Week 1-Electrical Activity

Question 1

far field

Answer 1

extra-cranial recordings
*cannot give full access to electrical activity, but sampling the response at various levels gives idea about integrity or sensitivity of the aud system

Question 2

stations/addresses/sampling

Answer 2

fixed number of vertical lines at fixed time at equal intervals

Question 3

analysis window

Answer 3

recording epoch or time ensemble

Question 4

stimulus repetitions/epoch/ sweeps

Answer 4

number of epochs in the average AEP

Question 5

time locked

Answer 5

electric signal concurrent with the onset of the electric response

Question 6

digitizer triggers

Answer 6

when to start the digitization process/the capture of a signal at some specified moment in time (1ms, 5ms, etc)

Question 7

digital computer

Answer 7

• changes analog to discrete, uses binary numbers (aka bits)

- –uses base 2 if not binary?

Question 8

three types of processing needed to find the evoked response in noise and EEG

Answer 8

1) differential amplification
2) filtering
3) averaging

Question 9

what are the 2 steps to A-D conversion

Answer 9

1) quantization= chopping a continuous signal into amplitude units (steps)
2) sampling= chopping a continuous signal into a limited number of units (samples) of equal duration/time

Question 10

what is the typical time window and number of samples in an ABR?

Answer 10

10ms time window and normally 256 sampling points?

Question 11

what happens at each address for signal averaging

Answer 11

1) A-D conversion (digitization)
- –in each address, the analog EEG activity is digitized (+ or -) and then the value is stored at the address and then all the digital values are added algebraically at each address
2) D-A conversion
- –digital values converted to analog values meaning a continuous trace on an oscilloscope (the waveform is seen)

Question 12

how does averaging affect noise?

Answer 12

reduction in the overall amplitude because random signals (noise) are cancelled out

Question 13

2 things that the fidelity of A-D and D-A conversions depend on

Answer 13

• amplitude resolution

* temporal resolution

Question 14

amplitude resolution

Answer 14

quantization

• set by binary word length of conversion
• no problem with low frequency
• problem with high freq= no digitization=high freq filtering
• fine resolution= accurate reproduction of the EP

Question 15

temporal resolution (of sweep)

Answer 15

is dwell time= separation between 2 successive addresses

• set by rate of sampling
• at least to points/cycle are sufficient resolution to reproduce the freq.

Question 16

period (T)

Answer 16

the reciprocal of frequency (F)

*T=1/F

Question 17

nyquist freq

Answer 17

the highest freq that can be reproduced

–sampling rate should be at least 2x the highest frequency in the signal of interest