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In the three-stimulus oddball procedure, there is an infrequent target in a background of frequently occurring standard stimuli and infrequently occurring distracter stimuli. My question is, since the target and the distracter are both infrequent, how do we make the difference between them? Why do we expect different responses to them? Since I am not allowed to answer my question I post here: I assume that the difference is done in the instruction done to the participant.

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Just as a small side point, you are welcome to write an answer to your own question, particularly if it is well reasoned. –  Jeromy Anglim May 30 '13 at 4:26
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I assume you are talking about a difference in neural activity?

The difference in processing of targets and distracters does not come from their relative frequency, but from their task-relevance: you are paying attention to the targets, thus increasing gain. In auditory MMN, this attention component becomes evident slightly later than the prediction component, and might be missing completely for ignored stimuli (e.g. when the participants are watching a movie while listening to a stream of sounds). Naatanen has more than one review paper that goes into this, this one probably the most recent.

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Thank you for your comments and the review, Ana. If you don't mind, could you suggest the best way to set an MMN experiment? –  Dana Sugu May 30 '13 at 15:04
    
@DS1 - That's a really broad question... I'm into MMN-like phenomena (predictive coding, to be precise) and my studies have MMN-like designs (you can download information on them from my webpage, which you can find in my profile), but they do not follow the classical MMN designs exactly. If I were you, I would read Naatanen first and Schroger second, to get an idea about various designs. But if you have some specific questions, I can try to answer them. –  Ana May 30 '13 at 19:16
    
Oh, and naturally, the exact design would depend on which question you would want to answer with your experiment. Or is there some other purpose to it? –  Ana May 30 '13 at 19:36
    
Yes, I am reading Naatanen. I am interested in surprise and looking for differences between MMN and P300 (P3a). I also wonder whether P3b could take place without P3a. Thank you for your suggestions and I shall go through the papers in your site. –  Dana Sugu May 31 '13 at 4:50
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