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Cognitive Psychology Class Notes > Mental Imagery




DEMONSTRATIONS:

Imagine a capital letter N. Connect a diagonal line from the top right corner to the bottom left corner. Now rotate the figure 90 degrees to the right. What do you see? answer

Imagine a capital letter D. Rotate the figure 90 degrees to the left. Now place a capital letter J at the bottom. What do you see? answer

Mental Imagery Definition:

  • mental representations of physical objects or events that are no longer present

Why is Mental Imagery Important?

  • occurs in many cognitive tasks
  • may help to understand related phenomena:
    • hallucinations
    • daydreaming
    • dreaming
  • may be useful to understanding how to elicit imagery during therapy
    • systematic desensitization
    • empty-chair technique

What is the Nature of Mental Images?

Analog Code

Propositional Code

internal representation is a copy of the external stimulus

mental picture

internal representation is a description of the stimulus

verbal description

Example:

Stimulus:

 

Analog Code

Propositional Code

stored like a bitmap

binary code in memory:

0011100

0100010

1000001

0100010

0011000

a circle at the top

line comes straight down from bottom of circle

2 lines sticking out in either directions from middle and of straight line

 

Analog Code:

  • pictures in the head
  • similar mechanisms in the visual system are activated when objects or events are imagined as when they are the same objects or events are actively perceived (Finke, 1989, p. 41)
    • neurological evidence:
    • with PET Kosslyn et al. (1993) showed that when Ss perform visual imagery tasks, the occipital visual cortex is activated, analogous to how it activated when objects are physically present and (also interesting to note that this activation is GREATER with imagery tasks than with perception of physical stimulus -- greater effort??)
    • they also found that with a mental imagery task in which Ss had to imagine small versus large letters, in the small condition the visual cortex was activated in a more posterior region closer to where the center of the visual field is (topographically) represented in the visual cortex ... makes sense because a small visual image would be more concentrated at the center of one's visual field than a larger image

Evidence for Analog Code:

  • Mental Rotation (Shepard & Metzler, 1971)
    • Ss identify if two drawings of 3D objects are 'sam'e or 'different' type of rotation is manipulated:
      • two-dimensional rotation (rotation of picture plane - clock)
      • depth rotation (rotation of object into the picture)

Results (Fig. 6.1):

    • linear relationship between angle of rotation and fo same judgments
    • no difference between processing object in depth as in picture plane

Theoretical Implications:

    • Ss had to make some kind of mental transformation on the second to picture to determine if it was the same or not - mentally rotating
    • Ss must be operating on 3D representations of the objects in both conditions
    • these data seem to indicate that Ss are rotating the objects in a 3D space within their heads; the greater the angle of disparity the longer it takes to complete the rotation; of course Ss are not actually rotating an object in their heads, but whatever the mental process is, it appears to be analogous to the physical rotation
  • Image Scanning (Kosslyn, Ball, & Reiser, 1978)
    • it takes time to scan between two locations on a mental image

Task:

    1. study map to criterion (reproduce accurately 3 times)
    2. find and focus on object named
    3. after 5 s, a second object is named
    4. scan for second object and press a button when they have mentally focused on it

Results:

    • the farther apart the two objects were, the greater was the RT
    • the time it takes to scan between objects in a mental image is a function of distance between objects

Theoretical Implications:

    • Ss were going through a process that involved distance between imaged objects analogous to the physical operation involving physical objects
  • Size Judgments (Moyer, 1973)

Which is larger, moose or roach?

Which is larger, wolf or lion?

    • when objects are similar in size, Ss image both objects and then compare the size of the objects in their image
    • similar results when making comparisons of actual physical objects
  • Angle Judgments (Paivio, 1978)
  • Oblique Effect
  • Stabilized Images
  • Afterimages
  • Wallace (1984)
    • Ss given one of two stimuli:

 

 
    • Ss who saw (b) were asked to imagine an inverted V superimposed over the vertical lines
    • all Ss rated the length of the two vertical lines
    • Ss who saw (a) rated the top line as longer than the bottom line (replication of the Ponzo illusion)
    • Ss who saw (b) ALSO rated the top line as longer than the bottom line, even though the physical stimulus of the inverted V is NOT THERE

 

Evidence for Propositional Code:

  • Extracting Parts of Mental Image (Reed, 1974)
    • decide whether or not a pattern was part of a previous stimulus that they would have to image to decide
    • Ss performed slightly above chance levels (55%)
    • since Ss could not do this 55% of the time, Ss must not be storing the image as a picture, but rather as a description
  • Ambiguous / Reversible Figures (Chambers & Reisberg, 1985) -- DEMO
    • show picture briefly and ask Ss to form a mental image of it; only enough time to make one interpretation
    • Ss were asked to give a second interpretation of the figure
    • no Ss could do this task
    • Ss asked to draw the mental image of what they saw
    • Ss able to make second interpretation only after they reproduced the drawing themselves
    • verbal interpretation of mental image
    • propositional code can dominate over analog code

Conclusions:

  • Complex or abstract mental images may resort to some sort of verbal labeling, unlike simple mental images
  • both analog and propositional code seem to be at work in how we create mental images and how they are represented cognitively

 

 



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