Instrumentation and Calibration Flashcards
6 cards from real EEG practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Instrumentation and Calibration flashcards as text
What is the purpose of the notch filter in EEG recording?
Answer: To selectively attenuate 60 Hz (or 50 Hz) power line interference while preserving surrounding frequencies
The notch filter is a band-reject filter designed to selectively remove power line interference (60 Hz in North America, 50 Hz in other regions) while minimally affecting adjacent frequencies.
Analog-to-digital conversion in digital EEG requires an anti-aliasing filter because:
Answer: Without it, frequencies above the Nyquist frequency would be misrepresented as lower frequencies in the digital record
The anti-aliasing filter (a low-pass filter set below the Nyquist frequency) prevents aliasing — the phenomenon where frequencies above half the sampling rate are incorrectly represented as lower frequencies in the digital signal.
The input impedance of a modern EEG amplifier should be:
Answer: Very high, typically greater than 100 megaohms
Modern EEG amplifiers have very high input impedance (>100 megaohms) to minimize current draw from the scalp electrodes, ensuring accurate voltage measurement without loading the source.
What is the purpose of biological calibration at the beginning of an EEG recording?
Answer: To verify that electrodes are properly placed and functioning by observing known physiological signals like alpha blocking
Biological calibration uses known physiological signals (alpha rhythm with eye opening/closing, eye movements, muscle artifact) to verify that each electrode is properly placed, has good contact, and is recording genuine brain signals.
Dynamic range in digital EEG refers to:
Answer: The range of signal amplitudes the system can accurately digitize, from the smallest to the largest signal without distortion
Dynamic range is the ratio between the largest and smallest signal amplitudes the ADC can accurately represent, determined by the bit resolution of the analog-to-digital converter.
Impedance testing of EEG electrodes should ideally be performed using:
Answer: An alternating current (AC) impedance meter at a frequency similar to the signals of interest
AC impedance measurement at frequencies relevant to EEG (typically 10-30 Hz) is preferred because it accounts for the capacitive and resistive components of electrode impedance and avoids DC polarization that could affect recording quality.