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  • Ever since Aristotle, we've been told that we have five senses, but it's now thought we could have around 20 or more.

  • For example, the sense that tells you you're feeling hot or cold, the sense that tells you you're out of breath, and the sense of balance.

  • We don't consciously experience the raw information all these senses generate, because the brain is constantly engaged in the act of perceptionthe analysis, synthesis and interpretation of all that data.

  • Perception can utilise what's known as bottom-up processing, whereby the brain relies on analyzing sensory data.

  • But certain perceptions are produced in a different way, by top-down processinginstead of relying just on sensory data, the brain calls on past experiences to make a best guess as to what might be there.

  • In certain situations though, this type of processing results in mistakes.

  • Like thisyou're probably seeing two different colours here, but in fact there's only one.

  • Based on past experiencethat surfaces in brighter light are darker than they appear, and surfaces in shadow are lighter.

  • The brain expects that there should be two shades, and so that's what it puts into the virtual model it's creating.

  • This top-down processing accounts for a number of human perception traits.

  • We very often see faces, because we're hardwired to tune into them.

  • The fact that we're all living in our own virtual recreations of the world is revealed most sharply by cases of people with malfunctioning perception, known as agnosia.

  • It's a general term that covers many different conditions.

  • What they all have in common is that the senses are still working perfectly.

  • The brain is receiving the same information it always did, but its ability to process, interpret, and recognize is damaged.

  • Someone suffering from prosopagnosia, for example, has serious difficulty recognizing people by looking at their faces, but could still recognize them instantly from the sound of their voice.

  • In extreme cases, sufferers can't recognise their own image in a mirror.

  • A person with akinetopsia is able to perceive objects normally when they're still, but can't recognise, or make sense of anything that's moving.

  • When someone with auditory verbal agnosia hears words, they just hear meaningless noises, so they can't have a conversation.

  • But it's only the hearing of words that's affectedthey can still talk, read and write.

  • So, our ability to navigate the world is entirely dependent on the complex mechanisms, which interpret all the noise our senses make and give it meaning.

  • Or, as the famous neurologist Oliver Sacks put it: "Every act of perception is to some degree an act of creation."

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Ever since Aristotle, we've been told that we have five senses, but it's now thought we could have around 20 or more.

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    Annie Huang posted on 2020/05/26
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