WHITES EFFECT

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WHITES EFFECT
in Brightness color

• Stuart Anstis
• Dept of Psychology
• UCSD

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• From a conference at York University, 2003,
  honouring
• MARTIN REGAN

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Unpublished photos of Martin Regan
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Simultaneous contrast
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Whites Effect
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Theories of Whites effect
Level Low Low High High

• Assimilation or contrast ?
• Geometry T-junctions, elongated RFs
• Belongingness
• Transparency

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Theories of Whites effect
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Geometrical theories of Whites effect
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Belongingness theory of Whites effect

• Benary 1924

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Transparency theory(Bart Anderson 1997)
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Theories of Whites effect
Level Low Low High High
x
x

• Assimilation or contrast ?
• Geometry T-junctions, elongated RFs
• Belongingness
• Transparency

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Results

• Whites effect
• increases with spatial frequency
• can generalise to colour

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Whites effect increases with spatial frequency
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Colored Whites effect

• (All grays in the next four slides are the same)

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All annuli are the same gray
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Colored Whites effect Why does grey test patch
look yellow-green? Contrast (negative induced
hues) or assimilation (positive induced hues) ?

• Use non-complementary colored stripes
• End-wise contrast from embedding magenta stripes
  (to minus-magenta green)?
• Or
• Assimilation (to orange) from flanking orange
  stripes?

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Whites effect increases with spatial frequency,
for black/white and also for color.
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• Colored Whites effect increases with spatial
  frequency

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Ratio of assimilation to contrast increases with
spatial frequency
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Conclusion from coloured Whites effect

• At low spatial frequencies
• Contrast Assimilation
• At high spatial frequencies
• Assimilation Contrast
• ( big overall effect)
• So Assimilation has smaller spatial range!

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Why geometrical theories are WRONG

• Stuarts Rings in next slide are isotropic --
  no bars or T-junctions -- yet give brightness
  illusions like Whites Effect.

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Stuarts Rings

• 3 rings in each column are the same grey

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Stuarts Rings stronger (larger vertical gap)
for dark rings
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Theories of Whites effect
Level Low Low High High
x
x

• Assimilation or contrast ?
• Geometry T-junctions, elongated RFs
• Belongingness
• Transparency

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Conclusions

• Assimilation AND contrast
• NOT geometry T-junctions, elongated RFs
• Whites effect precedes motion perception

6 CogMovie
thank you sanstis_at_ucsd.edu www-psy.ucsd.edu/san
stis
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the end
To be published in Visual Processing of Spatial
Form (Conference Proceedings), Ed. Michael
Jenkin Laurence Harris