Hearing is Believing?

Our auditory systems have played a vital role in the survival and evolution of our species. Hearing helps situate us within our immediate environment by detecting motion, recognizing voices and sensing threats. Hearing functions as both a compass and radar, endlessly informing us of the nature of our surroundings and our position within them. Without it, our ancestors would have been promptly gobbled up by unheard carnivores.

We owe our existence to a long chain of descendants who endlessly whispered in the language of the day—what hell was THAT?

But make no mistake: hearing lies to you. And you do fall for it.

Our brains can be easily fooled by audio illusions. Distinct from auditory hallucinations, which are perceived sounds that do not exist, these illusions occur when our brains misread or find nonexistent patterns within audio cues that we do receive.

One such illusion is the “Shepard tone” — a computer generated sound that appears to perpetually descend in pitch without actually doing so. It is comprised of a looped series of overlapping tones which are separated by octaves. The Shepard tone makes the listener think that they are hearing the pitch drop lower and lower, while it in fact it is a small, repeating, overlapped loop that "goes" nowhere. Much as an old-fashioned barber’s pole projects downward motion without actually moving, the Shepard tone fools the brain into perceiving an extended “motion pattern” that isn’t really there.

Holophonic and binaural recordings present another method of deceiving our hearing through technological trickery.  Did you ever wonder how you can tell when a sound is coming from above? Think about it: you only have two auditory receptors, one on each side of your head. Determining the horizontal (x-axis) directionality of sound is simple enough — the balance of which ear detects the sound more determines which side of you a sound is coming from, and the volume of the sound within that ear suggests the distance or strength of the sound. Done. Simple. But, since the holes to your ear are horizontal, how do we determine the vertical (y-axis) directionality?

The answer lies in the subtleties of the tone of the sound you hear. The inside of our ears and ear canals have unique folds that reflect sound waves toward the ear drum with slightly different tones, depending on the angle of origin (including up and down). Also, the ear drum detects vibrations that reverberate through our skull and sinus cavities; this is why our voices sound deeper to us than they do to answering machines.

Binaural recording techniques utilize a “dummy head” microphone setup — a realistically weighted mannequin head containing a fake skull (complete with sinus cavities) and several microphones — to capture a sufficiently detailed audio image to fool the listener’s ear. Knowledge of the illusion does not prevent it from occurring. Directionality is imposed on the listener’s mind.

[Use headphones – effect does NOT occur without them!]

Finally, there’s the “McGurk Effect” – a consequence of clashing audio and visual input. While we use all of our senses to situate ourselves in our environment, our sense of sight dominates our perceptions. If the brain receives audio and visual input that is slightly incongruent, it will tend to neglect the former and let the listener “hear what they see.” As demonstrated in the clip below, if the sound of a man saying “ba ba ba” is mixed with video of him saying “fa fa fa,” the brain will interpret the latter as real and hear accordingly.

It's not eay being a brain, constantly scrambling amidst bustling sea of sensory input while coordinating all signals simultaneously. No wonder it gets fooled every now and then. We shouldn't blame our hearing for its fallibility, since it is such a demanding and complex sense. Like everything else, they're part of an unimaginably complex system burdened with the task of

MAKENIG OREDR OUT OF CHOAS BY F1NDNIG PAETTRNS AND CO-ODRINTAING SESNES



Comments

[Scott Kennel]

Wow, every time the person shaking the matchbox walks in front of me, I feel compelled to watch him pass. Very weird feeling.