Why do things happen the way they do in your imagination? - PowerPoint PPT Presentation

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Why do things happen the way they do in your imagination?


Why do things happen the way they do in your imagination? Is it because of the format of your image or your cognitive architecture? Or because of what you know? – PowerPoint PPT presentation

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Title: Why do things happen the way they do in your imagination?

Why do things happen the way they do in your
  • Is it because of the format of your image or your
    cognitive architecture? Or because of what you
  • Did it reveal a capacity of mind?
  • Or was it because you made it do what it did?
  • Can you make your image have any properties you
    choose? Or behave in any way you want? Why not?
  • How about imagining an object from all directions
    at once, or from no particular direction?
  • How about imagining a 4-dimensional object?
  • Can you imagine a printed letter which is neither
    upper nor lower case? A triangle that is not a
    particular type?

More on Representation of space and arguments
from neuroscience
  • The intuition that images are spatial (or, as
    some put it, that they have space) is an
    interesting one and deeper than most other
    questions being studied in laboratories. I have
    discussed this in excruciating detail in the
    last chapter of my Things and Places.
  • According to Kosslyn, the argument has now
    entered the third and final stage, where
    neuroscience evidence has put an end to the
    debate. I will look at some of this alleged
    debate-ending evidence and will show that it is
    characterized by desperation and lack of critical

A brief look at whether we may be storing
information in the form of an icon
  • For present purposes I want to look at the issue
    of explanation and I will do this by considering
    the sense in which spatial information may
    (must?) itself be spatial
  • This matters to the question of what forms of
    representation we have in our minds and how these
    refer to things in the world.

Our studies of mental scanning
(Pylyshyn Bannon. See Pylyshyn, 1981)
There is even reason to doubt that one can
imagine scanning continuously (Pylyshyn Cohen,
Does visual imagery use the visual system?
Major Question 2
  • It depends on what you mean by use and visual
  • To use vision can mean actually to perceive the
  • Only early vision is relevant to this use of
    perceive, since general vision can involve all
    of cognition
  • This question is of interest to picture theorists
    because if vision is involved it may suggest that
    images are uninterpreted picture-like (or
    depictive) spatial displays. The visual module
    cannot be applied to already-interpreted data
  • Lets assume that the visual system is active
    during mental imagery as some have suggested
  • What follows from that?
  • Why should we believe that vision may be
  • In the last 15 years the main support for the
    assumption that vision is involved has come from

Reasons for thinking that images are interpreted
by the visual system
  • Similar phenomenology of imagining seeing
  • This reason overshadows all others
  • Superposition interference studies
  • Visual illusions with projected images
  • The ubiquitous role of attention
  • Re-perceiving and novel construals
  • A large but very problematic literature

More demonstrations of the relation between
vision and imagery
  • Images constructed from descriptions
  • The D-J example(s)
  • The two-parallelogram example
  • Amodal completion
  • Reconstruals Slezak

Can images be visually reinterpreted?
  • There have been many claims that people can
    visually reinterpret images
  • These have all been cases where one could easily
    figure out what the combined image would look
    like without actually seeing it (e.g., the J D
  • Pedersons careful examination of visual
    reconstruals showed (contrary to her own
    conclusion) that images are never ambiguous (no
    Necker cube or figure-ground reversals) and when
    new construals were achieved from images they
    were quite different from the ones achieved in
    vision (more variable, more guessing from cues,
  • The best evidence comes from a philosopher
    (Slezak, 1992, 1995)

Slezak figures
Pick one (or two) of these animals and memorize
what they look like. Now rotate it in your mind
by 90 degrees clockwise and see what it looks
Slezak figures rotated 90o
Do this imagery exerciseImagine a parallelogram
like this one
Connect each corner of the top parallelogram with
the corresponding corner of the bottom
Now imagine an identical parallelogram directly
below this one
What do you see when you imagine the connections?
Did the imagined shape look (and change) like the
one you see now?
Amodal completion by images?
Is this what you saw?
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
Anorthoscope Scan view What is the shape?
Vision is involved when images are superimposed
onto vision
  • Many experiments show that when you project an
    image onto a display the image acts very much
    like a superimposed display
  • Shepard Podgorny, Hayes,
  • Interference effects (Brooks)
  • Mental scanning
  • Interaction with the motor system (Finke)

Shepard Podgorny experiment
Both when the displays are seen and when the F is
imagined, RT to detect whether the dot was on the
F is fastest when the dot is at the vertex of the
F, then when on an arm of the F, then when far
away from the F and slowest when one square off
the F.
Brooks spatial interference study
Respond by pointing to symbols in a table or by
saying the words left or right
Visual-Motor adaptation and motor adaptation to
  • The basic prism adaptation setup arm movement
    towards a target while wearing prism glasses
  • Now repeat with arm unseen but subject told where
    it is (actually where it would have been in the
    prism case)
  • Get adaptation Finke, R. A. (1979). The
    Functional Equivalence of Mental Images and
    Errors of Movement. Cognitive Psychology, 11,
  • But in the original experiment you dont need to
    see a hand, any indicator of where the hand is
    will do as long as the subject believes it is
    where indicated

Standard view of saccadic integration by
Is it plausible? Is it true?
Superposition does not work (Oregan 1983)
This is what our conscious experience suggests
goes on in vision
This is what the demands of explanation suggests
must be going on in vision
Are there pictures in the brain?
  • There is no evidence for cortical displays of the
    right kind to explain visual or imaginal phenomena

Is there very short iconic storage?
  • 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.

Sperlings partial report method for showing an
iconic memory
Posners demonstration of short lasting shape
So what does the visual system produce?
  • The best hypothesis so far (i.e., the only one
    that has not been shown to be clearly on the
    wrong track) is that the brain is a species of
    computer in which representations of the world
    are encoded in the form of symbol structures, and
    actions are determined by calculations (i.e.,
    inferences) based on these symbolic encodings.
  • Therefore vision (and other sensory systems)
    compute symbolic expression for the rest of the
    (Turing) computing machinery to use.

So why does it not feel like we are doing
  • The content of our conscious experience is a very
    poor guide to what is actually going on that
    causes both our experiences and our behavior.
    Science is concerned with causes, not just
  • We have learned (since Galileo) that we cant
    assume that the way things seem has much to do
    with how it works (consider the example of
    language understanding)
  • As in most sciences, the essential causes are far
    from obvious (e.g., How can the moon exert a pull
    on the earth without contacting it? What is this
    table made of? etc.).
  • In the case of cognition, what is going on is a
    delicate mixture of the obvious (what Granny or
    Shakespeare knew about people and why they do
    what they do) and the incredible.

We cant even be sure that we have the right
methods or instruments
Mental Scanning
  • Some hundreds of experiments have now been done
    demonstrating that it takes longer to scan
    attention between places that are further apart
    in the imagined scene. In fact the relation is
    linear between time and distance.
  • These have been reviewed and described in
  • Denis, M., Kosslyn, S. M. (1999). Scanning
    visual mental images A window on the mind.
    Cahiers de Psychologie Cognitive / Current
    Psychology of Cognition, 18(4), 409-465.
  • Rarely cited are experiments by Pylyshyn Bannon
    which I will summarize for you.

Studies of mental scanningDoes it show that
images have metrical space?
(Pylyshyn Bannon. See Pylyshyn, 1981)
  • Conclusion The image scanning effect is
    Cognitively Penetrable
  • i.e., it depends on goals and beliefs, or on
    Tacit Knowledge.

What is assumed in imagist explanations of mental

  • In actual vision, it takes longer to scan a
    longer distance because real distance, real
    motion, and real time is involved, therefore this
    equation holds due to natural law
  • Time distance speed
  • But what ensures that a corresponding relation
    holds in an image? The obvious answer is
    Because the image is laid out in space!
  • But what if that option is closed for empirical
  • Imagists appeal to a Functional Space which
    they liken to a matrix data structure in which
    some cells are adjacent to other cells, some are
    closer and others further away, and to move from
    one to another it is natural that you pass
    through intermediate cells
  • Question What makes these sorts of properties
    natural in a matrix data structure?

Thou shalt not cheat
  • There is no natural law that requires the
    representations of time, distance and speed to be
    related according to the motion equation. You
    could equally easily imagine an object moving
    instantly or according to any motion relation you
    like, since it is your image!
  • There are two possible answers why the relation
  • Time Representation of distance
    Representation of speed
  • typically holds in an image-scanning task
  • Because subjects have tacit knowledge that this
    is what would happen if they viewed a real
    display, or
  • Because the matrix is taken to be a simulation of
    a real-world display, as it often is in computer

Mental Rotation has been one of the most cited
demonstrations of all
  • Look at the following 3D figures and judge which
    pairs are the same except for orientation. The
    other pair are enantiomorphs 3D mirror images
    so they cant be put into correspondence by 3D
    rotation only.

Mental rotation
Time to judge whether (a)-(b) or (b)-(c) are the
same except for orientation increases linearly
with the angle between them (Shepard Metzler,
What do you do to judge whether these two figures
are the same shape?
Is this how the process looked to you?
When you make it rotate in your mind, does it
seem to retain its rigid 3D shape without
re-computing it?
Thou shalt not cheat
  • What happens in ALL imagist accounts of phenomena
    from mental scanning to mental rotation is that
    they assume the properties of real space in order
    to provide a principled explanation, then retreat
    to something not-quite-real space when it is
    pointed out that they are assuming that images
    are laid out in real space-in-the-head.
  • This happens with mental rotation as well, even
    though the tacit knowledge account is not
    plausible there (it is an involuntary and
    universal way of solving the rotated-figure task
    so long as the task involves tokens of

The missing bit of logic
  • According to Prinz (2002) p 118,If visual-image
    rotation uses a spatial medium of the kind
    Kosslyn envisions, then images must traverse
    intermediate positions when they rotate from one
    position to another. The propositional system
    can be designed represent intermediate positions
    during rotation, but that is not obligatory.
  • Given that this happens in 3D so that it cant be
    a literal brain space, the question arises What
    makes this obligatory in functional Space?

Sources of obligatory constraint
  • It could be that there is a medium or a set of
    analog properties that together happen to
    simulate a virtual space, and the physical
    properties of this medium enforce the continuity
    of motion through it. This is very unlikely.
  • It could be that the constraint comes from the
    fact that it holds in the world. Then its
    transfer from the real to the mental world occurs
  • Voluntarily, because we know how it would happen
    and we can use that fact to solve the problem
  • Naturally, because the constraint got built in
    over time through evolutionary pressures
  • Naturally, but not because the constraint is
    built in, but because of other properties of the
    architecture that make it more efficient to
    compute the rotated shape incrementally until
    there is a match

Do images have low-level psychophysical
  • Bring the bars closer and closer together. In
    which can you see the bars when the spacing is
  • In experiments, it was shown that the oblique
    effect occurs in mental images just as it does in
  • Kosslyn, Thompson Ganis (2006) argued that this
    is because there are more vertical and
    horizontally tuned cells than obliquely tuned
    cells in visual cortex. Does this explain the

Do images have low-level visual properties?
  • Imagine a grating in which the bars are
  • Horizontal
  • Vertical
  • Oblique (45)

A final point
  • In Kosslyn, Thompson Ganis (2007) the authors
    cite Ned Block to the effect that one does not
    need an actual 2D surface, so long as the
    connections upstream from the cortical surface
    can decode certain pairs of neurons in terms of
    their imagined distance. Imagine long stretchy
    axons going from a 2D surface to subsequent
    processes. Now imagine that the neurons are
    randomly moved around so they are no long on a 2D
    layout. As long as the connections remain fixed
    it will still behave as though there was a 2D
  • Call this the encrypted 2D layout version of
    literal space.

The encrypted-spatial layout alternative
  • By itself the encrypted-layout alternative will
    not do because without referring to the original
    2D locations, the relation between pairs of
    neurons and scan time is not principled. In the
    end the only principle we have is
    Timedistance/speed so unless the upstream system
    decrypts the neuron locations into their original
    2D surface locations the explanation for the
    increase in time with increased imagined distance
    remains a mere stipulation. It stipulates, but
    does not explain why, when two points are further
    away in the imagined layout it takes longer to
    scan between them or why scanning between them
    requires that one visit intermediate locations
    along the way.
  • But this is what we needed to explain! One can
    apply such a mere stipulation to any form of
    representation. What was a principled
    explanation with the literal 2D display has now
    been given up for a mere statement of how it
    shall be.

The Imagery Debate Redux
  • According to Kosslyn there have been 3 stages in
    the debate over the nature of mental images
  • The role of images in learning and memory
    (Paivios Dual Code theory). Influential at the
    time but now abandoned except for a few
    recidivists like Barsalou.
  • Spatial properties of images and their role in
    dynamic processes, as assessed by reaction time
    measures (Kosslyns research on metric
    properties of images)
  • Discovery of brain mechanisms underlying visual
    imagining, which led to the resolution of the
    imagery debate.

Mental imagery and neuroscience
  • Neuroanatomical evidence for a retinotopic
    display in the earliest visual area of the brain
  • Neural imaging data showing V1 is more active
    during mental imagery than during other forms of
  • The form of activity differs for small vs large
    images in the way that it differs when viewing
    small and large displays
  • Transcranial magnetic stimulation of visual areas
    interferes more with imagery than other forms of
  • Clinical cases show that visual and image
    impairment tend to be similar (Bisiach, Farah)
  • More recently psychophysical measures of images
    shows parallels with comparable measures of
    vision, and these can be related to the receptive
    cells in V1

Neuroscience has shown that the retinal pattern
of activation is displayed on the surface of the
There is a topographical projection of retinal
activity on the visual cortex of the cat and
Tootell, R. B., Silverman, M. S., Switkes, E.,
de Valois, R. L. (1982). Deoxyglucose analysis of
retinotopic organization in primate striate
cortex. Science, 218, 902-904.
Problems with drawing conclusions about the
nature of mental images from neuroscience data
  • The capacity for imagery and for vision are known
    to be independent. Also all imagery results are
    observed in the blind.
  • Cortical topography is 2-D, but mental images are
    3-D all phenomena (e.g. rotation) occur in
    depth as well as in the plane.
  • Patterns in the visual cortex are in retinal
    coordinates whereas images are in
  • Your image stays fixed in the room when you move
    your eyes or turn your head or even walk around
    the room
  • Accessing information from an image is very
    different from accessing it from the perceived
    world. Order of access from images is highly
  • Conceptual rather than graphical properties are
    relevant to image complexity (e.g., mental

Problems with drawing conclusions about mental
images from the neuroscience evidence
  1. Retinal and cortical images are subject to
    Emmerts Law, whereas mental images are not
  2. The signature properties of vision (e.g.
    spontaneous 3D interpretation, automatic
    reversals, apparent motion, motion aftereffects,
    and many other phenomena) are absent in images
  3. A cortical display account of most imagery
    findings is incompatible with the cognitive
    penetrability of mental imagery phenomena, such
    as scanning and image size effects
  4. The fact that the Minds Eye is so much like a
    real eye (e.g., oblique effect, resolution
    fall-off) should serve to warn us that we may be
    studying what observers know about how the world
    looks to them, rather than what form their images

Problems with drawing conclusions about mental
images from the neuroscience evidence
  • Many clinical cases can be explained by appeal to
    tacit knowledge and attention
  • The tunnel effect found in vision and imagery
    (Farah) is likely due to the patient knowing what
    things now looked like to her post-surgery
  • Hemispatial neglect seems to be a deficit in
    attention, which also explains the
    representational neglect in imagery reported by
  • A recent study shows that imaginal neglect does
    not appear if patients have their eyes closed.
    This fits well in the account I will offer in
    which the spatial character of a mental images
    derives from concurrently perceived space.
  • What if colored three-dimensional images were
    found in visual cortex? What would that tell you
    about the role of mental images in reasoning?
    Would this require a homunculus?

Should we welcome back the homunculus?
  • In the limit if the visual cortex contained the
    contents of ones conscious experience in imagery
    we would need an interpreter to see this
    display in visual cortex
  • But we will never have to face this prospect
    because many experiments (including ones by
    Kosslyn) show that the contents of mental images
    are conceptual (or, as Kosslyn puts it, contain
    predigested information).
  • And finally, it is clear to anyone who thinks
    about it for a few seconds that you can make your
    image do whatever you want and to have whatever
    properties you wish.
  • There are no known constraints on mental images
    that cannot be attributed to lack of knowledge of
    the imagined situation (e.g., imagining a 4D
  • All currently claimed properties of mental images
    are cognitively penetrable.

Explaining mental scanning, mental rotation and
image size effects in terms of functional space
  • When people are faced with the natural conclusion
    that the iconic position entails space (as in
    scanning and size effects) they appeal to
    functional space
  • A Matrix in a computer are often cited as an
  • Consider a functional space account of scanning
    or of mental rotation
  • Why does it take longer to scan a greater
    distance in a functional space?
  • Why does it take longer to rotate a mental image
    a greater angle?

But there are examples of solving geometry
problems easily with imagery
  • There are many problems that you can solve much
    more easily when you imagine a layout than when
    you do not.
  • In fact many instances of solving problems by
    imagining a layout that seem very similar to how
    would solve them if one had pencil-and-paper.
  • The question of how pictures, graphs, diagrams,
    etc help in reasoning is very closely related to
    the question of how imagined layouts function in
    reasoning. That is not in question. What is in
    question is what happens in either the visual or
    imagined cases and how images can benefit from
    this processes even though there is no real

How do real visual displays help thinking?
  • Why do diagrams, graphs, charts, maps, icons and
    other visual objects help us to reason and to
    solve problems?
  • The question why visual aids help is nontrivial
    and Seeing Visualizing, chapter 8 contains some
    speculative discussion, e.g., they allow the
    visual system to
  • make certain kinds of visual inferences
  • make use of visual demonstratives to offload some
    of the memory load
  • Capitalize on the fact that the displays embody
    the axioms of measure theory and of geometry
    (which are then inherited by thought)
  • The big question is whether any of these
    advantages carry over to imaginal thinking! Do
    mental images have some (or any) of the critical
    properties that make diagrams helpful in

Visual inferences?
  • If we recall a visual display it is because we
    have encoded enough information about its
    visual-geometrical properties that we can meet
    some criteria, e.g., we can draw it. But there
    are innumerably many ways to encode this
    information that are sufficient for the task
    (e.g. by encoding pairwise spatial relations,
    global spatial relations, and so on). For many
    properties the task of translating from one form
    to another is much more difficult than the task
    of visually encoding it the translation
    constitutes visual inference.
  • The visual system generalizes from particular
    instances as part of its object-recognition skill
    (all recognition is recognition-as and therefore
    assumes generalization from tokens to types). It
    is also very good at noticing certain properties
    (e.g., relative sizes, deviations from square or
    circle, collinearity, inside, and so on). These
    capabilities can be exploited in graphical

Memorize this map so you can draw it accurately
From your memory
  • Which groups of 3 or more locations are
  • Which locations are midway between two others?
  • Which locations are closest to the center of the
  • Which pairs of locations are at the same
  • Which is the top-most (bottom-most) location?
  • If you could draw the map from memory using
    whatever properties you noticed and encoded, you
    could easily answer the questions by looking at
    your drawing even if you had not encoded the
    relations in the queries.

Draw a rectangle. Draw a line from the bottom
corners to a point on the opposite vertical side.
Do these two lines intersect? Is the point of
intersection of the two lines below or above the
midpoint? Does it depend on the particular
rectangle you drew?
Which properties of a real diagram also hold for
a mental diagram?
  • A mental diagram does not have any of the
    properties that a real diagram gets from being on
    a rigid 2D surface.
  • When you imagine 3 points on a line, labeled A,
    B, and C, must B be between A and C? What makes
    that so? Is the distance AC greater than the
    distance AB or BC?
  • When you imagine drawing point C after having
    drawn points A and B, must the relation between A
    and B remain unchanged (e.g., the distance
    between them, their qualitative relation such as
    above or below). Why?
  • These questions raise what is known as the frame
    problem in Artificial Intelligence. If you plan
    a sequence of actions, how do you know which
    properties of the world a particular action will
    change and which it will not, given that there
    are an unlimited number of properties and
    connections in the world?

One view Images as depictive representations
  • A depictive representation is a type of picture,
    which specifies the locations and values of
    configurations of points in a space. For
    example, a drawing of a ball on a box would be a
    depictive representation.
  • The space in which the points appear need not be
    physical, but can be like an array in a
    computer, which specifies spatial relations
    purely functionally. That is, the physical
    locations in the computer of each point in an
    array are not themselves arranged in an array it
    is only by virtue of how this information is
    read and processed that it comes to function as
    if it were arranged into an array (with some
    points being close, some far, some falling along
    a diagonal, and so on).
  • Depictive representations convey meaning via
    their resemblance to an object, with parts of the
    representation corresponding to parts of the
    object When a depictive representation is used,
    not only is the shape of the represented parts
    immediately available to appropriate processes,
    but so is the shape of the empty space
    Moreover, one cannot represent a shape in a
    depictive representation without also specifying
    a size and orientation.
    (Kossyln, 1994, p 5)

If all else fails there is always parsimony and
generality(they worked well in physics and
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