ERPs - Sensory, Prepatory, and Cognitive Processes

Question 1

Write brief notes on ERPs and smell.

Answer 1

Not usually considered but has been done. P3 is much later than you see in auditory and visual domains. Smell has a later, delayed response, sensory registration process is much different. Happens about 1s, whereas it’s at about 300ms in the auditory and visual domain.

Question 2

Write brief notes on ERPs and taste.

Answer 2

Compared water, sweet, salty, sour, and bitter stimuli. All stimuli showed an early component, makes sense as it is sensory registration. Only salty and sour showed a late wave.
Therefore it is not an oddball effect as the oddballs would be sour and bitter.
Why no late components to sweet and bitter?
Small surface area for these -> smaller cortical response
Methodologically challenging. Where do you deliver those stimuli if you want the same proportion of receptors?

Question 3

Write brief notes on ERPs and somatosensory receptors.

Answer 3

Typically do it on the back of the hand.

• Studies have found that stimuli above the detection threshold resulted in somatosensory ERPS. Below the threshold did not. Compared to auditory and visual domains, very minor stimulation leads to strong activation of many areas of the brain.
• Timing is a little delayed, around 400ms

Question 4

Write brief notes on ERPs and attention.

Answer 4

Attention is the primary mediator of attention processing. What difference do we get when someone is directing their attention to a stimulus at an ERP level, and what happens when they are directing their attention elsewhere?
- Increased amplitude ERP to attended vs. ignored stimuli. However, stimuli presentation was regular, differences may be related to arousal.

• New paradigm: unpredictable, random ISI, can’t predict when the stimulus is coming, high load (fast presentation rate). No ERP differences to relevant vs. irrelevant stimuli using this paradigm. With differential preparation controlled, no ERP difference
• Selective attention - target and standard tone to each ear. Enhanced ERP components from 60-80ms to attended tones. The differentiation in the wave form is long. Starts at the N1 but moves all the way through the wave form.

Question 5

Describe contingent negative variation (CNV).

Answer 5

Functionally it is really important, otherwise we are just measuring waveforms. CNV is what happens in the brain when somebody is getting ready to respond to a stimulus. Can occur in the absence of motor response so it is not purely due to motor activity
- Long lasting negative shift
- Develops between warning stimulus (S1) and second stimulus (S2)
- Reflects state of expectancy
- Reflects increased cortical excitability – contingent negative shift/variation in the lead up to S2
- Fixed timing
- If 1000ms interval between S1 and S2 – CNV starts 200-400ms after S1, peaks 400-900ms after S1, drops abruptly after S2
- If S1-S2 interval is longer then CNV shows early and late portions. Won’t see immediate cortical excitability when you have to wait 6s for stimulus. Ability to see how people cortically prepare for the oncoming stimulus
o Early wav peaks 1-3 seconds after S1
o Late wave peaks before S2
- Early component – O wave (orientation)
- Late component – E wave (expectancy

There are two types of CNV wave shapes:

• Type A: fast rise time (when subject is unsure about when S2 would occur). Not very efficient, using up resources
• Type B: slow rise time (subject more certain).

Question 6

Describe the readiness potential (RP).

Answer 6

Also known as the bereitschaft potential. It is the preparation to act. Occurs 500-1000ms prior to voluntary and spontaneous movements. It is a measure of activity in the motor cortex and supplementary motor area of the brain leading up to voluntary muscle movement.

Question 7

Do the CNV and RP differ? If so, how?

Answer 7

Yes, they are.

• Differences in eliciting paradigm. What we are getting the person to in these contexts is different
• We are seeing neural change which correspond with motor response different from CNV – cortical readiness and excitability related to second stimulus which is always coming
• They have vastly different scalp topography. RP is more central and strongly lateralised. RP is not evident in the frontal area, which CNV is.
• Simple vs. complex movements – RP wider scalp topography for complex relative to simple movements. For complex movements, an early frontal RP is seen, indicating the planning of a skilled motor act

Question 8

Write brief notes on the P300.

Answer 8

The P300 is the most investigated ERP component. It is functionally important as it is part of the cognitive processing sequence. If the stimulus is made relevant to you by the experimental situation, you are going to see a P3.
- Can occur from 250-900ms, depending on info processing required for the stimulus. If the load is light, closer to 250ms.
Studies suggest different task-specific functional significance of the P3
- Second of two rapidly presented stimuli, if second stimulus allows decision to be made
- Stimuli detected with confidence vs. less so
- Infrequent vs. frequent stimuli
- Subsequently recalled words vs. words not recalled

 
P3a vs. P3b – processing requirements are different:
- P3a to infrequent novel stimuli, more frontal. Not the same in all locations but certainly more evenly spread
- P3b to infrequent target stimuli, posterior maximum

Question 9

Describe the memory comparison process (Donchin, 1981).

Answer 9

Input -> different stimulus?
If yes -> neural representation, P300
If no -> N1/P2, N200

• If the stimulus is the same, neuronal model of the stimulus remains unchanged -> sensory components
• If the stimulus is different -> attentional resources allocated, NM is updated -> P3b

Question 10

Describe the model of resource allocation (Kahneman, 1973).

Answer 10

System is modulated by overall arousal level. This governs the amount of attention available for task performance. P3 represents allocation of attentional resources

• Undemanding task: amplitude is relatively large and latency short
• Demanding task: amplitude smaller and latency longer as processing resources are used for task performance
• Passive tasks: smaller P300 because stimulus and non-task events engage resources to reduce amplitude

Question 11

Describe Polich’s (2003) model of attention processing.

Answer 11

• Stimulus info maintained, monitored by ACC
• Target/distractor disrupts attention  P3a (via ACC and frontal area)
• Attention-driven activity signal may be transmitted to temporal-parietal areas
• Memory related storage operations are engaged  P3b via temporal/parietal structures
  Every P300 is composed of the P3a and P3b subcomponents