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General Science / Re: How can light hit one part of a ganglion cell but not another part?

« on: 21/11/2019 03:20:08 »

Where do you get the quote from? I want to know the context of the statement.

On wikipedia, google receptive field:

https://en.wikipedia.org/wiki/Receptive_field#Retinal_ganglion_cells

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General Science / Does the brain play a part in Magno and Parvo channel creation

« on: 20/11/2019 21:26:18 »

Regarding human vision and the retina:

The retina model presents two outputs that benefit from the above cited behaviors.

    The first one is called the Parvocellular channel. It is mainly active in the foveal retina area (high resolution central vision with color sensitive photo-receptors), its aim is to provide accurate color vision for visual details remaining static on the retina. On the other hand objects moving on the retina projection are blurred.
    The second well known channel is the Magnocellular channel. It is mainly active in the retina peripheral vision and send signals related to change events (motion, transient events, etc.). These outing signals also help visual system to focus/center retina on 'transient'/moving areas for more detailed analysis thus improving visual scene context and object classification.

Where are these channels produced? To put it simply, is it produced in the eye or in the brain. For example; does light enter the eye, hits the retina and it applies a series of filters to produce these 2 different channels (the parvo and magno) and it outputs this information to the brain via the optic nerve? Or does light enter the eye, hits the retina and it applies a series of filters, it excites certain ganglion cells that fire, those signals are grouped and output to the brain via the optic nerve and the brain is then responsible for converting this information into 2 channels; the parvo and magno?

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General Science / How can light hit one part of a ganglion cell but not another part?

« on: 20/11/2019 21:17:19 »

In regards to human vision and specifically the retina and ganglion cells.

Each receptive field is arranged into a central disk, the "center", and a concentric ring, the "surround", each region responding oppositely to light. For example, light in the centre might increase the firing of a particular ganglion cell, whereas light in the surround would decrease the firing of that cell.

I find it hard to comprehend that somehow the light can only hit one part of the retinal ganglion cells (either the centre or the surround) and not the other? Doesn't light go everywhere? Is the lens focusing light so accurately that light is hitting certain parts of a tiny cell (the centre) but not others (the outside/surround)?

Can anyone provide more insight as to how it works that light can hit one tiny part of a tiny cell but not another part of that tiny cell?

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General Science / Center surround detection explained?

« on: 16/05/2019 01:23:20 »

A while back I asked about human vision processing and if it is performed synchronously or asynchronously. One of the responses mentioned that the retina performs 'Center Surround Detection'. So I tried to google what this is but no relevant results came up.

Is anyone able to explain what this is and how its useful or point me to a link that explains it (that is not too high level/hard to understand)?

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General Science / Re: Retina pre-processing - what does it look like?

« on: 01/05/2019 03:31:46 »

these include steps to sharpen edges and reinforce contrasts, ways to enhance or bolster colour vision under low-light conditions, ways to electrically disconnect rods from vision during high light intensity situations, surround inhibition to improve acuity, and so on.

@chris Thanks this is exactly what I am looking for. Do you know how the retina is; reinforcing contrasts, bolstering colour vision, doing surround inhibition? Ie, what the retina filter techniques/algorithms are? I want to try to emulate them in code and create my own crude retinal filter/retina processing. Maybe you can point me to literature to better understand how the retina performs these 'filters'/processing?

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General Science / Retina pre-processing - what does it look like?

« on: 24/04/2019 23:05:49 »

Do we know what sort of preprocessing the retina does? And more importantly what the output of this preprocessing would look like? I'm interested from the perspective of computer vision uses, I can copy what the retina is doing to efficiently pre-process (and remove redundant information) and perform higher up processing that the brain would do.

If anyone could describe visually what the output of retinal pre-processing would look like that would be extremely helpful. For example, would an example output look like just edges (so black wheres theres no edges and white/colour? where there are edges). I am interested in any/all eyes that have retina's not just humans.

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General Science / What sort of culling of visual information does the brain do?

« on: 14/04/2019 03:38:37 »

The brain receives alot of visual information some of which is redundant visual information. I am imagining it like the brain receiving a 1000 pixel wide by 1000 tall image of a road. The brain has received 1,000,000 bits/pixels of information. I am assuming the brain doesn't need all that information in order to detect the road in the image and localise where in the image the road is. But correct me if I am wrong here.

So the brain must be culling information? Removing irrelevant information? Doing some other efficient processing to only look at N pixels not all 1 million right? Can you inform me on what sort of things its doing here to efficiently handle all 1 million bits of information?

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Physiology & Medicine / Is human vision processing performed concurrently or in a step-by-step process?

« on: 12/04/2019 01:46:17 »

Is most of human vision processing performed in a linear step-by-step fashion in the brain or is it concurrent? Lets take for example; for the process of us recognising a pen on a table.

- Light/information enters the eye, is focused on the fovea part of the retina because we are focusing on the pen on the table. This also means that many cones are being excited and emitting a signal (plus some rods are also receiving light and emitting a response I imagine?).
- The eyes/rods/cones do some sort of compression or pooling before emitting their signals via the ganglia through the optic nerve to the visual cortex. I imagine both rods and cones do this because there are 126 million photosensitive cells and only 1 million ganglia.
- The primary visual cortex starts finding edges and other low level stuff. Does this get performed before the secondary visual cortex or concurrently?
- The secondary visual cortex begins processing for object size, colours, shapes. The ventral system is involved here. Is the dorsal system involved aswell? Does the ventral system require the processed edge information (from the primary cortex) in order to do its work? Is its processing concurrent?
- Finally the ventral system recognises that there is a pen on the table.

Are you able to correct any mistakes I have above in the visual processing pipeline? Can you point out what steps in this pipeline are performed concurrently (if any) and what are step-by-step (and what that order of operations would be)?

Any advice about this process would be extremely helpful

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Physiology & Medicine / Do Rods play a role in daytime vision?

« on: 10/04/2019 00:50:42 »

Do Rod photo-sensitive cells contribute at all to daytime vision?

If so, what exactly do they contribute? For example, they contribute towards big homogenous shapes, slow moving big objects, etc. I'm interested in whether this applies to any animal not just humans.