EP
Evoked Potential Data Collection
Users Guide

                                                     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)

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.

(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.

      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

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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This page last modified on : Feb. 27, 2001