Ravi Kochhar
Oct. 3, 1996
Rev. Feb. 27,2001
The EP (Evoked Potential) program is used for recording evoked potentials in response to various auditory stimuli.
The program assumes that all the cables have been connected properly. A typical experimental setup is shown in Fig 1 below.
In a typical experiment, the program is used to present a series of tone pips (sine waves) from the DSS (Digital Stimulus System) to the animal's ears. The frequency and intensity of these tone pips may be varied. An electrode attached to the animal (e.g. at the round window) is used to pick up the evoked response. This evoked response is sampled via the A/D (analog to digital) converter, fed back to the computer, and displayed on the screen. Signal averaging is usually necessary to reduce the background electronic noise.
The program is started by typing EP at the "$" prompt.
It starts by displaying the following menu:
(note: in some cases a sub-set of this menu may be displayed)
(2) Menu choice 1. Use this when you are ready to proceed with
presenting the stimulus and averaging the response.
(3) Menu choice 6. This is used to specify what type of sound
stimulus should be produced from the DSS.
For example, you can enter TONE for tone pips,
or CLIK for rectangular clicks.
The DSS is capable of producing two independent sounds simultaneously.
If you want only one channel of sound, then specify OFF for DSS-2.
(4) Menu choice 9. The duration time is the time (in millisecs)
for which the sound stimulus is turned on for each repetition.
This parameter is not used for Clicks, whose width is specified elsewhere.
For tones, a default rise/fall ramp of 2 millisecs each is applied to
minimize onset/offset transients.
(5) Menu choice 10. The Repetition Time is the time after which
the next repetition (of the stimulus) is presented. For example, if clicks
are selected as the stimulus, and the repetition time is set to 50 msec, then
the clicks will be presented at the rate of 20 clicks per second.
(6) Menu choice 11. You can ask the program to alternate the
starting phase tones for every alternate tone pip.
This is used to cancel out the cochlear microphonic, which can hide
smaller evoked potentials.
(7) Menu choice 14. The sampling time is the time over which the
response is sampled and averaged. This is independent of the duration or
repetition times, but typically it is somewhat shorter than the rep. time.
The number of averages can be adjusted to improve the signal to noise
ratio.
In most cases, the signal to noise ratio improves as the square root of
the number of averages.
For the sampling rate, use the AUTO selection for most cases.
The program then automatically determines the optimal sampling rate.
(8) Menu choice 21. The smoothing is applied to the curves after
averaging and before plotting.
This should be an odd number, and 1 means no smoothing.
After you enter 1 to proceed with data collection, the program
asks for a range and increment for frequecy and SPL.
For clicks, only the SPL range is asked.
Finally, when all questions are answered, the sound stimulus is presented
with the specified parameters, and for the specified number of reps (the
number of averages).
After each intensity (SPL) is done, a graph is drawn on the screen showing
the averaged response.
When an entire intensity series is done, the program pauses, and you
have some choices.
If you plan to save the data then be sure to select option 8 (save
data in STATPK file) after every series of SPL's is completed - this is
the only way to save your work.
Also be sure to record the STATPK data set number in your log book.
You can press RETURN to continue, 0 to return to the main
menu, 5 to get a hardcopy of the plot on the laser printer,
4 to change the SPL range, or 6 to repeat the current
series once more.
A sample plot is shown in Figure 2 [22k gif].
If you have questions about, or suggestions for, this document,
please send them by e-mail to
kochhar@physiology.wisc.edu
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Select one of the following :
0 Exit
1 Proceed with data collection
2 Select/De-select hardcopy option, Current :YES
3 Set Y-axis scaling, Current :AUTO
4 Set intensity units (SPL or ATTEN),Current :SPL
5 Frequency increment (LOG or LIN), Current :LIN
6 Select DSS output modes, Current : TONE OFF
7 Select SPL fix or variable, Current :VAR VAR
8 Set DSS-2 delay RE DSS-1 (msecs), Current : 0.00
9 Duration time (msecs), Current : 8.0 8.0
10 Repetition time (msecs), Current : 50.0 50.0
11 Alternate tone phase/Unfrozen GW Current : N 0.00
12 Rise Time (millisecs), Current : 2.00 2.00
13 Fall Time (millisecs), Current : 2.00 2.00
14 Samp. time (ms), No. avgs., Srate Current : 6.0 50 AUTO
15 Sync. on DSS #, Current : 1
16 Subtract every alternate buffer Current : NO
17 A/D type, Analog amplifier gain Current :ADQ32 1.00
18 Y-axis units Current :VOLTS
19 STATPK file name Current :
20 Multi-Freq option Current :N
21 Smoothing factor Current : 1
The parameter values can be changed by typing in the number to the left.
For example, to change the Sampling Time, type 14 followed by the
RETURN key.
The program will then ask you to enter in the new values for Sampling Time,
Number of averages, and sampling rate.
The basic menu choices are explained below.
Select one of the following :
0 Quit
1 Next Frequency
2 This Freq. at new SPL
3 Change parameters
4 Change FREQ and/or SPL
5 Plot on laser printer
6 Repeat this series
7 Save plot file
8 Save data in STATPK file
RETURN Same as 1
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This page last modified on : Feb. 27, 2001
![Figure 2 [22k gif]](figs/epf2.gif){kind=link}