EEG Meta Data

This page specifies the meta-data for EEG recordings.

If a stream has the content-type EEG, we recommend that meta-data about the stream adheres to the structure and naming laid out in the following. While all meta-data is optional, we recommend that any stream should describe at least the channel labels.

<channels>            # per-channel meta-data; might be repeated 
  <channel>           # description of one channel, repeated (one for each channel in the time series) 
    <unit>            # measurement unit (strongly preferred unit: microvolts) 
    <type>            # channel content-type (EEG, EMG, EOG, ...) 
    <label>           # channel label, according to labeling scheme; 
                      # the preferred labeling scheme for EEG is 10-20 (or the finer-grained 10-5) 
    <location>        # measured location (note: this may be arbitrary but should then include 
                      # well-known fiducials (landmarks) for co-registration) 
      <X>             # coordinate axis pointing from the center of the head to the right, in millimeters 
      <Y>             # coordinate axis pointing from the center of the head to the front, in millimeters 
      <Z>             # coordinate axis pointing from the center of the head to the top, in millimeters 
    </location> 
 
    <hardware>        # information about hardware properties
      <model>         # model of the sensor
      <manufacturer>  # manufacturer of the sensor 
      <coupling>      # type of coupling used (can be Gel, Saline, Dry, Capacitive) 
      <material>      # conductive material of the sensor (e.g. Ag-AgCl, Rubber, Foam, Plastic) 
      <surface>       # type of the contact surface (e.g., Plate, Pins, Bristle, Pad) 
    </hardware> 
 
    <impedance>       # measured impedance value during setup, in kOhm 
 
    <filtering>       # information about the hardware/software filters already applied to the data (e.g. notch) 
      <highpass>      # highpass filter, if any 
        <type>        # type of the filter (FIR, IIR, Analog)
        <design>      # design of the filter (e.g., Butterworth, Elliptic) 
        <lower>       # lower edge of the transition frequency band (in Hz) 
        <upper>       # upper edge of the transition frequency band (in Hz) 
        <order>       # filter order, if any 
      </highpass> 
 
      <lowpass>       # highpass filter, if any 
        <type>        # type of the filter (FIR, IIR, Analog) 
        <design>      # design of the filter (e.g., Butterworth, Elliptic) 
        <lower>       # lower edge of the transition frequency band (in Hz) 
        <upper>       # upper edge of the transition frequency band (in Hz) 
        <order>       # filter order, if applicable 
      </lowpass> 
 
      <notch>         # notch filter, if any 
        <type>        # type of the filter (FIR, IIR, Analog) 
        <design>      # design of the filter (e.g., Butterworth, Elliptic) 
        <center>      # center frequency of the notch filter (in Hz) 
        <bandwidth>   # width of the notch frequency band (in Hz), if known 
        <order>       # filter order, if applicable 
      </notch> 
    </filtering> 
  </channel> 
</channels> 
 
<reference>           # signal referencing scheme 
  <label>             # name of the dedicated reference channel(s), if part of the 
                      # measured channels (repeated if multiple) 
  <subtracted>        # Yes if a reference signal has already been subtracted from the data, otherwise No 
  <common_average>    # Yes if the subtracted reference signal was a common average, otherwise No 
</reference> 
 
<fiducials>           # locations of fiducials (in the same space as the signal-carrying channels) 
  <fiducial>          # information about a single fiducial (repeated for each one) 
    <label>           # label of the location (e.g., Nasion, Inion, LPF, RPF); can also cover Ground and Reference 
    <location>        # measured location (same coordinate system as channel locations) 
      <X>             # coordinate axis pointing from the center of the head to the right, in millimeters 
      <Y>             # coordinate axis pointing from the center of the head to the front, in millimeters 
      <Z>             # coordinate axis pointing from the center of the head to the top, in millimeters 
    </location> 
  </fiducial> 
</fiducials> 
 
<cap>                 # EEG cap description 
  <name>              # name of the cap (e.g. EasyCap, ActiCap, CustomBiosemiCapA) 
  <size>              # cap size, usually as head circumference in cm (typical values are 54, 56, or 58) 
  <manufacturer>      # manufacturer of the cap (e.g. BrainProducts) 
  <labelscheme>       # the labeling scheme for the cap (e.g. 10-20, BioSemi-128, OurCustomScheme) 
</cap> 
 
<amplifier>           # information about the used amplification (e.g. Gain, OpAmps/InAmps...) 
  <settings>          # settings of the amplifier 
  </settings> 
</amplifier> 
 
<location_measurement>  # information about the sensor localization system/method 
  <model>               # model name of the system, e.g. CMS10 
  <manufacturer>        # manufacturer of the measurement system, e.g. Polhemus, Zebris 
  <locationfile>        # file system path of the (backup) location file, if any 
  <settings>            # settings of the location measurement system 
  </settings> 
</location_measurement> 
 
<acquisition> 
  <manufacturer>      # manufacturer of the amplifier (e.g. BioSemi) 
  <model>             # model name of the amplifier (e.g. BrainAmp)
  <precision>         # the theoretical number of bits precision delivered by the amplifier 
                      # (typical values are 8, 16, 24, 32)
  <compensated_lag>   # amount of hardware/system lag that has been implicitly 
                      # compensated for in the stream's time stamps (in seconds) 
</acquisition>