When you pick up an object, you might think that you are manipulating it, but in a sense, it is also manipulating you. Through a series of six psychological experiments, Joshua Ackerman from the Massachusetts Institute of Technology has shown that the properties that we feel through touch – texture, hardness, weight – can all influence the way we think.
Weight is linked to importance, so that people carrying heavy objects deem interview candidates as more serious and social problems as more pressing. Texture is linked to difficulty and harshness. Touching rough sandpaper makes social interactions seem more adversarial, while smooth wood makes them seem friendlier. Finally, hardness is associated with rigidity and stability. When sitting on a hard chair, negotiators take tougher stances but if they sit on a soft one instead, they become more flexible.
These influences are not trivial – they can sway how people react in important ways, including how much money they part with, how cooperative they are with strangers, or how they judge an interview candidate.
What part of the body do you listen with? The ear is the obvious answer, but it’s only part of the story – your skin is also involved. When we listen to someone else speaking, our brain combines the sounds that our ears pick up with the sight of the speaker’s lips and face, and subtle changes in air movements over our skin. Only by melding our senses of hearing, vision and touch do we get a full impression of what we’re listening to.
When we speak, many of the sounds we make (such as the English “p” or “t”) involve small puffs of air. These are known as “aspirations”. We can’t hear them, but they can greatly affect the sounds we perceive. For example, syllables like “ba” and “da” are simply versions of “pa” and “ta” without the aspirated puffs.
If you looked at the airflow produced by a puff, you’d see a distinctive pattern – a burst of high pressure at the start, followed by a short round of turbulence. This pressure signature is readily detected by our skin, and it can be easily faked by clever researchers like Bryan Gick and Donald Derrick from the University of British Columbia.
Gick and Derrick used an air compressor to blow small puffs of air, like those made during aspirated speech, onto the skin of blindfolded volunteers. At the same time, they heard recordings of different syllables – either “pa”, “ba”, “ta” or “da” – all of which had been standardised so they lasted the same time, were equally loud, and had the same frequency.
Gick and Derrick found that the fake puffs of air could fool the volunteers into “hearing” a different syllable to the one that was actually played. They were more likely to mishear “ba” as “pa”, and to think that a “da” was a “ta”. They were also more likely to correctly identify “pa” and “ta” sounds when they were paired with the inaudible puffs.
This deceptively simple experiment shows that our brain considers the tactile information picked up from our skin when it deciphers the sounds we’re listening to. Even parts of our body that are relatively insensitive to touch can provide valuable clues. Gick and Derrick found that their fake air puffs worked if they were blown onto the sensitive skin on the back of the hand, which often pick up air currents that we ourselves create when we speak. But the trick also worked on the back of the neck, which is much less sensitive and unaffected by our own spoken breaths.
While many studies have shown that we hear speech more accurately when it’s paired with visual info from a speaker’s face, this study clearly shows that touch is important too. In some ways, the integration of hearing and touch isn’t surprising – both senses involve detecting the movement of molecules vibrating in the world around us. Gick and Derrick suggest that their result might prove useful in designing aids for people who are hard of hearing.
Reference: Nature doi:10.1038/nature08572
More on perception:
Having your arm in a cast can be a real pain but immobilising your hand in plaster has consequences beyond itchiness, cramps and a growing collection of signatures. Silke Lissek from Bergmannsheil University found that just a few weeks in a cast can desensitise the trapped hand’s sense of touch, and lower neural activity in the part of the brain that receives signals from it. The uninjured hand, however, rises to the occasion and picks up the sensory slack by becoming more sensitive than before.
Lissek recruited 31 right-handed people, each of whom had one fractured arm encased in a cast, and compared them to 36 uninjured people. She measured the sensitivity of their fingertips by touching them with a pair of needles that were brought increasingly close together, and noting the distance at which the two needles felt like just one.
She found that the uninjured recruits had equally sensitive fingers on both hands, but for the cast-wearers, the fingers of the injured hand had become less receptive (no matter which arm was plastered). The threshold distance at which they perceived two needles rather than one was further than the same distance for the uninjured recruits. The healthy hand, however, became more sensitive and could tell the needles apart even if they were closer together than normal.