ActiveTwo: A powerful high-resolution biosignal acquisition system with active electrodes

High density surface EMG as described in the recent publications on the Biosemi site is possible with the addition of the sEMG accessories. The original model of the high density sEMG probe was made for ActiveOne, so the connector differed. The current version separates the electrode grid from the preamp as in:

• reusable grid
• sEMG preamplifier

Less dense sEMG can be accomplished with an elastic fabric with electrode holders like the EEG cap stretched over a muscle.  This would need to be custom-made, but would not be expensive.

Fine wire EMG would require either spring contact adapters or safety socket leads with inline active headstage. If your fine wire electrodes will be stripped but unterminated, you need spring contacts, and if your electrodes terminate in safety sockets, you need inline adapters.

We expect the new red-rubber reinforced ActiveTwo active electrodes to last more than 1000 uses, based on our experience so far, and based on automated repeated-strain testing.

The way ActiveTwo electrode sets are built, they are not repairable by the end-user, but we can replace single electrodes for you. We can so this quickly (24 hours plus transit), efficiently, and at low cost (or free under warranty). Electrodes are warranted against material/manufacturing defects for one year, and we charge by the repair after that. We find that offering extended warranties motivates less careful handling, so we don’t offer extended warranties.

Follow the steps in the other FAQ linked here to identify the problem before contacting us to ask about the procedure and the cost of a repair.

We do offer individual EXG pin-type electrodes that you can insert in the cap as substitutes for faulty ribbon cable leads. This would be a short term stop gap solution only. We strongly recommend having a backup set of electrodes on hand after a year or two so that if the first set needs repair, you can continue to run with the other set while the repair is undertaken. You would not need to buy the spare set right away — just budget to have it once the electrodes have had enough use that they may begin experiencing problems. After you have made 200-300 recordings with your primary electrode set would be a good rule of thumb for when you should have a spare set of electrodes on hand.

You CAN install current versions of ActiView on Windows 10. But, before you do so, if the system was orignally delivered before January of 2017 you should update the firmware on the optical receiver / USB interface so that you do not have to go through the very long and arduous process of installing an unsigned driver on Windows 10.

You can update the firmware using any Windows 7 or 8 computer with the MSWinUSB2 driver installed, even if it is not the computer you have been using for ActiView. If you are just using a Windows 7 or 8 computer to update firmware on the optical receiver / USB interface, there is no need to install the LabVIEW Runtime Engine or ActiView on this computer. You WILL need the LabVIEW Runtime Engine and ActiView on the new Windows 10 computer, but you WILL NOT need to install a driver after the firmware update has been performed.

See the procedure outlined at biosemi.com/ faq/install_USB.htm for detailed instructions.  The section at the bottom marked IMPORTANT is the place to begin.

The positions in these caps come from the Oostenveld and Praamstra 5% system.  See http://robertoostenveld.nl/electrode/ for background and for links to electrode coordinates in a variety of formats. Depending on what software you are using for analysis, we might be able to provide another file format. The Biosemi channel assignments (relating electrode labels to electrode sites in the Oostenveld and Praamstra nomenclature) are below:

1. In the ActiView software, select About ActiView > Load CFG.
2. Navigate to the folder called Configuring and select the CFG that matches your head caps.  For example, if you have Biosemi standard 32 channel head-caps and want the 10-20 labels to be displayed, the file you want is “10-20system32+8.cfg”.
3. Once this CFG is loaded, go back to the Monopolar display tab in ActiView, and check the Decimation Ratio. This indirectly controls the sampling rate, being a fraction by which the AD rate defined by the speedmode (AD rate on the AD box) is multiplied.  If you are operating in speedmode 4 (2048 Hz on the AD box), then a decimation ratio of 1/4 could be used to arrive at 512 Hz sampling rate to file, for example.
4. After setting the Decimation Ratio, check the settings for the Filters and Reference on the left side of the Monopolar Display tab.  We recommend un-checking (turning off) both of the display filters and setting the Reference to None (Raw). This gives the operator the truest picture of the saved data as data are being recorded.
5. Next, verify that any auxiliary sensors you will be using have been selected in the Auxiliary Sensors tab.  It is best to select (highlight) only the sensors you will be using (or the superset of sensors you may use) so that unused sensor channels are not added to your data file.
6. Save a dummy data file in ActiView by selecting Start File, verifying that the right subset of EEG electrodes is selected (in the example case, A1-32), verifying that the EXG1-8 channels are being added if you want them, and selecting Add Displayed Sensors (the ones you selected before in the Auxiliary Sensors tab).
7. When ActiView asks for a path / file name (it may produce an error message about the default path not existing — just click to close), navigate to the default folder for data to be saved in for this experiment (or if this CFG will serve several experiments, point to the parent folder that contains folders for various experiments) and enter a file name like this “CHANGE THIS FILE NAME AND PATH AS NEEDED”.
8. Click Stop at the top left side of the ActiView screen to stop writing to the dummy data file.
9. Navigate to About ActiView > Save CFG and save the CFG file to the folder where the ActiView software executable is located. If you name this CFG as DEFAULT.CFG, it will be used automatically when ActiView opens. If you will have various CFG files for various experiments, then you should save the new CFG with a name that relates to the associated experiment, and be sure to rename the existing DEFAULT.CFG to _DEFAULT.CFG. By doing this, ActiView will force the operator to select a CFG file each time the ActiView software is opened. One important note – if the operator does not close ActiView at the end of a recording, the CFG file will still be loaded, and the next operator may not notice. For this reason, operators should be vigilant about closing ActiView at the end of a recording, and if they enter the lab to find ActiView open, they should close it, then reopen it so that it will remind them to load the correct CFG for their study.

Since mid-2016, Biosemi has included a black USB virtual serial port trigger cable with each new ActiveTwo system.  The device is depicted below.

Inside the shell of the 37 pin connector is a microchip that appears to the stimulus computer as a virtual serial port but provides 8 bit parallel TTL output to the ActiveTwo trigger input port.  Because it appears as a virtual serial port on the stimulus computer, this cable is a relatively universal solution for triggering ActiveTwo from virtually any software on any platform.  There are a few simple parameters you need to know to send triggers via this device.  For details, see:

• https://www.biosemi.com/faq/USB%20Trigger%20interface%20cable.htm

To use this trigger cable with MATLAB, Roee Gilron at UCSF (thanks, Roee!) provides a code sample at Github:

• https://github.com/roeegilron/BioSemiUSBtrigger

ActiveTwo is provided with drivers and host data acquisition software for Windows, Mac, and Linux computers.

Note that certain applications, such as event-related potentials, often require a separate computer to run experimental control / stimulus delivery software. The requirement for a separate computer for stimulus delivery is more a function of the experimental control software needing full control of computer resources to do its job.

In brief, the computer requirements for the ActiView data acquisition software are:

• Operating system:
  • Windows 10 / 11
  • MacOS 11 Big Sur, Monterey
  • Linux 64 bit or Linux X86 with library GNU-C V2.2.4 or later
• RAM: 8 GB or more
• Hard Drive: recommend 500 GB, but user should anticipate free space needed for data (file size in bytes is approximately = 3 X AD rate in Hz X number of channels X number of seconds recorded)
• Display: 1440 X 900 or higher resolution display
• One free USB port
  • SPECIAL NOTE ABOUT USB CHIPSETS: Small form factor computers without PCIe expansion slots should be avoided. The Intel W480 chipset found in many brands of small form factor desktop computer is not capable of keeping up with USB 2.0 High Speed data rates, which prevents operation in speed modes 2 and 3 for AD boxes that have high speed firmware installed. This is of particular importance in systems used in settings where ABR and cortical ERP will be measured concurrently or alternately. If you opt for a small form factor computer, be sure to use a computer that has at least one free PCIe expansion slot that you can add a PCIe expansion card with one or more USB 2.0 or higher ports.

Note: The ActiveTwo computer DOES NOT NEED A PARALLEL PORT.  A parallel port on the experimental control computer can be used to send stimuli to ActiveTwo, but we provide a USB virtual serial port trigger cable with every new system, so a parallel port is not needed for triggering.

In addition, the following are recommended for the ActiView computer:

• Network interface and remote storage for data backups
• Accessories such as KVMA switch box, extra monitor / keyboard / mouse, extension cables, etc to permit access to the EEG display from the separate room for the subject

The blue CM in Range light reflects two things: 1) whether the CMS and DRL electrodes are adequately connected to the participant’s body, and 2) whether all of the other active electrodes, cables and connectors are intact.  If any of these are NOT true, then the blue CM in Range light will flicker and the signals and offsets will pulsate once every half second until the problem is rectified.  We call this state CM Out of Range (CMOR).  The blue LED labeled CM in Range on the front panel of the AD box is reflected on the top right of the ActiView software display. This makes it easy to recognize there is a problem.  To identify which electrodes are involved, use the one-bucket test.

Once you identify the faulty electrodes, contact us at via the Request Info form and let us know the serial number of the electrode, and if it is a set of electrodes on a ribbon cable let us know which electrode is (or electrodes are) causing the problem.  On occasion, this type of problem may be caused by a loose or damaged connector on the ribbon cable, but this is rare.  Most often, the problem is caused by a single broken wire on an electrode.  If both wires on an electrode are broken, then the CM in range light will not go off, but the offset on that channel will read -262 mV (the negative extent of the input range).

The ActiveTwo Base System has no channels. The Base System consists of the parts that every ActiveTwo system needs to have, but excludes the parts that are used to custom configure ActiveTwo for various purposes, like amplifier/converter (AC modules).  The AC modules give the system the capacity to record from active electrodes. With four of the eight channel modules, the base system will have the capacity for 32 channels. If you want 32 electrodes on the scalp, then you need four modules, but if you also want to use four individual flat-type electrodes, you need another eight-channel module (four modules for EEG and one module for EXG1-8). The modules have eight channels, so you can only expand the system in increments of eight channels. You don’t have to buy the electrodes to use with EXG5-8, but you need the eight channel module.

Maybe.  There is no way the EEG system can harm the TMS system, but there are some TMS systems that are essentially useless with some EEG systems.  You need a a suitable combination of features in each to be successful at all in using TMS with EEG.

Desirable attributes:

• Coils designed specifically for use with EEG will have a cable that exits the coil tangential to the head surface so that the coil does not pass close by EEG electrodes and cables.
• A coil to be used with EEG should be passively cooled, since active cooling by means of a fan will induce electromagnetic interference in the EEG.
• The TMS recharge mechanism should be designed to avoid inducing electromagnetic artifacts in the EEG.
• The TMS system should be shielded so that no more than 3 milligauss of electromagnetic interference from the TMS system’s power supply reaches the electrodes and cables.
• The TMS system should be able to produce a TMS pulse in response to an input trigger with a low and predictable latency.  Long, but especially unpredictable latency in responding to an input trigger will result in TMS artifacts that are difficult to impossible to remove from the EEG.

Aside from attributes of the TMS system, there are also important considerations regarding the EEG system in this relationship. See the other FAQ entry on that topic.

Electrodes and head caps can have positions derived from systems based on the International 1020 System.  When the positions are based on 1020, the labels on the caps and electrodes can either be the actual 1020 position names (such as Fp1, Cz, etc) or they can be what is called ABC, which actually means A1, A2, …A32, B1, B2,…B32, etc  Another way to refer to the ABC labeling is arbitrary alphanumeric.  The 1020 system is not arbitrary because the names are based on anatomical landmarks and the odd=left and even=right numbering is predictable and interpretable.  When you have only one type of cap in your lab, it makes sense to use 1020 labels for caps with positions based on the 1020 system.  However, if you have 32 channel caps AND 64 channel caps, then you might find it useful to be able to use the A1-32 labels for the A cable and the B1-32 labels for the B cable and complementary A1-32 labels on the 32 channel caps and A1-B32 labels on the 64 channel caps.  This way, the A cable can be used for the whole head in 32 channel studies of for just the left side of the head in 64 channel studies.  This does provide a short term savings if you don’t want to have two A cables on-hand, but using 1020 labels on everything is more convenient and at the limit it will not cost any more (because cables that are used less frequently will last longer).

If you have more than one item to be repaired, we will normally issue a separate work order number for each item.  In that case, it is not necessary to ship the items to us separately.  They can be packed together, assuming you pack carefully and include the documentation we request when we send you the work order number:

• Include the “work order number” on the package and on any documentation in the package.  If a repair is undertaken, the work order number will become the “invoice number” if the repair results in a bill for parts or services.
• Write a note describing the problem you are having with the part and include it in the package with the part you are returning.  We need to be sure that we are focusing on the same problem that you have been experiencing to do the best job of reporting back to you on the status of the product.
• Be sure that the note you include with the shipment references as many of the following as possible: the date of purchase, name of purchaser or customer account number.
• Let us know the address to which repaired parts should be shipped (must be a physical address with a phone number and person’s name).

The inside diameter of adhesive ring should be about the same size as, or larger than, the diameter of the electrode contact.  The inside diameter of the adhesive ring should not be larger than the outer diameter of the electrode housing.  The outside diameter minus the center hole determines how much surface area contacts the skin, thus determining how tightly the adhesive will adhere to the skin.  Also, the outside diameter will limit how close you can place electrodes to one another and to other features, such as the eyes.

Using ActiveTwo as an example, the electrode contact on a flat-type electrode has a diameter of about 4.5 mm.  An adhesive ring with 5 mm id (center hole) would be  idea, but the 5×13 adhesives are rather expensive because they are manufactured in Europe.  We recommend using a 4×19 or a 4×12 adhesive ring.  The 4×12 is a good choice when placing the electrodes close to one another or close to the eyes for startle measurements.  The 4×19 is a good choice when you have plenty of room and the primary concern is how well the electrodes stick to the skin.