Synaesthesia

hello folks.

I have spoken to a friend of mine who does psychology at uni and he has helped me with understanding what synaesthesia is and not to mention a couple of cool examples of what this little thing. Here is a small report of what the subject is all about.



I guess first things first, you need to know about how sound is transformed into a perception of hearing (you don't hear, you just think you do, as I'll demonstrate later with some illusions).

Sound comes in via the earholes (the outside bit focuses the sound, or at least that's the theory.) It hits the eardrum, which is as one would suspect, a sealed drum. The inside membrane of the drum is attached to one of the three bones in the ear (the hammer, stirrup and anvil- so called due to their shape). These transmit the vibration directly onto the oval window of the cochlea, which is just a hole filled by the end of the 'anvil'

The cochlear is filled with fluid and has a load of epithelial (flat cells) with hairs (cilia) attached to them. When sound waves travel through the fluid, they cause the hairs to move. This movement triggers a nerve impulse (electrical charge) to be sent down the nerve attached to the ear (the 8th cranial nerve). This nerve travels into the brain stem and then up into the brain to the primary auditory cortex.

So the pathway is

Sound-->earhole-->eardrum-->Bones (hammer, stirrup, anvil)-->Oval window-->Cochlea--> Vibrations bend hair cells-->nerve signal-->Brain stem-->primary auditory cortex

In the primary auditory cortex, the nerve signal is transformed into a perception of sound. The hair cells further into the cochlea (further away from the oval window if we were to uncurl it) are more sensitive to bassier sounds and so are triggered by these. Conversely, ones closer to the oval window are more sensitive to more trebly sounds.

This is why as we get older, we tend to be able to hear bass more than treble, as loud noises eventually degrade the ability of the cells closer to the oval window to send nerve impulses. The hairs on these cells are literally worn or blasted off.

So at this point in the game, we have a perception of sound. Other parts of the brain (secondary and tertiary visual cortices (cortice is the plural of cortex) etc) tranform this perception into a fully formed idea of what we are hearing. The brain is also able to interpret variation in the signal from each ear in order to tell where a noise is coming from.

SYNAESTHESIA- When the brain gets confused.

There is a youtube link I'll send you on facebook that goes over the brain anatomy you need to know in about ten minutes, and it's not too high falluting or anything.

Synaesthesia is a condition where the brain confuses one sense with another- i.e. seeing sound or percieveing colour with numbers. It's quite rare, but can create odd sensory perceptions. It's believed that famous Indian musician Ravi Shankar (not sure on the spelling) and Jimi Hendrix (needs no introduction) are both alleged to have this condition in a musical sense.

Now this isn't suprising- the area in the middle of the sensory cortex (back of the frontal lobe), auditory cortex (top of the temporal lobe) and visual cortex (back of the brain, the occipital lobe) is involved in combining all of our senses in order to get a better idea of what is actually going on.

Consider this example- you are walking along at night, and you hear a noise. You localise this noise to somewhere to your right, where out of the corner of your eyes you see a bush rustle. Your brain connects the two effects into a single perception. You can see a perfect example of this reliance on both senses in the McGurk effect.

The McGurk effect consists of a video of someone mouthing a syllable, along with a recording of a different syllable being pronounced simultaneously. When you listen to the noise with your eyes closed, you will hear a different syllable to when you watch the syllable being pronounced (usually ga or ba). The effect is so strong that even when you know it is going to happen, it still works.

Another cool effect is the doppler effect. You know when an ambulance runs past you and it sounds like the pitch changes? That's the doppler effect. Basically if something is moving towards you, the soundwaves are compressed (put closer together, hence the rise in pitch) and after is it is past you, the soundwaves are stretched out (causing the drop in pitch)

What is even cooler is that you can create an illusion of the doppler effect by panning from all the way left to right or visa versa whilst lowering pitch. A perfect example of this is on Pink Floyd's 1974 song from Dark Side of the Moon "On The Run". Throughout this track, odd panning effects are used, creating an often disquietening and confusing effect- see the plane crash/explosion at the end of the track for a perfect example.

for more info check out Ryan's Blog at night-worker.blogspot.com