Eg. Participants watching silent video (attending to it) while passively listening to a series of acoustic events. Standards is a syllabus 'ba' (90% of the time) and deviants are stimulus 'ga' (10%).
How will standards and deviants differ in mismatch negativity graphs?
Standards and deviants elicit ERPs which differ in amplitude
The amplitude difference can typically be observed between 150-200ms after stimulus presentation.
Why is MMN useful?
Useful to study acoustic processing without the contamination of attention.
Automatic, so it can also be used to study acoustic processing in non-verbal participants (eg. infants and coma patients)
What are the two important ERP waves related to higher cognitive functions you should know about?
What is P300 thought to be the reflection of?
A sum of overlapping waves (why it's sometimes called P300 complex)
Usually thought to be a reflect...
1. stimulus categorization
2. working memory updating processes
When does P300 appear?
to task-relevant and attended stimuli in many different task contexts
Observed in conscious oddball task
What is the typical latency of P300? What is the latency a reflection of?
Latency depends on task difficulty (more difficult, the longer the latency)
Why might a wave of latency 300ms and 900ms in two different tasks be both categorized as P300?
because researchers assume that similar brain functions underlie the generation of the waves in both tasks irrespective of the differences in task difficulty.
[This illustrates the importance of considering task context when interpreting ERP waves/phenomena].
What are the two frequent potential constituents of the P300 waves?
[both can be observed in the conscious oddball task situations)
What are the respective topography of the P3a and P3b?
P3a: a more frontal topography
P3b: occipito-parietal topography
What do P3a and P3b each reflect?
P3a: typically appears to unexpected or less typical (but consciously observed stimuli)
P3b: thought to be the constituent which reflects the categorization and working memory processes related to task-relevant stimuli.
[Although take these two with a pinch of salt - ASK!]
The distinction of P3a and P3b waves illustrates what about analysis of EEG?
Illustrates the importance of considering the topography of ERPs when trying to interpret them.
(They will oftenb fuse together as they have similar amplitude and latency.)
When does N400 appear?
When participants encounter semantically unexpected stimuli.
(so when the meaning is weird)
In what kind of a test would N400 be observed in?
In tests where the participants view sentences word-by-word.
Often the wave corresponding to the last word is observed.
When the last word is semantically anomalous with the preceding part of the sentence, then the negative N400 wave appears. (eg. She spread the warm bread with socks.)
What happens when there are anomalous physical stimulus features?
N400 will not appear (only, it seems, for anomalous semantic stimuli).
Eg. When the last word is semantically congruent but is written with large caps (SHOES).
In such case, an enhanced P3b (not P3a? ASK!) rather than N400 appears.
Where, topographically, does the N400 wave maximum amplitude appear?
Over the parieto-occipital scalp.
In many contexts, the __ and __ appear together forming a _____ complex.
P300/N400 complex (eg. 3+4=.. 9, 7 or 16?)
Why might electric brain potentials related to hand and limb movements be relatively easy to measure?
Motor cortex is well defined
Motor cortex is close to the scalp
What is one of the most important motor potentials we should be aware of? What does it mark?
Lateralized Readiness Potential (LRP)
It is an event-related potential which marks the lateralized movement preparation in the motor cortex.
(in other words, preparation for movement on a certain side of the body - limb usually).
Typically, what kind of situation is LRP measured in?
Where the participant has to respond to stimulation either with a right or left hand response finger.
Eg. has to press a response button
What is an important property of LRPs?
LRPs can be detected even before the movement happens
or if no movement happens at all but the participant is preparing for it.
Used for observing unconsciously or latently planned movement procedures.
Give an example of a test that works well when trying to observe Lateralized Readiness Potential. What does it show?
The LRP can measure a latent movement preparation of a left hand even though she uses the right hand in the end - by inhibiting the automatic response of using the left.
Shows that the to-be-neglected aspects of the stimuli (the semantic meaning of the word) were not only semantically processed but also resulted in a movement command which did not manifest. Important for some psycho-physiological theories.
What fact is the computation of LRP based on?
The fact that lateralized hand movement result in lateralized ERP phenomena.
What are the electrodes corresponding to the left and right scalp respectively? And what are the computations needed to calculate the LRP?
C3 - left scalp (right hand movement)
C4 - right scalp (left hand movement)
C3minusC4 will give a negative voltage if the right hand moves/planning to move.
Average of C3-C4 and C4-C3 gives a voltage which is a general index of response hand movement. (This is the LRP).
What is the advantage of LRP?
The functional interpretation is very clear.
If the experiment is well-designed to elicit movement related brain activity it is very straightforward to interpret the data.
Contralateral and Ipsilateral.
Contralateral: opposite side of body
Ipsilateral: same side of the body
What is an artifact?
Electrical signals detected along the scalp by an EEG, but that originate from non-cerebral origin.
Eg. head movement, eye movement
Why do we need to measure the electric activity of eye muscles? What is this called?
Electro-oculogram (EOG) - to detect Ocular Artifact Propagation
Very important for detecting eye movement artifacts (helpful when detecting noise when analysing EEG).