Home Replications

Feeling someone else’s sensation of touch – the neural background, the examples, and you

Touch is the only sensation which we cannot share with another person. The immediacy of touch differentiates it from the distant impressions which sight and audition can give us. However, modern neuroscience is currently revising this picture: you can touch at a distance. One just doesn’t notice it. Can we find people who do?

A very possessive romantic partner may mind when his love interest was looked at. But it is a whole different game if touch was involved. There is something intuitively different about touch which pervades every day culture. It is, arguably, the lack of distance, the necessary intrusion of the touching object into personal space. This makes touching a very personal experience, far more so than seeing or hearing.
Modern neuroscience is currently revising this picture. The first report to challenge the immediacy of touch came out in 2004. A team led by Christian Keysers found that when people saw someone else being touched on the leg they showed activation in the same brain area as when their legs were being touched directly. Curiously, seeing touch from a first person perspective led to similar brain region activity as seeing it from a third person.
What it looks like to touch and being touched in the secondary somatosensory cortex.

What it looks like to see touch and being touched in the secondary somatosensory cortex.

This got several laboratories around the world started on the topic. For example, recently, Schaefer and colleagues showed that when hands are touched or seen to be touched, perspective does actually matter – a first person view-point increases activation more in primary areas than a third person perspective. In any event, the general picture was not a statistical fluke but instead a replicable finding – being touched is represented in a very similar way in the brain as seeing someone else being touched. But this raises two questions: why can’t I feel anything then and why does it happen?
In 2009, Ramachandran and Brang published a paper which may provide an answer to the first question. They studied four amputees who had lost one hand due to accident. When they watched an experimenter being touched on her hand, the lost hand’s phantom ‘felt the touch’ after a few seconds. One anecdote shows the power of this finding:
‘Patient 1 even added that after we had demonstrated this, he had gone home and asked his wife to massage her own hand while he watched, and watching her do so seemed to relieve his phantom pain.’
Importantly, this was not the case for intact hands – whether of control participants or the amputees. The difference, thus, appears to be whether the sensation felt by others is in competition with the own direct input from the skin. If so, the own touch wins the competition and one does not consciously feel someone else’s experience. But without a hand providing direct sensory input – as in the case of amputees – the touch felt by others becomes vivid.
Apes (of the non-human variety) collaborating.

Apes (of the non-human variety) collaborating.

This still leaves the question as to why this happens. The common explanation is that having the capacity to feel the touch of someone else – even if it is so faint as to be below the level of awareness – aids our ability to understand others. As a social species we need a high level of empathy in order to work together efficiently. Evolutionary ancestors who had a touch-empathy link may have been better at collaborating and, thus, were better able to survive and reproduce.
The current account makes an interesting prediction. Next time you have an anaesthetized hand or foot – and thus no own skin-sensation – you might want to check whether you can feel someone else’s touch. Let me know whether it worked. This experiment has not, as far as I can tell, be done, yet. You yourself could disprove the immediacy of touch.

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Keysers C, Wicker B, Gazzola V, Anton JL, Fogassi L, & Gallese V (2004). A touching sight: SII/PV activation during the observation and experience of touch. Neuron, 42 (2), 335-46 PMID: 15091347

Ramachandran VS, & Brang D (2009). Sensations evoked in patients with amputation from watching an individual whose corresponding intact limb is being touched. Archives of neurology, 66 (10), 1281-4 PMID: 19822785

Schaefer M, Heinze HJ, & Rotte M (2012). Close to you: embodied simulation for peripersonal space in primary somatosensory cortex. PloS one, 7 (8) PMID: 22912698

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Figures:

1) adapted from Keysers et al., 2004, p. 337

2) By Ikiwaner (Own work)  via Wikimedia Commons

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The biological basis of orchestra seating

Many cultural conventions appear like the result of historical accidents. The QWERTY – keyboard is a typical example: the technical requirements of early typewriters still determine the computer keyboard that I write this text on, even though by now technical advances would allow for a far more efficient design. Some culturally accepted oddities, however, appear to reflect the biological requirements of human beings. The way musicians are seated in an orchestra is one such case, but the listener is, surprisingly, not the beneficiary.

When one goes to a concert one typically sees a seating somewhat like the one below: strings in the front, then woodwinds further back, then brass. What is less obvious is that, in general, higher pitched instruments are seated on the left and lower pitched instruments on the right. The strings show this pattern perfectly: from left to right one sees violins, violas, cellos and then basses. Choirs show the same pattern: higher voices (soprano and tenor) stand left of the lower voices (alt and basses). Why is that?

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orchestra; seating arrangement; Nijmegen; Nijmegen studenten orkest

An orchestra I have personally performed with.

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It turns out that this is not a historical accident but instead a biological requirement. Diana Deutsch has used a series of audio illusions which all showed a curious pattern: when you present two series of tones each to one ear, you have the illusion that the high tones are being played to your right ear and the low ones to the left ear. In case you don’t believe me, listen to this illustration of Deutsch’s scale illusion:
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Apparently, there is a right ear advantage for high tones. So, seating the higher instruments on the left side (as seen on the photo) makes complete sense as this way musicians on stage tend to hear higher tones coming from their right. However, from the point of view of the audience this is actually a really bad idea as their right ear advantage is not taken into account. It turns out that orchestra seating arrangements are not favouring the hearing of the audience or the conductor but instead the musicians!
The right ear advantage for high tones is even mirrored in musicians’ brains. We know that the right ear projects mostly to the left auditory cortex and vice versa for the left ear. So, one would expect that people who play high instruments have trained their right ear / left auditory cortex the most when they practiced their craft. These training effects should be mirrored in differences in cortex size. This would mean that people sitting on the left in an orchestra have bigger left auditory cortices. In a fascinating article Schneider and colleagues showed that by and large this is the case: professional musicians who play high instruments or instruments with a sharp attack (e.g., percussionists, piano players) tend to have greater left auditory cortices than right auditory cortices. Their figure says is all.
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Schneider; orchestra; seating; brain; Heschl's gyrus; primary auditory cortex; cortical size

How the brains are seated in an orchestra.

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The orchestra seating arrangement mirrors not only the listening biases of most human ears but on top of that the brain differences between musicians. By and large, the orchestra is organised according to biological principles. Thus, not all cultural conventions – like the seemingly arbitrary seating arrangement of orchestras – have their roots in historical accidents. Cultural oddities are sometimes merely down to biology.

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Deutsch, D. (1999). Grouping Mechanisms in Music The Psychology of Music, Second Edition, 299-348 DOI: 10.1016/B978-012213564-4/50010-X

Schneider P, Sluming V, Roberts N, Bleeck S, & Rupp A (2005). Structural, functional, and perceptual differences in Heschl’s gyrus and musical instrument preference. Annals of the New York Academy of Sciences, 1060, 387-94 PMID: 16597790

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Figures:

1) Nederlands: Symfonieorkest Nijmegen in de grote zaal van de Vereeniging, The SON photo library, via wikimedia

2) as found in Schneider et al., 2005, p. 392

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Three fun ways to have three hands – for you at home

Tired of having been born with only two hands?

Jealous of Indian goddesses?

Doubtful about Psychology and Neuroscience’s ability to replicate findings?

Then this set of exercises is for you. No need for any technical equipment. If all goes well you will grow* a hand as part of all this. You will have the strong feeling that you have three hands. You will feel and/or care about the illusory third limb. Let’s get started.
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1) An additional cheeky hand
Equipment: none
Partners needed: 1
Time: 3 minutes
Success rate: 43% (70% report some sort of self-touch illusion)
Publication: Davies & White (2011)
a) Your partner and you place your hands on the same warm water bottle in order to have equally warm hands.
b) Sit down and close your eyes. Your partner sits opposite you. Her eyes are open.
c) Your partner takes your right hand and makes you stroke and tap yourself lightly on your right cheek. At the same time she herself administers synchronous, identical strokes and taps with her hand to the corresponding location on your face’s left side. Your own left hand simply rests.
d) Vary pressure and frequency of strokes and taps. Mind that on each side of the face timing and pressure have to match. Do so for three minutes.
Davies and White, 2011_cheeky hand illusion

Set-up to add a cheeky hand.

Outcome: The feeling that some sort of third hand, a disconnected one for example, strokes your left cheek.
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2) Two rubber hands
Equipment: two rubber/plastic/wooden or otherwise somewhat realistic feeling right hands, a table, one double paint brush (see picture), one normal paint brush
Partners needed: 1
Time: 2 minutes
Success rate: not reported
Ehrsson, 2009_two rubber hands

Set-up to induce two rubber hand illusions simultaneously.

Publication: Ehrsson (2009)
a) Sit at a table. Place your right hand underneath the table, e.g., on your leg.
b) Place the rubber hand models of right hands in front of you over the area where your real right hand is. The models should be 10cm apart.
c) Look at the rubber hands. At the same time you partner uses the double paint brush to stroke the rubber hands and the single paint brush to stroke your real hand. These strokes need to be absolutely in synchrony.
Outcome: The feeling that both rubber hands are your right hands.
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3) An additional rubber hand
Equipment: a rubber/plastic/wooden or otherwise somewhat realistic feeling right hand, a table, two paint brushes, a piece of cloth
Partners needed: 1
Time: unknown
Success rate: unknown
Publication: Guterstam, Petkova, & Ehrsson (2011)

Left: Set-up to add rubber hand to one’s own body. Right: Testing how real the ownership of the rubber hand really is (don’t do this test at home).

a) Sit at a table. Put your real right hand on the table in front of you.
b) Place the rubber hand in a similar position slightly to the left of your real hand, about 12cm apart. Cover the space from your real shoulder to the arm-bit of the rubber hand with the cloth.
c) Look at the rubber hand. At the same time your partner uses the two paint brushes to stroke both your real right hand and the rubber hand simultaneously on the index and middle fingers. She needs to do so absolutely synchronously, matching the strokes in time and speed. It is best to stroke irregularly but still synchronously.
Outcome: The feeling that both the real hand and the rubber hand are your right hands.
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Did these illusions work for you? Let me know!
As a bonus for all those still in for some more, the following two techniques substitute your real hand for a fake one.
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Bonus 1) A rubber hand (with vision)
Equipment: a rubber/plastic/wooden or otherwise somewhat realistic looking hand (it can be a bit bigger – but not smaller – than your real hand and it can also have a different ‘skin’ colour), two identical paint brushes, one standing screen (a big book would do as well), one table
Partners needed: 1
Time: 10 minutes
Success rate: 42%
Publication: Botvinick & Cohen (1998)
a) Sit at a table. Place the screen in front of you and hide your left hand behind it. Be sure you cannot see your left hand.
b) Place the rubber hand model of a left hand in front of you on the table.
c) Look at the rubber hand. At the same time your partner uses the two paint brushes to stroke both your hidden hand and the rubber hand simultaneously. She needs to do so absolutely synchronously, matching the strokes in time.
Outcome: The feeling that the rubber hand is your own hand.
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Bonus 2) A rubber hand (without vision)
Equipment: a rubber/plastic/wooden or otherwise somewhat realistic feeling hand, three pairs of rubber gloves, a table
Partners needed: 1
Ehrsson et al., 2005: rubber hand illusion without vision

Top: Set-up for inducing rubber hand illusion without vision. Bottom: same in a MRI scanner.

Time:  60 seconds
Success rate: 78%
Publication: Ehrsson, Holmes, & Passingham (2005)
 a) Both you, your partner and the rubber hand need to wear rubber gloves.
b) Sit at a table. Place the rubber hand model of a right hand in front of you on the table. Close your eyes.
c) Your partner takes your left hand and makes you touch the rubber hand’s index finger’s knuckle. At the same time she herself administers synchronous, identical touches with her hand to the corresponding location on your own right index finger’s knuckle.
Outcome: The feeling that you are touching your own hand even though you are touching the rubber hand.
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Finally, if you now wonder whether scientists have also found a way to make you lose a hand, just watch this video. Unfortunately, the techniqual requirements go beyond what is available in most homes and so your own private replication of this illusion will be rather difficult to implement.
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Aimola Davies, A.M., & White, R.C. (2011). Touching my face with my supernumerary hand: A cheeky illusion Perception, 40, 1245-1247 DOI: 10.1068/p6956

Botvinick, M., & Cohen, J. (1998). Rubber hands ‘feel’ touch that eyes see. Nature, 391 (6669) PMID: 9486643

Ehrsson, H.H. (2009). How many arms make a pair? Perceptual illusion of having an additional limb. Perception, 38 (2), 310-312 PMID: 19400438

Ehrsson, H.H., Holmes, N.P., & Passingham, R.E. (2005). Touching a rubber hand: feeling of body ownership is associated with activity in multisensory brain areas. The Journal of neuroscience : the official journal of the Society for Neuroscience, 25 (45), 10564-10573 PMID: 16280594

Guterstam, A., Petkova, V.I., & Ehrsson, H.H. (2011). The illusion of owning a third arm. PloS one, 6 (2) PMID: 21383847

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images: from respective journal publications

*in a psychological sense

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