PSYC20006 Lecture Notes - Lecture 8: Bonferroni Correction, Receptive Field, Haemodynamic Response
10 May 2018
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Lecture 8
- While blood oxygen levels are influenced by neural activities, they are influenced by
other factors as well (such as limitations in blood flow)
- When neuron is activated, more blood will directed to it (causes blood oxygen level
around it to increase); does not happen immediately, there is haemodynamic lag, this
is why fMRI signals lag the neural activity
- Haemodynamic response function: delayed in time and spread out over time;
determines the temporal resolution of fMRI
- Blood flow cannot be directed precisely to neurons that need it; can be directed to
general area where neurons need it (precise to about 1 mm); when neurons become
excited and needs more blood, blood will go to an area about 1 mm of it; limits spatial
resolution of fMRI, cannot distinguish structures that are closer than 1 mm
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- One of the most famous fMRI studies
- First study to demonstrate that there is a specialised part of the brain for processing
just faces, not all objects are processed the same way, and great example of how to
do fMRI properly
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- In first experiment: 2 conditions
- Condition A: subjects were shown a series of faces, shown one face at a time after
another, while they sat in scanner and just looked at the stimulus
- Condition B: subjects were shown a series of other random objects
- Subtracted BOLD fMRI activity in Condition B from Condition A to find out those
areas of brain which are more active when the subject viewed faces as opposed to
viewing other random objects
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find more resources at oneclass.com
- Found areas of the brain that responded more strongly to faces than objects
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- Three virtual slices through the brain, showing same area of brain, the fusiform gyrus
(located at centre of green cross)
- Sagittal: front to back
- Axial: horizontal
- Coronal: straight down
- This area of brain was preferentially activated by faces, more active when the
subjects saw faces than when the subjects saw all the other stuff
- Nowadays this area is referred to as fusiform face area
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- Replicates the study
- To verify the results could be replicated → ran the same subject several times and got
the same result
- Can replicate within a subject
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find more resources at oneclass.com
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- Exact location varies from subject to subject but it’s in the same part of the brain
- Most are right handers which had activity in the left area of brain
- Left handers got activity bilaterally or in the right area of brain, left handers usually
show lateralised results bilaterally or the other side of brain
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
While blood oxygen levels are influenced by neural activities, they are influenced by other factors as well (such as limitations in blood flow) When neuron is activated, more blood will directed to it (causes blood oxygen level around it to increase); does not happen immediately, there is haemodynamic lag, this is why fmri signals lag the neural activity. Haemodynamic response function: delayed in time and spread out over time; determines the temporal resolution of fmri. One of the most famous fmri studies. First study to demonstrate that there is a specialised part of the brain for processing just faces, not all objects are processed the same way, and great example of how to do fmri properly. Condition a: subjects were shown a series of faces, shown one face at a time after. In first experiment: 2 conditions another, while they sat in scanner and just looked at the stimulus. Condition b: subjects were shown a series of other random objects.
