EEG Instrumentation and Calibration 2

Question 1

What is the standard calibration signal used to verify EEG amplifier function?

Accepted Answer

A 50 µV square wave at 1 Hz

Answer

The standard calibration signal is a 50 µV square wave at 1 Hz. This verifies amplifier gain accuracy, frequency response, and channel matching across the system.

Question 2

The common mode rejection ratio (CMRR) of an EEG differential amplifier measures its ability to:

Accepted Answer

Reject signals that are identical at both inputs while amplifying their difference

Answer

CMRR quantifies how effectively the differential amplifier rejects common-mode signals (those appearing equally at both inputs, such as 60 Hz noise) while preserving the differential signal (brain activity).

Question 3

The high-frequency filter (low-pass filter) in EEG recording at a typical setting of 70 Hz will:

Accepted Answer

Attenuate frequencies above 70 Hz while passing lower frequencies

Answer

The high-frequency (low-pass) filter attenuates signals above its cutoff frequency. At 70 Hz, it progressively reduces muscle artifact and electrical noise above 70 Hz while preserving brain activity which is predominantly below 70 Hz.

Question 4

What is the minimum recommended sampling rate for routine digital EEG recording?

Accepted Answer

256 Hz

Answer

A sampling rate of at least 256 Hz is recommended for routine EEG to adequately capture frequencies up to 70-100 Hz according to the Nyquist theorem (sampling rate must be at least twice the highest frequency of interest).

Question 5

The time constant of an EEG amplifier determines:

Accepted Answer

The rate at which a DC-shifted signal decays back to baseline through the low-frequency filter

Answer

The time constant represents the time it takes for a DC-shifted square wave calibration signal to decay to 37% of its initial value. It is directly related to the low-frequency filter setting.

EEG - Electroencephalography Practice Test

EEG - Electroencephalography Practice Test

EEG Instrumentation and Calibration 2