b57 - chapter 11 - VISUAL KNOWLEDGE

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10 Apr 2012
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B57: Chapter 11- Visual Knowledge
VISUAL IMAGERY
Introspections about Images
Francis Galton: asked various ppl to describe their images and to rate them for vividness; so he asked
them to introspect- to “look within” and report on their own mental contents
The self report data he obtained fit well w/ common sense; the participants reported that they could
inspect their images much as they would inspect a picture. This implies a mode of representation that is
picture like
Another founding is that his participants differed widely from e/o:, many described images of
photographic clarity, rich in detail, as if they could see the object whereas others reported very sketchy
images/none at all
Concerns: cannot take self reports for face value; participants may be seeing similar things but
describing them differently
Chronometric Studies of Imagery
Researchers have been sensitive to concerns of self report (from Galtons observations), so they don’t
usually ask participants to describe their image, instead to gain more objective data, they ask people to
do something w/ their images to read info off of them or to manipulate them in some way
o Chronometric studies- (“time measuring”); generally a study that measures the amount of time
a task takes, often used as a means of examining the tasks components or used as a means of
examining which brain events are simultaneous w/ specific mental events
o These studies allow us to ask what sorts of info are prominent in a mental image and what is
not. i.e. write a paragraph describing a cat, you would mention nose, whiskers etc…but you may
not include head because that seems to obvious. However if you were to draw a cat, you would
include the head in the sketch, but not the paragraph.
The pattern of what info is included depends on the mode of presentation
People have the option of thinking about an image (i.e. a cat) via imagery and also the option of thinking
about cats w/o imagery (to think about it without picturing it)= depending if
you are just thinking about it VS picturing it, as this mode of representation
changes, so does the pattern of info availability
Image scanning procedure- an experimental procedure in which participants
are asked to form a specific mental image and then are asked to scan, with
their “minds eye”, from one point of the image, to another. By timing these
scans, the experimenter can determine how long “travel” takes across a
mental image. Example (in lecture notes too)
o In an experiment, results show that participants scan across their
images at a constant rate, so that doubling the scanning “distance”
doubles the time required for the scan, and tripling the distance
triples the time required
o Similar results when they are asked to “zoom in” or “zoom out” of their images = response times
are proportional to the amount of zoon required
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o Thus there is a relationship between “travel time” + “travel distance”…travelling more distance
requires more time
This data tells us a lot about the nature of mental images: according to results, images represent a scene
in fashion that preserves all of the distance relationships within that scene…it represents geometry and
spatial relations that are like pictures/maps
Mental Rotation
Mental rotation- a process that participants seem to use in comparing one
imaged form to another. To make the comparison, they seem to imagine one
form rotating into alignment w. the other, so that the forms can be compared
o Transformation of mental images
Response times are influenced by how far apart the two forms were in the
initial orientation
Rotations leave the pictures within the 2D plane in which they were presented; rotation in depths are
done too (make few errors)
Avoiding Concerns about Demand Character
In mental rotation, distance relations seem to be preserved and the idea that the farther the imagined
“travel” the longer it takes
But there is another way to interpret this data participants in the studies know that movements
through the world takes time and that moving a longer distance takes more time. They can simply be
controlling the timing of their responses tin order to recreate this ‘normal’ pattern
o So they may not be imagining rotations or scanning images at all they may be thinking “they
experimenter asked me to scan an image..i have to make it look like I am obeying..i know that a
long scan takes a long time so let me wait a moment before hitting the response button”
o Demand character- cues that might signal how they are ‘supposed’ to behave in that situation
o This simulation may be what imagery is all about= BUT you can set aside those concerns about
demand character
The scanning and rotation data are as they are because of how images represent spatial layout
(evidence supports this claim) so mental rotation does occur, demand characteristic isn’t much of an
issue.
Interactions BW Imagery and Perception
What is the relation bw imaging and perceiving?
o Study where participants were asked to detect very faint signals either dim visual stimuli or
soft tones. On each trial they were to indicate whether a signal has been represented or not.
They were either forming a visual image before the ‘minds eye’, or while forming an
auditory image before their “minds ear”
Results: forming a visual image interferes w/ seeing, and that forming an auditory image
interferes w/ hearing
They were trying to visualize one thing while perceiving something altogether different.
o Can visualizing a stimulus “pave the way” for perception? Studies show yes, i.e. visualizing a T
made it easier to perceive a T. thus visualizing and perceiving draw on similar mechanisms, so
that one of these activities can serve to prime the other.
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