Which EEG electrode site is half the distance from O1 to T3?

The correct answer is T5, as it is indeed located approximately halfway between the occipital electrode O1 and the temporal electrode T3. EEG electrode placement follows the international 10-20 system, which is based on specific locations on the scalp that correspond to underlying brain structures.

In the 10-20 system, the distance between these points (O1 and T3) is standardized, making it possible to identify T5 as the midpoint location. Given the positions of the electrodes, T5 is defined as being positioned laterally between the occipital region and temporal region, thus fulfilling the requirement of being half the distance from O1 to T3.

Oz, P3, and C3 are located in different regions of the brain relative to O1 and T3. Oz, which is placed at the midline of the occipital area, does not fit the required halfway point. P3 is located in the parietal region, further away from both the occipital and temporal locations in question. C3 is positioned over the central region of the scalp, distinctly removed from the required segment between O1 and T3. Hence, T5 is the only correct electrode site that fits the specified criteria.