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Lessons

3h - Reflex Vision

Posted by Helen St Clair Tracy in Level 3 - Introduction to the Visual Brain
Published: 07/03/2019, 12:09am | Updated: 15/03/2019, 6:16am

Video Link: https://vimeo.com/323531139

It is easy to think that everything we see is all about creating a picture - but the information that goes through the eyes does more than create a picture.

In addition to the process of creating the visual world (as introduced in the preceding lessons in this section), separately, in a different part of the brain called the thalamus, which is deep in the centre of the brain, another process may be taking place.

Vision is also separately processed in the thalamusVision is also separately processed in the thalamus

Where there is a fast movement from the side, there is a process, in the thalamus, that creates a very fast reaction, a reflex. It is faster than you can consciously process what you are looking at, and is automatic. This visual reflex is called blindsight.

Blindsight is a reflex, that may make you:

  • Blink
  • Duck
  • Brace yourself
  • Jump out of the way
  • Brake (if cycling or driving)

Because something is moving fast towards you, and your brain has calculated that there may be a threat, and is automatically protecting you, before you can consciously protect yourself. How clever is that?

But there's more...

In addition to this simple reflex, some people have been able to create useful visual images from moving information. In some cases where brain damage has meant the part of the brain that creates the picture (V1, the Primary Visual Cortex, see lesson 3b) no longer works, so they should not be able to see anything, people can see movement and describe it with remarkable accuracy, down to the detail of single raindrops.

This visual reflex is called Riddoch Syndrome, where people who cannot create a picture of what they are looking at due to occipital lobe injury, can still see detail where there is movement. With practice, people have learnt to read visually using movement alone to create the image. It is thought there is a link between the thalamus and MT/V5 (see lesson 3e) to create these images.

But there's more...

Profoundly disabled children who are visually completely unresponsive, can return smiles they cannot see! They cannot see the smile in the way a smile is pictured, but amazingly, it is thought that certain key facial expressions are so important to recognise, that the brain comes pre-wired to recognise them, when seen, not through the usual process of creating a picture that is recognised as a smiling face, but skipping that, and going straight to another automatic reflex. This is called affective blindsight.

But there's more...

We hear reports of the most remarkable things brain's do to reorganise themselves, where there is damage, particularly in children, to create order as best they can. Brains finding ways to do things they shouldn't be able to do - blind brains that can see. We will look more closely at individual case studies in future lessons.

We mention these visual reflexes, and the many different ways the brain can reorganise itself, because vision is not simply the process of creating a picture with colour, acuity, movement, depth and visual attention.

Where vision is altered, by developmental damage, injury or disease to the brain, we have come across many examples of people using these reflexes in extraordinary ways.

Checklist:

Before you move onto the next lesson, please check:

  • You understand the difference between reflex vision and the visual picture your brain creates that you are consciously aware of.
  • You understand the difference between blindsight, Riddoch Syndrome & affective blindsight.

Next lesson: Level 3i An Introduction to the Visual Brain - Visual Recognition

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At CVI Scotland we are devoted to helping people understand cerebral visual impairments, and together working towards developing the understanding of this complex condition.