Assuming you're human (which isn't reported in blogger.com stats), you'll clearly see that the line in the top figure is slightly longer than the line in the bottom figure.
But wait! What's this?
Tricked you! Except, I didn't trick you - your brain tricked you.
Optical illusions like this are a lot of fun. They can do my head in. But then, thinking about visual perception in general can do my head in.
How does vision work again? Easy, you remember the uni textbooks. Light hits cells in the retina, the retinal cells then send the signal to the primary visual cortex for processing, then....
Wrong! We're now clever enough to know that the processing of the pattern of visual stimuli is something which starts as soon as a photon hits a rod or cone, since the complex but orderly distribution of those cells across the retina has been genetically programmed. And there's more information processing by other cells in the retina, and then more at the first 'relay station', the lateral geniculate nucleus in the thalamus. And then on to more processing in the primary visual cortex, which then packages things up and sends it all on to the other visual cortices, and something out of all this is sent on to the brain's motor control area, and its consciousness/executive area, and whoever else is in the group email.
That sure is a lot of processing.
But actually. We're now clever enough to know that this model, of a signal proceeding along a set path, and being processed at each stop along the way, doesn't quite capture what's really going on. Since many nerve fibres from all over the rest of the brain terminate at each point of the visual pathway. These meddlers and micromanagers themselves influence how the visual signal is processed at each point. Starting at that first relay station, the LGN. And these meddling nerve fibres come in similar numbers to those of the visual pathway itself. So, visual perception is more like mutual, continuous, simultaneous, information processing in all directions, if this model is to be believed.
This really is getting out of hand. Who decided that vision has to be this complicated?
Evolution decided. Or however you prefer to frame that - the need for organisms to survive and procreate decided it. Or, engineering 'design principles' decided it. The selfish gene decided it. Any which way, what matters is that the system works. It works in terms of having produced a tool which helped humans survive and procreate.
It helped achieve that by turning patterns of photon energy quanta into perception. The perception of a straight or curved border, where one object ends and another begins. The perception of movement (the just-perceptible and unexpected movement of a lurking predator). The perception of colour (the pastel hues of edible fruits and veges). Etc.
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"What's your point, blog dude?? If I wanted a slice of Neuroscience Lite, I would have, well, opened the current issue of any major medical or psychology journal!"
Fair call. My point is that the cliché that 'Each person sees the world in their own individual way' is true, more fundamentally than metaphorically. And just like that, we've jumped from Hard Neuroscience into subjective experience - ewwww!
No, don't be like that. People fool themselves that early neurodevelopment and its disorders can be understood without worrying about subjective experience. But they can't be.
This is especially relevant in autism. The life stories of some autistic people are amazing for how difficult life was for them and their family, at a very young age, compared to the success and happiness they achieve in adulthood. This sometimes happens 'before your eyes' in paediatric practice, a kid who looks very autistic at 2yo might barely at all, 5 or 10 years later (I mean even without intensive therapies of any sort, in some instances).
This doesn't happen in other situations, like intellectual disability. If a very young kid is found to have an IQ of, say, 50, and if it's an accurate measurement, then one can look 20+ years ahead, and (sadly) predict a lot, at least what sort of work or role in society is very unlikely for them.
The difference for some autistic people is their subjective experience of how their body works, and of what happens around them, and to them. They might have a brain which works very well, with that native intelligence underpinning their success in later life. But that's little help to them at a very young age, if as soon as they walk into a new kindergarten, their conscious mind is assaulted by a cacophony of sights and sounds, including those from unfamiliar people, with each of these percepts experienced as a visceral threat to them.
In that situation, the kid's future-blooming native intelligence isn't much material help.
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Random additional points:
Francis Crick was a pretty annoying guy. Crick, as in 'Crick and Watson', as in discovered the structure of the genetic code. Nah I'm being silly, I only mean annoying in envy, as one of those people who seem to achieve more in their life than is temperate or considerate.
Having discovered DNA, he felt that emerging neuroscience sounded like a bit of a lark. He teamed up with a younger neuroscientist who has also made big important contributions, Christof Koch.
In 1995 they published a paper titled "Are we aware of neural activity in the primary visual cortex?" Yes that primary visual cortex I talked about earlier in this post, please pay attention, this will be on the examination!
Are we aware of neural activity in the primary visual cortex? Their short answer was - probably not.
But it's the primary visual cortex! What sort of cortical area does it call itself, if its activity doesn't even reach the conscious mind? Has it no shame??
In a 2016 paper, Koch and his mates addressed this question again. The question is "the subject of ongoing debate". Awesome.
So, that's what 20+ years of neuroscience gets you. Turns out the brain really is pretty complicated.
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Hang on. I opened this post by saying that I didn't trick you, your brain tricked you.
But what does that even mean? Does it mean that your brain's sitting there, waiting for its chance to deceive you, to deceive your mind? Like a guide dog leading its blind master into the deluxe pet food store, instead of Aldi?
It means nothing, it's nonsense. The brain isn't something neatly separate to the mind. It can't play, well, mind games, with its own mind. There's no little mini-woman or mini-man sitting somewhere in your cranium, sifting through your brain's discharges and sending a sensible synopsis to your mind.
But trying to avoid describing things this way can be tricky. It's a natural habit to do so, in The Contemporary Sociocultural Context.
These days I try to consciously (irony alert!) restrict my use of the word 'brain' to mean 'unconscious mind' in some situations; and not more loosely than that. I admit, this approach doesn't make sense either - the brain is just as much a part of conscious experience as it is a stable of 'zombie agents'. But it seems a useful shorthand, which people generally understand.
There you go! You thought you'd get through this post without having to trudge through any philosophy of mind.
Tricked you.
Further reading:
Mitchell KJ, "Innate: How the Wiring of Our Brains Shapes Who We Are" (2018) Princeton University Press; Chapter 7.
Varela FJ et al., "The Embodied Mind: Cognitive Science and Human Experience" (1991) MIT Press; Chapter 8.
Related papers:
Crick F and Koch C, "Are we aware of neural activity in the primary visual cortex?" (1995) 375 Nature 121.
Koch C et al., "Neural correlates of consciousness: progress and problems" (2016) 17 Nature Reviews Neuroscience 307.
