Electrode holders do just what their name says -- they hold the pin-type active electrodes in place. These holders are designed to be used with the elastic fabric material of the standard head caps we offer, but they can also be used in other types of head caps or even other types of garments for holding the pin-type electrodes on the body. Each electrode holder consists of three parts: a flared base with gel cavity, top tab with recessed circular insert for label and a rubber X-ring that provides friction to hold the electrode in place. The holders can be disassembled and relocated in the cap to change electrode positions or they can be removed from an old cap and installed in a new cap.
Caps are available in a wide range of sizes and with a variety of electrode position layouts:
Standard cap layouts for 16, 32 and 64 channels are based on the International 10/20 System. Layouts for 128, 160 and 256 channels have electrode positions that are radially equidistant from CZ. Click on the images below to enlarge the view of each standard cap layout diagram:
The electrode position coordinates of standard ActiveTwo head caps are available from the downloads page.
The standard steps for applying the head cap and electrodes are:
1 - Place the cap on the subject's head.
2 - Fill the electrode holders with electrode gel from a syringe.
3 - Insert the electrodes, taking care to match the color-coded label on the electrode to that on the electrode holder.
Because of the characteristics of the active electrode, high electrode impedance can be tolerated, so no skin preparation is required. Thus, the usual, unpleasant and time-consuming abrasion of the scalp is omitted. After the electrode holders are filled with gel, the active electrodes are plugged in the cap one by one. The procedure is fast and reliable, and allows high density EEG measurement with a minimum of preparation time and subject discomfort.
It is also possible to pre-assemble the head cap (insert electrodes into the electrode holders) and pre-gel the electrodes for placement on subjects with shorter hair (e.g. infants). This shortens application time by eliminating the need to apply gel and insert electrode while the subject waits.
Surgical-style caps with slightly lower coverage on the sides and in the back of the head are available upon request. The surgical-style cap incorporates an elastic band at the lower border of the cap, which eliminates the need for a chin-strap or body harness. The surgical style cap also provides slightly lower coverage in temporal and occipital areas.
A special full-coverage head cap (not pictured here) for use with 128 and 256 channel systems was developed in conjunction with Dr. Scott Makeig and colleagues at the Swartz Center for Computational Neuroscience in La Jolla, CA. This cap provides coverage in the cheek and neck regions that is expected to be useful for better identification of signals by means of independent component analysis (ICA). For details about this special cap configuration, contact Dr. Scott Makeig.
Different electrode layouts are possible on client specification. It is also possible to assemble your own cap layout.
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