LRH was supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada. SD was partly supported from the NSERC CREATE program.

All of the experiments were approved by the York Ethics board and all participants signed informed consent forms. The experiments were performed in accordance with the Treaty of Helsinki.
1. Stimuli
<ol>
	<li>Tactile Detection Stimulus
	<ol>
		<li>Use a tactor (1.17&#34; diameter and 0.30&#34; thick) to deliver tactile stimuli of 250 Hz vibration for 100 msec. Using a purpose-built tactor provides a linear relationship between the amount of travel and the voltage applied.</li>
		<li>Control tactile stimulus delivery with a 64 bit sound card.
		<ol>
			<li>To drive the tactor, treat it as a loudspeaker. Connect a stereo audio amplifier to a 64-bit computer stereo sound card. Connect the tactor to one of the outputs of the amplifier (e.g., the &#39;left speaker out&#39;). Connect the second channel (e.g., the &#39;right speaker out&#39;) of the amplifier to a regular loudspeaker to provide auditory signals to the participant.</li>
			<li>In the computer code that is controlling the experiment, generate the waveform that will be used to vibrate the tactor (e.g., a 250 Hz sinewave of duration 100 msec), and another waveform for the auditory signal (e.g., a 3,000 Hz sinewave with a duration of 100 msec). See Example Code 1 in the Supplemental Code File.</li>
			<li>Put each of these two waveforms into a two-dimensional array. For the tactor array put the signal in the first dimension and set the second dimension to all zeros. For the sound array put the signal in the second dimension and set the first to all zeros. Play the appropriate array to the soundcard at the appropriate point in the program. See Example Code 1 in the Supplemental Code File for a demonstration of how this is done.</li>
		</ol>
		</li>
		<li>Attach the tactor to a strap with a mechanical-based fastening product.</li>
	</ol>
	</li>
	<li>Masking Stimulus
	<ol>
		<li>Provide the masking stimulus by an electric, hand-held vibrator (4 cm diameter; 83 Hz when set on &#34;low&#34;).</li>
		<li>Based on the areas where masking is to be tested, select the sites where the masking stimulus is to be applied.</li>
	</ol>
	</li>
</ol>
2. Experimental Setup and Design
<ol>
	<li>Arrange the computer and equipment on a desk, with a chair in front of it, for the experimenter.</li>
	<li>Set up a table on which participants rest their left (test) arm. Place a chair to the right side of the table. Put an armrest stand next to the chair on which the participants rest their right (masking arm) elbow. Add cushioning to the table and armrest for comfort.</li>
	<li>Arrange a loudspeaker on a mechanically isolated surface. Arrange foot pedals (connected to the left and right buttons of a computer mouse) so that the participant&#39;s feet will rest comfortably on them (Figure 1).</li>
	<li>Choose the parameters of the study, including the appropriate number of trials required to obtain a reliable estimate of the threshold (typically, between 40-50 trials) and the number of blocks into which the experiment is to be divided (e.g., two blocks of 20-25 trials per condition).</li>
	<li>Make a list of the order in which the conditions will be run. Use this list to determine where to hold the masking stimulus for each block.</li>
	<li>Enter the number of trials directly into the computer program code (e.g., ntrials = 25; See Supplemental Code File). Ensure that each block is no longer than 10 min to maintain attention.</li>
	<li>Program a two-alternative-forced-choice tactile detection task11in which stimulus intensity is controlled with a Bayesian adaptive psychophysical staircase psychometric procedure12.
	<ol>
		<li>For each trial, present two 1 sec intervals, marked by three beeps (5 kHz, 3 kHz and 5 kHz, duration 100 msec), with the tactile stimulus presented in the middle of one of the intervals. Have the participant indicate in which interval the stimulus was presented by means of foot pedals (left for first, right for second). See Example Code 2, which shows how the intervals are run and scored. 
		Note: The computer scores the response as &#34;correct&#34; or &#34;wrong&#34; and the adaptive staircase chooses the next value to be presented accordingly. 
		Note: This method determines a threshold value for detecting the vibration at the test site.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 1" src="/files/ftp_upload/53733/53733fig1.jpg" /> 
Figure 1. Experimental Design. This figure shows the set up of the experiment and the materials used. See text for details.
3. Experimental Procedure
<ol>
	<li>Obtain written informed consent. Seat the participant in the chair with their feet resting comfortably on the response foot pedals and explain the experimental procedure.</li>
	<li>Measure and record the length of the dorsal surface of the left forearm. Apply the strap so the tactor is positioned in the middle of the arm halfway between the inner angle of the elbow and the wrist crease.</li>
	<li>Wrap a tensor bandage loosely around the arm several times to hold the tactor in place.</li>
	<li>Instruct participants to place their left arm on the table and rest their right elbow on the armrest. Blindfold the participant to prevent them looking at the stimulus or masking location and instruct them to look straight ahead throughout the experiment.</li>
	<li>Start with a block of 20 practice trials (without the masking stimulus) in order to familiarize participants with the tactile detection task and to allow them to become familiar with the tactile stimuli.</li>
	<li>Following the practice trials, begin the experiment, running the blocks of conditions in a random, counterbalanced order. Before beginning each block, ensure that the arms and the masking stimulus are in the correct positions.
	<ol>
		<li>For each condition, hold the masking stimulus on the chosen site, referring to the list of conditions made earlier. Cross off each condition as it is run. Hold the masking stimulus throughout each block of data collection trials maintaining approximately constant pressure. The masking stimulus can be applied through thin clothing.</li>
		<li>Run the experimental program which will run through a set number of trials as previously selected. Introduce a 2 min rest period after each short block of trials. After a given block of trials is completed, select the next site for the masking stimulus and run the program again. Repeat until all trials are completed.</li>
	</ol>
	</li>
</ol>
4. Data Analysis
<ol>
	<li>To visualize and confirm the estimate of the threshold value returned by the adaptive staircase program12, fit the participants&#39; data with a cumulative Gaussian The formula for a cumulative Gaussian (sigmoid) that goes from 50% (chance level - equal number of 0s - wrong and 1&#39;s- correct) to 100% (all 1&#39;s, all correct) is: 
	probability of a correct response = 0.5 + 0.5/(1+exp(-(x-x0)/std)) 
	where x is the intensity value tested, x0 is the 75% threshold value, and std is the standard deviation of the estimate. This formula can be fitted to the data using any curve-fitting software and the resulting x0 value compared to the adaptive staircase value.
	<ol>
		<li>Ensure that the curve goes between 50% (chance performance) and 100%. Conduct statistical analyses (e.g., t-tests or ANOVAs) on the 75% threshold values obtained under each condition of the experiment (e.g., between different masking sites) to determine if there are any differences between the conditions tested.</li>
	</ol>
	</li>
	<li>In order to identify outliers, calculate the mean and the standard deviation for a given condition. Compare each participant&#39;s score with the mean and if an individual score is more than 2 standard deviation from that mean then regard this score as an outlier and remove it from the analysis. Alternative criteria may be used if desired.</li>
	<li>To standardize the values of the intensity of the tactors (which are in in arbitrary units), convert them to decibels relative to the control thresholds (measured when the masking stimulus is applied to the control site, e.g., the shoulder). Use this formula: 
	dB = 10 x log10 (threshold value/control threshold value).</li>
</ol>

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<li>Fechner, G. T. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aFechner%2C+GT+%22Elemente+der+Psychophysik+%22">Elemente der Psychophysik </a>. , Breitkopf & Härtel. Leipzig. (1860).</li>
<li>Watson, A., Pelli, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((QUEST-A+Bayesian+adaptive+psychophysical+method%5BTitle%5D)+AND+%22Percept.+Psychophys%22%5BJournal%5D)">QUEST-A Bayesian adaptive psychophysical method.</a> Percept. Psychophys. 33, 113-120 (1983).</li>
<li>D'Amour, S., Harris, L. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Contralateral+tactile+masking+between+forearms%5BTitle%5D)+AND+%22Exp.+Brain.+Res%22%5BJournal%5D)">Contralateral tactile masking between forearms.</a> Exp. Brain. Res. 232 (3), 821-826 (2014).</li>
<li>D'Amour, S., Harris, L. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Vibrotactile+masking+through+the+body%5BTitle%5D)+AND+%22Exp.+Brain.+Res%22%5BJournal%5D)">Vibrotactile masking through the body.</a> Exp. Brain. Res. 232 (9), 2859-2863 (2014).</li>
<li>Gescheider, G. A., Herman, D. D., Phillips, J. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Criterion+shifts+in+the+measurement+of+tactile+masking%5BTitle%5D)+AND+%22Percept.+Psychophys%22%5BJournal%5D)">Criterion shifts in the measurement of tactile masking.</a> Percept. Psychophys. 8, 433-436 (1970).</li>
<li>Iwamura, Y., Tanaka, M., Iriki, A., Taoka, M., Toda, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Processing+of+tactile+and+kinesthetic+signals+from+bilateral+sides+of+the+body+in+the+postcentral+gyrus+of+awake+monkeys%5BTitle%5D)+AND+%22Behav.+Brain.+Res%22%5BJournal%5D)">Processing of tactile and kinesthetic signals from bilateral sides of the body in the postcentral gyrus of awake monkeys.</a> Behav. Brain. Res. 135 (1-2), 185-190 (2002).</li>
<li>Killackey, H. P., Gould, H. J., Cusick, C. G., Pons, T. P., Kaas, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+relation+of+corpus+callosum+connections+to+architectonic+fields+and+body+surface+maps+in+sensorimotor+cortex+of+new+and+old+world+monkeys%5BTitle%5D)+AND+%22J.+Comp.+Neurol%22%5BJournal%5D)">The relation of corpus callosum connections to architectonic fields and body surface maps in sensorimotor cortex of new and old world monkeys.</a> J. Comp. Neurol. 219 (4), 384-419 (1983).</li>
<li>Reed, J. L., Qi, H. X., Kaas, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Spatiotemporal+properties+of+neuron+response+suppression+in+owl+monkey+primary+somatosensory+cortex+when+stimuli+are+presented+to+both+hands%5BTitle%5D)+AND+%22J.+Neurosci%22%5BJournal%5D)">Spatiotemporal properties of neuron response suppression in owl monkey primary somatosensory cortex when stimuli are presented to both hands.</a> J. Neurosci. 31 (10), 3589-3601 (2011).</li>
<li>Hlushchuk, Y., Hari, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Transient+suppression+of+ipsilateral+primary+somatosensory+cortex+during+tactile+finger+stimulation%5BTitle%5D)+AND+%22J.+Neurosci%22%5BJournal%5D)">Transient suppression of ipsilateral primary somatosensory cortex during tactile finger stimulation.</a> J. Neurosci. 26 (21), 5819-5824 (2006).</li>
<li>Nihashi, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Contralateral+and+ipsilateral+responses+in+primary+somatosensory+cortex+following+electrical+median+nerve+stimulation--an+fMRI+study%5BTitle%5D)+AND+%22Clin.+Neurophysiol%22%5BJournal%5D)">Contralateral and ipsilateral responses in primary somatosensory cortex following electrical median nerve stimulation--an fMRI study.</a> Clin. Neurophysiol. 116 (4), 842-848 (2005).</li>
<li>Tamè, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+contribution+of+primary+and+secondary+somatosensory+cortices+to+the+representation+of+body+parts+and+body+sides%3A+an+fMRI+adaptation+study%5BTitle%5D)+AND+%22J.+Cognitive.+Neurosci%22%5BJournal%5D)">The contribution of primary and secondary somatosensory cortices to the representation of body parts and body sides: an fMRI adaptation study.</a> J. Cognitive. Neurosci. 24 (12), 2306-2320 (2012).</li>
<li>Tamè, L., Farnè, A., Pavani, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Vision+of+the+body+and+the+differentiation+of+perceived+body+side+in+touch%5BTitle%5D)+AND+%22Cortex%22%5BJournal%5D)">Vision of the body and the differentiation of perceived body side in touch.</a> Cortex. 49 (5), 1340-1351 (2013).</li>
<li>Tamè, L., Pavani, F., Papadelis, C., Farnè, A., Braun, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Early+integration+of+bilateral+touch+in+the+primary+somatosensory+cortex%5BTitle%5D)+AND+%22Hum.+Brain.+Mapp%22%5BJournal%5D)">Early integration of bilateral touch in the primary somatosensory cortex.</a> Hum. Brain. Mapp. 36 (4), 1506-1523 (2015).</li>
<li>Gilson, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Vibrotactile+masking%3A+Some+spatial+and+temporal+aspects%5BTitle%5D)+AND+%22Percept.+Psychophys%22%5BJournal%5D)">Vibrotactile masking: Some spatial and temporal aspects.</a> Percept. Psychophys. 5 (3), 176-180 (1969).</li>
<li>Alliusi, E., Morgan, B., Hawkes, G. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Masking+of+cutaneous+sensations+in+multiple+stimulus+presentations%5BTitle%5D)+AND+%22Percept.+Motor.+Skill%22%5BJournal%5D)">Masking of cutaneous sensations in multiple stimulus presentations.</a> Percept. Motor. Skill. 20, 39-45 (1965).</li>
<li>Geldard, F. A., Sherrick, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Multiple+cutaneous+stimulation%3A+The+discrimination+of+vibratory+patterns%5BTitle%5D)+AND+%22J.+Acoust.+Soc.+Am%22%5BJournal%5D)">Multiple cutaneous stimulation: The discrimination of vibratory patterns.</a> J. Acoust. Soc. Am. 37, 797-801 (1965).</li>
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</ol>

The authors declare that they have no competing financial interests.

Here, a detailed protocol for contralateral tactile masking is described and previously published results using the technique to test tactile detection thresholds are shown. The advantage of this method is that thresholds are measured using a psychophysically rigorous technique. The two-alternative forced choice (2AFC) procedure is relatively insensitive to response bias and therefore from attentional effects. The adaptive staircase procedure for honing in on the actual threshold value is very efficient as most of the da...

Tactile masking is where a tactile stimulus at one location on the body alters the perception of a touch at another location. This is a technique pioneered by von Bekesy1to reveal location interactions, especially lateral inhibition, between areas of skin that are adjacent on the body surface. While tactile masking has been studied extensively over the years, research has mainly investigated ipsilateral tactile masking using electrical stimulation2,3, pressure4, and vibrotactile stimulation5,6. In contrast, few studies have looked at contralateral tactile masking in which the masking and probe sites may be far removed. Long-range tactile masking effects have been shown between mirror-symmetric points on the hand and arm5,7-9but these studies have been largely restricted to looking at the hands and fingers7,10, with more extensive parts of the whole body being largely ignored. A goal of such long-range masking experiments is to indicate how components of the body&#39;s representation in the brain may be functionally linked. Here, the phenomenon of long-range tactile masking is explored by investigating how vibration applied to one forearm might affect tactile sensitivity thresholds on the opposite forearm. Threshold refers to the minimum stimulus that is needed to detect a stimulus. We define this as the intensity at which the stimulus is detected 75% of the time. We used a tactile masking technique in which tactile sensitivity (the reciprocal of threshold) on one forearm is measured in the presence of a vibrating stimulus (the mask) on another part of the body. Effective masking is revealed by an increase in the detection threshold i.e., a reduction in sensitivity. The technique can be used in conjunction with other manipulations such as varying limb position or movement to explore their effects on the effectiveness of masking.
Here we used vibrotactile stimuli as the masking stimulus. The advantage of this is that the frequency, and hence the receptor type that it stimulates can be controlled. The technique could be extended to look at pain using electrical stimuli as the probe or mask or both. Also, any site can be used as the masking site allowing the investigation of acupuncture sites for example.

<table><tbody><tr><td>C-2 tactor</td><td>ATAC Technology; Engineering Acoustics, Inc.</td><td></td><td>http://www.atactech.com/PR_tactors.html</td></tr><tr><td>Magic Wand</td><td>Hitachi</td><td></td><td>http://magicwandoriginal.com/magic-wand-original/</td></tr><tr><td>FC5 Foot Pedals</td><td>Yamaha Corporation</td><td></td><td>http://ca.yamaha.com/en/products/music-production/accessories/footpedals/fc5/?mode=model</td></tr><tr><td>MATLAB</td><td>The Mathworks, Inc.</td><td></td><td>http://www.mathworks.com/products/matlab/</td></tr><tr><td>Velcro</td><td>Velcro Industries B.V.</td><td></td><td>http://www.velcro.com/</td></tr></tbody></table>

testing tactile masking between the forearms

Masking, in which one stimulus affects the detection of another, is a classic technique that has been used in visual, auditory, and tactile research, usually using stimuli that are close together to reveal local interactions. Masking effects have also been demonstrated in which a tactile stimulus alters the perception of a touch at a distant location. Such effects can provide insight into how components of the body's representations in the brain may be linked. Occasional reports have indicated that touches on one hand or forearm can affect tactile sensitivity at corresponding contralateral locations. To explore the matching of corresponding points across the body, we can measure the spatial tuning and effect of posture on contralateral masking. Careful controls are required to rule out direct effects of the remote stimulus, for example by mechanical transmission, and also attention effects in which thresholds may be altered by the participant's attention being drawn away from the stimulus of interest. The use of this technique is beneficial as a behavioural measure for exploring which parts of the body are functionally connected and whether the two sides of the body interact in a somatotopic representation. This manuscript describes a behavioural protocol that can be used for studying contralateral tactile masking.

Analyses of the data was reported in13. Tactile sensitivity (expressed relative to the thresholds measured in the control condition) on the forearm was significantly reduced (thresholds were significantly increased) when vibrotactile masking stimulation was applied to the opposite arm (Figure 2A), demonstrating a contralateral masking effect between forearms. The effect depended on the position of the masking stimulus on the masking arm, with the largest effect...

Watch this Scientific Journal Video about Testing Tactile Masking between the Forearms at JoVE.com

Testing Tactile Masking between the Forearms

Here we explore contralateral tactile masking between the forearms in which tactile detection thresholds are modulated by vibration applied to a remote site. The details of which remote sites have an effect can tell us about how the body is represented in the brain.

Masking, in which one stimulus affects the detection of another, is a classic technique that has been used in visual, auditory, and tactile research, ...

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6.3K Views.  York University. Here we explore contralateral tactile masking between the forearms in which tactile detection thresholds are modulated by vibration applied to a remote site. The details of which remote sites have an effect can tell us about how the body is represented in the brain. 

Video: Testing Tactile Masking between the Forearms

The Crossmodal Congruency Task as a Means to Obtain an Objective Behavioral Measure in the Rubber Hand Illusion Paradigm

The rubber hand illusion (RHI) is a popular experimental paradigm. Participants view touch on an artificial rubber hand while the participants' own hidden hand is touched. If the viewed and felt touches are given at the same time then this is sufficient to induce the compelling experience that the rubber hand is one's own hand. The RHI can be used to investigate exactly how the brain constructs distinct body representations for one's own body. Such representations are crucial for successful interactions with the external world. To obtain a subjective measure of the RHI, researchers typically ask participants to rate statements such as "I felt as if the rubber hand were my hand". Here we demonstrate how the crossmodal congruency task can be used to obtain an objective behavioral measure within this paradigm.
The variant of the crossmodal congruency task we employ involves the presentation of tactile targets and visual distractors. Targets and distractors are spatially congruent (i.e. same finger) on some trials and incongruent (i.e. different finger) on others. The difference in performance between incongruent and congruent trials - the crossmodal congruency effect (CCE) - indexes multisensory interactions. Importantly, the CCE is modulated both by viewing a hand as well as the synchrony of viewed and felt touch which are both crucial factors for the RHI.
The use of the crossmodal congruency task within the RHI paradigm has several advantages. It is a simple behavioral measure which can be repeated many times and which can be obtained during the illusion while participants view the artificial hand. Furthermore, this measure is not susceptible to observer and experimenter biases. The combination of the RHI paradigm with the crossmodal congruency task allows in particular for the investigation of multisensory processes which are critical for modulations of body representations as in the RHI.

We demonstrate how an objective measure can be employed in the widely employed rubber hand illusion paradigm. This measure is obtained by modifying the well-established crossmodal congruency task. This task allows the investigation of multisensory processes which are critical for modulations of body representations as in the rubber hand illusion.

The rubber hand illusion (RHI) is a popular experimental paradigm. Participants view touch on an artificial rubber hand while the participants' own hidden ...

Creating Virtual-hand and Virtual-face Illusions to Investigate Self-representation

Studies investigating how people represent themselves and their own body often use variants of &#34;ownership illusions&#34;, such as the traditional rubber-hand illusion or the more recently discovered enfacement illusion. However, these examples require rather artificial experimental setups, in which the artificial effector needs to be stroked in synchrony with the participants&#39; real hand or face&#8212;a situation in which participants have no control over the stroking or the movements of their real or artificial effector. Here, we describe a technique to establish ownership illusions in a setup that is more realistic, more intuitive, and of presumably higher ecological validity. It allows creating the virtual-hand illusion by having participants control the movements of a virtual hand presented on a screen or in virtual space in front of them. If the virtual hand moves in synchrony with the participants&#39; own real hand, they tend to perceive the virtual hand as part of their own body. The technique also creates the virtual-face illusion by having participants control the movements of a virtual face in front of them, again with the effect that they tend to perceive the face as their own if it moves in synchrony with their real face. Studying the circumstances that illusions of this sort can be created, increased, or reduced provides important information about how people create and maintain representations of themselves.

Here, we describe virtual-hand and virtual-face illusion paradigms that can be used to study body-related self-perception/-representation. They have already been used in various studies to demonstrate that, under specific conditions, a virtual hand or face can be incorporated into one&#39;s body representation, suggesting that body representations are rather flexible.

Studies investigating how people represent themselves and their own body often use variants of &#34;ownership illusions&#34;, such as the traditional ...

Using Facial Electromyography to Assess Facial Muscle Reactions to Experienced and Observed Affective Touch in Humans

"Affective" touch is believed to be processed in a manner distinct from discriminatory touch and to involve activation of C-tactile (CT) afferent fibers. Touch that optimally activates CT fibers is consistently rated as hedonically pleasant. Patient groups with impaired social-emotional functioning also show disordered affective touch ratings. However, relying on self-reported ratings of touch has many limitations, including recall bias and communication barriers. Here, we describe a methodological approach to study affective responses to touch via facial electromyography (EMG) that circumvents the reliance on self-report ratings. Facial EMG is an objective, quantitative, and non-invasive method to measure facial muscle activity indicative of affective responses. Responses can be assessed across healthy and patient populations without the need for verbal communication. Here, we provide two separate datasets demonstrating that CT-optimal and non-optimal touch elicit distinct facial muscle reactions. Moreover, facial EMG responses are consistent across stimulus modalities, e.g. tactile (experienced touch) and visual (observed touch). Finally, the temporal resolution of facial EMG can detect responses on timescales that supersede that of verbal reporting. Together, our data suggest that facial EMG is a suitable methodology for use in affective tactile research that can be used to supplement, or in some cases, supplant, existing measures.

We describe a protocol to assess facial muscle activity in response to experienced and observed tactile stimulation using facial electromyography.

"Affective" touch is believed to be processed in a manner distinct from discriminatory touch and to involve activation of C-tactile (CT) afferent fibers. ...

Applying Incongruent Visual-Tactile Stimuli during Object Transfer with Vibro-Tactile Feedback

The application of incongruent sensory signals that involves disrupted tactile feedback is rarely explored, specifically with the presence of vibrotactile feedback (VTF). This protocol aims to test the effect of VTF on the response to incongruent visual-tactile stimuli. The tactile feedback is acquired by grasping a block and moving it across a partition. The visual feedback is a real-time virtual presentation of the moving block, acquired using a motion capture system. The congruent feedback is the reliable presentation of the movement of the block, so that the subject feels that the block is grasped and see it move along with the path of the hand. The incongruent feedback appears as the movement of the block diverts from the actual movement path, so that it seems to drop from the hand when it is actually still held by the subject, thereby contradicting the tactile feedback. Twenty subjects (age 30.2 &#177; 16.3) repeated 16 block transfers, while their hand was hidden. These were repeated with VTF and without VTF (total of 32 block transfers). Incongruent stimuli were presented randomly twice within the 16 repetitions in each condition (with and without VTF). Each subject was asked to rate the difficulty level of performing the task with and without the VTF. There were no statistically significant differences in the length of the hand paths and durations between transfers recorded with congruent and incongruent visual-tactile signals &#8211; with and without the VTF. The perceived difficulty level of performing the task with the VTF significantly correlated with the normalized path length of the block with VTF (r = 0.675, p = 0.002). This setup is used to quantify the additive or reductive value of VTF during motor function that involves incongruent visual-tactile stimuli. Possible applications are prosthetics design, smart sport-wear, or any other garments that incorporate VTF.

We present a protocol to apply incongruent visual-tactile stimuli during an object transfer task. Specifically, during block transfers, performed while the hand is hidden, a virtual presentation of the block shows random occurrences of false block drops. The protocol also describes adding vibrotactile feedback while performing the motor task.

The application of incongruent sensory signals that involves disrupted tactile feedback is rarely explored, specifically with the presence of vibrotactile ...

A Tactile Automated Passive-Finger Stimulator (TAPS)

Although tactile spatial acuity tests are used in both neuroscience research and clinical assessment, few automated devices exist for delivering controlled spatially structured stimuli to the skin. Consequently, investigators often apply tactile stimuli manually. Manual stimulus application is time consuming, requires great care and concentration on the part of the investigator, and leaves many stimulus parameters uncontrolled. We describe here a computer-controlled tactile stimulus system, the Tactile Automated Passive-finger Stimulator (TAPS), that applies spatially structured stimuli to the skin, controlling for onset velocity, contact force, and contact duration. TAPS is a versatile, programmable system, capable of efficiently conducting a variety of psychophysical procedures. We describe the components of TAPS, and show how TAPS is used to administer a two-interval forced-choice tactile grating orientation test.
Corresponding Author: Daniel Goldreich

A Tactile Automated Passive-Finger Stimulator TAPS

We describe a computer-controlled device for investigating the sense of touch: the Tactile Automated Passive-finger Stimulator (TAPS). We describe the components of TAPS, and show how TAPS is used to administer a two-interval forced-choice tactile grating orientation test.

Although tactile spatial acuity tests are used in both neuroscience research and clinical assessment, few automated devices exist for delivering ...

Biology

Tactile Semiautomatic Passive-Finger Angle Stimulator (TSPAS)

Passive tactile perception is the ability to passively and statically perceive stimulus information coming from the skin; for example, the ability to sense spatial information is the strongest in the skin on the hands. This ability is termed tactile spatial acuity, and is measured by the tactile threshold or discrimination threshold. At present, the two-point threshold is extensively used as a measure of tactile spatial acuity, although many studies have indicated that critical deficits exist in two-point discrimination. Therefore, a computer-controlled tactile stimulus system was developed, the tactile semiautomated passive-finger angle stimulator (TSPAS), using the tactile angle discrimination threshold as a new measure for tactile spatial acuity. The TSPAS is a simple, easily operated system that applies raised angle stimuli to a subject&#39;s passive fingerpad, while controlling movement speed, distance, and contact duration. The components of the TSPAS are described in detail as well as the procedure to calculate the tactile angle discrimination threshold.

Tactile Semiautomatic Passive-Finger Angle Stimulator TSPAS

Presented is the tactile semiautomated passive-finger angle stimulator TSPAS, a new way to assess tactile spatial acuity and tactile angle discrimination using a computer-controlled tactile stimulus system that applies raised angle stimuli to a subject&#39;s passive fingerpad, while controlling for movement speed, distance, and contact duration.

Passive tactile perception is the ability to passively and statically perceive stimulus information coming from the skin; for example, the ability to ...

Virtual Hand with Ambiguous Movement between the Self and Other Origin: Sense of Ownership and 'Other-Produced' Agency

The feeling that a body part is one&#8217;s own body (sense of ownership; SoO) and the feeling based on the causal relationship between one&#8217;s will and action (sense of agency; SoA) have been recognized as the basis of our bodily self-consciousness. Previously, the illusory SoO over a fake body part (e.g., rubber hand) was introduced as the rubber hand illusion (RHI). Furthermore, it was determined that one could also evoke a SoA over an object with movements linked to the one&#8217;s prior intention. On the other hand, the postdictivity of our spontaneity implies that it is essentially inseparable whether actions originate from self or others. In other words, our SoA or daily experiences are obtained in such as inseparable scenario. Previous research, however, has maintained the premise that self- and other-origin movements are perceptually distinguishable. Here, we implement a protocol to make these aspects ambiguous for the participants and to estimate whether they can feel SoO and/or SoA and how. To this end, we employ an experiment using virtual reality, under which participants observe virtual fingers moving very slowly (or quickly or not moving) while their own fingers do not move. For evaluation of the illusory SoO, measurements of skin conductance responses against a knife threat are adopted. Additionally, we introduce face-to-face interviews to determine whether the feelings regarding the slow movement match the conventional SoA definition. Our representative results suggest that the SoO is evoked over the hand, and various attitudes to accept its movement as the participant&#8217;s own with awareness that they did not originate it are reported by the majority. As the results show, the novelty of this protocol is discovering that in such a situation, the SoO cooperates with an externally produced SoA to establish one&#8217;s own bodily experience rather than the independence of the SoO and SoA.

While previous research on bodily self-consciousness assumed that self- and other-origin movements were perceptually distinguishable, this protocol allows them to be ambiguous on a virtual hand with unintentional slight movements. This enables us to observe one&#8217;s experience formed by SoO and other-produced SoA, rather than the absence of SoA.

The feeling that a body part is one&#8217;s own body (sense of ownership; SoO) and the feeling based on the causal relationship between one&#8217;s will ...

Estimation of Contact Regions Between Hands and Objects During Human Multi-Digit Grasping

To grasp an object successfully, we must select appropriate contact regions for our hands on the surface of the object. However, identifying such regions is challenging. This paper describes a workflow to estimate the contact regions from marker-based tracking data. Participants grasp real objects, while we track the 3D position of both the objects and the hand, including the fingers' joints. We first determine the joint Euler angles from a selection of tracked markers positioned on the back of the hand. Then, we use state-of-the-art hand mesh reconstruction algorithms to generate a mesh model of the participant's hand in the current pose and the 3D position. 
Using objects that were either 3D printed or 3D scanned-and are, thus, available as both real objects and mesh data-allows the hand and object meshes to be co-registered. In turn, this allows the estimation of approximate contact regions by calculating the intersections between the hand mesh and the co-registered 3D object mesh. The method may be used to estimate where and how humans grasp objects under a variety of conditions. Therefore, the method could be of interest to researchers studying visual and haptic perception, motor control, human-computer interaction in virtual and augmented reality, and robotics.

When we grasp an object, multiple regions of the fingers and hand typically make contact with the object's surface. Reconstructing such contact regions is challenging. Here, we present a method for approximately estimating the contact regions by combining marker-based motion capture with existing deep learning-based hand mesh reconstruction.

To grasp an object successfully, we must select appropriate contact regions for our hands on the surface of the object. However, identifying such regions ...

Non-Invasive Modulation and Robotic Mapping of Motor Cortex in the Developing Brain

Mapping the motor cortex with transcranial magnetic stimulation (TMS) has potential to interrogate motor cortex physiology and plasticity but carries unique challenges in children. Similarly, transcranial direct current stimulation (tDCS) can improve motor learning in adults but has only recently been applied to children. The use of tDCS and emerging techniques like high&#8211;definition tDCS (HD-tDCS) require special methodological considerations in the developing brain. Robotic TMS motor mapping may confer unique advantages for mapping, particularly in the developing brain. Here, we aim to provide a practical, standardized approach for two integrated methods capable of simultaneously exploring motor cortex modulation and motor maps in children. First, we describe a protocol for robotic TMS motor mapping. Individualized, MRI-navigated 12x12 grids centered on the motor cortex guide a robot to administer single-pulse TMS. Mean motor evoked potential (MEP) amplitudes per grid point are used to generate 3D motor maps of individual hand muscles with outcomes including map area, volume, and center of gravity. Tools to measure safety and tolerability of both methods are also included. Second, we describe the application of both tDCS and HD-tDCS to modulate the motor cortex and motor learning. An experimental training paradigm and sample results are described. These methods will advance the application of non-invasive brain stimulation in children.

We demonstrate protocols for the modulation (tDCS, HD-tDCS) and mapping (robotic TMS) of the motor cortex in children.

Mapping the motor cortex with transcranial magnetic stimulation (TMS) has potential to interrogate motor cortex physiology and plasticity but carries ...

Neuroscience

Capturing Dynamic Finger Gesturing with High-resolution Surface Electromyography and Computer Vision

Finger gestures are a critical element in human communication, and as such, finger gesture recognition is widely studied as a human-computer interface for state-of-the-art prosthetics and optimized rehabilitation. Surface electromyography (sEMG), in conjunction with deep learning methods, is considered a promising method in this domain. However, current methods often rely on cumbersome recording setups and the identification of static hand positions, limiting their effectiveness in real-world applications. The protocol we report here presents an advanced approach combining a wearable surface EMG and finger&#160;tracking system to capture comprehensive data during dynamic hand movements. The method records muscle activity from soft printed electrode arrays (16 electrodes) placed on the forearm as subjects perform gestures in different hand positions and during movement. Visual instructions prompt subjects to perform specific gestures while EMG and finger positions are recorded. The integration of synchronized EMG recordings and finger tracking data enables comprehensive analysis of muscle activity patterns and corresponding gestures. The reported approach demonstrates the potential of combining EMG and visual tracking technologies as an important resource for developing intuitive and responsive gesture recognition systems with applications in prosthetics, rehabilitation, and interactive technologies. This protocol aims to guide researchers and practitioners, fostering further innovation and application of gesture recognition in dynamic and real-world scenarios.

The paper presents a comprehensive protocol for simultaneously recording hand-electromyography (EMG) and visual finger tracking during natural finger gesturing. The visual data is designed to serve as the ground truth for the development of accurate EMG-based computational models for finger gesture recognition.

Finger gestures are a critical element in human communication, and as such, finger gesture recognition is widely studied as a human-computer interface for ...