Psyc 351: Psychology of Perception Week 8 Overview of Perceptual Organization

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Psyc 351 Psychology of PerceptionWeek 8
Overview of Perceptual Organization

• Adapted from lectures given at
• BISCA, 2001 Bolzano, Italy

James R. Pomerantz Department of Psychology Rice
University
Houston, Texas, USA
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Perceptual Organization in the 1930s Karl
Dallenbachs photograph
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Perceptual Organization in the 1970s R. C.
Jamess Photograph
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Perceptual Organization in the 2000s Bev
Doolittles Painting
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Key Issues Raised byDallenbachs Cow

• Where are the objects in the image? Where does
  one object stop and the next one start?
  
• Which edges represent illumination changes and
  which reflectance changes?
  
• What are the objects?
• What is the role of knowledge, top-down
  processing in segmentation and identification?

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What Is Perceptual Organization?

• the processes by which the bits and pieces of
  visual information that are available in the
  retinal image are structured into the larger
  units of perceived objects and their
  interrelations
• Stephen E. Palmer, Vision Science, 1999

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What Is Perceptual Organization?

• Perceptual Organization is central to the key
  question of perception how do we make the leap
  from information detected by our sensory
  receptors to our perceptions of the world?
  This requires not just the detection of
  information but the organization of that
  information into veridical percepts.
• Pomerantz Kubovy, 1986

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What Is Perceptual Organization?

• Perceptual organization is the process by which
  particular relationships among potentially
  separate elements (including parts, features, and
  dimensions) are perceived (selected from
  alternative relationships) and guide the
  interpretation of those elements in sum, how we
  process sensory information in context.
• Pomerantz Kubovy, 1986

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Why Study Perceptual Organization?

• It is arguably among the earliest steps in
  perception
  
• It is an essential tep, solving basic questions
  that must be resolved before further image
  analysis takes place

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Note The Problem of PO Extends Beyond Images of
Animals!
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There Are Many, Many Others
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More Classic Examples of Perceptual Organization
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More Classic Examples of Perceptual Organization
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More Classic Examples of Perceptual Organization
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More Classic Examples of Perceptual Organization
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More Classic Examples of Perceptual Organization
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More Classic Examples of Perceptual Organization
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Component Issues in Perceptual Organization

• Grouping and segmentation Dalmatian, Laws of
  Grouping, Part Whole relations
  
• Figure ground segregation Rubins Vase
  Doolittles ponies
  
• Emergent Features Subjective Contours,
  Configural Superiority Effects
  
• Perceptual coupling (constancies) Shepards
  Boxtops, Ames Room
  
• Multistability Necker cube Barber Pole
• Globality, Simplicity

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Grouping and Segmentation
From Wertheimer, 1923
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Lower illustration from Koffka
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Grouping of Separated Elements
We can perceive objects well despite interruptions
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Segmentation Edges
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Figure Ground Segregation
From Rubin
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Rubins Figure Brought to Life
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From Kanizsa
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From Escher
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From Bregman
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From Rock
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Emergent Features
From Wertheimer, 1912 Phi (or beta) apparent
motion, plus the Correspondence problem from
Grouping
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From Kanizsa
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From Coren,Ward, and Enns, Sensation Perception.
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Two Veteran Emergent FeaturesRevealed through
Configural Superiority Effects
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Slide 37
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Important ControlConfigural Inferiority Effects
Pomerantz, Sager, Stoever, 1977
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Slide 38
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Virtual lines and edges
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Perceptual Coupling
From Shepard, 1981 Two two yellow parallelograms
have identical shapes.
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The Ames Room
Note Kubovy and others dont always regard coupl
ing
as a Gestalt problem
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Multistability
From Necker, Kopferman
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From Ternus Phenomenal Identity,
or, the Matching Unit problem
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More Ternus
Short ISI (0 msec)
Long ISI (200 msec?)
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From Boring
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From Wallach Wallachs overlooked variation po
lka dots
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Pointing Triangles In which direction do they
point? cf. control buttons on a cd player, etc
.
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From Attneave
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From Palmer
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Globality

• Configural effects work over large expanses of
  the visual field, not just local patches
  
• Eg color. We achieve color constancies by
  comparing wavelength distributions across the
  entire visual field.
  
• E.g. the aperture problem in motion.

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Simplicity Prägnanz (the minimum principle)

• At the heart of the Gestalt approach.
• Claim We organize our percepts in the simplest
  way that is consistent with the information in
  the stimulus.
  
• Cf. distribution of electromagnetic fields.

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Soap Bubble Metaphor
The soap bubble computes an answer to a complex
problem, finding the simplest solution possible.
Question Does the human perceptual system work
in a similar fashion?
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PO and the Gestalt Psychologists

• Max Wertheimer
• Kurt Koffka
• Wolfgang Kohler
• They identified the basic problem, in some
  respects in its current terms, and uncovered many
  of its phenomena.
  
• They attempted a theory as well, but it has has
  less impact.

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The Key to Gestalt EffectsNon-Additivity

• Stimulus A activates Representation A
• Stimulus B activates Representation B
• Q Will Stimuli A B activate
• Representations A B
• Something additional beyond this
• Something less than this
• Something simply different from this?

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Non-Additivities in Perception

• Widely Heralded Slogan of Gestalt Psychology
• The whole is greater than the sum of its parts?
  No.
  
• No, not the sum
• Summing is a meaningless procedure
• Koffka,
  1935

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Non-Additivities in Perception

• Rather,
• The whole is different from the sum of its
  parts
  
• Sometime greater than, sometimes less than, often
  different from
  
• Better to say the Gestalt claim was that elements
  interact non-linearly in perception.

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Examples of Non-Additivities

• All involve the emergence of new features
• Color
• Apparent Motion
• Orientation
• Subjective Contours

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Orientation Glass Patterns
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Orientation Glass Patterns
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Orientation Glass Patterns
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Apparent Motion
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Apparent Motion
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Apparent Motion
Distinguish pure Phi motion from beta motion
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More Apparent Motion
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Apparent Motion of Holes
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Dunckers Rolling Wheel
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Dunckers Rolling Wheel
Rolling wheel demo (download requires Flash plu
g-in)
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Kanizsas Subjective Contours
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Shadow Fonts

• a b c

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Slide 69
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Combine Subjective Contours with Apparent Motion
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Combine Subjective Contours with Apparent Motion
Reversed direction of apparent
motion in the bottom panel compared with the top
indicates non-additivitity and suggests the domi
nance of subjective contours in deciding what
is moving. Bottom panel from Ramachandran
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This time, use dots
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This time, use dots
Even here with stimuli formed from discrete eleme
nts, it is possible to see reversed direction of
apparent motion in bottom panel compared with
top.
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Blocks forming continuous line
This display also shows reversed motion in the b
ottom panel, indicating that subjective contours
are not critical for producing this
non-additivity.
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Gestalt Psychology in 2001?

• Perceptual organization has languished in
  relative obscurity since the end of the Gestalt
  era In the latter half of the 1900s, vision
  scientists have generally ignored organizational
  issues, as though such things as grouping,
  part-whole relations, reference frames did not
  really matter, secure in their belief that linear
  systems analysis and single cell recording
  studies of cortical area V1 would lay bare the
  mysteries of perception The next frontier of
  vision science will be to solve the problems of
  perceptual organization and its effects on visual
  processing.

Stephen Palmer, in press
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On the Other Hand
Some of the researchers publishing on PO since
1950 Hochberg, Rock, Kanizsa, Treisman, Attneave
, Garner, Spelke, Palmer, Kubovy, Gerbino,
Shepard, Biederman, Metzger, Leeuwenberg,
Metelli, Graham, Julesz, Kahneman, Miller,
Neisser, Shepard, Wolfe. Reads like a Whos Who
in Psychology.
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Why is PO Such a Hard Problem?

• Perceptual organization is difficult to
  study because it lies on the border between our
  experience of the world and unconscious
  perceptual processing. Even the term perceptual
  organization is ambiguous it means both the
  outcome of perceptual processeshow things
  lookand the mechanism that produces itthe
  psychophysical processes that precede awareness.
  Perceptual organization is difficult to study for
  a second reason because it Involves both
  bottom-up and top-down processes. It islike
  respirationa semi-voluntary process Michael
  Kubovy, in press.

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Grappling with Basic Concepts

• Example What is an object?

object is not an easy term to define. Indeed,
textbooks with chapters on object perception
generally just assume that we all know what is
being talked about.
Jeremy Wolfe
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Barriers to Understanding Perception

• The problem of subjective experience
• Complexity of the stimulus, confounds
• Transparency of perception The main barrier may
  be our own perceptual system!

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The Proximal Stimulus
What object does this figure depict?
How many objects are shown? Where are the object
boundaries?
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A Simpler Example
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The Answer Revealed
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Another example
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Slide 84
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Organizing a Stimulus Is Work!

• Looking at the last figure, it seems obvious that
  there are figures there, and clear how many there
  are and in what arrangement
  
• None of this is given for free, however it must
  be computed by the visual system.
  
• The belief that the organization is in the
  stimulus and not computed is a fundamental error,
  one of two the experience error and the stimulus
  error.

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Paradox of PO

• Everybody knows what it is, yet nobody seems to
  know what it is
  
• Its effects are robust and seemingly obvious
• Yet difficult to measure Palmer, Kubovy
• Complicating matters two errors we make.

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The Stimulus and Experience Errors

• In psychology we have often been warned
  against the stimulus error, i.e., against the
  danger of confusing our knowledge of the physical
  conditions of sensory experience with this
  experience as such. As I see it, another
  mistake, which I propose to call the experience
  error, is just as unfortunate. This error occurs
  when certain characteristics of sensory
  experience are inadvertently attributed to the
  mosaic of stimuli (Kohler 1929/47, p. 95).

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The Stimulus Error

• A presumption of what the stimulus is.
• We know that a physical object is built out of
  certain parts, so when we describe our
  perception, we use those same parts.
  
• Or, we enter a room lit with one candle,
  illuminate a second candle, and report that the
  room is now twice as bright.
  
• Striking counterexample the Gelb Effect, where
  knowledge has little effect on perception.

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The Experience Error

• A presumption that our perception is governed by
  the stimulus array.
  
• We experience a percept that is organized, e.g.,
  is segmented into regions, objects, and parts.
  So we assume that this organization is available
  in the proximal (retinal) image, rather than
  having to be computed on the image by our visual
  system.

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An Example of These Errors?

• This stimulus is described as a box with a line
  drawn across it, both containing a gap. Do we
  see it that way? If so, is it because we
  constructed it that way? And are these the real
  physical parts?
• (From Duncan, 1984)

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An Example of These Errors?

• Recall that this is a better description of the
  proximal stimulus? Are the parts directly
  represented here? Does this array support the
  notion of a box and a line with gaps?

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Another Example?

• Steve Palmer, Element Connectedness

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The Link Between Perceptual Organization
Representation?

• The key issues are
• What in the stimulus is represented?
• How to represent elements in and out of context?
• PO defines the fundamental units and establishes
  the hierarchy in which they are later organized.
  The representation of a stimulus defines its
  organization.

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Example Multistability

• Any one stimulus can have multiple
  representations
  
• Each of these may respond to a different
  organization
  
• Thus, representation and organization issues are
  fundamentally intertwined.

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Roadmap to the Phenomena, Methods, and Findings
of PO

• Phenomena Grouping, figure-ground segregation,
  multistability, constancies
  
• Methods demonstration vs. behavioral measures
• Findings Many examples, but based organizational
  phenomena appear to govern how the rest of
  perception functions.

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Theories of Perceptual Organization

• Lists of Laws
• General summarizing principles
• Full Blown Theories (Marrs categories)
• Computational
• Cognitive Neuropsychological

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Laws of Grouping
There are many, many
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Helson, 1933

• Listed 114 Gestalt Laws!
• Others estimate that over 700 have been proposed
  over the decades.
  
• Boring, 1942 narrowed them down to 14.

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Borings 14

• Naturalness of form
• Figure and ground
• Articulation
• Good and poor forms
• Strong and weak forms
• Open and closed forms
• Dynamic basis of form

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Borings 14, continued

• Persistence of form
• Constancy of form
• Symmetry of form
• Integration of similars and adjacents
• Meaningfulness of forms
• Fusion of forms
• Transposition of forms.

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Borings 14, continued

• Note that Borings list of 14 omits some
  important principles, including
  
• Good continuation
• Area
• Convexity
• Common fate
• One-sided function of contour

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Vagueness of These Laws
Number 5 Strong Weak Forms A strong form cohe
res and resists disintegration by analysis into
parts of by fusion with another form.
Many of these laws are a bit vague
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General Principle of Grouping

• Similarity
• Proximity similar location
• Common fate similar motion
• Similarity is too broad a term to be useful?

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General Principle of Grouping
Prägnanz (global minimum principle) return of
the soap bubbles Dynamic self-distribution if t
he kind of function which Gestalt Psychology
believes to be essential in neurological and
psychological theory.
Köhler, 1929
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Definition of Prägnanz
Psychological organization will always be as
good as the prevailing conditions allow. In
this definition the term good is undefined. It
embraces such properties as regularity, symmetry,
simplicity and others Koffka, 1935, building o
n Wertheimer
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Issues Entailed in Prägnanz

• Nature of simplification
• How much distortion to allow (illusions, etc.) at
  the expense of veridicality?
  
• Simplify the process of perception or the
  outcome?
  
• Quantification How to Measure Simplicity?
• Work of Attneave, Garner, Leeuwenberg, Mumford
• How to test the claim?
• Do our perceptions minimize complexity?
• Is this plausible given evolution?

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Alternative to Prägnanz Likelihood Principle

• From Helmholtz, 1910
• Definition Sensory elements will be organized
  into the most probable objects or event (distal
  stimulus) in the environment consistent with the
  sensory data (the proximal stimulus)

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Major Advocates of Likelihood Principle

• Helmholtz
• Hebb
• Hochberg
• Gregory
• Brunswik
• Rock

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Key Issues for Likelihood Principle

• Major Idea We organize our percepts in the way
  that is most likely to be correct
  
• Evolutionarily plausible
• Question how to determine whats most likely
  (Brunwick, Geisler, Palmer)?
  
• How to test?

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Challenges to Prägnanz

• Kanizsa many devastating counterexamples

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Challenges to Prägnanz

• Attneave, Rock the search for symmetry
• If symmetry is so important, why is our search
  for it so brief and unsuccessful?

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Challenges to Likelihood

• Impossible Figures

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Prägnanz or Likelihood?
The evidence favoring the prägnanz principle is
somewhat thin the Gestalt explanations of
Gestalt phenomena are often inadequate, vague, or
simply wrong. The law of symmetry, which can be
regarded as the keystone of prägnanz , lacks the
kind of clean and robust demonstration one should
expect of so preeminent a principle The
Helmholtzean approach, with a few exceptions, has
provided a more promising framework. Most
Gestalt laws can be regarded as indicators of
what distal stimulus is most likely to have given
rise to the proximal stimulus.
Pomerantz Kubovy, 1986
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Could a Prägnanz Bias Be Useful?

• Attneave, 1982 Likelihood Principle can
  accommodate Prägnanz
  
• Simplicity is a diagnostic property of stimuli
• If a stimulus can be organized simply, that is
  probably the correct organization
  
• (Cf. Symmetry, parallelism as a non-accidental
  property).

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Attneaves Point

• A possible distal source that contains certain
  regularities is more probable than one that does
  not, or one that contains them to a lesser
  degree.
• His idea was subsequently echoed by Rock,
  Pomerantz Kubovy, and Palmer
  
• Palmer Simplicity acts as a surrogate for
  likelihood, since simple organizations are likely
  to be correct.

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Mach, 1906

• The visual sense acts therefore in conformity
  with the principle of economy, and, at the same
  time, in conformity with the principle of
  probability.

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Where the Field Is Headed

• Away from lists of principles
• Toward an analysis of specific mechanism, studied
  both behaviorally and with techniques from
  cognitive neuroscience
  
• Toward general models integrating processes
  across levels (Biederman, Palmer)

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