How do we see (and other sensory perception)?

[saor]

With regards to how we see:

The eye receives the reflected red light and sends a message to the brain.

The image captured by our retina is then transduced (or electrochemically decoded) by bipolar cells, also located at the retina. Ganglion cells then act as afferent nerves that send visual sensory information to the brain.

I'm always flummoxed by the 'sent as a signal to the brain' part of the explanation. What is the process by which visual stimuli (or any other sensory perception) is encoded and transmitted...and how does the brain use that information to re-create our own picture of reality?

I'm ok with the idea that we don't have direct access to reality, that the brain creates our view of reality from the signals received from our sense organs. The part I struggle with is how the sense organ turns the sensory input into a signal, the nature of that signal (how is it encoded?) and how the brain uses the 'data' in that signal to paint our mental picture of reality. It seems like such a complicated process, but yet most explanations usually seem to gloss over the actual data-stream.

Would appreciate some insight / further reading on the matter.

 

[BandwidthAddict]

I don't think anyone knows the exact mechanism of sight. The brain is a very dense and complex electro-chemical neural net and we don't have the technology to track both the exact chemical signals in time with the electrical signals. What is done is to use a special die with functional magnetic resonance imaging which provides a low resolution map of the brain as it processes information. Once imaging technology gets enough resolution to track in real time the chemical and electrical signals, then the brain can be understood rather than just guessed.

 

[RiaX]

simply put. Photons stimulate the cells in the retina viz cones and rods. They then send an impulse via the optic nerve that goes directly into the brain which processes these stimuli from each eye and builds a picture. It works on a similar principle as an LED screen.

Its encoded as electricity like everything in the body. Sight is very complex hence why about a quarter of the brain is used to process it. Now the brain doesnt build the image from scratch it uses its memory bank to create an image which you "see". This is why naturally your sight is always drawn to new objects, light or movement. The brain does not reprocess ever single detail.

This is a very simple explanation, sight is extremely complex. If you really interested then I suggest you youtube some lectures on the eye. The first world universities tend to put up their lectures on youtube

EDIT

http://www.youtube.com/watch?v=ajnsDVsP0Uk

 

[DJ...]

Well, scientists can reprogramme the brain to see light from other senses. The brain has evolved to decode the stimuli, not the other way around, so you can tap into the brain and send various signals directly to the visual cortex and perceive light in various forms. But the two processes evolved in tandem so as the light sensitive organs or in some simple species, receptors, sent signals, the brain began a process of interpretation of the data it was receiving. As the function of light perception began to become a better survival tool or benefited a species, natural selection took over and the eye as we know it began to evolve. It's still the same process effectively. Light is received and your brain decodes the information sent, as with any sensory input. We simply perceive that interpretation as vision.

With a single light receptor it's easy. Light is received, brain recognises the signal as light, and responds accordingly. Now add the plethora of receptors, proteins, cones, and other signal processors and distributors and the same principle takes place in the brain, albeit on a far larger scale. So if you can understand how simple light signals (on and off) can be received and interpreted, then you can understand the eye as we know it today. It's just a subjective interpretation of signal inputs that we perceive as vision...

 

[saor]

Its encoded as electricity like everything in the body. Sight is very complex hence why about a quarter of the brain is used to process it. Now the brain doesnt build the image from scratch it uses its memory bank to create an image which you "see". This is why naturally your sight is always drawn to new objects, light or movement. The brain does not reprocess ever single detail.

So what happens when you look at something relatively unique - like a huge 'where's wally' poster but with strange creatures and odd shapes. Or if you go to a museum and see life-size dinosaurs that you've never seen before; creatures with strange textures on their skin. I still don't quite get how all that new information gets 'encoded' as electricity. It seems like that data stream would be rather dense, in terms of how much information it contains, in order for the brain to re-create that image with such (apparent) accuracy.

Thanks for the links though - will go check 'em out. Maybe those questions are addressed .

 

[RiaX]

You need to understand when the brain interprets something it makes a memory bank.

As I said you need to look at an LED TV and you will understand how an image is built.