The feeling you get when nails scratch a blackboard has a name

It’s enough to make you shiver

Stuart Cox/Alamy Stock

You might not have heard of “grima”, but you have almost certainly felt it. Spanish speakers say they feel grima when they hear the sound of fingernails on a blackboard, or a knife scratching a plate. Now psychologists are suggesting it should be considered as distinct from other emotions.

Inge Schweiger Gallo of the Complutense University of Madrid has personal reasons for studying the phenomenon. “For as far as I can remember, I’ve had problems touching foam rubber,” she says. “Whenever I have to use it, for example, in packages, I try to ask somebody else to touch it for me.”

Schweiger Gallo and her colleagues began by asking Spanish speakers what grima means to them. The people most frequently mentioned an “unpleasant sensation”, “shivering”, “sounds” and “repulsion”. Stimuli that elicited grima included squeaking noises, scratching with fingernails and scratching on surfaces. The volunteers rated grima as being less pleasant  than disgust.


Next, the team turned to German and English speakers, who have no word for grima in their languages. When they heard grima-eliciting sounds, the volunteers’ heart rates fell very slightly at first, then rose sharply, before returning to normal after about 6 seconds. Sounds labelled as disgusting or unpleasant showed a different pattern, falling more sharply, and then returning more steadily to normal.

The effects on skin conductance – a sign of physiological changes – were similar for grima sounds and disgusting or unpleasant sounds.

Near disgust

The team then asked Spanish volunteers to try to suppress their responses to grima. Participants who were instructed to think “if I hear grima-eliciting sounds, I will ignore it” rated grima sounds as less unpleasant, but their ratings for disgust-inducing sounds did not change. This suggests grima is not a reflex reaction, but an emotional experience that can be influenced by thought, and is distinct from disgust.

Together, the results suggest grima is similar to disgust, but differs in terms of its triggers and the physiological response – even in people who don’t have a name for it in their language.

But although grima is most often associated with sounds, some participants said grima was triggered by the feel of certain objects – as foam rubber does for Schweiger. Some were objects associated with loud noises, but others were objects that don’t make noise, such as cork, velvet or sponges.

Sounding rough

Why fingernails on a blackboard stimulates such a strong aversive reaction is a mystery. A previous study, which earned an Ig Nobel Prize in 2006, found that frequencies in the middle of the audio range were the most irritating, and these frequencies are very similar to the warning cries of chimpanzees. Those researchers speculated that our reactions to these sounds have their roots in predator-fleeing instincts from our evolutionary past.

The frequency range in question, 2000-5000 Hz, is the range in which the ear canal resonates, making the sound transmit very efficiently. “It hits a range of frequency where your ear is particularly sensitive, and therefore you would expect a stronger response,” says Trevor Cox, an acoustic engineer at the University of Salford.

A brain imaging study in 2012 found that sounds in this range activate the amygdala, a part of the brain involved in fearful responses, which in turn heightens activity in the auditory cortex.

Another characteristic of sounds that trigger grima is their roughness, says Cox. “When you scrape your fingernails down a blackboard, you have this roughness caused by fingernails catching on the blackboard. It’s a bit like how a violin bow works.” When we scream, our vocal cords vibrate in an uncontrolled manner that creates the same effect.

Journal reference: Frontiers in Psychology, DOI: 10.3389/fpsyg.2017.00131

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