Perceptual Processes:
Double Dissociations, Bottom Up & Top Down Processes
Psychology 355: Cognitive Psychology
Instructor: John Miyamoto
04/04/2016: Lecture 02-1
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Outline
• Localization of cognitive functions
• Double dissociations in brain imaging
Lecture probably
ends here
• Unconscious inference in perception
• Bottom up and top down processes in perception
Psych 355, Miyamoto, Spr ‘16
Localization of Function - Definition
2
Localization of Function
• Localization of function is the hypothesis that specific cognitive
functions are served by specific areas of the brain.
• Localization of function can be demonstrated by:
1)
clinical studies of brain injuries;
2)
brain imaging of animals or humans while they perform cognitive tasks.
Psych 355, Miyamoto, Spr '16
Localization of Function in FFA and PPA
3
Next: fMRI Evidence for Brain Areas that Process
Information about Faces and Information about Places
O'Craven, K., & Kanwisher, N. (2000). Mental imagery of faces and places activates corresponding
stimulus-specific brain regions. Journal of Cognitive Neuroscience, 12, 1013-1023.
FFA: Fusiform face area.
Specialized for faces. (“ventral occipito-temporal cortex”)
PPA: Parahippocampal place area.
Specialized for representing location information.
(“ventromedial cortical region”)
Psych 355, Miyamoto, Spr '16
Graphic Showing Location of FFA & PPA
4
Location of the fusiform face area and
parahippocampal gyrus
Graphic from
http://labnic.unige.ch
/nic/htms/fmri.html
Parahippocampal
place area (PPA)
Fusiform face
area (FFA)
Diagram of Brain
Head Facing Left
•
Psych 355, Miyamoto, Spr '16
Graphic is from the article: Haynes, J-D., & Rees, G. (2006). Decoding
mental states from brain activity in humans. Nature Reviews Neuroscience,
7, 523-534.
fMRI Results for Face & Place Recognition
5
O’Craven & Kanwisher – Research Hypotheses
• Research Goal: To test the claim that the fusiform face area is
specialized for face perception.
• Prediction:
FFA will be activated by face stimuli but not by location stimuli.
PPA will be activated by location stimuli but not by face stimuli.
Psych 355, Miyamoto, Spr '16
Graph of Activity in FFA & PPA when Viewing Faces and Places
6
% Signal Change
fMRI Study of Face and Place Perception
% Signal Change
FFA: Fusiform face area.
Specialized for faces.
PPA: Parahippocampal
place area. Specialized
for representing location
info.
Perception
Subjects views a face
Psych 355, Miyamoto, Spr '16
or a place
.
Look at Just the Upper Half of this Graph
7
% Signal Change
fMRI Study of Face and Place Perception
% Signal Change
FFA: Fusiform face area.
Specialized for faces.
PPA: Parahippocampal
place area. Specialized
for representing location
info.
Perception
Subjects views a face
or a place
.
Face stimulus activates FFA; place stimulus does not.
Psych 355, Miyamoto, Spr '16
Look at Just the Lower Half of this Graph
8
% Signal Change
fMRI Study of Face and Place Perception
% Signal Change
FFA: Fusiform face area.
Specialized for faces.
PPA: Parahippocampal
place area. Specialized
for representing location
info.
Perception
Subjects views a face
or a place
.
Place stimulus activates PPA; face stimulus does not.
Psych 355, Miyamoto, Spr '16
Point Out that There Is a Double Dissociation
9
% Signal Change
fMRI Study of Face and Place Perception
FFA: Fusiform face area.
Specialized for faces.
% Signal Change
PPA: Parahippocampal
place area. Specialized
for representing location
info.
Perception
Face and place stimuli have opposite effects on FFA and PPA.
Double dissociation! Supports claim that FFA serves face
perception and PPA serves spatial perception
Psych 355, Miyamoto, Spr '16
Define Double Dissociation; Discuss Double Dissociation
10
Double Dissociation as Demonstrated by Brain Imaging
Suppose you are studying the function of two brain areas, A and B.
Results of brain imaging exhibit a double dissociation if ....
(i) one class of stimuli activates area A and fails to activate area B;
(ii) a different class of stimuli activates area B and fails to activate
area A.
Example:
•
•
Viewing faces activates FFA but not PPA;
•
Viewing places activates PPA but not FFA.
Double dissociations are important because they provide evidence
for specialization of function in different areas of the brain.
(This is one type of evidence for localization of function.)
Psych 355, Miyamoto, Spr '16
Double Dissociation as Demonstrated by Clinical Studies
11
Double Dissociation as Demonstrated by Clinical Deficits
Suppose you are studying the function of two brain areas, A and B.
Clinical studies uncover a double dissociation if ...
(i) injuries to area A causes impairment on a cognitive task X
but not on a different cognitive task Y;
(ii) injuries to area B causes impairment on a cognitive task Y
but not on a different cognitive task X;
Example:
•
•
injuries to the fusiform face area (FFA) can cause inability to recognize
faces, but without causing an inability to recognize places;
•
injuries to the parahippocampal place area (PPA) can cause inability
to recognize places, without causing an inability to recognize faces.
Again, double dissociations are important because they provide
evidence for specialization of function.
Psych 355, Miyamoto, Spr '16
Return to Slide with fMRI Results that Display a Double Dissociation
12
Contrast Double Dissociations
in Brain Imaging and in Clinical Studies
Results of brain imaging exhibit a double dissociation if ....
(i) one class of stimuli activates area A and fails to activate area B;
(ii) a different class of stimuli activates area B and fails to activate
area A.
---------------------------------------------------------------------------------Clinical studies uncover a double dissociation if ...
(i) injuries to area A causes impairment on a cognitive task X
but not on a different cognitive task Y;
(ii) injuries to area B causes impairment on a cognitive task Y
but not on a different cognitive task X;
Psych 355,, Miyamoto, Spr '16
Return to fMRI Results for Face & Place Stimuli - Point Out Double Dissociation
13
% Signal Change
fMRI Study of Face and Place Perception
FFA: Fusiform face area.
Specialized for faces.
% Signal Change
PPA: Parahippocampal
place area. Specialized
for representing location
info.
Perception
Face and place stimuli have opposite effects on FFA and PPA.
Double dissociation! Supports claim that FFA serves face
perception and PPA serves spatial perception
Psych 355, Miyamoto, Spr '16
Summary: Localization of Cognitive Function & Double Dissociation
14
Summary
• Preceding results demonstrate a localization of function in the FFA
and PPA.
• The pattern of results was a double dissociation between the
response of the FFA and PPA to face stimuli and place stimuli.
Psych 355,, Miyamoto, Spr '16
Bottom Up & Top Down Processes - Definition
15
Bottom Up and Top Down Processing
• Bottom up processing – processing of current stimulation influences
what is perceived
• Top down processing – background knowledge, learning and
expectations influence what is perceived.
Bottom up processing is data driven.
Top down processing is theory-driven,
knowledge-driven, and context-driven.
Example of top down processing:
Your knowledge of rectilinear solids
informs your perception.
Psych 355, Miyamoto, Spr '16
Examples of Top Down and Bottom Up Processing
16
Examples of Bottom Up Processes
• Elementary feature detection, e.g., edge detectors, bar detectors,
motion detectors.
• The following color perception is bottom up:

Your perception of the red squares is dictated by the stimulus;
the perception is not influenced by prior expectations or beliefs.
• Similarly, the perceived motion
of the blue disk is bottom up.
It is controlled by the stimulus,
not by your beliefs or expectations.
Psych 355, Miyamoto, Spr '16
Example of Top Down Processing
17
Other Examples of Top Down Processes
• When people see a plane crash, at least some witnesses
always claim to have seen flames coming from the engines.
♦
(Top-down when claim is false; either top-down or bottom up when
it is true.)
• Scene understanding involves both top-down and bottom-up
processing.
Psych 355, Miyamoto, Spr '16
Classroom Experiment to Demonstrate Top Down Processes in Object Identification
18
Class Experiment: Demonstration of Top Down Processing
• Instructor:
Divide the classroom into a “left group” and “right group”.
• I will show you an image.
Briefly write down a label for what you see.
E.g., if you see a chair, write down “chair.”
• Left half of the room will close their eyes for the first image.
Right half of the room will close their eyes for the second image.
• Everyone will open their eyes and complete the experiment.
Psych 355, Miyamoto, Spr '16
Condition 1: View Image 1a
19
Students on Left – Eyes Open
Students on Right – Eyes Closed
Label this image “Image 1a”.
Write down a name for what you see.
Psych 355, Miyamoto, Spr '16
Condition 2: View Image 1b
20
Students on Left – Eyes Closed
Students on Right – Eyes Open
Label this image “Image 1b”.
Write down a name for what you see.
Psych 355, Miyamoto, Spr '16
View Image 2
21
Everybody’s Eyes Open
Label this image “Image 2”.
Write down a name for what you see.
Psych 355, Miyamoto, Spr '16
Collect Results of Class Demo Experiment
22
Results of Classroom Experiment
• We will only collect data for what you saw in Image
2.
• People on the LEFT SIDE:
Raise your right arm if you wrote down
“mouse” or “rat” for Image 2?
Raise your left arm if you wrote down
“old man” or “man” or “face” for Image 2?
• People on the RIGHT SIDE:
Raise your right arm if you wrote down
“mouse” or “rat” for Image 2?
Raise your left arm if you wrote down
“old man” or “man” or “face” for Image 2?
Psych 355, Miyamoto, Spr '16
Show Images 1a, 1b, 2
23
LEFT SIDE saw Image 1a
EVERYONE saw
Image 2
.
Psych 355, Miyamoto, Spr '16
RIGHT SIDE saw Image 1b
Top Down Processing:
What you see in
Image 2 depends in
part on what you expect
from Image 1.
Summary re Bottom Up & Top Down Processing - END
24
Summary re Bottom Up & Top Down Processing
• What we see is usually the consequence of both top-down and
bottom-up processing.
• Remember Helmholtz’s unconscious inference.
Top down processes (inferences) fill in information
that is not present in the actual stimulus.
Psych 355, Miyamoto, Spr '16
END
25