Lec week 9 Mismatch Negativity, P3 family, N2pc

oddball paradigms

a deviant stimulus (oddball) presented infrequently with a frequent standard stimulus

can be 2 stimuli or 3 stimuli

can be auditory, visual

2 types of deviant stimuli

task-relevant/target stimulus

irrelevant/nontarget stimulus

what can a deviant stimulus for a visual oddball paradigm be varied

novel deviant (ex: a different picture for every deviant stimulus)

3 advantages to 3 stimulus oddball paradigm

1. deviants (nontarget and target) are equally frequent → equal signal to noise ratio

2. controls for attention, motor responses

3. can make a deviant ‘novel’

are different cognitive processes involved in discriminating target and nontarget deviants?

yes

P3a = nontarget deviant

P3b = target deviant

is attention involved in processing deviant stimuli

yes, the deviant can demand attentional focus.

are there special processes for novelty detection

novelty detection is not entirely special because it is observed as P3a, which responds to difficult target and standard discrimination. This is not limited to just novel stimulus.

which modality of MMN is the true MMN

auditory

mismatch negativity arises from either 2 things

1. sensory memory trace (compare new stimulus w old one in memory)

2. expectancy deviation (what u expect)

3 ERP components elicited by oddball paradigm

1. mismatch negativity (MMN)

2. N2 family

3. P300 family

what is MMN

generated in auditory cortex near N1 peak

second generator in frontal cortex (right lateralized) → may signal need for attention shift to deviant stimulus

product of comparision between stimulus and representation of a recent stimulus in the sensory memory

components of N2 family

N2b/anterior N2

N2c/posterior N2

which component of N2 family occurs first

N2b occurs after N2a, while N2c occurs later

MMN elicited by

elicited by an infrequent and discriminable change (deviant) in a frequent auditory stimulus

discriminable change includes:

frequency/amplitude: beep, beep, boop

intensity (loudness): beep BEEP

when does MMN start

at peak of N1 component or area between the deviant minus standard difference wave

where is MMN found on the scalp? why?

MMN found on the fronto-central scalp, although its neural source is in the temporal lobe. This is due to volume conduction (electric fields picked up away from neural source)

what does the blue and red in a MMN indicate

the blue is negatvitiy, which is one side of the dipole, theerefore the red is the other end of the dipole. This is called a polarity flip. The neural source is found in the auditory cortex which is in green, and the dipole is towards the fronto-central scalp, explaining why MMN is found there.

difference between fMRI vs EEG of MMN activity

fMRi - bilateral frontal generator, bilateral auditory generator

EEG - right lateralized frontal generator, bilateral auditory generator

is EEG or MEG better for determining neural source

MEG because less volume conduction, thus better able to pinpoint neural source

whats the sensory memory model

standard stimuli is placed into echoic memory (short term) and compared with what you hear. If it is a deviant, it generates a mismatch negativity

is there MMN to repeated tones?

yes but this is due to predictor error rather than mismatch

P3 family

a positivity around 300 ms elicited from a infrequent stimulus

P3 family components

P3b

P3a/novelty P3

No-go P3

P3b

positivty at 300ms elicited by the target stimulus

midline -parietal scalp distribution

occurs later than P3a

often prominent in Pz electrode