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Is perception continuous Is perception continuous

Is perception continuous - PowerPoint Presentation

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Is perception continuous - PPT Presentation

with cognition The Cognitive Impenetrability of Vision Read Seeing amp Visualizing Chapter 2 or the BBS article on my web site ruccsrutgersedufacultypylyshynhtml The accepted answer goes along with intellectual and political fashions ID: 544904

perception vision amp visual vision perception visual amp motion detection effect evidence information figures knowledge appears theory view objects recognition room object

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Slide1

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.htmlSlide2

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.Slide3

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”)Slide4

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)Slide5

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)Slide6

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 effectSlide7

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.Slide8

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

.

Is a mental image something that is

seen

(with the mind’s eye)?Slide9

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 already-interpreted 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.Slide10

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.Slide11

Familiarity and the reconstruction of partially hidden patternsSlide12

This is what our conscious experience suggests goes on in vision…

KlibanSlide13

This is what the demands of explanation suggests must be going on in vision…Slide14

Standard view of saccadic integration by superposition

Is it plausible? Is it true?Slide15

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

TRLAVNEISlide16

Meaning and perception of phonemesThe ‘phoneme restoration effect’

The pitcher’s thoughts about the dangerous batt

made him nervous

The soldier’s thoughts about the dangerous batt

made him nervousSlide17

How to get someone to see fragmented figures?Slide18

Autostereogram or

Magic Eye

® figuresSlide19

Apparent motion is a function of early vision, yet is subject to various “intelligent” interpretationsSlide20

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)Slide21

Long time delays result in “group motion” because the middle object does not persist but is perceived as a new object each time it reappearsSlide22

But long delays, when the disappearance appears to be due to occlusion by an opaque surface, maintain objecthood, and therefore behave like short delaysSlide23

But long delays, when the disappearance appears to be due to occlusion by an opaque surface, maintain objecthood, and therefore behave like short delaysSlide24

Apparent “problem solving” in visionSlide25

Does the circle appear to move or are there two circles being covered?Slide26

Does the circle appear to move or are there two circles being covered?Slide27

Apparent “problem solving” in vision (Rock)Slide28

Another example from Irving RockBecause the rectangle is seen as transparent, the circle is seen to move in apparent motionSlide29

Here the rectangle is seen as opaque so it ‘explains’ the circle’s visible-invisible cycle. Therefore the circle is not seen to move.Slide30

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)Slide31

Centrifugal neural pathways

There are almost as many outward (efferent) nerve fibers as inward fibersThere 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.Slide32

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)Slide33

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).”Slide34

The

Blackboard Architecture

used in many AI applications is highly non-modular because all parts can communicate with one another.

e.g.

‘Hearsay’

speech recognition systemSlide35

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 psycho-logical models, including ones implemented as neural net (or connectionist) models.

Slide36
Slide37

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)Slide38

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.” Slide39

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

.

What evidence is there that vision is a modular process?Slide40

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. Slide41

Illusions don’t depend on what you believe!Slide42

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.Slide43

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.Slide44

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.Slide45

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)Slide46

Signal Detection Paradigm

Signal

Present

Absent

Response

Yes I see it

Correct Detection

False positive

No I don’t see it

False negative (misses)

Correct rejection

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.Slide47

Examples from the language module

Phoneme restoration effect appears to be a response bias effectLexical ambiguity appears to be resolved after a period of time, before which all options are available.Slide48

Meaning and perception of phonemes

The pitcher’s thoughts about the dangerous batt

er

made him nervous

The pitcher’s thoughts about the dangerous batt

le

made him nervous

The pitcher’s thoughts about the dangerous batt

made him nervous

The soldier’s thoughts about the dangerous batt

er

made him nervous

The soldier’s thoughts about the dangerous batt

le

made him nervous

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.Slide49

Maybe cognition has a post-perceptual selection function?

Swinney study of resolution of lexical ambiguity

Context

Ambiguous

Unambiguous

None

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.

Biased-insect

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.

Biased-Spying

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)Slide50

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.Slide51

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.Slide52

Visual Detection of Anomalous objects

BiedermanSlide53

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’ perceptionSlide54

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 propertiesSlide55

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.Slide56

Label propagation as an illustration of a natural constraint

Four types of edge labels

(

convex, concave, 2 boundaries

)Slide57

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

Arrow

T

Fork

LSlide58

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).

Arrow

T

Fork

LSlide59

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.Slide60

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

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.Slide61

The label consistency requirement can also explain why some figures are ambiguous… in this case because it has two globally consistent sets of labelsSlide62

Off-retinal info different from foveal infoSlide63

Off-retinal info different from foveal infoSlide64

Labels propagate over pictureSlide65

Anorthoscope: Scan view

How many contours are there?Slide66

Anorthoscope: Scan view

What is the shape?Slide67

The label consistency requirement can explain why this figure is impossible …

the interpretation of these figures depends on where you start labeling (where you look first), suggesting that label consistency gives more weight to neighboring partsSlide68

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.Slide69

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? Slide70

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.Slide71

Sperling’s partial report method for showing an iconic memorySlide72

Posner’s demonstration of short duration shape information

Fast

Fast

Slower

SlowerSlide73

Some special cases: Natural Constraints or cognitive penetration into early vision?

Solving the correspondence problemThe Constancies (Muller-

Lyer

, lightness demo)

Direction of light built in

Concavity-convexity of very familiar stimuli – e.g., face recognitionSlide74

Illusions of size and motionSlide75

Color MotionHere 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.Slide76
Slide77

Which is lighter: Square A or Square B?Slide78

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.Slide79
Slide80

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)Slide81

Mountain or crater?Slide82

The Ames distorting roomSlide83

The Ames distorting roomSlide84

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. Slide85

Micro-modules?Color, contour, motion and shadow; other information-flow constraintsSlide86

The visual system consists of minimodules that are restricted in their intercommunicationSlide87

Kavanagh Rotating Color WheelSlide88

Not all contours are alike:Equiluminous

boundaries are not interpreted as shadowsSlide89

Equiluminous boundaries also don’t yield a depth perceptSlide90

The color pathway does not affect motion detection

Example in which color-based motion appears to vanish under conditions of equiluminance

:

Kavanagh

Rotating Color WheelSlide91

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 world-properties (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.Slide92

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.Slide93

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)

.Slide94

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.Slide95

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.Slide96

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)