Optical Illusion of the Day

posted by Stal on 2009.06.26, under Stal
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The green and blue spirals are actually the same color (you can check this in Photoshop if you’re unconvinced). The reason the colors look distinct is because our brains process color based on the surrounding colors. If you look closely, the orange stripes pass through the “green” band and the magenta stripes pass through the “blue” band.

[ Discover via GeekPress ]

Illusion, Michael. Tricks are what whores do for money.

posted by Stal on 2009.05.19, under Stal
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A couple winners from the Best Visual Illusion of the Year Contest

The Break of the Curveball (requires flash):

In baseball, a curveball creates a physical effect and a perceptual puzzle. The physical effect (the curve) arises because the ball’s rotation leads to a deflection in the ball’s path. The perceptual puzzle arises because the deflection is actually gradual but is often perceived as an abrupt change in direction (the break). Our illusions suggest that the perceived “break” may be caused by the transition from the central visual system to the peripheral visual system. Like a curveball, the spinning disks in the illusions appear to abruptly change direction when an observer switches from foveal to peripheral viewing.

The Illusion of Sex:

In the Illusion of Sex, two faces are perceived as male and female. However, both faces are actually versions of the same androgynous face. One face was created by increasing the contrast of the androgynous face, while the other face was created by decreasing the contrast. The face with more contrast is perceived as female, while the face with less contrast is perceived as male. The Illusion of Sex demonstrates that contrast is an important cue for perceiving the sex of a face, with greater contrast appearing feminine, and lesser contrast appearing masculine.

Coin Flips–Fundamentally Unfair?

posted by Stal on 2009.04.16, under Stal
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Coin tosses are commonly used as a fair way to settle disputes and touted in probability classes as an example of an event with uniform probability distribution. However, it is perhaps time to reevaluate our faith in the fairness of the coin toss. I’m not talking about nicks and debris, or other after-market defects on a coin. In the study “Dynamical Bias in the Coin Toss,” Stanford mathematicians analyze coin tosses and conclude that the result is biased towards the side that you begin with.

How then, should you call coin tosses to your advantage? Some highlights of the research:

  1. If the coin is tossed and caught, it has about a 51% chance of landing on the same face it was launched. (If it starts out as heads, there’s a 51% chance it will end as heads).
  2. If the coin is spun, rather than tossed, it can have a much-larger-than-50% chance of ending with the heavier side down. Spun coins can exhibit “huge bias” (some spun coins will fall tails-up 80% of the time).
  3. If the coin is tossed and allowed to clatter to the floor, this probably adds randomness.
  4. If the coin is tossed and allowed to clatter to the floor where it spins, as will sometimes happen, the above spinning bias probably comes into play.
  5. A coin will land on its edge around 1 in 6000 throws, creating a flipistic singularity.
  6. The same initial coin-flipping conditions produce the same coin flip result. That is, there’s a certain amount of determinism to the coin flip.
  7. A more robust coin toss (more revolutions) decreases the bias.

[ via Coding the Wheel ]

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