Evoked Potentials 2

Question 1

Fourier Transform

Answer 1

Mathematical formula that calculates the frequency content of a signal - “Transforms” time domain signals into frequency domain

Question 2

Cut off frequency

Answer 2

Frequency at which the signal is reduced by 3 dB (approximately 30%)

Question 3

Filter rolloff

Answer 3

Slope (usually given in dB/octave) describing the degree of amplitude reduction of signal frequencies outside the cutoff

Question 4

Bandpass

Answer 4

Range of frequencies over which frequencies are allowed to “pass”. Outside the bandpass, frequencies are reduced in amplitude

Question 5

Filter setting for Cortical SSEP

Answer 5

30-500 Hz

Question 6

Filter setting for Peripheral SSEP

Answer 6

5-2000 Hz

Question 7

Filter setting for EMG

Answer 7

10-1000 Hz

Question 8

60 Hz Notch Filter

Answer 8

Filter designed to cut a single frequency (60 Hz) out of the spectrum, but can lead to “ringing artifact”

Question 9

Digital Filtering

Answer 9

Software filter that can carry out filtering. No phase effects imposed, and it can be reversed

Question 10

Smoothing

Answer 10

Using a certain number of data points averaged together to create a new point. The more points (up to 25), the smoother. Avoid excessive smoothing

Question 11

Analog signals

Answer 11

Continuous functions in amplitude and time

Question 12

Digital signals

Answer 12

Contain only discrete values of amplitude at discrete values of time (samples the analog data into the discrete values)

Question 13

Bin width

Answer 13

Time between samples (on x axis, the intervals between the sample points)… 1/Sampling Frequency

Question 14

Sampling Frequency

Answer 14

data points/second

Question 15

Aliasing

Answer 15

Misrepresentation of the signal due to loss of important data occurring between the samples - the sample rate is too slow

Question 16

The Nyquist Frequency

Answer 16

2 times the highest frequency of the recorded signal - sampling below the Nyquist causes aliasing

Question 17

Minimum number of bits required

Answer 17

8 bits… it gives 2^8 = 256 voltage steps

Question 18

Required bin width

Answer 18

Must be no more than 20 micro sec / data point

Question 19

Artifact reject

Answer 19

Sweeps with unacceptably high amplitude (outside the reject threshold) are not included in the average. The entire sweep gets rejected. But only effective for intermittent noise.

Question 20

Reject Delay

Answer 20

This feature delays the onset of the reject function until after (hopefully) the stim artifact has occurred