Mental imagery

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Mental imagery

• Why is imagery of interest?
• Self-report data on mental imagery
• Individual differences in imagery
• Evidence for mental images
• Interactions between imagery and perception
• Neural basis of imagery
• Imagery and memory

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What are images used for?

• Role in motor programming, e.g. reaching for a
  target
• Also used in sports to enhance performance
• Can be inspected to access information that has
  been stored in memory (e.g., answering questions
  such as, Does a frog have a long tail?)

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History of imagery (1)

• The notion that thoughts rely on images was
  common to many philosophers, including Plato
• Introspectionists, following Wundt, recorded
  peoples experiences of mental imagery
• Galton (1883) reported that 3 of people claim to
  have no visual mental images whatsoever, a
  finding that appears to be replicable in todays
  population

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History of imagery (2)

• Study of imagery was not considered scientific
  from 1913-1960
• Interest in imagery as a possible form of inner
  representation was revived after the cognitive
  revolution
• Perhaps not all forms of thinking could be
  described with a single computational mechanism,
  the digital symbol processor (uses lists and
  propositions)

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Individual differences in imagery

• Some people report their imagery as vivid, much
  like actually seeing
• Other people report that their images are more
  like descriptions, and not at all like actually
  seeing
• Imagery relies on a combination of abilities. A
  person could be good on some imagery tasks, but
  not others.

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Individual differences (cont.)

• Imagery has various components
• visual vs. spatial
• visual is useful for getting details of visual
  appearance (Does a kangaroo have a long tail?)
• spatial is useful for manipulating images, as in
  a mental rotation task
• generating images
• maintaining images

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What is a mental image?

• A species of internal representation
• Has some depictive (picture-like) properties, in
  contrast with propositional (sentence-like)
  representations
• Visual imagery has received more study than other
  types (auditory, kinesthetic)

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Evidence for use of images

• Mental rotation
• Mental scanning
• In both cases, imaging across greater distances
  takes longer

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Mental rotation (1)

• Shepard and Metzler (1971) showed subjects pairs
  of drawings of three-dimensional figures
• Pair A match (picture-plane pairs)
• Pair B match (depth pairs)
• Pair C do not match

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Figure 11.04
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Mental rotation (2)

• Subjects were asked to judge whether the objects
  were identical. Half of the time, the two
  objects were identical except for orientation.
  The other half of the time, the objects were
  mirror-images, so the correct answer was no.
• The time taken to make a yes judgment increased
  linearly as the angle of rotation between the
  objects increased.

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Figure 11.05
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Mental rotation (3)

• Data from rotation experiments has been taken to
  support that images are rotated in the mind
  through a functional space - distance is
  represented in the image
• The greater the degree of rotation required, the
  more time needed to complete the rotation

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Mental scanning (1)

• Kosslyn has done many experiments in which
  subjects are asked to study a map of locations,
  and to form an image of the map (e.g. Kosslyn,
  Ball, Reiser, 1978)
• They are asked to focus their attention at one
  location (house) and to press a button as soon
  as they can see a second named place (beach)

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Mental scanning (2)

• Map to be learned

beach
tower
windmill
house
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Mental scanning (3)

• The further apart the two locations, the longer
  it took subjects to report that they could see
  the second location in the image
• There were no distance effects when they
  memorized a list of location names and had to
  respond whether certain words were on the list

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Figure 11.02
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Imagery as a special form of representation

• Mental scanning and rotation experiments provide
  support for images as a depictive form of
  representation
• Imagery appears to use parts of the visual system

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Interactions between imagery and perception

• Segal and Fusella asked participants to detect
  very faint signals, either auditory or visual.
• Participants were instructed to form either a
  visual or auditory image
• Results forming a visual image interfered with
  visual detection, EXCEPT when the image matched
  the target
• Visualizing an H made it easier to see H

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Segal and Fusella (cont.)

• Forming a visual image did not interfere with
  detecting an auditory signal (sound)
• Forming an auditory image did interfere with
  detecting an auditory signal
• Researchers had two dependent measures
• percentage correct detections
• percentage false alarms

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Figure 11.06
Conclusion Visual imagery and visual perception
use some of the same resources, so there is
interference when both tasks must be done at the
same time.
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Imagery in blind people

• Can do many imagery tasks (e.g., scan a mental
  map). Reisberg suggests that they use spatial,
  rather than visual, images. Their images can be
  shown to differ from those of sighted people.
• They were asked to image familiar objects of
  different sizes (car, card table, typewriter).
  Each object was imaged at three distances (3, 10,
  or 30 feet away).

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Blind subjects (cont.)

• Blind and sighted subjects were asked to point to
  where the left and right sides of the objects
  would be. All subjects produced larger angles for
  the larger objects.
• Sighted subjects produced smaller angles as
  distance to the object increased blind subjects
  did not.
• Blind subjects appreciated the concept of spatial
  extent, but did not appreciate the uniquely
  visual property of perspective effects

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What can neuroscience tell us about mental
imagery?

• Scan peoples brains while they are doing imagery
  tasks
• fMRI functional magnetic resonance imaging
• TMS transcranial magnetic stimulation
• Measures of blood flow to different areas of the
  brain
• Evidence from brain-damaged patients

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Brain activity during imagery tasks

• fMRI results V1 (an area dedicated to vision)
  is activated during visualization
• TMS results disrupting V1 with magnetic pulses
  causes problems with vision and with visual
  imagery
• V1 is important both for visual perception and
  mental imagery

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Blood flow during imagery tasks

• Self-described vivid imagers showed greater
  blood flow to visual areas of the brain than
  nonvivid imagers, while they formed mental images.

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Evidence from brain-damaged patients

• Some patients with perceptual problems have
  parallel problems in imagery
• e.g., Cannot recognize or visualize faces
• One patient with unilateral neglect syndrome also
  neglected one side of his images
• Conclusion There is a considerable overlap
  between brain areas for imagery and perception

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Imagery and memory

• Imagery improves memory
• Word list memorization improves when people are
  instructed to form images of the words
• Memory is better for imageable words (piano,
  but not context). This is true for both blind
  and sighted subjects.
• Memory is helped when people form images of
  objects interacting

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Imagery and memory (2)

• Images provide a way of coding information that
  is different from a purely verbal description.
• Imageable words can be represented twice in
  memory with a verbal code and an image. This
  dual coding leads to a memory advantage. When
  retrieval is attempted, there are two ways of
  accessing the information.

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Memory for pictures

• When asked to memorize pictures, people will
  often create a verbal description of the picture.
• This will bias the way that they remember the
  picture.
• When people were given verbal labels for
  ambiguous shapes, their drawings were influenced
  by the label.

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Figure 11.10
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Conclusions

• Imagery requires a combination of mechanisms
  (visual, spatial, image generation...), and
  people vary greatly in how they use images
• Stored visual knowledge can be used in many
  cognitive tasks, such as finding information in
  memory, navigating using a mental map, and
  planning sequences of movements.

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Conclusions (cont.)

• Imagery helps memory
• Words that we can form images of are easier to
  remember than those that we cannot form images
  of.
• Vision areas are also used for imagery, but the
  two systems do not completely overlap