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Visual Imagery

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Title: Syllabus P140C (68530) Cognitive Science Author: Mark Steyvers Last modified by: Mark Steyvers Created Date: 1/7/2003 4:10:48 AM Document presentation format – PowerPoint PPT presentation

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Title: Visual Imagery


1
Visual Imagery
2
Solving problems through imagery
  • What shape are mickey mouses ears?
  • How many windows are there in your apartment?
  • Which is a darker red a cherry or an apple?
  • What is the shortest path from RH104 to Phoenix
    Grill?

3
Study of Imagery
  • Banned by behaviorists
  • Possible subject of study in cognitive psychology
  • Cognitive psychology is distinguished from the
    earlier behaviorism by its claim that there are
    internal representations of knowledge on which
    the mind operates
  • However, this is a difficult area of study
  • Mental images are subjective
  • How can we show that images are used?
  • How are they represented?

Stephen Kosslyn (did much of the research on
mental imagery)
4
How are mental images represented?
  • The analog vs. propositional debate
  • analog the representation has the same structure
    as the thing represented
  • propositional a sentence-like description of the
    image, non-spatial
  • Most studies mentioned seem to argue for analog
    representations (e.g., mental rotation, brain
    imaging studies). Yet mental images are not
    processed exactly the same as visual images

5
Analog Images vs. Propositions
Imagine The can is on the box. The can is black
Analog
Propositions
on( can, box ) black( can )
6
Some Questions about Mental Images
  • What is the relationship between imagery and
    perception?
  • How are mental images processed and transformed?

7
Imagery perception in reverse?
8
Imagery in Neural Networks
  • Mental images in neural networks can be produced
    by running the network in reverse -- activate
    class nodes (e.g. digit 3) and running
    activation downwards to the input nodes

output (e.g. digit class)
hidden nodes
input
9
Imagery Perception
  • If the mechanisms used to perceive stimuli are
    also used to generate mental images, then we
    should predict
  • Mental images should be quasy pictorial
  • Mental images should activate some of the brain
    areas involved with visual processing

10
Just as in visual images, level of detail in
mental images can vary
Imagine a bee next to a rabbit
Imagine a elephant standing next to a rabbit
Does a rabbit have eyebrows?
Does a rabbit have eyebrows?
11
Finke and Kosslyn (1980) experiment
fixation
dot separation
Angle of separation
Experiment measures field of resolution the
angle of separation into the visual periphery
where you cannot distinguish dots any longer
12
Fields of resolution are similar in perception
and imagery
  • Horizontal and vertical fields of resolution in
    perception and imagery as a function of dot
    separation and vividness of imagery. Data from
    Finke and Kosslyn (1980).

13
Visual Imagery and Hemispatial Neglect
Mental images from opposite sides of an imagined
public landmark
(Bisiach and Luzzatti, 1978)
14
Evidence from brain imaging (fMRI) for
involvement of visual processing areas during
visual imagery
(Le Bihan et al., 1993)
15
Mental Rotation
  • Can mental images be transformed in a way
    analagous to physical objects? How could we tell?
  • Mental rotation task look at the time it takes
    to rotate two shapes into correspondence
  • Demo experimenthttp//bjornson.inhb.de/?p55

16
Example Trials
same
different
different
different
same
different
same
different
17
Results
  • linear relationship between angle of rotation and
    reaction time in object comparison
  • The mental process seems to be analogous to the
    physical process of rotation.

18
Are visual images also subject to visual
illusions? Ponzo Illusion
Imagine an inverted V over these lines.Which
horizontal line is longer?
Which horizontal line is longer?
19
Differences between pictures and mental images
  • Mental images are more difficult to be
    reinterpreted
  • Mental image perception interpretation
  • Strong influence of conceptual knowledge on
    imagery
  • Simplification of object models
  • Distortions in cognitive maps

20
Imagery and Ambiguous Figures
What would this object look like when rotated 90
degrees?
21
Imagery and Ambiguous Figures
  • If you see one interpretation, it is very
    difficult to then imagine the other
    interpretation (unless you are trained in this
    task)
  • One difference between imagery and visual
    perception visual images, unlike mental images,
    can be easily reinterpreted

22
Mental Images might miss important aspects of
object being imagined
  • Imagine you have a cube between your thumb and
    index finger. One corner of the cube touches your
    thumb, and the diagonally opposite corner touches
    your index finger. Now, point to the locations
    of the rest of the corners in space.

Many people point (incorrectly) to four points on
the same plane half way between the top and
bottom corners.
Correct Solution
23
Imagine this object
  • Does this figure contain a parallelogram?
  • no
  • yes
  • not sure
  • what is a parallelogram??

24
Mental distortions in Cognitive Maps
25
  • Which is further west?
  1. atlantic entrance to the panama canal
  2. pacific entrance to the panama canal

26
  • Which is further east?
  • Florida
  • Chile

27
  • Which is further south
  • Philadelphia
  • Rome

28
Which is further east? a) Reno b) San Diego
29
Cognitive maps are affected by conceptual
knowledge
  • Relative locations of small regions is determined
    by a conceptualization of larger regions.
  • Line of reasoning
  • Nevada is east of California
  • Reno is in Nevada, San Diego in California,
  • Therefore, Reno must be east of San Diego

30
Experimental evidence for hierarchical
organization in cognitive maps
  • Ss. study maps. Later, from memory, they judge
    relative position of locations x and y
  • Performance was better when superordinate
    information was congruent with question

Congruent
Incongruent
(Stevens and Coupe, 1978)
31
Summary
  • Imagined information is processed in similar ways
    to perceptual information
  • Neuroscience evidence (fMRI)
  • Neuropsychological evidence
  • Behavioral evidence
  • Kosslyn studies/ Scanning studies
  • Mental rotation
  • Some visual illusions
  • But there are also differences
  • Mental images are difficult to reinterpret
  • Cognitive distortions in mental maps

32
Example Question (1)
  • Stevens and Coupes (1978) studied spatial
    judgments of cities where subjects studied maps
    of cities in alpha-county and beta-county.
    They showed that
  • A. people are more accurate at judging the
    relative positions of cities if the superordinate
    information is congruent.
  • B. people use route knowledge but not survey
    knowledge to make spatial judgments.
  • C. people use analog representations but not
    propositional representations to make spatial
    judgments.
  • D. people are more accurate at judging the
    relative positions of cities if they rely on
    hierarchical information.

33
Example Question (2)
  • Suppose you do a study where people imagine a
    rabbit next to an elephant. It will probably take
    ________ to find the whiskers on the rabbit,
    relative to when people imagine a rabbit next to
    an ant.
  • A. the same amount of time
  • B. more time
  • C. less time
  • D. Details can't be seen on mental images.

34
Example Question (3)
  • The neuroscience evidence on the imagery question
    shows that
  • A. imagery and perception involve entirely
    different neural processes
  • B. during mental imagery, some portions of the
    visual processing regions of the cortex seem to
    be activated.
  • C. the primary similarity between imagery and
    perception is that the visual receptors in the
    retina are stimulated in both cases.
  • D. the neuroscience research in this area has a
    major problem with demand characteristics, so we
    cannot draw clear-cut conclusions.
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