EmotivBCI
  • EmotivBCI
  • Getting started
    • System requirements
    • Installing and Updating
    • Logging in
    • Create an account
    • Forgot password
    • Access account
    • Logging out
    • Offline use
  • Setting up your EEG device
    • Connecting your headset
      • USB Dongle Connection
      • Bluetooth Connection
      • Connecting EPOC Flex
    • Disconnecting your headset
    • Fitting your headset
    • Contact quality map
      • Contact Quality (CQ) vs. EEG Quality (EQ)
    • EEG quality indicator
    • Battery indicator
    • EPOC+ and EPOC X configurations
  • Demographic data collection
  • Menu and navigation
  • Training profiles
    • Your training profiles
    • Creating a training profile
    • Changing training profile
    • Editing training profile name
    • Deleting training profile
    • Guest mode
    • Readonly training profile
    • Convert readonly training profile
  • Mental Commands
    • Overview
    • Training neutral
    • Training your first command
    • Accept or reject training
    • Training feedback
    • Command level
    • Brain Space Diagram
    • Adding new commands
    • Deleting commands
    • Deactivating commands
    • Training modes
    • Live mode
    • Adjusting sensitivity
    • Tips and Tricks
  • Facial Expressions
    • Overview
    • Training facial expressions
    • Training neutral
    • Training your first expression
    • Expression level
    • Adding new expressions
    • Delete expression
    • Live mode
    • Adjusting sensitivity
    • Use default detections
  • Performance Metrics
    • Overview
    • Definitions
    • Frequency rate
    • Turn streams on/off
    • Toggle all streams on/off
  • Motion sensors
    • Overview
    • Definitions
    • Frequency rate and resolution
    • Turn streams on/off
    • Toggle all streams on/off
  • OSC
    • Example connection with MaxMSP
  • Release notes
    • v2.0
    • v2.1
    • v2.2.1
    • v2.3
    • v2.4.1
    • v2.5
    • v2.6
    • v2.6.1
    • v2.6.2
    • v2.6.3
    • v2.7
    • v2.7.1
    • v3.0.0
    • v3.1.0
    • v3.2.0
    • v3.6.5
    • v3.6.8
    • v3.7.0
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On this page
  • What is EEG Quality?
  • How is EEG Quality Different to Contact Quality?
  • Okay, but what actually is EQ?
  • How is Overall EQ Calculated?
  1. Setting up your EEG device
  2. Contact quality map

Contact Quality (CQ) vs. EEG Quality (EQ)

What is EEG Quality?

EEG Quality (EQ) has been built to give you an easy way to assess whether you are recording high quality brain signals or not. Basically, it is a scoring system for the quality of the signal in each sensor. Each sensor is given a black, red, orange, light green or dark green colour to indicate the quality of the EEG signal for that specific sensor.

Overall EEG Quality as displayed in your EMOTIV application is presented as a score of 0-100. This number makes it easy to understand the quality of your signal at a glance. How do we calculate it? See below.

How is EEG Quality Different to Contact Quality?

Contact Quality is a simple measurement of impedence of the channel. While this measurement is used widely in neuroscience and medical settings, it is really only a useful reading to a trained EEG professional and does not give the full picture on the quality of the signal. Signals that have low impedance are not necessarily brain signals - and you might have found that sitting your headset on the table can produce a false positive - leading the user to falsely believe they are recording high quality brain data.

Okay, but what actually is EQ?

EEG Quality is a machine-learning trained algorithm that automatically determines the quality of the signal based on multiple metrics. Each of these metrics are important in assessing whether the recording data accurately captures the underlying brain signal. These metrics include

  • Contact Quality (CQ) (as above) - an impedance measurement that indicates the quality of the electrical signal passing through the sensors and the reference. It can be one of 4 values: 0 - very bad (black), 1 - bad (red), 2 - ok (orange) and 4 - good (green).

  • ML Signal Quality (SQ): A machine learning algorithm trained on high quality EEG recordings that were assessed and collected by the EMOTIV Research team. The Signal Quality algorithm assess data over 2 seconds and is scored 0 - very bad (black), 1 - bad (red), 3 (light green) and 4 -good (dark green)

  • Signal Magnitude Quality (SMQ): A measure of the signal amplitude. Sometimes, the above metrics i.e. CQ, SQ are good but the signal amplitude is very small and therefore small power fluctuations in the FFT would be undetectable. Often, this is due to poor sensor hydration or poor scalp contact. SMQ gives scores for the average signal magnitude within a 2 second epoch. The scores can be 0 - very low (black), 1 - low (red), 4 - ok (green).

Each of these metrics are important in determining the quality of the signal, therefore the sensor colour will not be dark green unless all of these metrics have a “good” score of 4. The “EQ Map” UI in your EMOTIV software displays the minimum score of any of these metrics. The resulting EQ Score for each channel can be 0,1,2,3,4 corresponding to the colours black, red, orange, light green and dark screen, respectively.

How is Overall EQ Calculated?

Overall EQ is calculated and displayed as a number out of 100 so you can see your EEG Quality for all channels at a glance. Overall EQ is calculated as the sum of the worst 3 channels divided by the sum of the maximum score of these 3 channels, as a percentage. The resulting mathematical formula is (min1 + min2 + min3 / 12) * 100.

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Last updated 3 years ago