Mind Hacks™: Tips & Tools for Using Your Brain (24 page)

Why we perceive pitch at all is a story in itself. Pitch exists for sounds because our
brains calculate it, and to do that, they must have a reason.

An illusion called the missing fundamental demonstrates the construction of sounds in
the ear. The fundamental and then harmonics of a tone are successively removed, but the
pitch of the tone sounds the same. Play the sound file at
http://en.wikipedia.org/wiki/Missing_fundamental
, and you’ll hear a series of bleeps. Even though the lower harmonics are
vanishing, you don’t hear the sound get higher. It remains at the same pitch.
³

The way pitch is computed from tones with multiple harmonics can be used to construct
an illusion in which the pitch of a tone appears to rise continuously, getting higher and
higher without ever dropping. You can listen to the continuously rising tone illusion and
see a graphical illustration of how the sound is constructed at
http://www.kyushu-id.ac.jp/~ynhome/ENG/Demo/2nd/05.html#20
.

Each tone is made up of multiple tones at different harmonics. The harmonics shift up
in frequency with each successive tone. Because there are multiple harmonics, evenly
spaced, they can keep shifting up, with the very highest disappearing as they reach the
top of the frequency range covered by the tones and with new harmonics appearing at the
lowest frequencies. Because each shift seems like a step up on a normal scale, your brain
gives you an experience of a continuously rising tone. This is reinforced because the
highest and lowest components of each tone are quieter, blurring the exact frequency
boundaries of the whole sound.
⁴

The ear isn’t just for hearing; it helps you keep your balance.

It’s a good thing the system detects only acceleration, not absolute motion, otherwise
we might be able to tell that we are moving at 70,000 mph through space round the sun. Or,
worse, have direct experience of relativity — then things would get really confusing.

— T.S.

You can try and use this blind spot for motion next time you’re on a train.
Close your eyes and focus on the rocking of the train side to side. Although you can feel
the change in motion side to side, without visual information — and if your train isn’t
slowing down or speeding up — you don’t have any information except memory to tell you in
which direction you are traveling. Imagine the world outside moving in a different way.
See if you can hallucinate for a second that you are traveling very rapidly in the
opposite direction. Obviously this works best with a smooth train, so readers in Japan
will have more luck.

Any change in our velocity causes the fluid in the channels of the vestibular system
to move, bending hair cells that line the surface of the channels (these hair cells work
the same as the hair cells that detect sound waves in the cochlea, except they detect
distortion in fluid, not air). Signals are then sent along the vestibular nerve into the
brain where they are used to adjust our balance and warn of changes in motion.

Dizziness can result from dysfunction of the vestibular system or from a disparity
between visual information and the information from the vestibular system. So in motion
sickness, you feel motion but see a constant visual world (the inside of the car or of the
ship). In vertigo, you don’t feel motion but you see the visual world move a lot more than
it should — because of parallax, a small movement of your head creates a large shift in the
difference between your feet and what you see next to them. (Vertigo is more complex than
just a mismatch between vestibular and visual detection of motion, but this is part of the
story.)

This is why, if you think you might get dizzy, it helps to fix on a moving point if
you are moving but your visual world is not (such as the horizon if you are on a ship).
But if you are staying still and your visual world is moving, the best thing to do is not
to look (such as during vertigo or during a motion sickness–inducing film).

Can you sort the signal from the noise? Patterns and regularity are often
deeply hidden, but we’re surprisingly adept at finding them.

A sample of Bing Crosby’s “White Christmas” has been hidden in the sound file on our
book web site (
http://www.mindhacks.com/book/48/whitechristmas.mp3
; MP3
). The sound file is 30 seconds long and is mostly noise, so you will
have to listen carefully to detect when the song starts. The song will start either in the
first, second, or third 10 seconds and will be very faint, so pay close attention.

If you managed to hear the strains of Bing Crosby in the noisy background of the sound
file, you may be in for a surprise. The sound file is pure noise, and despite what we
promised earlier, “White Christmas” is not hidden in there at all (if you read ahead
without trying it out for yourself, try it out on someone else). Not everyone is likely to
detect meaningful sounds in the background noise, but it’s been shown to work on a certain
subset of the population. An experiment conducted by Merckelbach and van de Ven
¹
reported that almost a third of students reported hearing “White Christmas”
when played a similar noisy sound track.

There’s been a lot of debate about why this might happen and what sort of attributes
might be associated with the tendency to detect meaning in random patterns. In the study
mentioned earlier, the authors found that this ability was particularly linked to measures
of fantasy proneness — a measure of richness and frequency of imagination and fantasy — and
hallucination proneness — a measure of vividness of imagery and unusual perceptual
experiences. If you, or someone you tested, heard “White Christmas” amid the noise and are
now worried, there’s no need to be. The tendencies measured by Merckelbach and van de
Ven’s study were very mild and certainly not a
marker of anything abnormal (after all, it worked in a third of people!), and
we all hallucinate to some degree (not seeing the eye’s blind spot
[
Map Your Blind Spot
]
is a kind of
hallucination).

However, there is evidence that people who believe in certain paranormal phenomena may
be more likely to find patterns in unstructured information. Brugger and colleagues
²
found that people who believe in ESP are more likely to detect meaningful
information in random dot patterns than people who do not. Skeptics are often tempted to
argue that this sort of experiment
disproves
ESP and the like, but
the other finding reported in the same study was that meaningful patterns were more likely
to be detected if the random dot pattern was presented to the left visual field,
regardless of the participant’s belief in ESP. The left visual field crosses over to
connect to the right side of the brain, meaning that random patterns presented to be
preferentially processed by the right hemisphere, seem to be more “meaningful” than those
presented either to both or to the left hemisphere alone. This demonstrates another aspect
of hemispheric asymmetry
[
Use Your Right Brain — and Your Left, Too
]
but also hints that
people who have high levels of paranormal beliefs may be more likely to show greater
activation in their right hemisphere than their left, an effect that has been backed up by
many further studies.

This pattern of hemispheric activation is linked to more than paranormal beliefs.
Researchers have argued that it may be linked to a cognitive style that promotes “loose”
associations between concepts and semantic information, a style people have if they often
see connections between ideas that others do not. This is not necessarily a bad thing, as
this tendency has been linked to creativity and lateral thinking. Detecting patterns where
other people do not may be a very useful skill at times. Although it may result in the
occasional false positive, it almost certainly allows genuine patterns to be perceived
when other people would be confused by background perceptual noise.

— Vaughan Bell