1. (A): The differential amplifier used in clinical neurophysiology amplifies the differences in potentials between its two inputs. This allows amplification of potential differences and cancellation of contaminating potentials present at both inputs like in the case of 60-Hz noise from line voltage devices. (Daube 2002, pp. 15-16)

2. (C): Digital signals are quantified in discrete nonoverlapping amplitude levels, expressed in terms of bits where every bit is a power of two.

Signal amplitude of analog-to-digital converter (ADC) depends on both its voltage range and the maximum number of bits discrimination it can resolve.

ADCs used in both EEG and evoked potential recordings should have a minimum of 12 bits (12² = 4,096 voltage levels spread over +2,048 and −2,048). This will allow good visual resolution of signals <1μV. (Fisch 1999, pp. 60-62)

3. (A): Digital recording allows linear display, convenient storage and retrieval, montage reformatting, filter, sensitivity and time-based changes, and annotation recording. All these features have been shown to enhance reliability of interpretation. The disadvantages of digital recording when compared to analog recording are cost, incompatible data formats and softwares, and need for close maintenance by IT services. (Daube 2002, pp. 42-43)

4. (B): In digital EEG display, monitor resolution is the number of pixels in each direction that can be used to fill in points on the EEG tracing.

In this case, of the 1,024 horizontal pixels, 100 pixels are higher used for screen margin leaving 924 pixels for a 10 second of EEG. One second of EEG display will have approximately 92 pixels devoted to it.

5. (C): Before EEG recording, the impedance of each electrode should be routinely measured. This is performed with an impedance meter to evaluate the contact of each electrode with the scalp. The impedance should be between 100 and 5,000 Ω. (Fisch 1999, p. 25)

6. (B): The Sampling Theorem states that if a signal contains component frequencies ranging from 0 to f N, then the minimum sampling frequency that can be used for a digitized data to adequately represent the frequency content of the original signal is 2 f N, called the Nyquist frequency (equal to two times of the original frequency sampled). Aliasing refers to the distortion of a signal caused by sampling frequency lower than the Nyquist frequency. (Ebersole and Pedley 2003, p. 47; Daube 2002, pp. 46-47)

7. (C): EEG amplifiers are designed to amplify out of phase potentials to reveal differences in electrical potentials between its two inputs and to reject potentials that are common to the two inputs. This property is referred to as common mode rejection. (Fisch 1999, pp. 40-42)

8. (B): A high-pass filter (low-frequency filter) consists of a capacitor in series and a resistor in parallel. Its output current potential is generated across a resistor. Filters are used for noise attenuation and identification of signals, immeasurable under normal recording conditions. On the other hand, filters distort waveforms because of their frequency attenuation and phase shift characteristics. (Daube 2002, pp. 12-13)

9. (B): Good mechanical and chemical contact of electrodes to the scalp is achieved with the use of collodion. Because of the chemical interactions with acetone (a substance used to remove collodion), a well-ventilated area is required for safe use of these chemicals. (Fisch 1999, pp. 20-21)

10. (B): Electrode impedance evaluates the contact between the electrode and the scalp. Electrode impedance should measure >100 Ω and <5,000 Ω for stable waveform recording. Very low impedance will act like a shunt between the recording electrodes and will short circuit EEG potential differences.

An electrode with very low impedance often makes contact with other electrode as a result of excess electrode paste or sweat connecting the two electrodes. (Fisch 1999, pp. 25-26)

11. (C): To faithfully represent a particular frequency, the sampling rate should be at least equal to the Nyquist frequency that is twice the frequency of the signal resolved. If sampled at a lower rate, distortion of the waveform occurs, a phenomenon referred to as aliasing. (Ebersole and Pedley 2003, p. 47; Fisch 1999, pp. 58-59)

12. (B): EEG records continuous brain activity that is filtered and amplified. It is continuous and uninterrupted and as such remains an analog signal, analogous to the source signal. When digitized, it becomes discontinuous and less smooth because of sampling. (Ebersole and Pedley 2003, pp. 44-45)

13. (D): Digitization is the process by which analog signals are converted to digital signals. Quantization consists of assigning a value to every potential input to the analog-to-digital converter. Sampling determines the temporal resolution and the frequency needed for waveform reproduction. (Ebersole and Pedley 2003, pp. 44-45; Daube 2002, pp. 44-45)