Tag Archives: touch

The Science of Touch and Emotion

2933605871_601998ca2dIn social species, prosocial emotions are those that promote the well-being of the group. By engaging in acts of trust and cooperation, social groups survive. Parents and offspring form attachments, and individuals act in mutually beneficial, altruistic ways to sow trust between one another. A growing number of studies on touch and emotion reveal our deep-seated need for human contact and warmth. Touch may be the key for communicating prosocial emotions, and for promoting group cohesion and survival.

Dr. Dacher Keltner from the UC Berkeley Department of Psychology and Dr. Matthew Hertenstein (now at DePauw University) have conducted extensive research on how touch communicates emotions. In their 2006 paper Touch Communicates Distinct Emotion, Keltner and Hertenstein investigated the ability of touch to convey various emotions. Given the importance of cooperation and altruism in social groups, Keltner and his colleagues hypothesized that it should be possible to communicate prosocial emotions through touch alone. For their study, 212 volunteers between the ages of 18-40 were sorted into pairs called dyads. In each dyad, one person did the touching (the “encoder”) and the other received the touch (the “decoder”).

Each dyad sat at a table that was bisected by an opaque black curtain, and had no opportunity see or hear one another. The decoder was instructed to place a bare forearm through the curtain. On the other side of the curtain was the encoder, who presented one of twelve emotions to the decoder by touching the decoder’s exposed arm. In addition, the encoder was given freedom to choose how best to communicate each of the emotions, including anger, disgust, fear, happiness, sadness, surprise, sympathy, embarrassment, love, envy, pride, or gratitude. The decoder then chose which of the twelve emotions best described what the encoder was attempting to communicate. Keltner and Herenstein found that anger, fear, and disgust were communicated at levels above chance (which was set at 25%) along with prosocial emotions such as love, gratitude, and sympathy.

Interestingly, this experiment revealed that we use consistent types of touch to communicate particular emotional states. Research assistants, unaware of the emotions that the encoders were instructed to communicate, monitored the “tactile displays” of the encoder on a second by second basis. Research assistants used a survey of coding systems that is routinely used by researchers investigating touch. The types of tactile displays, including tapping, stroking, squeezing, poking, pushing, and tickling, among others, were noted and quantified in terms of frequency, duration, and intensity. Although 106 different encoders participated in the experiment, they tended to use similar tactile displays to convey emotion.  For example, sympathy was most likely to be communicated with patting or stroking, while anger was most likely communicated with pushing.

In a 2009 paper that re-examined this data, Keltner and his team found some interesting patterns of gendered communication. The dyads were either Male-Female (where the encoder was male and the decoder was female, and vice-versa), Male-Male, or Female-Female. Only when the dyad consisted of males was anger communicated at greater-than-chance levels. Only when the dyad consisted of females was happiness communicated at greater-than-chance levels. Sympathy was communicated at greater-than-chance levels only when there was at least one female in the dyad. One of the more humorous findings of the study was how helpless men and women were at communicating specific emotions to one another. As Dr. Keltner explained in a public lecture, “When women tried to communicate anger to the man he had no idea what she was doing and he got nothing right. And when the man tried to communicate compassion to the woman she got zero right. She had no idea what he was doing.”
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Make Awesome: the story of elastic electronic skin

Of the five senses, touch is the most widely distributed throughout the body, and perhaps the most fundamental. A single fingertip has over 2500 touch receptors, which sense and transmit enough information to allow us to discriminate spatial distances as small as 40 micrometers (Tee, et al, 2013). Receptors distributed throughout our hands can sense extremely gentle pressures of around 100 pascals (equivalent to the feeling of a penny resting on a fingertip) as well as pressures of greater than 100 kilopascals (the feeling of gripping an object very tightly). Having such a wide range of sensitivities allows us to perform extremely delicate tasks, such as flipping the pages of a textbook, or pipetting primers into tiny PCR tubes.

From a materials engineering point of view, human skin is nature’s version of an elastomer-based pressure sensor, or, in layman’s terms, an extremely flexible material that is able to feel when it’s being pushed on, pulled, flexed or grazed. For many years, recreating the features of human skin by artificial means eluded researchers. Recently, however, several labs have made enormous strides in recreating the properties of human skin electronically. Over the past decade, Prof. Ali Javey and colleagues at Lawrence Berkeley National Laboratory developed a number of plastic- and rubber-based electronic skin prototypes. Meanwhile, in the laboratory of Prof. Zhenan Bao at Stanford University, graduate student Benjamin Tee helped develop two types of flexible electronic skin, including one that is able to repair itself after being damaged.

skinThe first prototype developed in the Bao laboratory relies on capacitors to detect changes in pressure and flexible organic transistors to amplify and relay signals emitted by the capacitors in a system known as a capacitive pressure sensor. This system is likely familiar to you, because a form of capacitive sensing is used in touch screens for smartphones and tablet computers. The basic building block of capacitive sensing systems are capacitors, devices that are used to temporarily store electrical energy. Though there are several types of capacitors, all contain at least two electrical conductors—usually metal plates—separated by a non-conductive insulator known as a dielectric. When current flows through a circuit and hits the capacitor, a difference in electrical potential is created between the capacitor’s plates, causing positive charge to collect on one plate and negative charge on the other. This in turn causes an electrical field to develop across the dielectric. The electrical field that is created can remain in the capacitor even if the current ceases to flow through the circuit. In this way, energy can be stored by the capacitor in the form of a static voltage spanning the conductors. When stored energy is released, the resulting current can be picked up by devices called transistors and amplified into a readable output current that is much stronger than the input current.
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Learning about touch sensation from an unlikely creature, the star-nosed mole

This is the first in a three part series introducing the science of touch sensation.

TouchMe Star

1) The molecular basis of touch sensation – Learning about touch sensation from an unlikely creature, the star-nosed mole
2) Engineering touch sensation for robotics and prosthetics
3) Communicating emotion through touch

All in preparation for our Bay Area Science Festival event, Touch Me! Sunday, October 27th, from 6-10 PM at The David Brower Center in Berkeley. Click here to learn more and purchase tickets.

There’s a big difference between abruptly bumping into a stranger and being touched gently by someone we love.  We use touch to interact and communicate with other people, as well as to sense the physical objects and forces within our world each day.  We encounter a wide variety of different sensations, and need to be able to distinguish between them.  But how do we actually sense mechanical forces on our skin?  This is an important and long-standing question in neuroscience, and Professor Diana Bautista and members of her lab at UC Berkeley are working to find an answer.

In humans and other animals, nerve cells (called neurons) extend out from the brain and the spinal cord, the major processing regions of the nervous system, to the rest of the body. In order to sense signals at your fingertips and toes, neurons must send out projections that travel the entire length of your arm or leg. Many types of sensory neurons extend into the skin, where they detect different types of stimuli, including touch, temperature, and pain.

Neuroscientists have worked out the mechanism by which neurons respond to pain by using a natural compound that produces painful sensations.

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