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The anchoring effect in lightness perception in humans


The anchoring effect in lightness perception in humans Alexander D. Logvinenko School of Psychology, Queen s University of Belfast Neuroscience Letters 334(2002) – PowerPoint PPT presentation

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Title: The anchoring effect in lightness perception in humans

The anchoring effect in lightness perception in
  • Alexander D. Logvinenko
  • School of Psychology, Queens University of
  • Neuroscience Letters 334(2002)

  • Introduction
  • Lightness and brightness
  • Munsell color system
  • Anchoring effect
  • Conclusion

  • Introduction
  • Lightness and brightness
  • Munsell color system
  • Anchoring effect
  • Conclusion

  • Simultaneous lightness contrast is a classical
    visual illusion, which has been the focus of
    research for several generations of visual
  • Simultaneous lightness contrast is not
    specifically a lightness illusion,
  • yet it is a particular case of a
  • more general phenomenon
  • known as the anchoring effect.

  • Introduction
  • Lightness and brightness
  • Munsell color system
  • Anchoring effect
  • Conclusion

Lightness and brightness
  • Ref. form Alan L. Gilchrist, Current Biology,
    2007 Apr 17Volume 17, Issue 8, Pages R267-R269
  • Lightnessthe perceptual dimension that runs from
    black, through gray, to white.
  • Reflection of the surface
  • White--about 90 of the light
  • Black--about 3 of the light
  • Lightness is perceived reflectance.

Lightness and brightness
  • Low-level theories stemming largely from Ewald
    Heringknown, relatively simple, peripheral
    neural mechanisms, such as lateral inhibition and
    spatial filtering.
  • These theories, of which there are many, are very
    concrete and consistent with the received wisdom
    of sensory physiology.
  • Failureto predict what humans actually perceive
    when viewing typical scenes from our everyday
  • Scenes that contain multiple depth planes or
    projected illumination boundaries(such as the
    edge of a shadow)

Lightness and brightness
  • High-level theoriesthe perceptual process as a
    thought-like process
  • Helmholtz through an unconscious process of
    inference let us taking into account the level of
    illumination in different parts of the scene.
  • The computerage spawned more modern high- level
    theories which argue that reflectance can be
    recovered by decomposing the retinal image into
    those physical properties, like reflectance and
    illumination, that became entangled in the
    formation of the image.

Lightness and brightness
  • Not found support in the empirical data.
  • High- level theories resonate with our visual
    experience of surfaces, especially in complex
    scenes, but are criticized as abstract and
    physiologically implausible.

Lightness and brightness
  • Mid-level theories are more sophisticated than
    the low-level theories, yet more concrete than
    the high- level theories.
  • using simple properties of the image, like fuzzy
    boundaries or depth edges, to parse the image
    into separate frameworks of illumination and then
    apply a simple computation, using a different
    standard of white within each framework.

Lightness and brightness
  • Brightness is the perceptual dimension that runs
    from dim to bright.
  • Luminance--the absolute intensity of light
    reflected in the direction of the observers eye
    by a surface
  • Brightness is perceived luminance.

Lightness and brightness
  • The reflectance of an object is a relatively
    permanent property, whereas its luminance is
  • Lightness concerns the objective side of visual
    experience while brightness concerns the
    subjective side.
  • When we track a golf ball in flight we attend to
    the path of the ball, ignoring that the image of
    the ball remains stationary in our field of view.

Lightness and brightness
  • The special visual attitude, typically adopted by
    an artist painting a scene, is known as the
    proximal mode of perception.
  • Brightness perception then, falls within this
  • Brightness is our experience of the raw energy
    emanating from a surface, and the impact of that
    raw energy on our sensorysystem.

Lightness and brightness
  • That energy includes the combined effects of the
    surface reflectance and the intensity with which
    it is lit.
  • A white surface appears brighter than a gray
    surface in the same illumination, but a sunlit
    white surface also appears brighter than a
    shadowed white surface.

Lightness and brightness
  • All the properties of the world that we perceive
    through vision size, motion and reflectance
    come to the eye via light.
  • Prior to the computer revolution the distinction
    between energy and information was less clear,
    and the term brightness was used to refer to both
    lightness and brightness, without distinction.

Lightness and brightness
  • There are more theories of brightness than of
  • Brightness theorists make the tacit assumption
    that lightness is based on brightness.

  • Introduction
  • Lightness and brightness
  • Munsell color system
  • Anchoring effect
  • Conclusion

Munsell color system
  • Professor Munsell first started work on the
    system in 1898 and published it in full form in
    Color Notation in 1905.
  • Some deficiencies as a physical representation of
    the theoretical system were improved
    significantly in the 1929 Munsell Book of Color
    and through an extensive series of experiments
    carried out by the Optical Society of America in
    the 1940s resulting in the notations (sample
    definitions) for the modern Munsell Book of
  • Because of this basis in human visual perception,
    Munsells system has outlasted its contemporary
    color models, and though it has been superseded
    by models such as CIE Lab and CIECAM02, it is
    still in wide use today.

Munsell color system
  • HueRed, Yellow, Green, Blue, and Purple, along
    with 5 intermediate hues halfway between adjacent
    principal hues. Each of these 10 steps is then
    broken into 10 sub-steps, so that 100 hues are
    given integer values.

Munsell color system
  • Value(lightness )from black (value 0) at the
    bottom, to white (value 10) at the top
  • N0(??)?N1?N2...N10(??),N?Neutral???,???????
  • Chromameasured radially from the center of each
    slice, represents the purity of a color, with
    lower chroma being less pure.
  • ?0(???)??,??????????,??5R???14??,?5BG??6??,???
    ???????????,????? /1?/2????
  • ????? ??/?? Hue Value/Chroma H V/C

Munsell color system
  • ??? 10YR???????????

  • Introduction
  • Lightness and brightness
  • Munsell color system
  • Anchoring effect
  • Conclusion

Anchoring effect
  • Munsell 31-point neutral scale
  • The difference (0.5 Munsell units) was
    statistically significant (Wilcoxon signed-rank
    test, P , 0001).
  • Wilcoxon signed-rank test?????????

Anchoring effect
  • an even larger difference (0.75 Munsell unit)
    between the perceived lightness of the diamonds
    and squares lying on the main diagonal

Anchoring effect
Anchoring effect
  • The illusion is even stronger (1.25 Munsell
    units) than in the previous figures.

Anchoring effect
  • While we cannot point out any sensory factors,
    which could possibly make the diamonds lightness
    change in the presence of another grey patch,
    there is a remarkable resemblance between this
    lightness shift and another famous visual

Anchoring effect
  • The presence of a particular stimulus arbitrarily
    selected as an anchor affects the shape of the
    psychophysical scale, namely, it becomes steeper
    in the neighbourhood of the anchor. In lightness
    perception, the anchoring effect is produced by
    the background on which the patches to be scaled
    are presented.

Anchoring effect
  • First, the anchoring effect in Figs. 24 is
    caused by relatively small anchors (squares off
    the main diagonal in Figs. 2 and 3 and hoops in
    Fig. 4) rather than the background.
  • Second, there is no common border thus no local
    luminance contrast between the anchors and the
  • In this theory anchoring is a hypothetical
    process converting luminance into lightness.

Anchoring effect
  • The anchoring effect observed in Figs. 24 is an
    effect (not a process), which is experienced as a
    lightness shift induced by introducing a patch
    called an anchor.
  • When presented alone the diamonds median
    lightness was found to be 5.75 Munsell units.
    Introducing the lighter anchor (Fig. 2a) shifts
    the diamond lightness towards the darker end of
    the lightness scale by one small Munsell step
    (0.25). At the same time, the darker anchor (Fig.
    2b) shifts the lightness of the same diamond
    towards the lighter end of the lightness scale by
    two small Munsell steps (0.50).

  • Introduction
  • Lightness and brightness
  • Munsell color system
  • Anchoring effect
  • Conclusion

  • The anchoring effect observed in forward figures
    is an error of judgement that probably takes
    place at the decision-making rather than the
    sensory level.
  • A satisfactory explanation of this effect is to
    be sought within the broader context of
    psychophysical scaling rather than lightness
    perception per se.
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