays on locomotor performance during four gait-based tasks ranging in difficulty | continuous feedback was superior. | - trunk-based vibrotactile feedback system that provided real-time feedback regarding their medial-lateral (M/L) trunk tilt when they exceeded a subject-specific predefined tilt threshold during slow and self-paced walking, walking along a narrow walkway, and walking on a foam surface. Two feedback display configurations were evaluated: the continuous display provided real-time continuous feedback of trunk tilt, and the gated display provided feedback for 200 ms during the period immediately following heel strike - Use of continuous feedback resulted in significant decreases in M/L trunk tilt and increases in percentage times below the tilt thresholds during narrow and foam trials. The gated display produced generally smaller changes - Vibrotactile feedback improved subjects’ control of M/L tilt without sacrificing pace, which suggested that subjects had adequate time to perceive, process, and respond to the vibrotactile cues given the training received. Improved control was more apparent during the more difficult tasks (narrow and foam), most likely due to the greater room for improvement on the baseline metrics. Since these two “difficult” tasks were performed near the end of the ses- sion, some of the improvement was attributed to subjects’ increased experience. The |
walking on different grounds | 7 w/ vestibular deficits | |||||||||
| 2015 | Brugnera2015 | Brugnera, Cibele Bittar, Roseli Saraiva Moreira Greters, Mário Edvin Basta, Dietmar |
Effects of vibrotactile vestibular substitution on vestibular rehabilitation - preliminary study | Brazilian Journal of Otorhinolaryngology | controlled study | Vestiguard RT | Sensory Organization Test (SOT) protocol of the Computerized Dynamic Posturography (CDP) and two scales of balance self-perception, Activities-specific Balance Confidence (ABC) and Dizziness Handicap Inventory (DHI) | SG showed statistically significant improvement in C5 (p = 0.007) and C6 (p = 0.01). On the ABC scale, there was a significant difference in the SG (p = 0.04). The DHI showed a significant difference in CG and SG with regard to the physical aspect, and only in the SG for the functional aspect (p = 0.04). | - adjustable belt placed around the patient’s waist (Fig. 1) containing a main unit fitted with two gyroscopes, which detect the direction of the body oscillation (anterior/posterior, R/L side), and four vibrating stimulators arranged at angles of 90◦ between them - VertiguardTM vibrotactile stimulation device was able to improve the body balance of patients who did not achieve good response to training by vestibular rehabilitation. |
waist | 15 elderly w/ postural impairment that could not improve with conventional vestibular rehab | |||||||||
| 2017 | Xu2017 | Xu, Junkai Bao, Tian Lee, Ung Hee Kinnaird, Catherine Carender, Wendy Huang, Yangjian Sienko, Kathleen H. Shull, Peter B. |
Configurable, wearable sensing and vibrotactile feedback system for real-time postural balance and gait training: proof-of- concept |
Journal of NeuroEngineering and Rehabilitation | system, 2 studies | MPU-9150 9-DoF IMU | ERM / Dots | sensor / actor „Dots“ | - proof-of-concept design of a configurable, wearable sensing and feedback system for real-time postural balance and gait training targeted for home-based treatments and other portable usage. Sensing and vibrotactile feedback are performed via eight distributed, wireless nodes or “Dots” (size: 22.5 × 20.5 × 15.0 mm, weight: 12. 0 g) that can each be configured for sensing and/or feedback according to movement training requirements. - first experiment, four healthy older adults were trained to reduce medial-lateral (M/L) trunk tilt while performing balance exercises. - second experiment wasconducted with thesamewearablesystemtotrain sixhealthy older adults to alter their foot progression angle in real-time by internally or externally rotating their feet while walking |
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| 2017 | Sienko2017 | Sienko, Kathleen H. Whitney, S. L. Carender, W. J. Wall, Conrad III |
The Role of Sensory Augmentation for People with Vestibular Deficits: {{Real}}-Time Balance Aid and/or Rehabilitation Device? | Journal of Vestibular Research | narrative review | - … suggests that there are short-term improvements in balance performance following a small number of training sessions with a sensory augmentation device. Long-term clinical and home-based controlled training studies are needed. It is hypothesized that sensory augmentation provides people with vestibular deficits with additional sensory input to promote central compensation during a specific exercise/activity; however, research is needed to substantiate this theory. Major obstacles standing in the way of its use for these critical applications include determining exercise/activity specific feedback parameters and dosage strategies. This paper summarizes the reported findings that support sensory augmentation as a balance aid and rehabilitation device, but does not critically examine efficacy or the quality of the research methods used in the reviewed studies. - Sensory augmentation has been shown to reduce body sway in patients with balance disorders during real-time use while performing a subset of traditional balance rehabilitation exercises (e.g., semi-tandem Romberg, tandem Romberg). Retention and carry- over effects appear to be limited to days to week and it is unclear based on the existing data that there are significant benefits of training with a sensory augmentation device versus training alone. How- ever, no systematic studies have been performed over extended periods of time. - Constant feedback (provided continuously throughout rehabilitation training pro-grams) promotes quick learning, but may negatively affect retention. Variable (provided periodically) or summed feedback (provided after a set of similar exercises are performed),would likely slow learning, but improve retention. Delayed feedback (provided after a slight delay) or terminal feedback (provided post completion of a particular activity) are also effetive methods for delivering feedback regarding the accuracy or quality of movement depending on the application, the user’s capability, and the goals of the training program [75]. The majority of studies exam-ining retention effects have provided subjects with constant feedback.A few recent studies have begun to explore the use of variable feedback [10], but the ideal “dose” (including factors such as the frequency of use and the feedback activation thresholds) within and across training sessions is unknown. - The mechanism by which information is integrated and used by the CNS is not well understood.Thedom- inant hypothesis, which has not been supported by rigorous experimental evidence, holds that observed balance improvements are due to sensory reweight- ing: feedback of body motionp rovides the CNS with a correlate to the inputs from its intact sensory channels (e.g., vision, proprioception), so subjects receiving sensory augmentation learn to increasinglydependon these intact systems. Other possible mechanisms for observed improvement that merit further exploration include, but are not limited to: cognition (processing of sensory augmentation information is solely cogni- tive with no selective adjustment of sensory weights by the CNS), “sixth” sense (CNS interprets sen- sory augmentation information as a new and distinct sensory channel), context-specific adaptation (new sensorimotor program is developed through repeated interaction with the device and is accessible only when the device is used), and combined volitional and non-volitional response [53, 55–57, 68]. |
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| 2018 | Sienko2018 | Sienko, Kathleen H. Seidler, Rachael D. Carender, Wendy J. Goodworth, Adam D. Whitney, Susan L. Peterka, Robert J. |
Potential mechanisms of sensory augmentation systems on human balance control | Frontiers in Neurology | critical review | - summarizes the reported sensory augmentation findings spanning postural control models, clinical rehabilitation, laboratory-based real-time usage, and neuroimaging to critically evaluate each of the aforementioned mechanistic theories. Cognition and sensory re-weighting are identified as two mechanisms supported by the existing literature. - Studies that apply long-term SA are needed to see if a balance aid with features of a sensory addition mechanism can evolve through motor learning to behave as a sensory substitution mechanism where the augmented sensory information is used in a manner that is essentially indistinguishable from natural sensory feedback. Prolonged balance training with SA would ideally improve balance after the augmentation is removed. However, there are mixed results supporting this positive retention and carryover.When retention and carryover are found, evidence supports the notion that SA altered sensory integration via a sensory reweightingmechanism. Finally, application of system identification methods employing model-based interpretation of experimental results can provide detailed quantitative measures of the balance control system to assess the effectiveness of SA technologies and rehabilitation strategies. |
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| 2018 | Bao2018 | Bao, Tian Carender, Wendy J Kinnaird, Catherine Barone, Vincent J Peethambaran, Geeta Whitney, Susan L Kabeto, Mohammed Seidler, Rachael D Sienko, Kathleen H. |
Effects of Long-Term Balance Training with Vibrotactile Sensory Augmentation among Community-Dwelling Healthy Older Adults: A Randomized Preliminary Study | Journal of NeuroEngineering and Rehabilitation | tactor activation signal was defined as the tilt angle plus one half times the tilt angular rate for Categories 1, 2, 4 and 5 (standing, arm movement, gait), and as the tilt angle for Category 3 (weight shifting) exercises (Wall2010b) | battery of clinical balance tests (Activity Balance Confidence Scale, Sensory Organization Test, Mini Balance Evaluation Systems Test, Five Times Sit to Stand Test, Four Square Step Test, Functional Reach Test, Gait Speed Test, Timed Up and Go, and Timed Up and Go with Cognitive Task) before training, after four weeks of training, and after eight weeks of training. | significantly greater improvements in Sensory Organization Test and Mini Balance Evaluation Systems Test scores than control | first true longitudinal study, showing concrete benefits in functional scores | trained in their homes for eight weeks, completing three 45-min exercise sessions per week using smart phone balance trainers that provided written, graphic, and video guidance, and monitored trunk sway. During each session, participants performed six repetitions of six exercises selected from five categories (static standing, compliant surface standing, weight shifting, modified center of gravity, and gait). | 12 | ||||||||||
| 2019 | Kingma2019 | Kingma, Herman Felipe, Lilian Gerards, Marie-Cecile Gerits, Peter Guinand, Nils Perez-Fornos, Angelica Demkin, Vladimir van de Berg, Raymond |
Vibrotactile feedback improves balance and mobility in patients with severe bilateral vestibular loss | Journal of Neurology | 6 DOF Acc, Gyr | belt with 12 ERMs | 300 Hz sinusoidal signal delivered in sequences of 150 ms with a repetition rate of 4 Hz. Patients experience a vibratory pulse from a tactor when they tilt more than 2.5° towards that tactor. The stimulus is turned off when their tilt becomes less than 1.5° towards that sensor | We observed that a period of 2 h wearing the balance belt, allowed a good preselection of patients that might have a clear benefit of using continuous vibrotactile feedback. Twenty-three out of the 31 patients selected this way expe- rienced a clear benefit in daily life, 8 no benefit at all (study 2). The lack of any effect of vibrotactile feedback at low intensities in different placebo settings, suggest that the effect quantified in the 2nd study is not placebo. The posi- tive responders experienced a relatively big improvement in quality of life (60% or more on the MBS scale) and wanted to keep the belt and use it permanently. | ||||||||||||
| 2020 | Ballardini2020 | Ballardini, Giulia Florio, Valeria Canessa, Andrea Carlini, Giorgio Morasso, Pietro Casadio, Maura |
Vibrotactile Feedback for Improving Standing Balance | Frontiers in Bioengineering and Biotechnology | accelerometric measurement / BNO055 | two vibration motors placed on the anterior and posterior part of the body, at the L5 level | encoding a combination of the position and acceleration of the body center of mass in the anterior-posterior direction | RMS acceleration, 95% power spectral density frequency | vibration always on vs vibration with a dead zone vs sham feedback | sway amplitude reduced,frequency increased in both AP/ML. only deadzone led to short-term after-effect, sham increased sway | - Maintaining balance standing upright is an active process that complements the stabilizing properties of muscle stiffness with feedback control driven by independent sensory channels: proprioceptive, visual, and vestibular.Considering that the contribution of these channels is additive, we investigated to what extent providing an additional channel, based on vibrotactile stimulation, may improve balance control. - Postural control is a complex sensorimotor skill with two main functions: stabilizing balance and maintaining the relative position of body segments (Massion, 1994; Ivanenko andGurfinkel, 2018). It requires the interaction of the sensory,muscular, and nervous systems (Horak andMacpherson, 1996). In particular, the central nervous system must process and integrate concurrent feedback from the vestibular, somatosensory, and visual sensory channels (Hirabayashi and Iwasaki, 1995; Horak and Macpherson, 1996). If those are impaired or absent, postural control and balance are compromised, increasing also the risk of falling (Maki, 1989; Brown et al., 1999; Melzer et al., 2004; Horak, 2006). These impairing sensory deficits could be caused by aging (Peterka and Black, 1989; Melzer et al., 2004), diabetes (Najafi et al., 2010), vestibular disorder or neurodegenerative diseases, such as Parkinson (Mancini et al., 2011, 2012;Marchesi et al., 2019). - synchronized vibrotactile feedback reduces significantly the sway amplitude while increasing the frequency in anterior-posterior andmedial-lateral directions. The two encoding methods had no different effects of reducing the amount of postural sway during exposure to vibration, however only the dead-zone feedback led to short-term after effects. The presence of sham vibration, instead, increased the sway amplitude, highlighting the importance of the encoded information. - For simplicity, in the following we refer to changes in intensity (its amplitude and frequency of the vibration) of the vibration and we express it only in terms of frequency. The reason for choosing this kind of coupled vibration motors was 2-fold: they are inexpensive and the vibration feedback is more effective when frequency and amplitude are coupled (Cipriani2012) [decreased frequency (or amplitude) is properly perceived only if the amplitude (or frequency) has not increased. / the concurrent and coherent vari- ations of the two components virtually improve the discrimina- tion ability] |
waist | stand still with their eyes closed | 24 |