Which of the following factors is most likely to cause 60Hz artifact?

• A. High and unequal electrode impedance
• B. Incorrect low and high frequency filter settings
• C. Incorrect placement of the reference electrodes
• D. Direct pressure against one of the electrode

Answer: (A)

60 Hz artifact comes from mains power-line interference entering the EEG signal. It shows up most when electrode impedance is high and unequal because the amplifier’s ability to reject common-mode noise relies on similar impedances across leads. When impedances are balanced and low, common-mode signals like the 60 Hz pickup are largely canceled, so you see less line noise. Other factors can affect the signal, such as filter settings shaping the spectrum, reference electrode placement altering the baseline, or direct pressure on an electrode changing contact quality, but they don’t inherently create the steady 60 Hz interference the way mismatched and high impedances do.