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PSYC 351C > ERPs and Attention (1) > Flashcards

ERPs and Attention (1) Flashcards

1
Q

What did Hans Berger do in 1924?

A
  • first to record EEG signals
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2
Q

How did people look at EEG signals in the beginning?

A
  • looked at the wave pattern over time

- see changes in the wave pattern when sleeping for example

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3
Q

What does EEG stand for?

A
  • electroencephalogram
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4
Q

Who conducted the first cognitive ERP study?

A
  • Gray Walter and the CNV 1964
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5
Q

What was the first cognitive ERP study?

A
  • it looked at ERPs for 4 conditions
  • A: when you hear a click
  • B: light flashes
  • C: click followed by flashes
  • D: click, followed by flashes and press a button
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6
Q

What was found in the first cognitive ERP study?

A
  • when the participant needed to press a button after the ERP waveform differed as they anticipated the flashes
  • there was no difference in stimuli, just the mental state/process
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7
Q

What is an ERP?

A
  • looking at a specific point in time in response to stimulus or event
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8
Q

When looking at an ERP, which way is up? What is CNV?

A
  • negative is up
  • contingent negative variation
  • contingent: dependent, negative: plotted up
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9
Q

What is the most important difference between EEG/ERPs and TMS?

A
  • manipulation vs measurement
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10
Q

What is the instrument used for recording EEG?

A
  • EEG cap with electrodes in specific places
  • international 10-20 system
  • place cap by measuring head and using bony bumps to mark certain places
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11
Q

What is the EEG lab on campus called?

A
  • Brain and Cognition Event-related Potential Laboratory
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12
Q

What are strong signals caused by?

A
  • eye blinks

- can also be from eye, neck or mouth movements

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13
Q

Where do ERPs come from?

A
  • many orthogonal cortical pyramidal cells
  • excitatory transmitter released on apical dendrites causes positive charges to flow into dendrites (net negative on outside)
  • polarity reverses with inhibitory transmitter
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14
Q

What does the polarity at the scalp depend on?

A
  • orientation of the cortical surface and the position of the reference electrode
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15
Q

In what conditions are scalp-related potentials possible?

A
  • only for open field or layered structures with consistent orientations
  • primarily cerebral cortex
  • if a closed field, the neurons are all facing in different directions and the consequent electromagnetic fields will cancel out instead of summing
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16
Q

How are voltages spread out?

A
  • voltages are spread through the brain by “volume conduction”
  • skull causes lateral spread
  • measured as positive in direction of flow and negative in opposite direction of flow
  • not much recorded where positive and negative meet
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17
Q

How do we get ERPs from EEG?

A
  • stimulus is presented repeatedly and EEG averaged over all trials
  • consistent peaks and troughs come through that are associated with the stimulus
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18
Q

What are the ERPs “locked” to?

A
  • stimulus locked: line up on stimulus and then average

- response locked: line up on responses and then average

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19
Q

What is the temporal resolution of ERPs?

A
  • about 1 ms (because recording 250 to 1000 per second)
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20
Q

What are some typical ERPs?

A
  • brainstem responses
  • mid-latency response
  • long-latency responses
21
Q

What is N170?

A
  • voltage reflects face-related activity plus everything else that is active at 170 ms
  • difference reflects only brain activity that differentiates between faces and cars
22
Q

What is the difference wave?

A
  • difference wave shows what is changing in brain activity between two different types of trials
  • can sometimes reveal the time course of the underlying component
23
Q

What is the superposition problem?

A
  • the voltage at an electrode at time t is a weighted sum of all components that are active at time t
  • this makes it difficult to determine underlying components from observed waveforms
  • the recorded wave will look different depending on where we record it on the scalp
24
Q

What is rule #1 about peaks a d components?

A
  • peaks and components are not the same thing
  • there is nothing special about the point at which the observed waveform reaches a local maximum
  • peaks are maximums and minimums in observed waveform
  • components are possible waves that made up the waveform
25
Q

What is rule #2 about peaks and components?

A
  • it is impossible to estimate the time course or peak latency of an underlying ERP component by looking at a single ERP waveform
  • there may be no obvious relationship between the shape of a local part of the waveform and the underlying components
26
Q

What is rule #3 of peaks and components?

A
  • an effect during the time period of a particular peak may not reflect a modulation of the underlying component
  • as in it may look like one component is being affected, when it’s really a different one
27
Q

What might difference waves look like for different electrodes/areas of the brain?

A
  • the waveforms will look very different bu the difference waves will look the same with different magnitudes
  • this is because they are recording the same component from different locations
28
Q

What is rule #4 of peaks and components?

A
  • differences in peak amplitude do not necessarily correspond to differences in component size and differences in peak latency do not necessarily correspond to changes in component timing
29
Q

Why is there an inverse problem (source localization)?

A
  • we are using the resulting waveform to try to figure out the components that caused it
  • there is no unique solution and an infinite amount of combinations are possible
  • given noise, the correct solution may differ substantially
30
Q

What does a single superficial dipole look like?

A
  • creates relatively focused scalp distribution
  • distribution changes if dipole is rotated or shifted
  • easy to localize
31
Q

What does a single deeper dipole look like?

A
  • creates broader scalp distribution
  • changes in dipole location have smaller impact on scalp distribution
  • harder to localize
  • hard to distinguish from broadly distributed superficial activity
32
Q

What does two superficial dipoles look like?

A
  • can still localize reasonably well with 2 dipoles if they are far apart and superficial
33
Q

What does two collinear dipoles look like?

A
  • looks very similar to single superficial dipole

- makes localization very difficult

34
Q

How is ERP spatial resolution?

A
  • as number of dipoles increases, it becomes more difficult to localize
  • spatial resolution is poor and it is complex and hard to define
  • it’s easier to say where it doesn’t come from
  • computer programs will give best guess
35
Q

What are some example ERP components?

A
  • visual sensory
  • auditory sensory
  • P3 family
  • mismatch negativity (MMN): flash red change to green
  • language related (N400): hear ungrammatical sentence
  • response-related (Lateralized readiness potential and error-related negativity: brain processing it made mistake)
36
Q

What are two visual sensory responses?

A
  • P1

- N1

37
Q

What is P1?

A
  • Extrastriate cortex

- sensitive to visual features, arousal and attention

38
Q

What is N1?

A
  • Extrastriate, parietal and frontal subcomponents
  • sensitive to attention
  • N170 is a subcomponent
39
Q

What are later components associated with?

A
  • higher levels of processing
40
Q

What are some auditory sensory responses?

A
  • brainstem auditory evoked responses: brief clicks, cochlea, auditory nerve and brainstem nuclei
  • midlatency responses: medial geniculate nucleus and primary auditory cortex, modulated by highly focused attention
  • auditory “long-latency” sensory responses: at least 3 N1 subcomponents, sensitive to attention
41
Q

What is P3?

A
  • P3 is a component that is much larger when a rare name is said (amplitude depends on probability of a task-defined stimulus category)
  • processing that the category is different which occurs after earlier auditory processing
  • latency is tied to amount of time required to perceive and categorize
42
Q

What is mismatch negativity (MMN)?

A
  • elicited by an auditory stimulus that physically mismatches preceding stimuli
  • generated in auditory cortex
  • appears to reflect comparison of incoming stimulus with echoic memory
  • largely automatic but can be attentuated with strong attention
43
Q

What is N400?

A
  • negativity happening at about 400 ms after stimulus

- responds to semantic violations: word does not make sense in context

44
Q

What is lateralized readiness potential?

A
  • lateralized: only found in one side of the brain
  • ex. if responding with right hand, see LRP in left hemisphere
  • difference starts when you figure out what hand you’re going to use
  • response occurs at peak
45
Q

What is error-related negativity?

A
  • flanker task: respond to central letter (XXOXX) or (XXXXX)
  • more likely to make mistake when flanked by wrong letter
  • the wave shows one initiating the response and realizing they’ve made a mistake as they’re responding
46
Q

What are the risks to ERPs?

A
  • almost non-existent
  • discomfort from cap and gel
  • need to remain still
47
Q

What are ERPs good for?

A
  • determine if an experimental manipulation influences process A or process B
  • identifying multiple neurocognitive processes
  • covert monitoring of processing (person may not be consciously aware of change but something still occured in brain)
48
Q

When are ERPs not useful?

A
  • want certainty of neuroanatomical location
  • interested in slow activity (greater than 2 s) that is not time-locked to something
  • cannot collect large numbers of trials
  • process of interest does not have an ERP component
  • subject frequently moves or needs to move for experiment (talking)

PSYC 351C (13 decks)

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