What term describes the increase in magnitude of the input signal by the differential amplifier?

The term that accurately describes the increase in magnitude of the input signal by the differential amplifier is "Gain." Gain refers specifically to how much an amplifier increases the strength of a signal, measured as the ratio of output signal to input signal. It indicates the ability of the differential amplifier to enhance small electrical signals, which is crucial in EEG systems where the brain's electrical activity produces relatively weak signals that need to be amplified for analysis.

While sensitivity, resolution, and amplification factor are closely related to the performance characteristics of amplifiers, they are not synonymous with the increase in signal magnitude. Sensitivity usually refers to how well a system can detect a signal amidst noise, resolution relates to the smallest change in signal that can be discerned, and amplification factor is a broader term that can sometimes refer to the same concept as gain but lacks the specific implications that "gain" has in the context of amplifying input signals in EEG devices.