Play with your Blind Spot

03 Mar

These illustrations and accompanying explanations are reproduced from the book Phantoms in the Brain by V.S. Ramachandran to act as an addendum to my review of the book.

Blind Spot Demonstrations


Figure 5.2 Blind spot demonstration. Shut your rißht eye and look at the black dot on the right with your left eye. From about one and a half feet away, move the book slowly toward you. At a critical distance the circular hatched disk on the left will fall entirely on your blind spot and disappear completely. If you move the screen closer still, the disk will reappear. You may need to “hunt” for the blind spot by moving your head to and fro several times until the disk disappears. Notice that when the disk disappears you don’t see a dark void or hole in its place. The region is seen as being covered with the same light gray color as the background. This phenomenon is loosely referred to as “filling in.”


Figure: A vertical black line running through the blind spot. Repeat the procedure described for Figure 5.2. Shut your right eye, look at the small black dot on the right with your left eye and move the page to and fro until the hatched square on the left falls on your blind spot and disappears. Does the vertical line look continuous, or does it have a gap in the middle? There is a lot of variation from person to person, but most people “complete” the line. If the illusion doesn’t work for you, try aiming your blind spot at a single black−white edge (such as the edge of a black book on a white background) and you will see it complete.


Figure: The upper half of the line is white and the lower half black. Does your brain complete the vertical line in spite of this internally contradictory evidence.


Figure: Repeat the experiment, “aiming” your blind spot at a pattern that resembles a swastikaan ancient Indo−European peace symbol. The lines are deliberately misaligned, one on either side of the blind spot. Many people find that when the central hatched disk disappears, the two vertical lines get “lined up” and become collinear, whereas the two horizontal lines are not lined upthere is a slight bend or kink in the middle.


Figure: Move the screen toward you until the hatched disk falls on the blind spot. Does the corner of the square get completed’? The answer is that most people see the corner “missing” or “smudged”; it does not get filled in. This simple demonstration shows that filling in is not based on guesswork; it is not a high−level cognitive process.


Figure: Amazingly, when the blind spot is aimed at the center of a bicycle wheel, no gap is seen. People usually report that the spokes converge toward a vortex.

Referenced from  Phantoms in the Brain by V.S. Ramachandran.

All rights belong to the publisher and author.

1 Comment

Posted by on March 3, 2012 in Book Reviews, Books, Creative


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One response to “Play with your Blind Spot

"Stranger, if you passing meet me and desire to speak to me, why should you not speak to me? And why should I not speak to you?" - Walt Whitman

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