Problem 4

Question 1

Event related potentials

Answer 1

Refers to an electrical potential generated by the firing of cortical neurons in response to a specific events

–> Direct measure of neural activity

Question 2

How are ERP signals extracted ?

Answer 2

From an ongoing EEG wave

–> must filter the signal from the background EEG noise

Question 3

2 Major classes of ERP waveforms are of interest for SCAN researchers.

Name them.

Answer 3

1. Stimulus locked waveform
   - -> arise at onset of the stimulus
2. Response locked waveform
   - -> arise when the behavioral response was made

Question 4

How are ERPs scored for analysis/quantified ?

Answer 4

Determining the time window in which a component of interest emerges

–> then measuring the average voltage within that window for each subject

Question 5

P3/P300

Answer 5

Refers to a relatively large + positive deflection that peaks between 300 and 800 ms post-stimulus

–> increases when a given stimulus represents a category that is different from that of preceding stimuli

Question 6

What are the advantages of ERP methods

Answer 6

1. High temporal resolution
2. Ability to measure psychological processes independently from behavioral response
3. Lower costs
4. Upright position when conducting it
   - -> cloesly mimics how people typically interact in the social world

Question 7

What are the Disadvantages of ERP methods ?

Answer 7

1. Low spatial resolution
   - -> insensitive to activity in subcortical structures
2. The neural source of a particular ERP component is likely involved in multiple psychological functions and a one-to-one mapping of a psychological construct can never be assumed

Question 8

How was the P3 component used to assess attitudes ?

Answer 8

Participants were presented with images of

a) white peoples faces b) black peoples faces c) positive objects

each of which appeared in the context of negative images

–> white faces increased P2 and N2 compared to black faces

Question 9

Affective congruency

Answer 9

An affective target word is categorized in terms of its valence more quickly when preceded by prime words of the same valence

ex.: smiling while feeling happy

Question 10

N170

Answer 10

Responds selectively to faces

–> can reveal differences in the extent to which an individual perceives another as a fellow human

Question 11

Can N170 component assess in-group favoritism ?

Answer 11

Yes,

They found larger N170 to ones in-group compared to outgroup faces

BUT: only when intergroup competition is absent and one is somewhat indifferent towards outgroups

Question 12

Can N170 assess racism ?

Answer 12

yes,

as in context of race, the outgroup may be threatening which could lead to enhanced processing of outgroup faces

Question 13

Which components become active/increase in response to stereotyping ?

Answer 13

1. P3/LPP component
2. N400/N4 component
   - -> when someone violates rather than confirms gender stereotypes

Question 14

Magnetoencephalography

MEG

Answer 14

Records magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers

–> its traces can also be recorded and averaged to obtain ERPs

BUT: more reliable than EEG

Question 15

MEG has 2 drawbacks.

Name them.

Answer 15

1. Can only detect current flow if it is oriented parallel to the surface of the skull
2. Magnetic fields generated by the brain are extremely weak

Question 16

What is the MEG primarily used for ?

Answer 16

To study

1. human brain functions non-invasively at time resolutions of better than a ms
2. the way the brain processes signals
3. the functional significance of brain rhythms

Question 17

How does the MEG work ?

Answer 17

1. A neuromagnetometer is positioned around the outside of the head to record magnetic fields
2. SQUIDs are placed at various points on the surface of the scalp
3. Magnetic fields generated by electrically active regions of the brain are transmitted to the SQUIDs

–> magnetic fields must be sampled over a range of locations so the distribution of electrical currents in the brain are accurately calculated

Question 18

Neuromagnetometer

Answer 18

Refers to a helmet shaped device that covers the whole scalp and measures magnetic field or magnetic dipole moment

–> measure the direction, strength, or relative change of a magnetic field at a particular location

Question 19

Superconducting quantum interference device

SQUID

Answer 19

Refers to a very sensitive magnetometer used to measure extremely subtle magnetic fields

–> are in the neuromagnetometer helmets and placed around the scalp

Question 20

Neuromagnetic inverse problem

Answer 20

How can we identify which currents in the brain are responsible for a particular MEG signal by using only info about the magnetic field patterns and the shape of the brain ?

Question 21

How is the neuromagnetic inverse problem solved and the source of the magnetic fields calculated ?

Answer 21

1. Assuming the brain is approximately spherical + its active areas can be represented by single or multiple current dopes
2. Computer guesses where the dipoles might be based on the measured distribution of magnetic fields
3. Computer calculates the external magnetic field that these dipoles would produce
4. Computed + measured field are compared
5. Dipole calculation is repeated at different positions until the calculated + experimental results match as closely as possible

Question 22

Minimum current estimate

Answer 22

Technique to calculate the source of the magnetic fields

–> best as it doesn’t make assumptions about the way in which currents are distributed

Question 23

EEG vs MEG

Answer 23

1. MEG is better than EEG in pointing out where in the brain particular activity takes place
   - -> less distortive measurement of electric potentials
2. MEG only measures the tangentially oriented currents
3. EEG can more reliably pick up currents that originate deep inside the brain or are radially oriented

THUS: to obtain the most info one must monitor the brain w/ both MEG and EEG at the same time - but not possible

Question 24

Normative EEG activity can be divided into … ?

Answer 24

Low EEG frequencies
–> show large synchronized amplitudes (delta + theta)

vs high EEG frequencies
–> show small aptitudes due to high degree of desynchronization
(beta + gamma)

Question 25

Delta Band

1-4 Hz

Answer 25

Low frequency activity

–> typically associated with sleep and neurological pathology.

BUT: Delta activity is mainly an inhibitory rhythm

Question 26

Theta Band

4-8 Hz

Answer 26

Prominent during sleep

–> during wakefulness, there are two types of theta activity:

a) Widespread scalp distribution linked to decreased alertness (drowsiness) and impaired information processing
b) Frontal midline theta activity frontal midline distribution, associated with focused attention, mental effort and effective stimulus processing.

BUT: Theta activity may subserve a gating function on the info processing flow in limbic regions

Question 27

Alpha band

8-13 Hz

Answer 27

Is recorded during states of relaxed wakefulness, especially when eyes are closed

a) Lower alpha
- -> due to stimulus-unspecific + taks-unspecific increases in attentional demands

b) Upper alpha
- -> due to task-specific processing of info

Question 28

Beta Band

13-30 Hz

Answer 28

Has a symmetrical fronto-central distribution

–> Replaces alpha rhythm during cognitive activity and increases with attention and vigilance

Question 29

Gamma Band

36-44 Hz

Answer 29

Associated with attention, arousal, object recognition, top-down modulation of sensory processes, and sometimes perceptual binding

–> brain’s ability to integrate various aspects of a stimulus into a coherent whole

Question 30

What are electrode interpolation methods needed for ?

Answer 30

To deal with artifacts “noise”

Question 31

Linear interpolation

Answer 31

Corrupted activity/noise is reconstructed through weighted average using data from neighboring electrodes

Question 32

Spline interpolation 
(more accurate)

Answer 32

Info from all sensors is used to represent the overall potential distribution on the entire scalp

–> to reconstruct the activity at missing channels

Question 33

How are EEGs used for Data acquisition ?

Answer 33

EEG activity represents the difference between 2 electrodes

–> active vs reference electrode

Question 34

How does the EEG work ?

Answer 34

1. Performed with 20-256 electrodes embedded in an elastic cap that record signals from the cortex and sub-cortex
2. The EEG signal arises from synchronized synaptic activity in populations of cortical neurons

–> higher number of electrodes is not necessarily better as it becomes difficult to ensure high quality data due to poorer signal quality and lower statistical power

3. The electrical potential (voltage) is recorded from each electrode, resulting in a separate waveform for each electrode (x-axis: time; y-axis: voltage).

–> This waveform is a mixture of actual brain activity, artifactual electrical potentials produced outside the brain, and electrical activity induced from external sources

4. Voltage refers to the potential for an electrical charge that moves between two locations
   - -> EEG signal is therefore the voltage between two electrodes

a) active electrode
b) reference electrode that is used for all electrodes

5. This voltage is sampled from each electrode channel
6. Filters are used to remove very slow voltage changes (<0.01-0.1Hz) and very fast voltage changes (>15-100Hz) as they are likely to represent noise emerging from non-neural sources.