Psychophysiology Experiment Setup
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[edit] Things To Do
In order to run a psychophysiology experiment, you must (not necessarily in this order):
- Setup I: Hardware (PP transducers & MP150 system)
- Setup II: AcqKnowledge for proper data recording
- Setup III: E-Prime experiment to send markers at appropriate times to sync with the PP data
Digression: While none of these are necessarily trivial steps consider that before the computer age (which you're living in now), PP data was printed out onto reams of paper, which scientists (that's you) then had to hand-mark and hand-calculate the PP measures. You sometimes see this in movies that use the lie detector test. So just wonder in amazement of how good we (you) have it now as you read on.
[edit] Setup I: Hardware
Besides making sure the Biopac machine is turned on and connected to both the PP transducers and the experiment computer, past members have documented some helpful guidelines regarding these procedures:
If your BIOPAC is connected to the testing computer properly, there should a green circle will appear at the bottom right of your AcqKnowledge program. You can also check by going to the menu: MP150 -> Select MP150
 Connected! |  Connected system reports the BIOPAC serial number |
 Not connected. |  Not connected system can only operate as "No hardware mode" |
[edit] Setup II: AcqKnowledge Set Up
Before you push the START button in AcqKnowledge to begin PP recording, you have to set up all the channels, analog and digital, for smooth functioning and analysis.
First download and open the sample .ACQ file: EMG_GSR_Example.acq.
This example shows 2 EMG & 1 GSR Analog channels, 8 Digital binary channels, and 1 Calculated marker channel (combines the 8 binary channels into a single number):
[edit] Acquisition Time
Go to MP150 -> Set Up Acquisition... and set the experiment acquisition time. AcqKnowledge will stop recording if it runs over this time, so set it to something sufficiently long.
[edit] Analog (PP Data) Channels
The MP150 has different modules for connecting different PP transducers. For each MP150 machine, each module is assigned a unique channel number that is referred to by the AcqKnowledge software. Different testing cubes have different available modules and assigned analog channels (using a switch on top of the module), which you must assign appropriately in AcqKnowledge.
See ACL's Channel assignments.
In the example, go to the MP150 -> Set Up Channels... and select Analog to see:
These are typical data collection sample rates used for EMG and GSR. PP signals with faster responses like EMG's startle require higher sample rates (more data), while slower responses like GSR can use lower rates (less data). You should still read up on your particular PP measure to see what the appropriate sample rate should be. The Nyquist Rate states that your sampling rate should be at least twice as fast as the frequency of the effects you want to measure. For example, if you want to digitally record a 10 Hz sound, your minimum sampling rate should be 20 Hz.
Factoid: given roughly 20 - 20,000 Hz human hearing frequency range, CD audio has a standard sampling rate of 44,100 Hz (x 2 + some additional room).
[edit] Digital (Marker) Channels
Digital channels are used for collecting the Markers and must also be enabled properly in AcqKnowledge. Because the parallel port is inputting 8 binary channels, the first 8 digital channels (D0 - D7) must be enabled and labeled appropriately for later analysis.
In the example, go to the MP150 -> Set Up Channels... and select Digital to see:
[edit] Calculated Marker Channels
A calculated channel is used for simplifying the 8 digital bit channels into one number from 0 - 255.
In the example, go to the MP150 -> Set Up Channels... and select Calc. Then push Setup to see the calculated channel's equation. The equation to use is:
(D0 + D1*2 + D2*4 + D3*8 + D4*16 + D5*32 + D6*64 + D7*128)/5
This is a straightforward base conversion from binary to decimal, except for a final division by 5 because AcqKnowledge treats a "ON" binary value as a 5.
The example looks like this:
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Finally, since the Marker channel contains all the information you need, you can hide the 8 digital channels (CTRL+click on the channel boxes at the top) to simplify the screen to look like:
