Sound of fingernails scraping chalkboard
Encyclopedia
Scraping a chalkboard
with the fingernails produces a sound which most people find unpleasant. The basis of this innate reaction has been studied in the field of psychoacoustics
.
. However, a study using Cottontop Tamarin
s, a New World Monkey
, found that they react similarly to both high-pitched sounds similar to fingernails on chalkboard, and to amplitude-matched white noise
. In contrast, humans are less averse to the white noise than to scraping.
This technique was used to good effect in the Pink Panther Movie of 1976, the Pink Panther Strikes Again.
A 1986 study used a tape-recording of a three-pronged garden tool similar to a fork
being "grided" across a chalkboard, which roughly reproduces the sound of fingernails on chalkboard. The recording was then manipulated, removing pitches at the extremities and the median. The results were then played back. It was determined that the median pitches are in fact the primary cause of the adverse reaction, not the highest pitches as previously thought. The authors hypothesized that it was due to predation early in human evolution; the sound bore some resemblances to the alarm call of macaque monkeys, or it may have been similar to the call of some predator. This research won one of the authors, Randolph Blake, an Ig Nobel Prize
in 2006. More recent research contradicts this hypothesis.
due to the shape of the human ear canal which amplifies certain frequencies
, especially those in the range of 2000 to 4000 Hz (the median pitches mentioned above), at such a level that the sound would trigger pain in our ears.
Chalkboard
A chalkboard or blackboard is a reusable writing surface on which text or drawings are made with sticks of calcium sulfate or calcium carbonate, known, when used for this purpose, as chalk. Chalkboards were originally made of smooth, thin sheets of black or dark grey slate stone...
with the fingernails produces a sound which most people find unpleasant. The basis of this innate reaction has been studied in the field of psychoacoustics
Psychoacoustics
Psychoacoustics is the scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound...
.
The primate heritage hypothesis
One explanation for the adverse reaction is that the sound is similar to the warning call of a primatePrimate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
. However, a study using Cottontop Tamarin
Cottontop Tamarin
The cotton-top tamarin , also known as the Pinché tamarin, is a small New World monkey weighing less than 1 lb...
s, a New World Monkey
New World monkey
New World monkeys are the five families of primates that are found in Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Platyrrhini parvorder and the Ceboidea superfamily, which are essentially synonymous since...
, found that they react similarly to both high-pitched sounds similar to fingernails on chalkboard, and to amplitude-matched white noise
White noise
White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
. In contrast, humans are less averse to the white noise than to scraping.
This technique was used to good effect in the Pink Panther Movie of 1976, the Pink Panther Strikes Again.
A 1986 study used a tape-recording of a three-pronged garden tool similar to a fork
Garden fork
A garden fork, spading fork, digging fork or graip is a gardening implement, with a handle and several short, sturdy tines. It is used for loosening, lifting and turning over soil in gardening and farming...
being "grided" across a chalkboard, which roughly reproduces the sound of fingernails on chalkboard. The recording was then manipulated, removing pitches at the extremities and the median. The results were then played back. It was determined that the median pitches are in fact the primary cause of the adverse reaction, not the highest pitches as previously thought. The authors hypothesized that it was due to predation early in human evolution; the sound bore some resemblances to the alarm call of macaque monkeys, or it may have been similar to the call of some predator. This research won one of the authors, Randolph Blake, an Ig Nobel Prize
Ig Nobel Prize
The Ig Nobel Prizes are an American parody of the Nobel Prizes and are given each year in early October for ten unusual or trivial achievements in scientific research. The stated aim of the prizes is to "first make people laugh, and then make them think"...
in 2006. More recent research contradicts this hypothesis.
The physical hypothesis
A recent study by musicologists Michael Oehler and Christoph Reuter has lead its authors to hypothesize that the unpleasantness of the sound is caused by acoustic resonanceAcoustic resonance
Acoustic resonance is the tendency of an acoustic system to absorb more energy when it is forced or driven at a frequency that matches one of its own natural frequencies of vibration than it does at other frequencies....
due to the shape of the human ear canal which amplifies certain frequencies
Equal-loudness contour
An equal-loudness contour is a measure of sound pressure , over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones. The unit of measurement for loudness levels is the phon, and is arrived at by reference to equal-loudness contours...
, especially those in the range of 2000 to 4000 Hz (the median pitches mentioned above), at such a level that the sound would trigger pain in our ears.