[sazr (OP)]

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

[syhprum]

If I want to find something say a bunch of keys I delve into my memory and imagine what a bunch of keys looks like and then start hunting.
With any luck my eyes will pick up a similar image from the missing keys rather like a computer recognising a password and I will be able to retrieve them, does this work this way for everyone or is it just a matter of old age .?

[alancalverd]

It is always easier to see something if you know what you are looking for, even if you can't describe it and it's a bit variable. That is what, for instance, distinguishes radiologists from ordinary humans: a huge store of both normal variant and abnormal images.   

[evan_au]

Is most of human vision processing performed in a linear step-by-step fashion in the brain or is it concurrent?

It is both serial and parallel (concurrent).

Even within the retina, the processing is serial (through multiple layers of cells) and parallel (different areas of the retina process light in their region of the retina concurrently).

The image processing power in the retina alone exceeds the power of many computer vision systems.

This is even before images reach the brain. The brain has parallel paths for processing vision, producing both conscious vision, and unconscious analysis of images from the eyes.
https://en.wikipedia.org/wiki/Retina