Mind Hacks™: Tips & Tools for Using Your Brain by Tom Stafford, Matt Webb Page B

for detecting light is behind the fibers
     for carrying the information into the brain. That’s right — the light-sensitive part is on
     the side furthest from the light. Not only does this seem like bad design, but also it
     means that there has to be a gap in surface of the retina where thefibers gather together to exit the eyeball and run to the brain — and that exit
     point is the blind spot.
    Figure 2-7. Matt’s blind spot mapped
    At first sight, there doesn’t appear to be any particular reason for this structure
     other than accident. It doesn’t have to be this way. If the light-detecting parts of the
     cells were toward the light, you wouldn’t need a blind spot; the fibers could exit the eye
     without interrupting a continuous surface of photoreceptors on the retina.
    Can we be sure that this is a bug and not a feature? One bit of evidence is that in
     the octopus eye it was done differently. The eye evolved independently in octopuses, and
     when it did, the retinal cells have the photoreceptors in front of the nerve fibers, not
     behind, and hence no blind spot.
    ----
    Note
    Conversely, there are benefits to the arrangement of the human retina: it
     allows a good blood supply close to the retina to both nourish the photoreceptors and
     help metabolize debris that accumulates there. Both orientations of the retina have
     their advantages.
    ----
    We don’t normally notice these two great big holes in our field of vision. Not only do
     our eyes move around so that there’s no one bit of visual space we’re ignoring, but the
     blind spots from the two eyes don’t overlap, so we can use information from one eye to
     fill in the missing information from the other.
    However, even in situations in which the other eye isn’t providing useful information
     and when your blind spot is staying in the same place, the brain has evolved mechanisms to
     fill in the hole. 1 This filling in is why, in the demostration above, you see a continuous
     grey background rather than a black hole.
    Hacking the Hack
    The Cheshire Cat experiment ( http://www.exploratorium.edu/snacks/cheshire_cat/ ; full instructions) shows a really good interaction of the blind spot, the
     filling-in mechanisms and our innate disposition to notice movement competing against our
     innate disposition to pay attention to faces. With a blank wall, a mirror, and a friend,
     you can use your blind spot to give yourself the illusion that you can slowly erase your
     friend’s head until just her smile remains.
    End Note
    “Seeing More Than Your Eye Does” ( http://serendip.brynmawr.edu/bb/blindspot1.html ) is a fun tour through the capabilities of your blind spot (the link at
     the bottom of each page’s article will lead you to the next page). It demonstrates how
     your brain uses colors and patterns in the area surrounding the blind spot to make a
     good guess of what should be in the blind spot itself and will report that to your
     conscious mind.
    See Also
    Ramachandran, V. S. “Blind Spots.” Scientific American , May
     1992, 86–91.
Ramachandran, V. S., & Gregory, R. L. (1991). Perceptual filling in of
     artificially induced scotomas in human vision. Nature, 350 ,
     699–702.
There is an interesting discussion of the blind spot, filling in, and what
     that implies for the nature of experience in Daniel Dennett’s Consciousness
     Explained , 344–366. Boston: Little, Brown and Co., 1991.
    Glimpse the Gaps in Your Vision
    Our eyes constantly dart around in extremely quick movements called saccades. During
     each movement, vision cuts out.
    Despite the fact that the eye has a blind spot, an uneven distribution of color
     perception, and can make out maximal detail in only a tiny area at the center of vision, we
     still manage to see the world as an uninterrupted panorama. The eye jumps about from point
     to point, snapshotting high-resolution views, and the brain assembles them into a stunningly
     stable and remarkably detailed