Seeing Red and Green: The McCollough Effect

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Seeing Red and Green The McCollough Effect
Mary Portillo Psychology 351Rice University
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After Effects

• Occur in all modalities
• Most last only seconds
• An exception The McCollough Effect - an
  orientation-contingent color aftereffect.
• Source McCollough, Celeste (1965). Color
  adaptation of edge-detectors in the human visual
  system. Science, 149, 9, 11151116.

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Test Image 1
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Test Image 2
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Test Image 4 Reduce size
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Test Image 2 again
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What is going on withthe McCollough Effect?

• Its like a regular color aftereffect, except
• Its contingent on retinal edge orientation (i.e.
  depends on the pairing of the vertical lines with
  the green color and the horizontal lines with the
  red color but it can be induced with different
  stimuli)
• It does not depend on precise fixation (while
  adapting you can move your eyes away from the
  center of the slide and still get the effect)
• Normally doesnt transfer between eyes
• It lasts a long time (recall that regular
  afterimages last only a minute or less)

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Simple Color Aftereffects
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Is the effect still there?
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Perceptual reorganization reverse figure/ground
The McCollough effect depends on perceptual
organization. Remember that the diagonal lines
are not really there, if the test slide is seen
as boxes inside each other (with no depth),
instead of a diamond on top of another diamond,
the effect will disappear. Look again at the
test slide and try to see the figure as nested
boxes rather than as one diamond on top of
another.
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Explaining the McCollough Effect

• Opponent processes
• Subsystems pitted against one another in dynamic
  equilibrium (such as opposed muscle pairs)
• Fatiguing half of an opponent pair yields
  aftereffects (rising arm effect)
• Double opponent cells
• How do we perceive millions colors from 3 cones?
• Transform 3D information into a 2D plane with
  luminance held constant (the cie plane). The
  most saturated colors are on the periphery of the
  plane and the least saturated are in the center
• Blue-Yellow and Red-Cyan axes define opponent
  colors and Afterimages

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Double Opponent Process Cells
Receptive fields of cortical cells that show
center-surround organization and color opponency
in both the center and the surround.
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Explaining the McCollough Effect

• Functional Theory (Dodwell and Humphrey, 1990)
• Why pair color with orientation?
• An adaptation system with statistical properties
  finds a neutral point (i.e. we define light vs
  dark by computing the mid point between the
  lightest and darkest signal)
• Changes occur very slowly because of all the data
  accumulated over time
• In the real world there is no correlation between
  edge and color
• A strong discrepancy (a signal that correlates
  vertical with green, for example) will create a
  new neutral point

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• More reading
• Source McCollough, Celeste (1965). Color
  adaptation of edge-detectors in the human visual
  system. Science, 149, 9, 11151116.
• Sacks, Oliver (1997) Island of the Colorblind
  and Cycad Island
• Palmer, Steve (1999). Vision Science.
• Dodwell, Peter, Humphrey, G. Keith (1990). A
  functional theory of the McCollough effect.
  Psychological Review, 97, 1, 78-89.