When Emanuel cracks his knuckle right in the president’s ear, part of what makes that annoying is that Emanuel is trying to be annoying. “The intentionality behind a sound will also have a dramatic impact,” Huron says. The intent of the noisemaker seems to add or subtract to a noise’s annoyance level. Huron calls this a “cognitive overlay.” It’s the part of the signal analysis that goes beyond “What is this?” and into “How does this make you feel?”
“Why would Rahm want to annoy me? What’s wrong with Rahm that he feels the need to do this in public? Why would I select a chief of staff who feels the need to try to subvert me? Why do I feel subverted by knuckle cracking?” Those types of cognitive overlays might have amplified the president’s annoyance.
These swirls of thoughts can transform a neutral sound—a barely audible pop—into an unpleasant one.
Fingernails on a chalkboard seem to work without any cognitive overlays. Why does this sound get an instantly negative response from most people? Like retching, fingernails on a chalkboard may remind us of something bad; we’re simply not conscious of it.
“The automatic, almost visceral reaction to this sound makes us wonder whether it mimics some naturally occurring, innately aversive event,” Blake and his colleagues wrote. The researchers went to the library and thumbed through books filled with pictures of frequency analyses of sounds to see whether any looked like the pictures that Blake generated of the scraping sound. “One that jumped out to us was primate warning cries,” Blake says.
Specifically, the garden tool being scraped across slate looked a lot like the cries that some species of monkeys make to signal a predator.
Blake wondered—although he and his colleagues couldn’t prove it—whether the widespread aversive reaction to fingernails on a chalkboard is evolutionary, a holdover from the days when a primate screech meant serious trouble. “Regardless of this auditory event’s original functional significance, the human brain obviously still registers a strong vestigial response to this chilling sound,” the researchers concluded.
How did the research community react to the suggestion that the sound of fingernails on a chalkboard activates an evolutionarily encoded primal fear? “They largely ignored it,” Blake says. Yet it caught some people’s attention. In 2006, two decades after being published, the paper received its due.{16} Blake and his coauthors were awarded an Ig Nobel Prize, honoring science’s strangest discoveries.
Making a credible observation is easier than proving why something is the way it is. Knowing why requires mountains of data, replicated by study after study. This is how hypotheses grow into theories. Who knows if our reaction to fingernails on a chalkboard has anything to do with primate warning calls or ear preservation or neither? There haven’t been that many investigations into this mystery, but the question hasn’t died out, either.
Cotton-top tamarins (Saguinus oedipus) are strange-looking primates. The tamarin has a flat face (imagine a pug-monkey cross) and a fan of white hair sticking out of its head. Tamarins are small, weighing only a pound or so on average. They walk on all fours and hail from the Amazon. And they don’t listen to music. That was key for Josh McDermott’s study. Now a neuroscientist at New York University, McDermott studies music. He’s broadly interested in why we like certain types of music: Is there a biological component? Do monkeys show the same preferences?
“Of course, with a monkey you can’t just ask them whether they like something,” McDermott says. “You have to come up with another method to measure that.” The solution was a maze. While he was at Harvard, McDermott and his colleagues built a V-shaped wooden frame with two branches. A speaker was placed at the end of each branch. The monkey is free to run around. When the tamarin is in the left branch of the maze, the left speaker plays one sound. When the monkey moves over to the right branch, the left speaker turns off and the right speaker turns on with a different sound. “The idea was that the animal controlled what it heard by virtue of its position in this maze,” McDermott says. No food treats were given. The only reward was a change in sound.
The point of McDermott’s study was to ask whether monkeys show a preference for consonant chords over dissonant chords. Consonance is derived from the Latin com, “with,” and sonare, “to sound,” and is often described as having a stable feeling; dissonance, the opposite. In Western music, dissonant chords signal pain, grief, and conflict. Think of it like this: most dance music is consonant and most blues songs mildly dissonant. Early Beatles, mostly consonant. Late Beatles, more dissonant. Heavy metal is probably the most dissonant music you’ve ever heard.
One side of the maze piped out two-note consonant chords: an octave, “c” and “c”; a fifth, “c” and “g”, for example; a fourth, “c” and “f.” The other side played dissonant chords—minor seconds, tritones, and minor ninths. The monkeys showed no preferences between consonant and dissonant chords. Harvard undergrads, on the other hand, showed a clear preference for consonant sounds.
Even though the purpose of the experiment was to learn about music, McDermott was also curious whether tamarins would show a preference against the sound of fingernails on a chalkboard. He played the sound of fingernails on one branch and white noise from the other branch.
The cotton-top tamarins showed no significant preference for the white noise versus the scraping. They did, however, when given a volume option, choose to spend more time on the side of the maze with lower-volume white noise compared with higher-volume white noise.
This finding tempers Blake’s primate warning call theory. The tamarins didn’t seem to dislike the fingernail sound—meaning, at least, that these primates didn’t show a preference against it. McDermott offers another explanation for why we don’t like the sound of fingernails on a chalkboard. It’s rough on the ears. Roughness—remember from the buzzing fly or abrupt English elocution—is a technical term in acoustics that has to do with the amount of volume, or amplitude, modulation per second.
If you were to watch fingernails or garden tools running down slate with a high-speed camera, says David Huron, you would understand. “Your fingernail is grabbing the surface and then as you continue to move your hand down, it’s stuck to the board, and then all of a sudden it will slip and jump to the next position.” It’s called, Huron says, a “stick-slip sound production.” This produces a highly unpredictable, varied sound. “You get periods where it almost sounds like a whistle. And then there are periods where it becomes very rough—and those are the ones that tend to make people cringe the most,” says Josh McDermott.
Guitar players know roughness as beating. When you tune a guitar, you typically fret a string on its fifth fret and play the next string down. When the two notes are slightly out of tune, you hear the volume go up and down—kind of like wowuuuwowuuu. Those are the individual peaks and valleys in the waveform. The beating slows as the pitches approach each other and stops when the two pitches are perfectly in synch. “People don’t usually call that rough,” McDermott says. “Those are just beats.” As the pitches move farther apart, the beat frequency increases, and the sound will start to sound rough. When the notes are more than 20 Hz apart in frequency, McDermott says, you can’t hear the wowuuuwowuuu, and that’s roughness. Then when the beating goes up to 75 to 100 Hz, the roughness goes away—it’s too fast to resolve as rough.