1. fMRI: What Does It Measure?
Psychology 355: Cognitive Psychology Instructor: John Miyamoto 04/02/2018: Lecture 02-1
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2. Lecture probably ends here
Outline
fMRI – what does it measure?
Example of fMRI study of face recognition
Top down and bottom up processing
Lecture probably ends here
Psych 355,, Miyamoto, Spr '18

3. fMRI Uses a Big Magnet
This images is used with permission of the author, J. J. B. Allen at the University of Arizona.
Graphic Showing BOLD Contrast
Psych 355, Miyamoto, Spr '18

4. Measuring Activation – A Subtraction Measure
Control Condition
Test Condition
Oxygenated Blood
Deoxygenated Blood
Brain Activity = Oxygen Concentration in Test Condition MINUS Oxygen Concentration in Control Condition
Details of fMRI Measurement
Psych 355, Miyamoto, Spr '18

5. fMRI Dependent Measure
BOLD Signal
Blood Oxygen Level Dependent Signal
BOC Measure
Blood Oxygen Contrast Measure
Details of fMRI Measurement
Psych 355, Miyamoto, Spr '18

6. Measuring Activation – A Subtraction Measure
Control Condition
Test Condition
Oxygenated Blood
Deoxygenated Blood
Brain Activity = Oxygen Concentration in Test Condition MINUS Oxygen Concentration in Control Condition
Details of fMRI Measurement
Psych 355, Miyamoto, Spr '18

7. How Does fMRI Measure Brain Activity
Local neuronal activity
 Increased local metabolic rate
 Increased blood flow
 Increased oxygenated hemoglobin
 Uptake of O2 less than supply
 Decreased concentrations of deoxyhemoglobin
 Increased local fMRI T2* signal (electromagnetic signal)
BOLD signal – Blood Oxygenated Level-Dependent signal (the measured response is dependent on the level of oxygenated blood)
A.k.a. hemodynamic response: Change in blood response measured over time
Control Condition
Test Condition
Strengths and Weaknesses of fMRI
Psych 355, Miyamoto, Spr '18

8. Strengths and Weaknesses of fMRI Measures of Brain Activity
Excellent spatial resolution
Magnetic changes can be measured at a resolution of 1 - 3mm³.
Temporal resolution is poor.
In the 1990’s the temporal resolution was about 4 seconds.
Today the temporal resolution is about 2 seconds.
MRI machines impose physical limitations on the subjects.
Localization of Function
Psych 355, Miyamoto, Spr '18

9. Localization of Function
Specific functions are served by specific areas of the brain
Cognitive functioning breaks down in specific ways when areas of the brain are damaged
Brain imaging can identify areas of the brain that serve specific functions.
Localization of Function in FFA and PPA
Psych 355, Miyamoto, Spr '18

10. Next: fMRI Evidence for Brain Areas with Specialized Perceptual Functions
O'Craven, K., & Kanwisher, N. (2000). Mental imagery of faces and places activates corresponding stimulus-specific brain regions. Journal of Cognitive Neuroscience, 12,
FFA: Fusiform face area. Specialized for faces (“ventral occipito-temporal cortex”)
PPA: Parahippocampal place area Specialized for representing location info (“ventromedial cortical region”)
Face Recognition: Graphic Showing Location of FFA & PPA
Psych 355, Miyamoto, Spr '18

11. Location of the fusiform face area and parahippocampal gyrus
Graphic from
Parahippocampal place area (PPA)
Fusiform face area (FFA)
Diagram of Brain Head Facing Left
Graphic from the article: Haynes, J-D., & Rees, G. (2006). Decoding mental states from brain activity in humans. Nature Reviews Neuroscience, 7,
O'Craven & Kanwisher Research Hypotheses
Psych 355, Miyamoto, Spr '18

12. 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.
fMRI % Signal Change in FFA & PPA
Psych 355, Miyamoto, Spr '18

13. 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.
% Signal Change
Perception
Subject views a face or a place
Psych 355, Miyamoto, Spr '18
Look at Just the Upper Half of this Graph

14. fMRI Study of Face and Place Perception
% Signal Change
FFA: Fusiform face area. Specialized for faces.
PPA: Parahippocampal place area. Specialized for representing location information.
% Signal Change
Perception
Subject views a face or a place Face stimulus activates FFA; place stimulus does not.
Look at Just the Lower Half of this Graph
Psych 355, Miyamoto, Spr '18

15. 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.
% Signal Change
Perception
Subject views a face or a place Place stimulus activates PPA; face stimulus does not.
Psych 355, Miyamoto, Spr '18
Point Out that There Is a Double Dissociation

16. 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.
% Signal Change
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 '18
Define Double Dissociation; Discuss Double Dissociation

17. Double Dissociation in Brain Imaging
Suppose you are studying the function of two brain areas, A and B. Results exhibit a double dissociation if ...
one class of stimuli activates area A and fails to activate area B;
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.)
Summary re Physiological Methods
Psych 355, Miyamoto, Spr '18

18. Summary Physiological methods in cognitive neuropsychology
Single cell recordings
Event-related potentials (ERP’s)
Positron emission tomography (PET)
Functional magnetic resonance imaging (fMRI)
Localization of function – identifying parts of the brain that are involved in processing specific types of stimuli or performing specific tasks.
Double dissociation – demonstrating that the neural response is specific to particular types of stimuli or specific tasks.
Psych 355, Miyamoto, Spr '18
Start Perception Topic - Bottom Up & Top Down Processing

19. 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.
Examples of Top Down and Bottom Up Processing
Psych 355, Miyamoto, Spr '18

20. 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.
Example of Top Down Processing
Psych 355, Miyamoto, Spr '18

21. 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.
Classroom Experiment to Demonstrate Top Down Processes in Object Identification
Psych 355, Miyamoto, Spr '18

22. Monday, 2 April, 2018: The Lecture Ended Here
Psych 355,, Miyamoto, Spr '18