Transcript Some remarks on the architecture of the visual system

Is perception continuous
with cognition?
The Cognitive Impenetrability of Vision
Read Seeing & Visualizing Chapter 2 or the BBS article on my web site:
ruccs.rutgers.edu/faculty/pylyshyn.html
The accepted answer goes along with
intellectual (and political) fashions
The zeitgeist in the second half of the 20th century was one of
populist values which emphasized egalitarianism and the
limitless possibility of the human mind. In keeping with this
spirit, many scholars mistakenly repudiated innateness and,
emphasizing plasticity, embraced learning as the defining
character of human nature.
It was in this era that the belief arose that everything we
perceived or thought was dependent on our cultural or
linguistic context. Hence the popularity of Worf and Sapir, of
Bruner’s New Look in perception as well as deconstruction
movements in European (and, of course, Californian) thought.
The cultural ethos gave strong support to the view that the
mind is highly plastic and at the mercy of the environment
Through the last half of 1900s both the general public
and the social science community assumed that
perception and cognition were continuous – that you
could not distinguish between the two.
 Bruner’s New Look in Perception: Perception modeled on Science –
hypothesis formation, verification & modification
Bruner, J. S. (1957). On perceptual readiness. Psychological
Review, 64, 123-152.
 Effect on Philosophy of Science: Feyerabend, Hanson, Kuhn (These
philosophers assumed that there is no “innocent eye” so all
observations are “theory-laden”. Quine’s “The myth of the given”)
What are some reasons for thinking that vision
is cognitively penetrable (and not modular)
 Expectation and the perception of patterns






Perception in noise of words, sentences, and probable sequences
Assimilation of perception to the norms (Postman)
Visual recognition as involving the framing hypotheses (Potter)
Perceptual learning and expertise (bird watchers, wine tasters…)
Apparent motion and “problem solving” in vision (Rock)
The effect of hints and foreknowledge on fragmented figures or
stereograms
 Neuroscience evidence for top-down effects
 The experience in computer vision (Heterarchy)
Why should we doubt the continuity thesis?
 Illusions….
 Methodological concerns (signal detection theory)
What are some reasons for thinking that vision is
cognitively penetrable (and not modular)
Expectancy and the perception of patterns
 Perception in noise of words vs nonwords, sentences, statistical
properties of sequences
 Assimilation of perception to the norms (Postman)
 Explanation in terms of framing hypotheses (Potter)
 Perceptual learning (bird watchers, wine tasters…)
 Apparent motion and “problem solving” in vision (Rock)
 The effect of hints and foreknowledge on closure figures or stereograms
● Neuroscience evidence for top-down effects
● The experience in computer vision (Heterarchy –Shirai)
● Why should we doubt the continuity thesis?
 Illusions….
 Methodological concerns (signal detection theory)
Some reasons to assume that vision is
cognitively penetrable
 Informal


Magic tricks
The proofreader’s problem
 Speech perception
 Phonetic monitoring
 Cross modal effect on hearing (listening while reading)
 Phoneme restoration effect
Most people believe that we when we read we
make predictions about the word next which is why
why we often substitute the wrong word for an
unexpected word and is also why the predictability
index (the Cloze Score) is a useful measure of
readability, widely adopted in the past by newspapers
and language teachers.
Is a mental image something that is seen
(with the mind’s eye)?
If you think that mental imagery involves (uses) visual
processes, it is important to know which aspects or
stages or visual functions it uses. If it involves
reasoning and inferences based on what is sees then it’s
not an interesting thesis since mental imagery is
assumed to be a modality of thought. In that case the
thesis turns out to be the claim that imagery shares
cortical resources with thought which nobody doubted.
If, on the other hand, visual perception is used to
interpret mental images then this is a strong thesis since
it suggests that images themselves are (or can be) seen.
Seeing Mental Images
• The central tenet of the Picture Theory of mental imagery is
that mental images constitute the same kind of spatial
representations as are found on, say, the retinal or primary
visual cortex.
• If, on the other hand, a mental image is an alreadyinterpreted form of representation, this would support the
thesis I am putting forward; that images are only
phenomenologically picture-like while in their function
(i.e., in their causal role) they are conceptual and therefore
symbolic descriptions.
• This not only makes a big difference in one’s view about
the mind but also has repercussions for the treatment of
reports of conscious experience in scientific theories.
Is vision like science itself?
• Does vision involve hypothesis formation and testing,
as was once believed to be the method used in science?

Potter and Bruner’s hypothesis testing experiment
• If the answer is YES then the question whether mental
imagery uses vision becomes circular (or empty) since
clearly vision serves thought by providing new
information.
• So the question whether there are general top-down
hypotheses-proposing or hypothesis-tendering) effects
becomes central.
Familiarity and the reconstruction
of partially hidden patterns
Familiarity and the reconstruction
of partially hidden sounds


Signal detection theory helps to isolate stages in information processing
Signal detection theory helps to isolate slages in information processing
VERNALIT
INTERVAL
TRLAVNEI
Meaning and perception of phonemes
The ‘phoneme restoration effect’
1. The
pitcher’s thoughts about the dangerous batt▒ made him nervous
2. The
soldier’s thoughts about the dangerous batt▒ made him nervous
How to get someone to see fragmented figures?
Autostereogram or Magic Eye® figures
Apparent motion is a function of
early vision, yet is subject to
various “intelligent” interpretations
In the “Ternus Configuration” short time delays result in
“single element motion” (the middle object persists as the
“same object” so it does not appear to move)
Long time delays result in “group motion” because the
middle object does not persist but is perceived as a new
object each time it reappears
But long delays, when the disappearance appears to
be due to occlusion by an opaque surface, maintain
objecthood, and therefore behave like short delays
But long delays, when the disappearance appears to
be due to occlusion by an opaque surface, maintain
objecthood, and therefore behave like short delays
Apparent “problem solving” in vision
Condition A
Time 1
Time 2
Condition B
Does the circle appear to move or are there
two circles being covered?
Does the circle appear to move or are
there two circles being covered?
Apparent “problem solving” in vision (Rock)
Condition A
Time 1
Time 2
Condition B
Another example from Irving Rock
Because the rectangle is seen as transparent,
the circle is seen to move in apparent motion
Here the rectangle is seen as opaque so it
‘explains’ the circle’s visible-invisible cycle.
Therefore the circle is not seen to move.
Many reasons for thinking that vision
is cognitively penetrable
 Expectancy and the perception of patterns
 Perception in noise of words vs nonwords, sentences, statistical
properties of sequences
 Assimilation of perception to the norms
 Explanation in terms of readiness: Seeing as…
 Perceptual learning (bird watchers, wine tasters…)
 The effect of hints and foreknowledge on closure figures or
stereograms
►Neuroscience evidence for top-down effects
 The experience in computer vision
 Why should we doubt the continuity thesis?
 Illusions….
 Methodological concerns (signal detection theory)
Centrifugal neural pathways

There are almost as many outward (efferent)
nerve fibers as inward fibers
 There is evidence of top-down control of
sensors and top-down effects on percepts (e.g.,
filling-in effect for blind spot and other scotomas)
 Early attentional gating of a cat’s auditory signals
Hernandez-Péon, R., Scherrer, R. H., & Jouvet, M. (1956). Modification of
electrical activity in the cochlear nucleus during "attention" in unanesthetized
cats. Science, 123, 331-332.
Many reasons for thinking that vision
is cognitively penetrable
 Expectancy and the perception of patterns
 Perception in noise of words vs nonwords, sentences,
statistical properties of sequences
 Assimilation of perception to the norms
 Explanation in terms of readiness: Seeing as…
 Perceptual learning (bird watchers, wine tasters…)
 The effect of hints and foreknowledge on closure figures
or stereograms
● Neuroscience evidence for top-down effects
►The experience in computer vision
 Why should we doubt the continuity thesis?
 Illusions….
 Methodological concerns (signal detection theory)
Early experience in computational perception
(and AI) suggested that knowledge-based
perception leads to better performance
Minsky & Papert’s: “Heterarchy, not hierarchy” or the
knowledge- based approach to perception, Shirai’s success in
building an edge detector and other model-based vision systems.
Riseman & Hanson (1987):
“It appears that human vision is fundamentally organized to
exploit the use of contextual knowledge and expectations in the
organization of spatial primitives… Thus the inclusion of
knowledge-driven processes at some level in the image
interpretation task, where there is still a great degree of
ambiguity in the organization of the visual primitives, appears
inevitable (286).”
The Blackboard Architecture used in many AI applications is highly
non-modular because all parts can communicate with one another.
Phonetic/edge-finding
expert
Accoustic/optical
expert
e.g. ‘Hearsay’ speech
recognition system
Phone-pattern/contour
expert
Common Blackboard Communication Area
Semantic/object-recognition
expert
Word/2D shape
expert
Syntax/3D shape
expert
Pandemonium
An early architecture,
similar to the blackboard
architecture, was
proposed by Selfridge in
1959. This idea
continues to be at the
heart of many psychological models, including
ones implemented as
neural net (or
connectionist) models.
On the other hand ….

From a function perspective it makes sense
that the earliest stage of vision should be
built to be fast and very often (though not
necessarily always) veridical.
 The parable of the blind clockmaker and
Simon’s “partially decomposable systems”
 The influence of David Marr’s Principle of
least commitment: Do not do something that
you may later wish to undo (e.g., depth first
search)
The beginnings of a modular
view in computer vision
David Marr (1982):
“The principle of least commitment… requires not
doing something that may later have to be undone,
and I believe that it applies to all situations in which
performance is fluent. It states that algorithms that are
constructed according to a hypothesize-and-test
strategy should be avoided because there is probably a
better method.”
What evidence is there that
vision is a modular process?

There is a lot of prima facie evidence that vision
works independently of what we believe and what
we expect.
 In order to explain why that seems to be so we need
to distinguish between the part of vision that is
unique to vision and the part that is shared by all
intellectual processes. The unique part is called
Early Vision.
Irvin Rock produced a lot of the evidence that is cited
in support of the view that perception involves
“Inference” and “Problem Solving” in order to
account for the visual input, but he also says:
“The major difference between perception and thought
is that perception is based on a rather narrow range
of internalized knowledge, as far as inference and
problem solving are concerned… Perception must
rigidly adhere to the appropriate internalized rules, so
that it often seems unintelligent and inflexible in its
imperviousness to other forms of knowledge (p 340)”.
From: Rock, I. (1983). The Logic of Perception. Cambridge, Mass.: MIT Press.
Illusions don’t depend on what you believe!
A
B
C
Do hints speed up closure of fragmented figures?
According to Reynolds (1985) the only thing that makes a difference to
ease of closure is knowing that there is a sensible reading of the
fragmented figure. Knowing the name of the figure does not help.
Meaning and difficult percepts
What helps us see them?

Fragmented figures; autostereograms (“magiceye”);
Random dot stereograms
 Category hints?
 Description?
 Model of what you should see?
 Knowing where to look/attend?
 Knowing they are ambiguous?
 Having seen them once before?



Saye, A., & Frisby, J. P. (1975). The role of monocularly conspicuous features in facilitating
stereopsis from random-dot stereograms. Perception, 4(2), 159-171.
Frisby, J. P., & Clatworthy, J. L. (1975). Learning to see complex random-dot stereograms.
Perception, 4(2), 173-178.
Amodal completion is automatic
and non-inferential (not rational)
What would the figures look like if the black square
occluders were removed? Try to see through them.
Independence of feature detection
and object (pattern) perception
Evidence from brain-damage: visual agnosic with spared
nonvisual pattern-recognition [Humphreys & Riddoch, 1987. To see but
not to see: a case study of visual agnosia]
 This patient could had severe agnosia and could not visually recognize
familiar things (including his wife’s face) or discriminate shapes.
 But he had normal eye movements and sensory abilities (including
stereo and motion detection)
 He could see local features and, with enough time and effort, could
often infer the identity of the object (just as the New Look suggests)
 He could describe and draw objects from memory and could recognize
objects by touch, so his pattern memory was normal
 It “supports the view that the perceptual representation used in this
matching process can be ‘driven’ solely by stimulus information, so
that it is unaffected by contextual knowledge.” H&R, p104)
Signal Detection Paradigm
If correct detection improves without increase in false positives
it’s an increase in sensitivity. If it improves but so does the false
positive rate it suggests an increase in bias towards acceptance.
Signal
Present
Yes I see it
Response
No I don’t
see it
Absent
Correct
False
Detection
positive
False negative Correct
(misses)
rejection
Examples from the language module

Phoneme restoration effect appears to be a
response bias effect
 Lexical ambiguity appears to be resolved
after a period of time, before which all
options are available.
Meaning and perception of phonemes
1.
The pitcher’s thoughts about the dangerous batter made him nervous
2.
The pitcher’s thoughts about the dangerous battle made him nervous
3.
The pitcher’s thoughts about the dangerous batt▒ made him nervous
4.
The soldier’s thoughts about the dangerous batter made him nervous
5.
The soldier’s thoughts about the dangerous battle made him nervous
6.
The soldier’s thoughts about the dangerous batt▒ made him nervous

Signal detection analysis of responses shows that the effect is
connected to the response selection stage*
*Samuel, A. G. (1981). Phonemic restoration: Insights from a new methodology. Journal of
Experimental Psychology: General, 110(4), 474-494.
Maybe cognition has a postperceptual selection function?
Swinney study of resolution of lexical ambiguity
Context
None
Ambiguous
Unambiguous
The man was not surprised when
he found several bugs▲ in the
corner of his room.
The man was not surprised when he
found several insects▲ in the corner
of his room.
Biasedinsect
The man was not surprised when
he found several spiders,
roaches, and other bugs▲ in the
corner of his room.
The man was not surprised when he
found several spiders, roaches, and
other insects▲ in the corner of his
room.
BiasedSpying
The man was not surprised when
he found several microphones,
recorders, cameras, and other
bugs▲ in the corner of his room.
The man was not surprised when he
found several microphones,
recorders, cameras, and other illegal
devices▲ in the corner of his room.
Visual reading task at ▲: Ant (related), Spy (inappropriate), bag (unrelated)
Swinney ambiguous-word priming experiment



No context:
Rumor had it that for years the government building had been plagued with
problems. The man was not surprised when he found several bugs▲ in the
corner of his room.
Context biased to insects:
Rumor had it that for years the government building had been plagued with
problems. The man was not surprised when he found several spiders,
roaches, and other bugs▲ in the corner of his room.
Context biased to spying:
Rumor had it that for years the government building had been plagued with
problems. The man was not surprised when he found several microphones,
recorders, cameras, and other bugs▲ in the corner of his room.
At points marked with ▲ a word was presented visually and subjects had to
decide as fast as possible whether it was a word (a lexical decision task,
where half of the time it was not a word). Examples of these words are ant,
spy or sew. Nonwords were formed from the same letters: tna, ysp, swe.
Swinney ambiguous priming experiment

Swinney found that both senses of the ambiguous
word (eg “bug”) primed the decision task – so both spy
and ant were primed relative to the neutral word (sew)
 The priming effect for the inappropriate sense of the
word disappeared after about 0.7 to 1.0 seconds. After
this only words related to the appropriate sense were
primed.
Swinney, D. A. (1979). Lexical access during sentence comprehension:
(Re)consideration of context effects. Journal of Verbal Learning & Verbal
Behavior, 18(6), 645-659.
Visual Detection of Anomalous objects

Biederman
Alteration of perception with practice:
The case of expert perceivers
 Visual
expertise often arises from learning what
to attend to (pre-visual) as well as which
patterns are diagnostic (post-visual).
 Shiffrar & Biederman study of expert chicken sexers
 Perception & recall of board positions by chess masters
 Studies of athletes’ perception
Other fluent perceptions once thought
to require access to knowledge

Noninvertibility of 3D-to-2D mapping
There is an important difference between
constraints on visual interpretation being built in to
the architecture through evolution and the use of
knowledge about the likelihood of particular scenes
contents in visual interpretation of a particular scene
 David Marr and Natural Constraints
 Natural constrains involve only optical-geometrical
properties – not physical constrains or statistical
properties
Every perspective projection of edges is infinitely
ambiguous, yet is almost always perceived univocally
Any set of 2D edges could have arisen for an unlimited number
of 3D configurations. What makes the perception unique is the
‘assumption’ that certain configurations are non-accidental –
i,e. they would not change with a small change in perspective.
Label propagation as an illustration of a natural constraint
Four types of edge labels (convex, concave, 2 boundaries)
These are the only valid junction labels for a world of polyhedra
They are the only physically possible vertices formed by the 4 edge labels
L
Fork
T
Arrow
Three distinct types of trihedral junctions are recognized as part of the labeling scheme (referred
to as Y, T and Arrow junction), making a total of 192 trihedral junction labels and 16 dihedral
junction labels. But most of these label combinations cannot occur in the physical world. …
The complete Waltz set includes over 50 line labels. These can generate over 300 million
logically possible junctions, of which only 1790 are physically possible (see Waltz, 1975).
L
Fork
T
Arrow
Illustration of how to assign
possible labels to a figure using
the label-consistency constraint
Start with junction A, followed by B,
C, and D. The Arrows placed at A
limit the choices for L’s at B, which
in turn limit for Arrows at C. At C
automatic neighbor reexamination
has an effect, eliminating all but one
label at B and A. Finally, the C
boundary label limits the Fork
choices at D to the one shown.
Many natural constraints take the form of label-propagation. By
increasing the number of different label types, we increase the
possible constraints in interpretation. By adding shadow edges
and ‘cracks’ we end up with a unique labeling of figures like this
ss
C
c
+
c
S
+
C
-
S
+
S
S
--
s
Waltz, D. (1975). Understanding Line Drawings of Scenes with Shadows. In P. H. Winston (Ed.),
The Psychology of Computer Vision (pp. 19-91). New York: McGraw-Hill.
The label consistency requirement can also explain
why some figures are ambiguous… in this case
because it has two globally consistent sets of labels
-
-
+
+
+
-
+
+
+
+
+
+
++
+
+
+
+
+
-
+
+
-
-
+
Off-retinal info different from foveal info
Off-retinal info different from foveal info
Labels propagate over
picture
Anorthoscope: Scan view
How many contours are there?
Anorthoscope: Scan view
What is the shape?
Perceiving a real figure as an impossible one!
Because the visual system applies Natural Constraints blindly, it can be
tricked in reverse – to see an impossible figure knowing that it is real –
as this illusory figure constructed by Richard Gregory shows.
Amodal completion seems to defy rational
cues; vision has a logic of its own
What would this figure look like if the squares were removed?
Is there very short iconic storage
in the preconceptual stage?
●
Although the idea of pictorial long-term
memory is not supported, there is some
provisional evidence that sensory
information outlasts the duration of the
stimulus. Many people have studied these
“sensory buffers” including George
Sperling and Michael Posner.
Sperling’s partial report method
for showing an iconic memory
Posner’s demonstration of short
duration shape information
Fast
Slower
Slower
Fast
Some special cases: Natural Constraints or
cognitive penetration into early vision?

Solving the correspondence problem
 The Constancies (Muller-Lyer, lightness demo)
 Direction of light built in
 Concavity-convexity of very familiar stimuli –
e.g., face recognition
Illusions of size and motion
Color Motion
Here are two sets of rotating spokes. On the left, the relative
luminance of the two colours varies slowly over a range that might
include equiluminance (more likely on a CRT than a LCD monitor). If
it does, the coloured spokes will appear to slow down briefly as the
ratio moves through equiluminance, silencing the luminance response.
To help judge the slowing, light and dark spokes are shown in the
centre, moving at the same rate as the colour spokes. The slowing
effect should grow as you watch through several cycles. To observe the
slowing, you have to fixate the centre of the bull's-eye. If you look at
the spokes, you can of course track them and see their actual speed.
Which is lighter: Square A or Square B?
Apparent Motion – another Natural Constraint
(which of these two matches will vision choose?)
Dawson, M., & Pylyshyn, Z. W. (1988). Natural constraints in apparent motion. In Z. W.
Pylyshyn (Ed.), Computational Processes in Human Vision: An interdisciplinary perspective
(pp. 99-120). Stamford, CT: Ablex Publishing.
Whether these figures are seen as dimples or mounds depends on whether they are
viewed in this orientation or upside-down (relative to the head)
Mountain or crater?
The Ames distorting room
The Ames distorting room
Some special cases of modules

Micro-modules in vision (color & motion &
contour)
 Evidence for central (cognitive) architectural
modules is rarer – the best example being the
Theory of Mind Module (ToMM) – Leslie, 1994.
 Is there a visual-motor “module”?
 Milner & Goodale; patient DF.
 Ventral-dorsal pathways.
 Postural, grasping, eye-movement responses are not
subject to illusions that influence conscious vision and
sometimes vice-versa.
Micro-modules?

Color, contour, motion and shadow; other
information-flow constraints
The visual system consists of minimodules that are
restricted in their intercommunication
Luminance
Stimulus
?
Lumin
Color
Edge
Polarity
Motion
Binocular
Disparity
Color
Texture
Shape
Derived
Attributes
Shading,
Occlusion,
Surfaces,
Not all contours are alike:
Equiluminous boundaries are not interpreted as shadows
Equiluminous boundaries also don’t yield a depth percept
Where does this leave us?
● There is a large part of vision, called early vision (after
Marr) that is impervious to direct cognitive influences
 It can be affected by cognitively-determined selection at one of
two loci: prior to the vision module, where attention may select
individual objects, and after vision the vision module, where
cognition may select from among possible interpretations
● Vision seems to take into account many general worldproperties (including direction of light), but it nonetheless
remains “ignorant” and unable to utilize relevant
knowledge about a particular scene that the organism has.
● The built-in natural constraints appear to be highly
restricted and are mostly confined to geometrical-optical
properties and not to physical laws.
The Pulfrich Pendulum illusion shows that a basic physical
principle, such as the impenetrability of solid objects, is not part
of the build-in constraints on visual interpretation. Here the
visual system readily yields a physically impossible
interpretation.
Leslie, A. M. (1988). The necessity
of illusion: Perception and thought
in infancy. In L. Weiskrantz (Ed.),
Thought Without Language.
Oxford: Oxford Science.
Modularity is a common principle in nature
(Simon’s ‘Partially Decomposable Systems’)

The parable of the blind watchmaker (Simon)
 Perception may also have submodules. Vision
appears to have submodules for color, motion,
contour, stereopsis… and there is even
evidence for modules such as face recognition
 Evidence for central (cognitive) architectural
modules is rare – the best example being the
Theory of Mind Module (ToMM) (Leslie, 1994).
How does this connect with classical issues
in the philosophy of mind?

Early vision seems to include more than has been assumed to be part
of the sensorium (sensory transduction) since it involves complex
inference-like processes. However, it does not appear to permit
contact with information in memory so it does not allow recognition
of objects in the visual field as particular known objects.

The question of whether representations at this level are conceptual
has not been raised. I believe the answer may be tied to other
distinctions that we have not yet discussed – in particular to the
distinction between personal and subpersonal representations, and
architectural vs intentional or representation-governed processes.

The issue of accessibility to consciousness has not been raised, even
though it is central to some views of sensation (or sentience). I will
come back to this question later.


Humphreys and Riddoch study of a case of visual agnosia
A remarkable case of classical visual agnosia is described in a book by Glyn Humphreys and Jane Riddoch
(Humphreys & Riddoch, 1987). … the patient was unable to recognize familiar objects, including faces of
people well-known to him (e.g., his wife), and found it difficult to discriminate among simple shapes,
despite the fact that he did not exhibit any intellectual deficit. As is typical in visual agnosias, this patient
showed no purely sensory deficits, showed normal eye movement patterns, and appeared to have close to
normal stereoscopic depth and motion perception. Despite the severity of his visual impairment, the
patient could do many other visual and object-recognition tasks. For example, even though he could not
recognize an object in its entirety, he could recognize its features and could describe and even draw the
object quite well – either when it was in view or from memory. Because he recognized the component
features, he often could figure out what the object was by a process of deliberate problem-solving, much as
the continuity theory claims occurs in normal perception, except that for this patient it was a painstakingly
slow process. From the fact that he could describe and copy objects from memory, and could recognize
objects quite well by touch, it appears that there was no deficit in his memory for shape. These deficits
seem to point to a dissociation between the ability to recognize an object (from different sources of
information) and the ability to compute an integrated pattern from visual inputs which can serve as the
basis for recognition. As (Humphreys & Riddoch, 1987, p 104) put it, this patient’s pattern of deficits
“supports the view that ‘perceptual’ and ‘recognition’ processes are separable, because his stored
knowledge required for recognition is intact” and that inasmuch as recognition involves a process of
somehow matching perceptual information against stored memories, then his case also “supports the view
that the perceptual representation used in this matching process can be ‘driven’ solely by stimulus
information, so that it is unaffected by contextual knowledge.”
It appears that in this patient the earliest stages in perception – those involving computing contours and
simple shape features – are spared. So also is the ability to look up shape information in memory in order
to recognize objects. What then is damaged? It appears that an intermediate stage of “integration” of
visual features fails to function as it should. The pattern of dissociation shows the intact capacity to extract
features together with the capacity to recognize objects from shape information is insufficient for visual
recognition so long as the unique visual capacity for integration is absent. But “integration” according to
the New Look (or Helmholtzian) view of perception, comes down to no more than making inferences from
the basic shape features – a capacity that appears to be spared.
Independence of detection and
category selection bias
 Signal
Detection Theory shows that expectations
based on statistical frequency-of-occurrence are
response bias effects, and therefore post-perceptual
 Arthur Samuel’s study of phoneme restoration
 Visual
expertise often arises from learning where to
attend (pre-visual) and which patterns to retain
because they are diagnostic (post-visual).
 Shiffrar & Biederman study of expert chicken sexers
 Studies of athletes’ perception (and Chess masters’ memory)