CONSTRAINTS ON IMAGERY I

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CONSTRAINTS ON IMAGERY I

• David Pearson
• Room T10, William Guild Building
• d.g.pearson_at_abdn.ac.uk

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• Over last 30 years the majority of research on
  mental imagery has tended to focus on
  similarities between imagery and perception
  rather than potential differences.
• Finke argues for a functional role for imagery
  during cognition i.e., that imagery can support
  the same kind of discovery and interpretation
  processes that occur during normal perception.

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• For this to occur
• mental images must depict the geometry of a shape
  sufficiently well enough to allow for mental
  reinterpretation.
• individuals must be able to apply shape
  classification procedures to the information
  depicted by mental images.

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Detection of Embedded Patterns

• Reed and Johnsen (1975) contrasted the detection
  of embedded figures in abstract patterns in
  either a perceptual or imagery condition.
• Perceptual condition participants shown possible
  part, followed by an abstract pattern. Given 10
  seconds to decide whether previously presented
  part could be detected in pattern or not.

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IMAGERY CONDITION
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Results of Reed Johnsen (1975)

• In perceptual condition participants failed to
  detect parts embedded in the patterns on 14 of
  trials.
• In imagery condition this rose to 48.
• This increased to 72 if trials were eliminated
  in which the parts had been detected without
  inspecting a mental image.
• Results suggest that people may find it difficult
  to apply shape classification procedures to
  mental images in order to recognise embedded
  patterns.
• This mainly applies to the detection of implicit
  information within the pattern i.e., shapes
  which do not form part of the perceptually
  dominant structure.

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Restructuring Combining Within Imagery

• Verstijnen et al. (1998) argue that mental
  discoveries result from two main processes
  restructuring the initial conception of a
  pattern, and combining separate parts into a new
  pattern.
• Verstijnen et al. carried out a series of
  experiments using a Component Detection task.

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Results (Verstijnen et al., 1998)
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• Design students experience in drawing techniques
  allowed them to overcome the limitations of
  imagery by externally representing their mental
  image.
• This is known as providing stimulus support.
• In a second experiment, Verstijnen et al.
  examined how often novice and expert participants
  used sketching during the task with both explicit
  and implicit target component parts.

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age of time sketching for explicit and implicit
targets
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• Both groups used significantly more sketching for
  implicit rather than explicit targets.
• Provides support for idea that the restructuring
  of a pattern is difficult to accomplish in
  imagery without external support.

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Interpretation of ambiguous figures in imagery

• Other research which suggests that images do not
  function exactly as percepts has been carried out
  using perceptually ambiguous figures.

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• When ambiguous figures are visually presented to
  a naive viewer, a perceptual reversal occurs -
  viewer spontaneously shifts their perception of
  the figure between alternative interpretations.
• Ambiguous figures demonstrate conscious percept
  of an external stimulus contains more information
  than is specified in the retinal image alone.
• Percepts result from an interpretation of the
  information conveyed through our senses.
• If images are functionally equivalent to
  percepts, then ambiguous figures should
  spontaneously reverse in both imagery and
  perception.

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• This was directly tested by Chambers Reisberg
  (1985) using the Jastrow ambiguous figure (1900).

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• Participants shown figure for 5 seconds.
• Participants asked to form an image of the figure
  and then discover the alternative interpretation
  of the figure just by inspecting the mental
  image.
• Participants had previously been given examples
  of other ambiguous figures, and were given
  specific hints on how to reconstrue the figure.
• If participants were unable to reconstrue the
  image, they then drew it out onto a blank sheet
  of paper.

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• Results show
• Successful figure reversal using imagery alone 0
• Successful figure reversal using drawing 100
• This study was hugely influential as it seemed to
  demonstrate a massive difference between images
  and percepts.
• .... to say the least, this seems to be a
  regard in which visual images are conspicuously
  not like pictures. Reisberg (1996)

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• Result appear to conflict with those of Finke
  (Finke Slayton, 1988 Finke, 1990).
• Verstijnen argues that creative synthesis and
  invention require a combination process, while
  the reconstrual of ambiguous patterns and the
  discovery of embedded figures relies on the
  restructuring of an existing pattern.
• Evidence suggests restructuring is much harder to
  accomplish using imagery, unless some form of
  external support (like drawing) is available.

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• Pearson, Logie and Green (1996) examined
  performance of the guided image manipulation task
  (Finke et al., 1989) in either imagery or drawing
  conditions.

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Number of correct identifications with and
without drawing
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• Evidence suggests that under certain conditions
  imagery fails to support novel discoveries which
  can easily be made under comparable perceptual
  conditions.
• Two main factors may potentially limit imagery
  performance
• (a) constraints imposed by the resource
  limitations of the cognitive processes which
  underlie imagery.
• (b) constraints imposed by the differences
  between internally-generated images and
  externally-created percepts.

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The Resource Limitations Hypothesis

• Fundamental concept in modern cognitive
  psychology
• All forms of cognitive activity require mental
  resources to be carried out.
• 2. These resources are finite in nature, and
  subject to capacity limitations.
• 3. If the resources necessary to carry out a
  cognitive activity exceed the amount of resources
  available, then serious disruption of cognitive
  activity will result.

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Resource Limitations in Imagery

• The generation and maintenance of mental images
  requires mental resources.
• The more complex the imagery task, the more
  resources will be consumed.
• If the resource requirements of an imagery task
  exceed the capacity of the imagery system, the
  accurate performance of the imagery task will
  begin to fail.

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Effects of complexity on mental rotation (Rock,
1973)
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• The generation and maintenance of percepts does
  not place great demands on mental resources
  because they are externally-created.

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• The generation and maintenance of percepts does
  not place great demands on mental resources
  because they are externally-created.
• More mental resources will therefore be available
  when trying to make a discovery from a percept
  than will be available if using an equivalent
  mental image.