Name: the crossmodal congruency task as a means to obtain an objective behavioral measure in the rubber hand illusion paradigm
Uploaded: 2013-07-26T12:00:00
Duration: 6 min 43 s
Description: Watch this Scientific Journal Video about The Crossmodal Congruency Task as a Means to Obtain an Objective Behavioral Measure in the Rubber Hand Illusion Paradigm at JoVE.com

M.A.W. is funded by a Queen Elizabeth II Fellowship (DP 0984919) from the Australian Research Council.

1. Experimental Setup
<ol>
	<li>Material and Setup for the Rubber Hand Illusion Setup
	<ol>
		<li>Use a box for the RHI paradigm which includes a cover for the participants own hand. Use a gown to also cover the shoulder and arm of the participant as well as the part of the rubber hand which goes up to the wrist.</li>
		<li>Obtain an artificial hand. This hand does not necessarily have to be made out of rubber (the name 'rubber hand illusion' was given because a rubber hand was used in seminal work 7). For example prostheses can be used.</li>
		<li>Use two soft brushes to deliver brush strokes in the RHI.</li>
		<li>Use a metronome, a pre-recorded sound file or experimental software to provide timing signals for the experimenter who delivers the brush strokes.</li>
	</ol>
	</li>
	<li>Experimental Setup - Material and Setup for the Crossmodal Congruency Task
	<ol>
		<li>For the crossmodal congruency task, use tactors to deliver tactile stimuli. For example small speakers, bone conductors (from hearing aids) or electromagnetic solenoid-type stimulators can be employed. Use 'dummy tactors' for the rubber hand.</li>
		<li>Control tactile stimulus delivery via the computer sound output, via an interface card or TTL pulses.</li>
		<li>Fix the position of the speakers in the box.</li>
		<li>Use for example light emitting diodes (LEDs) to deliver visual stimuli. These can be controlled with TTL pulses from a computer parallel card and powered for example using an USB port or batteries.</li>
		<li>Use experimental software to program stimulus presentation.</li>
		<li>Block any potential sound which could arise during the delivery of tactile stimuli. For example use headphones and white noise.</li>
		<li>Record responses for example using a response box, a computer mouse or a keyboard.</li>
	</ol>
	</li>
</ol>
2. Participants
<ol>
	<li>All aspects of the experiment are in accord with the ethical standards laid down in the 1964 Declaration of Helsinki and have been approved by our local ethics committee (Macquarie University Human Research Ethics Committee, Australia).</li>
	<li>Obtain written informed consent for participation prior to the start of the experiment.</li>
	<li>Participants with visual or tactile deficits especially for the stimulated locations need to be excluded.</li>
</ol>
3. Experimental Procedure
<ol>
	<li>Ensure that participants are sitting in a comfortable position.</li>
	<li>Ensure participants can see the rubber hand and not their own hand.</li>
	<li>Include training blocks so participants become familiar with the crossmodal congruency task. Ideally first use practice trials without crossmodal visual stimuli in order to accustom participants to the tactile targets and then use practice trials with visual stimulus presentation and no-go trials (see below).</li>
	<li>On each crossmodal congruency trial present one tactile stimulus and one visual stimulus to one of the locations, either in spatially congruent locations (same fingers) or incongruent locations (different fingers).</li>
	<li>Instruct participants to respond and discriminate the location of the tactile targets as fast as and as accurately as possible.</li>
	<li>Locate a fixation point between the lights which participants should fixate throughout the experiment.</li>
	<li>Use no-go trials in order to ensure that participants are looking at the stimuli. For example ask participants to withhold their response if the lights in both locations turn on at the same time. When participants regularly press a button during these trials, then this can indicate that they are not looking at the lights.</li>
	<li>Use supra-threshold stimuli and make sure participants can see/feel the stimuli.</li>
	<li>Introduce a short delay (150-250 msec) between visuotactile crossmodal stimuli in order to reduce interference of these stimuli on the RHI itself.</li>
	<li>Include sufficient number of congruent and incongruent trials for each condition (about 60-100 trials).</li>
	<li>Present congruent and incongruent trials in different locations in a randomized sequence.</li>
	<li>Keep in mind that response requirements and mappings might affect the CCE magnitude 24.</li>
	<li>In order to induce the RHI use brush stroking for 1 to 3 min before the crossmodal congruency task and then stroke once before every crossmodal congruency trial.</li>
	<li>To induce the RHI illusion use synchronous brush stroking, where both hands should be touched at the same time and in the same location.</li>
	<li>Use asynchronous stroking as a control condition, where both hands should be stroked with a temporal offset.</li>
	<li>Make sure the experimenter can comfortably perform the stroking.</li>
	<li>You can also use RHI rating scales to monitor subjective experiences during the RHI paradigm. Some researcher suggest to use both objective and subjective measures for the rubber hand illusion paradigm for example 25. Obtain the rating responses after the task block if you would like to compare it to CCE effects because the task itself may modulate the RHI experience.</li>
</ol>
4. Data Analysis
<ol>
	<li>Trials in which participants responded too soon (e.g. faster than 200 msec after stimulus onset) or too slow (e.g. later than 1,500 msec) should be discarded from the analysis: check for potential significant differences between conditions for number of discarded trials.</li>
	<li>Analyze the number of false alarms in no-go trials: check for potential significant differences between conditions for number of false alarms.</li>
	<li>Obtain the average or median for performance measures (response time for speed and response error for accuracy) for each participant and each condition.</li>
	<li>Only use response times for correct trials.</li>
	<li>It is also possible to combine response time and error to a single measure: Inverse Efficiency (IE) = Response time/Error 17.</li>
	<li>Calculate and depict crossmodal congruency effects = performance on incongruent minus congruent trials for every trial and condition.</li>
	<li>Use statistical tests in order to assess the statistical significance of condition differences (e.g. ANOVA, t-tests).</li>
</ol>

<ol>
	<li>Ehrsson, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+experimental+induction+of+out-of-body+experiences.">The experimental induction of out-of-body experiences.</a> Science (New York, N.Y.). 317, 1048 (2007).</li><li>Lenggenhager, B., Tadi, T., Metzinger, T., Blanke, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Video+ergo+sum:+manipulating+bodily+self-consciousness.">Video ergo sum: manipulating bodily self-consciousness.</a> Science (New York, N.Y.). 317, 1096-1099 (2007).</li><li>Petkova, V. I., Ehrsson, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=If+I+were+you:+perceptual+illusion+of+body+swapping.">If I were you: perceptual illusion of body swapping.</a> PloS one. 3, e3832 (2008).</li><li>Tsakiris, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=My+body+in+the+brain:+a+neurocognitive+model+of+body-ownership.">My body in the brain: a neurocognitive model of body-ownership.</a> Neuropsychologia. 48, 703-712 (2010).</li><li>Ehrsson, H. H., Stein, B. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The New Handbook of Multisensory Processing. , (2012).</li><li>Blanke, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multisensory+brain+mechanisms+of+bodily+self-consciousness.">Multisensory brain mechanisms of bodily self-consciousness.</a> Nature Reviews Neuroscience. , (2012).</li><li>Botvinick, M., Cohen, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rubber+hands+'feel'+touch+that+eyes+see.">Rubber hands 'feel' touch that eyes see.</a> Nature. 391, 756 (1998).</li><li>Eshkevari, E., Rieger, E., Longo, M. R., Haggard, P., Treasure, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+plasticity+of+the+bodily+self+in+eating+disorders.">Increased plasticity of the bodily self in eating disorders.</a> Psychol. Med. , 1-10 (2011).</li><li>Moseley, G. L., Gallace, A., Spence, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bodily+illusions+in+health+and+disease:+physiological+and+clinical+perspectives+and+the+concept+of+a+cortical+'body+matrix'.">Bodily illusions in health and disease: physiological and clinical perspectives and the concept of a cortical 'body matrix'.</a> Neuroscience and Biobehavioral reviews. 36, 34-46 (2012).</li><li>Thakkar, K. N., Nichols, H. S., McIntosh, L. G., Park, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disturbances+in+body+ownership+in+schizophrenia:+evidence+from+the+rubber+hand+illusion+and+case+study+of+a+spontaneous+out-of-body+experience.">Disturbances in body ownership in schizophrenia: evidence from the rubber hand illusion and case study of a spontaneous out-of-body experience.</a> PloS one. 6, e27089 (2011).</li><li>Longo, M. R., Schuur, F., Kammers, M. P., Tsakiris, M., Haggard, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=What+is+embodiment?+A+psychometric+approach.">What is embodiment? A psychometric approach.</a> Cognition. 107, 978-998 (2008).</li><li>Tsakiris, M., Haggard, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+rubber+hand+illusion+revisited:+Visuotactile+integration+and+self-attribution.">The rubber hand illusion revisited: Visuotactile integration and self-attribution.</a> Journal of Experimental Psychology: Human Perception and Performance. 31, 80-91 (2005).</li><li>Armel, K. C., Ramachandran, V. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Projecting+sensations+to+external+objects:+evidence+from+skin+conductance+response.">Projecting sensations to external objects: evidence from skin conductance response.</a> Proceedings of the Royal Society of London Series B: Biological Sciences. 270, 1499-1506 (2003).</li><li>Ehrsson, H. H., Wiech, K., Weiskopf, N., Dolan, R. J., Passingham, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Threatening+a+rubber+hand+that+you+feel+is+yours+elicits+a+cortical+anxiety+response.">Threatening a rubber hand that you feel is yours elicits a cortical anxiety response.</a> Proceedings of the National Academy of Sciences of the United States of America. 104, 9828-9833 (2007).</li><li>Moseley, G. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Psychologically+induced+cooling+of+a+specific+body+part+caused+by+the+illusory+ownership+of+an+artificial+counterpart.">Psychologically induced cooling of a specific body part caused by the illusory ownership of an artificial counterpart.</a> Proceedings of the National Academy of Sciences of the United States of America. 105, 13169-13173 (2008).</li><li>Spence, C., Pavani, F., Maravita, A., Holmes, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multisensory+contributions+to+the+3-D+representation+of+visuotactile+peripersonal+space+in+humans:+evidence+from+the+crossmodal+congruency+task.">Multisensory contributions to the 3-D representation of visuotactile peripersonal space in humans: evidence from the crossmodal congruency task.</a> Journal of Physiology (Paris). 98, 171-189 (2004).</li><li>Spence, C., Pavani, F., Maravita, A., Lin, M. C., Otaduy, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Haptic rendering: Foundations, algorithms, and applications. , 21-52 (2008).</li><li>Makin, T. R., Holmes, N. P., Ehrsson, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+other+hand:+Dummy+hands+and+peripersonal+space.">On the other hand: Dummy hands and peripersonal space.</a> Behavioural Brain Research. 191, 1-10 (2008).</li><li>Austen, E. L., Soto-Faraco, S., Enns, J. T., Kingstone, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mislocalizations+of+touch+to+a+fake+hand.">Mislocalizations of touch to a fake hand.</a> Cognitive, Affective &amp; Behavioral Neuroscience. 4, 170-181 (2004).</li><li>Pavani, F., Spence, C., Driver, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visual+capture+of+touch:+out-of-the-body+experiences+with+rubber+gloves.">Visual capture of touch: out-of-the-body experiences with rubber gloves.</a> Psychological Science. 11, 353-359 (2000).</li><li>Walton, M., Spence, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cross-modal+congruency+and+visual+capture+in+a+visual+elevation-discrimination+task.">Cross-modal congruency and visual capture in a visual elevation-discrimination task.</a> Experimental Brain Research. 154, 113-120 (2004).</li><li>Zopf, R., Savage, G., Williams, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crossmodal+congruency+measures+of+lateral+distance+effects+on+the+rubber+hand+illusion.">Crossmodal congruency measures of lateral distance effects on the rubber hand illusion.</a> Neuropsychologia. 48, 713-725 (2010).</li><li>Aspell, J. E., Lenggenhager, B., Blanke, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Keeping+in+touch+with+one's+self:+multisensory+mechanisms+of+self-consciousness.">Keeping in touch with one's self: multisensory mechanisms of self-consciousness.</a> PloS. 4, e6488 (2009).</li><li>Gallace, A., Soto-Faraco, S., Dalton, P., Kreukniet, B., Spence, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Response+requirements+modulate+tactile+spatial+congruency+effects.">Response requirements modulate tactile spatial congruency effects.</a> Experimental Brain Research. Experimentelle Hirnforschung. 191, 171-186 (2008).</li><li>Kalckert, A., Ehrsson, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Moving+a+Rubber+Hand+that+Feels+Like+Your+Own:+A+Dissociation+of+Ownership+and+Agency.">Moving a Rubber Hand that Feels Like Your Own: A Dissociation of Ownership and Agency.</a> Frontiers in Human Neuroscience. 6, 40 (2012).</li><li>Zopf, R., Harris, J. A., Williams, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+body-ownership+cues+on+tactile+sensitivity.">The influence of body-ownership cues on tactile sensitivity.</a> Cognitive Neuroscience. 2, 147-154 (2011).</li><li>Zopf, R., Truong, S., Finkbeiner, M., Friedman, J., Williams, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Viewing+and+feeling+touch+modulates+hand+position+for+reaching.">Viewing and feeling touch modulates hand position for reaching.</a> Neuropsychologia. 49, 1287-1293 (2011).</li><li>Shore, D. I., Barnes, M. E., Spence, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temporal+aspects+of+the+visuotactile+congruency+effect.">Temporal aspects of the visuotactile congruency effect.</a> Neuroscience Letters. 392, 96-100 (2006).</li><li>Rohde, M., Di Luca, M., Ernst, M. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Rubber+Hand+Illusion:+feeling+of+ownership+and+proprioceptive+drift+do+not+go+hand+in+hand.">The Rubber Hand Illusion: feeling of ownership and proprioceptive drift do not go hand in hand.</a> PloS one. 6, e21659 (2011).</li></ol>

The authors declare that they have no competing financial interests.

We demonstrated how an objective measure of effects in the commonly employed RHI paradigm can be obtained by combining this paradigm with the well-established crossmodal congruency task. The magnitude of the crossmodal congruency effect is significantly increased when the RHI is induced.
Stimulation as given in the rubber hand illusion paradigm modulates several aspects of body-related experiences such as body-ownership and body-location. Research has provided evidence that several processes related to perception, homeostasis and action are modulated in the RHI 14,15,22,26,27. Importantly, the combination of the RHI paradigm with the crossmodal congruency task allows in particular for the investigation of multisensory processes which are critical for all of these aspects.
Both viewing of the hand and the synchrony of stroking in the RHI, as well as in the whole body illusion, has been shown to also modulate the magnitude of the CCE 20,22,23. The crossmodal congruency task provides a relatively simple on-line measure which can be repeated many times and is not susceptible to observer and experimental biases.
Potential disadvantages of using this task are that it can be more time consuming and can be technically more sophisticated as compared to other measures. Furthermore, measuring the effects of the RHI can itself modulate the illusion. The important challenge for the crossmodal congruency task is that it involves multisensory visual and tactile stimuli, which can independently of brush stroking modulate body representation changes.The crossmodal congruency task itself might thus interfere with the effect of brush stroking in the RHI. We found that stroking prior to each crossmodal congruency trial is more effective than just stroking at the beginning of a whole set of trials 22. Furthermore, Aspell et al. (2009) found that presenting the visual and tactile stimuli for the crossmodal congruency task further apart (for example with a small delay of 150-250 msec) increases the effects of prior stroking. Such a small delay still allows for multisensory interactions 28, but reduces the interference of visuo-tactile stimuli on the RHI manipulation. Furthermore, we found that the effect of stroking synchrony is reduced when using the crossmodal congruency task while at the same time placing the rubber hand relatively close to the real hand 22. Most likely this is partly due to a relatively long stimulation interval (up to 15 min) and possibly partly because the asynchronous condition also includes crossmodal visuotactile stimulation making this condition "more synchronous" or "less asynchronous" than it usually would be. Therefore, we would recommend using a larger distance between the hands when implementing this method. All in all, the multisensory stimuli in the crossmodal congruency task can itself modulate body representations by changing the amount of overall synchronous or asynchronous multisensory stimulation. When comparing synchronous with asynchronous stimulations in the illusion paradigms, it is thus important to ensure that the brush stroking leads to relatively more overall synchronous or asynchronous visual-tactile stimulation. This can be achieved by trial-by-trial brush stroking and using a short delay between visuotactile crossmodal congruency task stimuli.
Our previous study demonstrated the effect of RHI manipulations on CCE 22. However, other aspects which have been studied for other RHI measures still need to be investigated. For example, it would be interesting to study if the degree of the RHI for example of the experience of ownership is related to CCE magnitude and if the CCE magnitude changes over time. Furthermore, it would be interesting to investigate if the CCE effects during the RHI are comparable to results observed with the same task on the real hand.
To summarize, we demonstrated that the crossmodal congruency task can be used to obtain an objective behavioral measure in the rubber hand illusion. This behavioral task is relatively simple and we think it is suitable for studying changes in body representations and underlying multisensory processing in both the general population as well as patient groups. However, it is important to note that this measure might not be causally related to subjective experiences in the rubber hand illusion 29. It is likely that both objective and subjective measures rely on common or similar multisensory mechanisms but possibly also on separate mechanisms. Depending on the research question, it might be advisable to obtain an objective behavioral measure and also a more subjective measure using rating scales.

We demonstrate how an objective measure of effects in the commonly employed rubber hand illusion paradigm can be obtained by combining this paradigm with the well-established crossmodal congruency task.
In the RHI 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 for the majority of participants. When touch is given asynchronously then the RHI is abolished or reduced. As the name suggests, the RHI paradigm typically involves a hand, however similar paradigms have also been established for whole bodies 1-3. Experiments using this paradigm can explore the conditions which modulate body representations. Previous experiments for example demonstrated that both viewing a body form as well as the synchrony of the given touch are important cues for the representation of one's own body 4,5. Thus, the RHI as an experimental paradigm can be used to shed light on how the brain constructs and updates distinct representations for one's own body 4-7. Such body representations support many vital processes when interacting with the external environment. Furthermore, body representation changes are related to many clinical disorders for example chronic pain, eating disorders and schizophrenia 8-10.
To investigate the mechanisms underlying the construction of distinct body representations researchers have employed several measures that are modulated in the rubber hand illusion paradigm. Typically, researchers ask participants to rate statements such as "I felt as if the rubber hand were my hand." on a scale from -3 to 3 7,11. Another more indirect measure which has often been employed involves asking participants to indicate the position of their own hand before and after the illusion was induced 12. The hand position is typically perceived to be closer to the rubber hand after the RHI is induced ("proprioceptive drift").
Researchers have also employed physiological measures to index the effect of experimental manipulations in the RHI, for example skin conductance responses when a sudden threat (for example an approaching knife) to the rubber hand is perceived 13,14. The RHI has also been related to small skin temperature changes which can be measured 15. The advantage of these physiological measures is that they occur automatically and thus are less susceptible to potential experimental biases. Potential disadvantages of these techniques include adaption of the physiological response throughout the experimental manipulation. Furthermore, the physiological processes these measures tap into can be generally deregulated in certain patient groups (for example chronic pain, eating disorders and schizophrenia, see supplementary material in 15).
Our specific aim was to obtain an objective behavioral measure of the effects in the rubber hand illusion, which is less susceptible to possible observer or experimenter biases. For this purpose we combined the RHI with the crossmodal congruency task. This task involves speeded forced-choice location discriminations of targets in one modality while, additional stimuli are presented in a different modality 16,17. This measure thus involves a relatively simple task which unlike physiological measures can be repeatedly administered many times. Furthermore, unlike "proprioceptive drift" this measure can be obtained on-line during the illusion while participants view the artificial hand. And 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 4,5,18. We think that the CCE measure is suited to study changes in body representations in patient groups. We think this is especially the case for the study of disorders which include a range of cognitive, motivational or physiological changes which might generally affect more subjective and physiological measures of the RHI.
In the variant we use for the RHI, tactile targets (short vibrations) are presented to different fingers (for example index and middle finger) of one hand. Participants are simply asked to indicate which finger received the tactile stimulation by pressing one of two buttons with the free hand. The distractors are visual stimuli (brief flickering of small lights) which are mounted above the fingers of the viewed rubber hand. These visual stimuli occur close in time to the tactile stimuli. Importantly, the visual stimuli appear on the same finger - spatially congruent - half of the time and occur on the other finger - spatially incongruent - the other half. Spatially congruent visual stimuli improve the localization of the tactile target, whereas spatially incongruent visual stimuli can slow this process down. The overall difference in performance between incongruent and congruent trials, known as the crossmodal congruency effect (CCE), reflects the influence of the visual information on discriminating the tactile target locations and thus indexes multisensory interactions.
Viewing a hand form 19-21 as well as the synchrony of the given touch 22 in the RHI determines the magnitude of the CCE. In other words, the CCE magnitude indexes how much the visual stimuli near the rubber hand influence the response to touches on one's own hand. When participants experience the rubber hand to be one's own hand then the CCE for visual-tactile stimuli is increased. It is thought that the RHI leads to changes in multisensory processing which likely increases the interactions between tactile and visual stimuli 5,18.
We have previously used the combination of the RHI and crossmodal congruency task to investigate experimental effects in the RHI 22. Others have shown that the CCE magnitude can be used as a measure in whole body illusions which involve more global aspects of body representations 23. In this study participants discriminated the location of tactile vibration stimuli on their backs. At the same time participants viewed their bodies from a position as if standing 2 m behind their own body via a camera and a head mounted display. Participants could also see lights which were either flashed in the same location as the tactile targets (congruent trials) or in a different location (incongruent trials). In addition to the crossmodal congruency task, the authors also stroked the backs of the participants. This stroking was either in synchrony with viewed strokes or in asynchrony. This manipulation caused on average a difference in the experience of body ownership and also affected the magnitude of the CCE. Thus, the CCE magnitude can be used as an objective measure for changes both in the RHI as well as in the 'whole body illusion'. Combinations of these paradigms with the crossmodal congruency task allow, in particular, probing of multisensory processes which are critical for the occurrence of these illusions. We will now provide a detailed step-by-step description of how we implemented the crossmodal congruency task in the RHI paradigm.

<table border="1">
	<tbody>
		<tr>
			<td>Name of Reagent/Material</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>artificial hand</td>
			<td>Otto Bock Australia Pty. Ltd</td>
			<td>passive arm prostheses</td>
			<td>other company or custom made is possible</td>
		</tr>
		<tr>
			<td>paint brushes</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>custom-made box</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>e.g. cardboard or wood</td>
		</tr>
		<tr>
			<td>2 tactors e.g. small speakers</td>
			<td>e.g. Altronics, China</td>
			<td>C0600 (Mylar Cone Speaker)</td>
			<td>other tactors can be used for example bone conductors (from hearing aids, e.g. Oticon) or electromagnetic solenoid-type stimulators (e.g. dancerdesign.co.uk)</td>
		</tr>
		<tr>
			<td>2 light-emitting diodes (LEDs)</td>
			<td>e.g. A-Bright Industrial Co., LTD</td>
			<td>AL-513YD-004</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>computer with mouse</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Presentation software</td>
			<td>Neurobehavioural Systems</td>
			<td>Presentation</td>
			<td>other software can be used</td>
		</tr>
		<tr>
			<td>headphones and recorded sound file as metronome</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
	</tbody>
</table>

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.

The magnitude of the CCE is significantly modulated in the RHI. In Figures 2 and 3 we present representative results from a previous study we have conducted 22. In Figure 2 both the CCE for response time and response error differed significantly between different RHI conditions. The CCE magnitude was significantly increased when the RHI was induced with synchronous stroking as compared to asynchronous stroking which reduces or abolishes the RHI. In Figure 3, we depict data from an experiment where brush stroking was not delivered prior to every crossmodal congruency task. Instead, brushing was blocked and given prior to an entire larger set of trials. In this design the CCE is not significantly modulated.
<img alt="Figure 1" fo:content-width="6in" fo:src="/files/ftp_upload/50530/50530fig1highres.jpg" src="/files/ftp_upload/50530/50530fig1.jpg" /> 
 Figure 1. Overview setup and procedure. The experimental setup includes a cover for the participant's real hand, a rubber hand, tactors, lights, brushes and a response device. The covered hand of the participant and the rubber hand are brushed synchronously to induce the RHI. Brush strokes are given prior to every crossmodal congruency trial. The difference in performance between incongruent and congruent trials - the crossmodal congruency effect (CCE) - indexes changes in the RHI. <a href="https://www.jove.com/files/ftp_upload/50530/50530fig1large.jpg" target="_blank"> Click here to view larger figure</a>.
<img alt="Figure 2" fo:content-width="4.5in" fo:src="/files/ftp_upload/50530/50530fig2highres.jpg" src="/files/ftp_upload/50530/50530fig2.jpg" /> 
 Figure 2. The crossmodal congruency effect (CCE) is shown for both response time and response error. Synchronous brushing (red) induces the RHI and asynchronous brushing (blue) abolishes the RHI. The crossmodal congruency effect (CCE) for response time and response error differs significantly between synchronous and asynchronous brushing. Adapted from Zopf et al. (2010), with permission (average for synchronous and asynchronous stroking from Experiment 2).
<img alt="Figure 3" fo:content-width="3in" fo:src="/files/ftp_upload/50530/50530fig3highres.jpg" src="/files/ftp_upload/50530/50530fig3.jpg" /> 
 Figure 3. Crossmodal congruency effect (CCE) does not differ significantly between RHI conditions when brush stroking is not performed prior to crossmodal congruency trials and in this case only as one block before a set of trials. Adapted from Zopf et al. (2010), with permission (average for synchronous and asynchronous stroking from Experiment 1).

Watch this Scientific Journal Video about The Crossmodal Congruency Task as a Means to Obtain an Objective Behavioral Measure in the Rubber Hand Illusion Paradigm at JoVE.com

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

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 ...

the-crossmodal-congruency-task-as-means-to-obtain-an-objective

Research

JoVE Journal

Behavior

The Resident-intruder Paradigm: A Standardized Test for Aggression, Violence and Social Stress

This video publication explains in detail the experimental protocol of the resident-intruder paradigm in rats. This test is a standardized method to measure offensive aggression and defensive behavior in a semi natural setting. The most important behavioral elements performed by the resident and the intruder are demonstrated in the video and illustrated using artistic drawings. The use of the resident intruder paradigm for acute and chronic social stress experiments is explained as well. Finally, some brief tests and criteria are presented to distinguish aggression from its more violent and pathological forms.

This video shows the resident-intruder paradigm in rats. This test is a standardized method to measure offensive aggression, defensive behavior and violence in a semi-natural setting. The use of the paradigm for social stress experiments is explained as well.

This video publication explains in detail the experimental protocol of the resident-intruder paradigm in rats. This test is a standardized method to ...

The Attentional Set Shifting Task: A Measure of Cognitive Flexibility in Mice

Cognitive impairment, particularly involving dysfunction of circuitry within the prefrontal cortex (PFC), represents a core feature of many neuropsychiatric and neurodevelopmental disorders, including depression, post-traumatic stress disorder, schizophrenia and autism spectrum disorder. Deficits in cognitive function also represent the most difficult symptom domain&#160;to successfully treat, as serotonin reuptake inhibitors and tricyclic antidepressants have only modest effects. Functional neuroimaging studies and postmortem analysis of human brain tissue implicate the PFC as being a primary region of dysregulation in patients with these disorders. However, preclinical behavioral assays used to assess these deficits in mouse models which can be readily manipulated genetically and could provide the basis for studies of new treatment avenues have been underutilized. Here we describe the adaptation of a behavioral assay, the attentional set shifting task (AST), to be performed in mice to assess prefrontal cortex mediated cognitive deficits. The neural circuits underlying behavior during the AST are highly conserved across humans, nonhuman primates and rodents, providing excellent face, construct and predictive validity.

The goal of this protocol is to perform a behavioral assay such as the attentional set shifting task (AST) to assess prefrontal cortex-mediated cognitive flexibility in mice.

Cognitive impairment, particularly involving dysfunction of circuitry within the prefrontal cortex (PFC), represents a core feature of many ...

The Use of the Puzzle Box as a Means of Assessing the Efficacy of Environmental Enrichment

Environmental enrichment can dramatically influence the development and function of neural circuits. Further, enrichment has been shown to successfully delay the onset of symptoms in models of Huntington&#8217;s disease 1-4, suggesting environmental factors can evoke a neuroprotective effect against the progressive, cellular level damage observed in neurodegenerative disorders. The ways in which an animal can be environmentally enriched, however, can vary considerably. Further, there is no straightforward manner in which the effects of environmental enrichment can be assessed: most methods require either fairly complicated behavioral paradigms and/or postmortem anatomical/physiological analyses. This protocol describes the use of a simple and inexpensive behavioral assay, the Puzzle Box 5-7 as a robust means of determining the efficacy of increased social, sensory and motor stimulation on mice compared to cohorts raised in standard laboratory conditions. This simple problem solving task takes advantage of a rodent&#8217;s innate desire to avoid open enclosures by seeking shelter. Cognitive ability is assessed by adding increasingly complex impediments to the shelter&#8217;s entrance. The time a given subject takes to successfully remove the obstructions and enter the shelter serves as the primary metric for task performance. This method could provide a reliable means of rapidly assessing the efficacy of different enrichment protocols on cognitive function, thus paving the way for systematically determining the role specific environmental factors play in delaying the onset of neurodevelopmental and neurodegenerative disease.

Environmental enrichment provides a potential protective effect against neurodegenerative disorders. Currently, however, there is no easy way of determining the efficacy of enrichment procedures. This protocol describes a simple &#8220;Puzzle Box&#8221; method for assessing an animal&#8217;s cognitive function, in order to reveal the effectiveness of environmental enrichment.

Environmental enrichment can dramatically influence the development and function of neural circuits.  Further, enrichment has been shown to successfully ...

Vagus Nerve Stimulation as a Tool to Induce Plasticity in Pathways Relevant for Extinction Learning

Extinction describes the process of attenuating behavioral responses to neutral stimuli when they no longer provide the reinforcement that has been maintaining the behavior. There is close correspondence between fear and human anxiety, and therefore studies of extinction learning might provide insight into the biological nature of anxiety-related disorders such as post-traumatic stress disorder, and they might help to develop strategies to treat them. Preclinical research aims to aid extinction learning and to induce targeted plasticity in extinction circuits to consolidate the newly formed memory. Vagus nerve stimulation (VNS) is a powerful approach that provides tight temporal and circuit-specific release of neurotransmitters, resulting in modulation of neuronal networks engaged in an ongoing task. VNS enhances memory consolidation in both rats and humans, and pairing VNS with exposure to conditioned cues enhances the consolidation of extinction learning in rats. Here, we provide a detailed protocol for the preparation of custom-made parts and the surgical procedures required for VNS in rats. Using this protocol we show how VNS can facilitate the extinction of conditioned fear responses in an auditory fear conditioning task. In addition, we provide evidence that VNS modulates synaptic plasticity in the pathway between the infralimbic (IL) medial prefrontal cortex and the basolateral complex of the amygdala (BLA), which is involved in the expression and modulation of extinction memory.

Vagus nerve stimulation (VNS) has emerged as a tool to induce targeted synaptic plasticity in the forebrain to modify a range of behaviors. This protocol describes how to implement VNS to facilitate the consolidation of fear extinction memory.

Extinction describes the process of attenuating behavioral responses to neutral stimuli when they no longer provide the reinforcement that has been ...

The Emotional Stroop Task: Assessing Cognitive Performance under Exposure to Emotional Content

The emotional Stroop effect (ESE) is the result of longer naming latencies to ink colors of emotion words than to ink colors of neutral words. The difference shows that people are affected by the emotional content conveyed by the carrier words even though they are irrelevant to the color-naming task at hand. The ESE has been widely deployed with patient populations, as well as with non-selected populations, because the emotion words can be selected to match the tested pathology. The ESE is a powerful tool, yet it is vulnerable to various threats to its validity. This report refers to potential sources of confounding and includes a modal experiment that provides the means to control for them. The most prevalent threat to the validity of existing ESE studies is sustained effects and habituation wrought about by repeated exposure to emotion stimuli. Consequently, the order of exposure to emotion and neutral stimuli is of utmost importance. We show that in the standard design, only one specific order produces the ESE.

The emotional Stroop effect (ESE) is the result of longer naming latencies to ink colors of emotion words than those of neutral words. This report refers to potential sources of confounding and includes a modal experiment that provides the means to control for them.

The emotional Stroop effect (ESE) is the result of longer naming latencies to ink colors of emotion words than to ink colors of neutral words. The ...

The Deese-Roediger-McDermott (DRM) Task: A Simple Cognitive Paradigm to Investigate False Memories in the Laboratory

The Deese,&#160;Roediger and McDermott&#160;(DRM) task is a false memory paradigm in which subjects are presented with lists of semantically related words (e.g., nurse, hospital, etc.) at encoding. After a delay, subjects are asked to recall or recognize these words. In the recognition memory version of the task, subjects are asked whether they remember previously presented words, as well as related (but never presented) critical lure words (&#39;doctor&#39;). Typically, the critical word is recognized with high probability and confidence. This false memory effect has been robustly demonstrated across short (e.g., immediate, 20 min) and long (e.g., 1, 7, 60 d) delays between encoding and memory testing. A strength of using this task to study false memory is its simplicity and short duration. If encoding and retrieval components of the task occur in the same session, the entire task can take as little as 2 - 30 min. However, although the DRM task is widely considered a &#39;false memory&#39; paradigm, some researchers consider DRM illusions to be based on the activation of semantic memory networks in the brain, and argue that such semantic gist-based false memory errors may actually be useful in some scenarios (e.g., remembering the forest for the trees; remembering that a word list was about &#34;doctors&#34;, even though the actual word &#34;doctor&#34; was never presented for study). Remembering the gist of experience (instead of or along with individual details) is arguably an adaptive process and this task has provided a great deal of knowledge about the constructive, adaptive nature of memory. Therefore, researchers should use caution when discussing the overall reach and implications of their experiments when using this task to study &#39;false memory&#39;, as DRM memory errors may not adequately reflect false memories in the real world, such as false memory in eyewitness testimony, or false memories of sexual abuse.

The Deese-Roediger-McDermott DRM Task: A Simple Cognitive Paradigm to Investigate False Memories in the Laboratory

Here we present the Deese,&#160;Roediger and McDermott&#160;(DRM) task, a tool to study false memories in the laboratory. Subjects study lists of semantically related words (e.g.,&#160;nurse, sick, etc.), and later falsely remember an unstudied word (doctor) that represents the gist, or theme, of the word list.

The Deese,&#160;Roediger and McDermott&#160;(DRM) task is a false memory paradigm in which subjects are presented with lists of semantically related words ...

Behavioral Disturbances: An Innovative Approach to Monitor the Modulatory Effects of a Nutraceutical Diet

In dogs, diets are often used to modulate behavioral disturbances related to chronic anxiety and stress caused by intense and restless activity. However, the traditional ways to monitor behavioral changes in dogs are complicated and not efficient. In the current clinical evaluation, a new, simple monitoring system was used to assess the effectiveness of a specific diet in positively modulating the intense and restless activity of 24 dogs of different ages and breeds. This protocol describes how to easily and rapidly evaluate improvement in a set of symptoms related to generalized anxiety by using a specific sensor, a mobile phone app, a wireless router, and a computer. The results showed that dogs treated with specific diets showed significant improvement in the times spent active and at rest after 10 days (p &lt; 0.01 and p &lt; 0.05, respectively). These dogs also showed an overall significant improvement in clinical and behavioral symptoms. A specific sensor, along with its related hardware, was demonstrated to successfully monitor behavioral changes relating to movement in dogs.

We report a simple approach to evaluate the effectiveness of a specific diet in positively modulating the daily activity and clinical and behavioral symptoms of dogs with evident behavioral disturbances.

In dogs, diets are often used to modulate behavioral disturbances related to chronic anxiety and stress caused by intense and restless activity. However, ...

Task Interruption and Resumption Paradigm for Testing the Activation and Pursuit of an Abstract Thinking Goal

This protocol is based on the task interruption and resumption paradigm, the premise of which is that active goals lead to persistent behavior and thus a higher resumption rate after a period of delay or interruption. The task interruption and resumption protocol described in this research is tailored to test the activation of cognitive goals (e.g., a goal to think more abstractly). Cognitive goals may be pursued even during the interruption period; thus, to prevent this, the protocol involves cognitive distraction. The protocol consists of several stages. Specifically, the initial stage includes the goal activation process, where the treatment (versus control) condition receives a manipulation to activate the cognitive goal being tested by the researcher. In the next stage, participants are presented with the introduction of a task that is perceived to either satisfy or not satisfy the cognitive goal of interest. Importantly, this task is interrupted a few seconds after it begins. The task interruption forces a delay period and introduces a cognitive distraction to prevent the automatic pursuit and fulfillment of the cognitive goal. After the interruption period, participants are given a choice between resuming the interrupted task and abandoning the interrupted task to complete an alternative task instead. Among participants whose cognitive goals had been activated at the earlier stage, the task resumption rate should be higher if the task was perceived as an opportunity to satisfy (versus not satisfy) the goal. Such a finding would provide empirical evidence that the cognitive goal has been activated and pursued. In previous research, this protocol has been used to test whether causal uncertainty activates an abstract thinking goal. Adapting the protocol to test the activation of other cognitive goals is also discussed.

This protocol was designed to test the activation and pursuit of cognitive goals (e.g., an abstract thinking goal) using the task interruption and resumption paradigm. The protocol is suitable for cognitive goals that are automatically pursued once activated, as the distraction procedure prevents goal pursuit during the interruption period.

This protocol is based on the task interruption and resumption paradigm, the premise of which is that active goals lead to persistent behavior and thus a ...

The Modified Temptation Resistance Task: A Paradigm to Elicit Children's Strategic Lie-telling

The protocol for the temptation resistance paradigm was designed to elicit 2- to 8-year-old children's strategic lie-telling behaviors. The reward of transgression was intended to be too tempting to resist, so that children's spontaneous lie-telling behavior in the presence of irreversible evidence due to the transgression could be observed. Conducted in a developmental psychology laboratory behind a one-way mirror and video recorded with a hidden camcorder, the protocol starts with a guessing game where the child is given three trials to guess the identities of hidden objects under an upside down cup. The experimenter gives hints in the first two trials to make sure the child "guess" them correctly. At the beginning of the final trial, the experimenter leaves the room briefly and asks the child not to peek under the cup. If the child could not resist the temptation and peeks, small particles previously filled in the cup would scatter on a grooved surface. Upon the experimenter's return, the child is asked if he/she has peeked. If he/she denies transgression contrary to the presence of the physical evidence, he/she is asked to explain why the particles are on the table. Three responses could be observed in the procedure, including the initial transgression, truth-telling or lie-telling behavior if the child peeked, and the strategic lie-telling behavior in the presence of the physical evidence.

The Modified Temptation Resistance Task: A Paradigm to Elicit Children&#039;s Strategic Lie-telling

The protocol for the temptation resistance paradigm was designed to elicit 2- to 8-year-old children&#39;s strategic lie-telling behaviors. The reward of transgression was intended to be too tempting to resist, so that children&#39;s spontaneous lie-telling behavior in the presence of irreversible evidence due to the transgression could be observed.

The protocol for the temptation resistance paradigm was designed to elicit 2- to 8-year-old children's strategic lie-telling behaviors. The reward of ...

Nest Building Behavior as an Early Indicator of Behavioral Deficits in Mice

Nest building is an innate behavior in male and female rodents, even when raised in laboratory settings. As such, many researchers provide rodents synthetic and/or natural materials (such as twine, tissue, cotton, paper, and hay) as a gauge of their overall well-being and as an ancillary assessment to predict the possible decline in cognition. Typically, changes in nesting behaviors, such as failure to create a nest, indicate a change in health or welfare. In addition, nesting behavior is sensitive to many environmental and physiological challenges, as well as many genetic mutations underlying pathological disease states. The following protocol describes a nesting behavior paradigm that explores the usage of four types of nesting material. In addition, the protocol utilizes intraclass correlations to demonstrate that inter-rater reliability is higher when nests are constructed out of shredded paper compared to other common nesting materials such as cotton squares, paper twists, and soft cob bedding. The chosen methodology and statistical considerations (i.e., intraclass correlation) for this assay may be of interest for those conducting experiments assessing the quality of living of mice.&#160;

Here, we present a protocol to quantify nest building behavior in mice, which is known to be impaired in several neurological disorders and diseases. This protocol examines the utility of four materials and offers the opportunity to quantify the rater agreement in scoring, improving the validity and reliability of the assay.