Final answer:
Electroencephalography (EEG) and event-related brain potentials (ERP) mainly measure brain waves (option A) and are different from ECG which records heart electrical impulses, or fMRI, which monitors blood flow changes in the brain.
Step-by-step explanation:
Electroencephalography (EEG) and event-related brain potentials (ERP) measure brain waves. EEG is a technique used to record the electrical activity of the brain through an array of electrodes placed around the person's head. This method charts brainwaves by capturing their frequency and amplitude with high precision. In contrast, event-related potentials are brain responses that are the direct result of a specific sensory, cognitive, or motor event. These techniques are invaluable for researchers, especially those studying neural processes and conditions like sleep disorders. Other techniques such as electrocardiogram (ECG) measure the electrical impulses in the heart, while functional magnetic resonance imaging (fMRI) measures changes in blood flow in the brain associated with neural activity.