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The Event-Related Potential (ERP)

The Event-Related Potential (ERP). Embedded in the EEG signal is the small electrical response due to specific events such as stimulus or task onsets, motor actions, etc. The Event-Related Potential (ERP).

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The Event-Related Potential (ERP)

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  1. The Event-Related Potential (ERP) • Embedded in the EEG signal is the small electrical response due to specific events such as stimulus or task onsets, motor actions, etc.

  2. The Event-Related Potential (ERP) • Embedded in the EEG signal is the small electrical response due to specific events such as stimulus or task onsets, motor actions, etc. • Averaging all such events together isolates this event-related potential

  3. Basic Elements of ERP Design • EEG, therefore ERP, doesn’t provide interpretable absolute voltage • The voltage is always relative to something else • That something else may be: • The pre-stimulus baseline • A control condition

  4. Basic Elements of ERP Design • Thus a fundamental aspect of ERP design is not to plan to report voltages but rather a difference in voltage between two or more conditions • What are some examples of conditions you might want to compare?

  5. First Demo • Contralaterality in Visual System • Hemifields project to contralateral cortex • Unrelated to which eye is stimulated! • Occular Albinism • Eyes project contralterally, irrespective of hemifield

  6. Basic Elements of ERP Design • The theory is that human visual cortex is organized contralaterally • The prediction is that right hemifield stimuli will drive electrical activity in the left visual cortex and left hemifield stimuli will drive electrical activity in right visual cortex • How do we test that prediction?

  7. Basic Elements of ERP Design • Experimental approach: • Choices: • 1. you could compare ipsi to contra ERP waveforms with a trial • E.g. O3 with O4 • What’s the problem? O4 O3

  8. Basic Elements of ERP Design • Experimental approach: • Choices: • 1. you could compare ipsi to contra ERP waveforms with a trial • E.g. O3 with O4 • What’s the problem? • You would be comparing ERPs from different parts of the brain! • How could you improve on that design?

  9. Basic Elements of ERP Design • Experimental approach: • Choices: • 2. you could compare electrodes ipsi to stimulus on one side with electrodes contra to stimulus on the other side • Notice those are the same electrode! Measure contralateral ERP magnitude O3

  10. Basic Elements of ERP Design • Experimental approach: • Choices: • 2. you could compare electrodes ipsi to stimulus on one side with electrodes contra to stimulus on the other side • Notice those are the same electrode! Measure ipsilateral ERP magnitude O3

  11. Basic Elements of ERP Design • Hands on agenda today: • Review recording and saving EEG data • Exporting EEG .ses to .raw • File management and backing up data • Intro to BESA and constructing an ERP wavform

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