The blind spot

After last Friday’s jury the main topic I am interested in is the Blind Spot

I have started to research what kinds of things blind spot can mean, starting with the physiological meaning.

A blind spot, scotoma, is an obscuration of the visual field. A particular blind spot known as the physiological blind spot, “blind point”, or punctum caecum in medical literature, is the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells on the optic disc of the retina where the optic nerve passes through the optic disc.[2] Because there are no cells to detect light on the optic disc, the corresponding part of the field of vision is invisible. Some process in our brains interpolates the blind spot based on surrounding detail and information from the other eye, so we do not normally perceive the blind spot. – wikipedia

Most interestingly is that again our brain uses a mechanism to prevent us from perceiving the blind spot. Our brain fills in the spot with what it guesses is there.

zeiss-test-blindspot

Small test: close your left eye and look at the black dot with your right eye. Move closer to the screen until the blue dot disappears.

Here’s another test with which you can draw your blind spot, I’ve tried it and it’s insanely difficult, haven’t yet managed to properly do it.

image006

Helmholtz[6] gives an excellent method for drawing your own blind spot. You close one eye (say the left) and you look at a fixation point marked on a piece of paper. You localize the region of the blind spot to the right (when looking with the right eye) of the fixated point, and with a pencil, you blacken the paper over all the area for which the tip of the pencil remains invisible. As soon as the tip of the pencil comes out of the blind spot, you stop marking. By proceeding in this way, and keeping the eye completely still (this is difficult!), it is possible to draw the vertically extended patch corresponding to the blind spot, and even to begin to draw the stumps of the two blood vessels that leave the spot at the top and at the bottom. The technique is illustrated below

blindspot1 blindspot2

 


 

Another thing to alert you to something that might have been residing in your blind spot, today’s Emergency Demo to protest Donald J. Trump’s invitation to the UK

protest video

protest

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