What rules are used to group objects?

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What rules are used to group objects?

• Definitions (Feature Lists)
• Family Resemblance
• Similarity to Prototypes
• Exemplar models

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Definitions and Features

• Dogs are animals that have four legs, have fur,
  bark, wag their tails

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Family Resemblance

• Ludwig Wittgenstein (1953) proposed that games
  could not be defined or categorized by features.
• Rather, any game shares some resemblance to some
  (but not all) other games.

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Similarity to Prototypes

• Rosch (1978). Prototype is a central, average,
  representation (real or constructed) of a
  category.
• Tokens sufficiently similar to the prototype are
  considered members of that category.
• Memory for specific exemplars.

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Exemplar Models

• To remember a category, just remember all the
  members of the category.
• Head-filling-up problem.
• Evidence for abstractions.

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Perception

• Top-down
• Or
• Bottom-up?

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The problem of perception

• How does our perceptual system arrive at a best
  representation of the world?
• Conflicting demands
• Accuracy
• Efficiency

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Data-driven processing(bottom-up)
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• Standard (naïve) assumption is that perception is
  entirely data-driven
• Why is this naïve?
• Perception must be accomplished in sub-optimal
  conditions
• Need for speed
• Need for computational efficiency
• But also need for accuracy!
• A common solution Best guess

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Concealed and bi-stable figures Evidence for a
role of knowledge in perception
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Application of knowledge changes the way
concealed and bi-stable figures are perceived

• Changes conscious processing (interpretation,
  object recognition)
• Changes unconscious processes (patterns of eye
  movements)

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Application of Knowledge

• Can be automatic
• Either innately, or once learned
• Can also be controlled

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Rabbit/Duck
Jastrow (1900)
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Impossible Trident
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Illusions Obligatory application of knowledge
in contradiction to available data.
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Application of knowledge is obligatory in these
illusions
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Sources of Illusions

• Illusions arise because our perceptual system is
  structured to act as if certain assumptions about
  the world are true.
• We can construct situations in which those
  assumptions appear to be true, but in fact are
  not. These situations are called illusions.

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Sources of Illusions

• Knowledge of visual cues to distance
• The Müller Lyer Illusion
• Filling in missing information
• Object occlusion
• Using context
• Circles of relative size
• Text tricks
• Shades of white
• Circularity in pitch perception

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The Müller-Lyer Illusion

• Which vertical line is longer?
• Neither! They are the same length!

Müller-Lyer (1889)
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Explanation

• We need to be able to adjust our knowledge of an
  objects size based on our perception of how far
  away from us it is.
• The arms of the arrows make the vertical lines
  look like the edges of corners one pointing
  toward us, one pointing away.
• That makes it appear as if the vertex of the
  corner (the vertical line) is a different
  distance from us in each figure.

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What triangle?
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Explanation

• Most things in the world do not have abrupt,
  regular discontinuities.
• It makes more sense to assume that the black
  spots are circles rather than Pac Men.
• It also makes sense, then, to assume that the 3
  bites are caused by the same object which lies
  in front of the circles.
• Makes sense means is more likely to be a
  correct representation of the world.

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Contextual cues
Which of the two middle circles is smaller?
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Is this a letter or a number?
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Circularity in pitch perception
PC/.wav
Mac/AIFF
Waterfall (M. C. Escher)
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Bibliography

• Sheperd, R. N. (1964). Circularity in judgements
  of relative pitch. Journal of the Acoustical
  Society of America, 36, 2346-2353.
• Rosch, E. (1978). Principles of categorization.
  In Rosch, E. Lloyd, B. (Eds.) Cognition and
  Categorization. Hillsdale, NJ, Lawrence Erlbaum
  Associates.
• Wittgenstein, L. (1953). Philosophical
  Investigations. New York, Macmillan.
• Note The illusions used in this demonstration
  come from various sources. When the original
  source is identifiable, it is given above.
  Otherwise, as much information as possible is
  provided to identify the illusions original
  author. Many illusions are so widely distributed
  that they appear to be in the public domain. The
  following texts and other sources are
  recommended
• Deutsch, D. (1975). Musical Illusions.
  Scientific American, 233(4), 92-104.
• Ernst, B. (1976). The Magic Mirror of M. C.
  Escher. New York, Ballantine.
• Ernst, B. (1992). Optical Illusions. Trans. K.
  Williams. Originally published as Het
  Begoochelde Oog. Taschen Verlag.
• Held, R. (1974). Image, Object, and Illusion
  Readings from Scientific American. Scientific
  American, Inc.
• Houtsma, A. J. M., Rossing, T. D., Wagenaars, W.
  M. (1987). Auditory Demonstrations (CD).
  Eindhoven, The Netherlands, Institute for
  Perception Research (IPO) and the Acoustical
  Society of America (ASA).