PSY100H1 Chapter Notes - Chapter 10: Image Scanner, Necker Cube, Mental Rotation

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Published on 16 Apr 2013
School
UTSG
Department
Psychology
Course
PSY100H1
Professor
PSYB57 Chapter 10: Visual Knowledge
Visual Imagery
Everyday use of visual images = a basis for making decisions, as an aid to remembering
Introspections About Images
Galton asked participants to describe their images and to rate them for vividness; he asked them
to introspect or look within and to report on their own mental contents
The self-report data he obtained fit well with common sense: participants reported that they
could inspect their images much as they would inspect a picture. Their descriptions made it clear
that they were viewing their images from a certain position and a certain distance; they also
reported that they could read off the image details of color and texture
Galton’s participants differed from each other in their self-reports; many described images of
photographic clarity, rich in detail while others reported very sketchy images or none at all
Perhaps all of the participants had the same imagery skill but some were cautious in how they
chose to describe their imagery while others were more extravagant; some chose to keep their
descriptions brief while other took pleasure in providing elaborate and flowery descriptions
In this way, Galton’s data might reveal differences in how people talk about their imagery rather
than differences in imagery per se
Chronometric Studies of Imagery
Imagery researchers have been sensitive to these concerns about self-reports and this is why
imagery experiments usually don’t ask participants to describe their images
To gain more objective fata, these experiments ask people to do something with their images, to
make a judgment based on the image and then examine how fast people are in the judgments
and use the measurements as a basis for testing hypotheses about imagery
The data are generally chronometric (time measuring) and give much more accurate portrait of
imagery than could ever be obtained with self-report
Chronometric studies allow us to ask what sorts of info are prominent in a mental image and
what sorts aren’t
The pattern of what info is included as well as what info is prominent depends on the mode of
presentation
o For a description, the features that are prominent will be those that are distinctive and
strongly associated with the object being described
o For a depiction, distinctiveness and association won’t matter, instead, size and position
will determine what’s prominent and what’s not
In a study by Kosslyn, participants were asked to form a series of mental images and to answer
yes/no questions about each
o Ex. They were asked to form a mental image of a cat and asked if the cat has a
head/claws. The participants responded faster to the head question than the claws
question
o The difference suggests that info quickly available in the image follows the rules for
pictures, not paragraphs
o Another group of participants were just asked to think about cats with no mention of
imagery; these people showed the reverse pattern (gave quicker response to claws than
to head)
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o People have the option of thinking about cats via imagery and also the option of
thinking about cats without imagery; as a mode of representation changes, so does the
pattern of indo availability
In an image scanning procedure, participants had to scan from one point on their mental image
to another point; they pressed a button to indicate when their mind’s eye had arrived at its
destination. Response times were closely related to the distance participants had to scan across
on the image, implying that mental images are similar to actual pictures in how they represent
position and distance
o Doubling the scanning distance doubles the time required for the scan
Similar results are seen if participants are given a task that requires them to zoom in on their
images or zoom out.
o In these studies, response times are directly proportional to the amount of zoom
required, suggesting once again that travel in the imaged world resembles travel in the
actual world, at least with regard to timing
Ex. Participants in one study were asked to imagine a mouse standing next to an elephant and
then asked to confirm by inspecting their image that the mouse had whiskers
o Participants were relatively slow in responding because they first needed time to zoom
in on the image in order to see the whiskers
o Response times were faster if they were asked to imagine the mouse next to a paper
clip (no zooming is required)
There’s a clear relationship between “travel time” (scanning done in the mind) and travel
distance
o The same relationship would be observed if participants are asked to move their eyes
across an actual map or literally to zoom in on a real picture
All this points to the similarity between mental images and actual out-in-the-world pictures
According to these results, images represent a scene in a fashion that preserves all of the
distance relationships within that scene
o Points closer to each other in the scene are somehow close to each other in the image
and vice versa
o In a very real sense, the image preserves the spatial layout of the represented scene
In this fashion, images directly represent a geometry of the scene and depict the scene rather
than describing it, and are much more similar to pictures/maps than they are to descriptions
Mental Rotations
In experiments done by Shepard, participants were asked to decide whether displays showed 2
different shapes or just one shape viewed from 2 different perspectives
To perform this mental rotation task, participants seem first to imagine of the forms rotating
into alignment with other. Once the forms are oriented in the same way, participants can make
their judgment
The amount of time it takes depends on how much rotation is needed
The farther you have to image a form rotating, the longer the evaluation takes
People have no trouble with mental rotation in depth. They make very few errors and the data
resembles those obtained with picture-plane rotation
Participants can represent 3D forms in their images, and they can imagine these forms moving
in depth
In some circumstances, visual images are not mental pictures; they are more like mental
sculptures
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Avoiding Concerns About Demand Character
In both mental rotation and metal scanning, the farther the imagined travel the longer it takes
Participants in these studies obviously know that movement through the world takes time and
that moving a longer distance takes more time. Perhaps, therefore, the participants simply
control the timing of their responses in order to re-create this normal pattern
Participants in these studies are not imagining rotations or scanning across an image at all.
Instead, they might be thinking “the experimenter just asked me to scan a long way, and I’d like
to make it look like I’m obeying
One reason is that participants in experiments usually want to be helpful, so they do all they can
to give the experimenter good data. As a result, they are very sensitive to the demand character
of the experiment
A different possibility is that this sort of simulation is what imagery is really all about, perhaps
whenever someone tries to imagine something, he draws on his knowledge about how an event
in the world would actually unfold, and then he does his best to simulate this event
o in this case, longer scan or a greater rotation requires more time, not because there
really is some travel involved, but because people know that these manipulations
should take more time and do their best to simulate the process
the scanning and rotation data are as they are, but indeed because of how images represent
spatial layout
in several studies, the experimenters have asked participants to make judgments about spatial
layout but have taken care never to mention to participants that imagery was relevant to the
task
o this should diminish the demand character
even without imagery instructions, the participants in these procedures spontaneously form
images and scan across them and their responses show the standard pattern: longer response
times observed with longer scans
this result really does emerge whenever participants are using visual imagery whether the
result is encouraged by the experimenters’ instructions or not
Interactions Between Imagery and Perception
What is the relation between imaging and perceiving? (Segal & Fusella)
o Participants were asked to detect very faint signals either dim visual stimuli or soft tones
o On each trial, the task was merely to indicate whether a signal had been presented or
not
o Participants did this is one of 2 conditions: either while forming a visual image before
their mind’s eye or while forming an auditory image before their mind’s ear
o 2X2 design: 2 types of signals to be detected, and 2 types of imagery
Hypothesis: there is some overlap between imaging and perceiving
o There are some mental processes that are used by both activities therefore if these
processes are occupied with imaging, they’re not available for perceiving and vice versa
o We should expect competition if participants try to do both activities at once
Segal & Fusella results indicate that forming a visual image interferes with seeing and that
forming an auditory image interferes with hearing
o Participants were less successful in detecting a weak visual signal if they were
simultaneously maintaining a visual image than if they were maintaining an auditory
image
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Document Summary

Everyday use of visual images = a basis for making decisions, as an aid to remembering. Galton asked participants to describe their images and to rate them for vividness; he asked them to introspect or look within and to report on their own mental contents. The self-report data he obtained fit well with common sense: participants reported that they could inspect their images much as they would inspect a picture. Their descriptions made it clear that they were viewing their images from a certain position and a certain distance; they also reported that they could read off the image details of color and texture. Galton"s participants differed from each other in their self-reports; many described images of photographic clarity, rich in detail while others reported very sketchy images or none at all. In this way, galton"s data might reveal differences in how people talk about their imagery rather than differences in imagery per se.

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