Updated 11/3/2014
BSL P R O Lesson H09: Auditory Evoked Potentials From a Human Subject
Abstract
Auditory Evoked Potentials are very small voltage potentials given off by the brain as a response to different
types of auditory stimulus. The Evoked Potential graph will show a succession of "peaks" in amplitude, latency,
duration, polarity and variable localization. These different events are commonly distinguished by the polarity
and latency of each peak.
The signals are typically recorded using surface recording electrodes placed on top of the scalp. The
potentials are extremely low level and require high quality amplifiers to record them. The signals are typically in
the 2-10 microvolt range for cortical AEPs and less than 1 microvolt for deep brainstem structures.
To perform off-line AEP studies, combine the auditory output options of the BSLSTMA Stimulator with the
signal averaging functions of the BSL P R O System. Use the OUT101 Tubephone to efficiently direct
acoustical stimuli. The software will display the results and allow users to take a variety of measurements
[such as the amplitude and time of Fast (2-12 msec), Middle (12-50 msec), Slow (50-300 msec), and Late
responses (250-600 msec)].
In order to record the signals accurately, it is important to follow a detailed setup protocol and use a specialized
averaging technique. The averaging technique allows the software to tease out low-level response potentials
that occur below the ambient noise level. The averaging technique assumes that the response, in this case the
AEP, always occurs within a time window following the stimulus presentation. The averaging function allows the
user to define the averaging time window and establish the number of averages required. By performing many
averages (1000 – 2000) the software is able to reduce the noise and isolate the Auditory Evoked Potential. This
same averaging technique is used to record a variety of different eventrelated potentials.
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BSL P R O Lesson H09
B I O P A C Systems, Inc.
Objectives
1. To present an auditory stimulus to a human subject.
2. To record Auditory Evoked Potentials.
3. To measure the effect of auditory interference (dichotic listening) on Auditory Evoked Potentials.
Equipment
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PC running Windows or Macintosh computer
BIOPAC Software: Biopac Student Lab PRO
BIOPAC Data Acquisition Unit (MP30/MP35)
BIOPAC Stimulator (BSLSTMA)
BIOPAC Tubephone (OUT101)
BIOPAC Interface Cable for BSL Stimulator to OUT101 Tubephone [BNC to 1/4"] (BSLCBL6)
o BSLCBL6 requires an inline adapter that
accepts 1/4" mono phone plug and fits
1/8" mono phone jack, such as Radio
Shack adapter "274-047"
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BIOPAC Disposable electrodes (EL503)
BIOPAC Electrode lead set (SS2L)
BIOPAC Abrasive pads (ELPAD)
BIOPAC Electrode gel (GEL1)
Alcohol swabs
Nylon swim cap or bandage
Setup – PSY315 Students: All of the equipment should be set-up to run on the NEURO8
computer. You should be able to skip to step #5 – double check connections.
Hardware:
1. Plug the BSLSTMA trigger cable into the Analog Out port on the back of the MP unit.
2. Plug the reference connector into CH 2 of the MP unit.
3. Plug the SS2L electrode lead into CH 1 on the MP Unit.
4. Plug the OUT101 into the BSLSTMA via interface adapters: BSLSTMA - BSLCBL6 - Inline Adapter - OUT101
a. Plug the BSLCBL6 interface cable into the BNC connector on the BSLSTMA.
b. Plug an inline adapter (such as RadioShack 274-047) into the BSLCBL6 interface cable.
c. Plug the OUT101 into the inline adapter.
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BSL P R O Lesson H09
B I O P A C Systems, Inc.
5. Turn on the computer.
6. Turn on the BSLSTM Stimulating Unit – Make sure that the Range to "0-10V." Make sure unit reads 1.00 or
adjust the level knob to achieve 1.00. See below.
7. Turn on the MP Data Acquisition Unit.
8. Launch the BIOPAC BSL 4.0 MP36 software on the NEURO8 computer.
9. Open the AEP template by choosing Create/Record a new experiment > Open graph template from disk …
>{click ok} choose Files of type: GraphTemplate (*GTL) > File Name: AEP.gtl (located on the desktop)
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10. Your data collection window will now open and look like the image below.
AEP.gtl (graph template) windows when file is opened
Subject—Electrode Connections
The electrode connections for setting up an AEP test consist of a pair of recording electrodes (with a ground) connected to
an MP Data Acquisition Unit.
Hints for minimizing measurement error:
a. Remove all jewelry from the subject.
b. Abrade the skin before placing electrodes. Usually not necessary.
c. Apply a small drop of electrode gel (GEL1) to the electrode, even if it is pre-gelled. Not too
much to interfere with the sticker.
d. Use a swim cap or bandage to keep the electrodes in place. There is a Velcro strap in the room that you can use
around the top of your head and under your chin to strap down the top electrode. The other electrodes should
stick fine.
e. Allow the electrodes to sit on the subject for 5-10 minutes -before commencing the
lesson.
f. The subject should be sitting in a relaxed position in a quiet room.
g. Clip the SS2L electrodes and the OUT101 transducer to a part of the subject's clothing so it
won't pull on the cables.
1. Place three EL503 disposable electrodes on the subject as follows:
a.
Place one electrode (red lead) on the vortex of the scalp.
b.
Place one electrode (white lead) on the neck immediately behind the right ear
that will receive the auditory stimulus.
Place one electrode (black lead) in the same location on the opposite ear.
c.
2. Attach the OUT101 transducer as follows:
a. Attach a foam cover to the end of the clear plastic tube.
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b. Squeeze the foam so that it will fit snuggly inside the ear canal.
c.
Place the foam inside the right ear so that it makes a nice snug fit.
d. Attach the OUT101 clip to a part of the subject's clothing so that it isn't pulling the transducer out of the ear.
3. Now that you have the electrodes and transducer in place, use a bandana or bandage to hold it all in place.
4. Carefully, place the headphones over the ears. Be careful to not disturb the tone stimulus tube or the
electrode sites.
• It is important to make sure that the electrodes are making good contact with the surface of the skin and to avoid the
electrode wires pulling the electrodes loose.
Calibration: No calibration is required.
Running the Experiment
You will run the experiment twice. The first time there will be no stimulus in the
headphones (baseline / silence). The second time you will have a dichotic listening task
played through the headphones. The recording procedure is identical each time.
1. Click on the Start button in the BSL window to begin recording data.
PLEASE NOTE:
The template is set to record 350 trials of data, which will take approximately 7
minutes. The system will stop automatically—only interrupt the recording if you
see that something is wrong.
2. The subject should sit in silence and wait approximately 7 minutes to allow the system to automatically stop the
recording.
You will see the click stimulus delivered in blue and 0.5 s of EEG data collected in red after each
tone. Beside the start / stop button you will see the recording segments counting up to 350.
Analysis continues on the next page.
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Analysis
1. Click the horizontal autoscale icon (on the toolbar) to show all of the experimental data. Your graph should look
like the example below. Save this data file as your SUBJECT’s name + 1 (Pittman1).
2.
Click on the Analysis menu and choose Find Cycle.
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3.
In the Cycle Detector box on the Cycles/Peak tab make sure that CH2, Stimulator is selected and the
Threshold Level is : 0.50000.
4.
In the Selection tab, choose Current Threshold and under Right Edge type Current Threshold + 0.45 seconds
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5.
In the Output tab, choose Averaging Tab and click the box for Construct an average from: CH1, EEG
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6. Now click Find All Cycles which will find each stimulator peak above the threshold of 0.5 volts and average the
EEG data for the next 0.45 seconds. A new ERP graph will be generated. If a warning that “no cycles were found”
occurs then just click ok.
6.
Save this file as “Averaging of SUBJECT1”
Analysis continues on the next page.
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Overall max peak
1st max peak
1st min peak
Overall min peak
The measurements should already be set as seen above.
5. Using the I-beam tool, to select the beginning of the wave to find the first max value point looking at the max channel.
Record the Time of the first max value.
6. Again using the I-beam tool, select the beginning of the wave to find the first min value point looking at the min
channel. Record the Time of the first min value.
7. Using the I-beam tool, measure the overall highest (most positive) response value by clicking at that point and
recording the time value.
8. Using the I-beam tool, measure the overall lowest (most negative) response value by clicking at that point and
recording the time value.
SAVE FILE – Close the BIOPAC program. Turn off the Biopac and then turn it back on and
reopen the Biopac AEP.gtl template file. REDO the experiment now with the DICHOTIC
LISTENING stimulus playing in the headphone (desktop of NEURO9).
The subject should try to focus on the story being played only in the right ear.
Make sure you start the dichotic listening stimulus first then click start on the AEP recording. Save this file as
SUBJECT2 (Pittman2) and repeat data analysis steps.
Enter your Auditory ERP data into the correct columns on the GOOGLE DRIVE data sheet (Link on Moodle page) in the
columns after the auditory threshold.
You are now done. Remove your foam ear stimulation piece from the stimulator tube and throw away. Clean up all
other supplies and close BIOPAC. Turn off the power to the BIOPAC recording unit and the stimulation unit. Leave
the computers on.
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