Task 4 - MEG & EEG Oscillations Flashcards
What is a more direct method of measurement? EEG or fMRI?
EEG
What is a field of research that benefits highly from the temporal resolution of EEG?
E.g. Implicit Racial Bias
When determining waveforms, EEG signals are often ____ or _____.
Stimulus-locked; Response-locked
Describe Ito et al.’s racism experiment.
Oddball paradigm: Presenting positive objects paired with either white or black faces -> Black faces had a larger P3 response as they were perceived as more different from positive stimuli
The fact that our attitudes towards certain faces influences basic perception is shown by…
That N170 is sensitive to face evaluation.
How does ECoG improve on EEG?
It has better spatial resolution
What exactly does EEG respond to?
post-synaptic potentials that change extracellular membrane potentials
When are alpha waves often observed and what frequency do they correspond to?
~10Hz
Observed at rest
What is often referred to as a good location for the reference electrode in EEG?
Mastoid Bone
How can a waveform be quantified?
Frequency (Hz)
Amplitude (Microvolt)
Phase (Degrees)
What happens in a Fourier Analysis?
When multiple frequencies act at the same time, Fourier analysis can disentangle them and show what frequencies are present how strongly.
What are the X and Y axes in a frequency spectrum?
X: Frequency
Y: Amplitude
What is the name of the MEG equivalent of ERP?
ERF - Event related field
Name two crucial differences in the information obtained from EEG/MEG studies vs RT studies.
- RT can only capture end results, whereas EEG and MEG show the whole process.
- EEG and MEG can also be analyzed when there is no reaction to be measured.
What anatomical feature is one reason why dipoles are large enough to be measured?
Cortical Organization in Columns
What is an important reason, that setting up MEG equipment is very costly?
You need to shield the entire room from the earth’s magnetic field.
As opposed to EEG, MEG can only detect ____ dipoles.
tangential
Which measurement techniques have the inverse problem?
Only MEG
Which subcortical structure is often said to be the motor of cortical oscillations?
The Thalamus
What are some alternatives to making use of a reference electrode?
- Using the average as reference
- Laplacian Transformation - average potential difference between each electrode and the nearest four electrodes
When are delta waves often observed and what frequency do they correspond to?
1-4 Hz
present during sleep
When are theta waves often observed and what frequency do they correspond to?
4-8Hz
drowsiness
when present in the frontal lobe: focused attention and mental effort
When are beta waves often observed and what frequency do they correspond to?
13-30Hz
During attention
When are gamma waves often observed and what frequency do they correspond to?
36-44Hz
Associated with arousal
Often occur in bursts
When investigating waveforms, what is a very important parameter of one’s setup to consider?
Sampling rate
What theorem says, that sampling rate should be at least two times the highest frequency under investigation?
Nyquist Theorem
What is Aliasing?
When a signal is sampled at a rate that is too low, and introduces irreparable distortion to the digital waveform.
What is the affective congruency effect?
Affective target words are categorized more quickly when preceded by a prime word of the same valence.
What neural mechanism explains the affective congruency effect?
Readiness Potentials
What is a different name for the Laplacian transformation?
Radial Current Flow
What is the reason and effect of a taper transformation?
It reduces amplitudes at both ends of an epoch to zero in order to keep variance stemming from other epochs low.
