After you opened a session with a headset, you can subscribe to one or more data streams.

Each data stream gives you real time access to data from the headset (EEG, motion...) or data calculated by Cortex (band powers, mental command...)

After you successfully subscribe to a data stream, Cortex will keep sending you data sample objects.

A subscription is linked to a session. All the subscriptions of a session are automatically cancelled when the session is closed. You can call unsubscribe to cancel a subscription.

The available data streams depend on the license of the user, and the model and settings of the headset. For an EPOC Flex, it also depends on the EEG sensor mapping.

Data streams

Each data stream is identified by its name: "eeg", "mot", "dev", "eq", "pow", "met", "com", "fac", "sys".

Data streams availability

Depending on the license and the model of the headset, some streams may be available or not, and may send at a different rate.

After you successfully subscribe to a data stream, Cortex will keep sending you data sample objects. See Data Subscription for details.

A data sample object contains these fields:

To interpret the values in the <stream> array, you must check the field cols from the result of the method.

How to interpret the values

Suppose you want to get the mental command stream. You successfully subscribe to the stream "com", and you receive this response:

The important part is the field cols:

So, the labels for the mental command samples are "act" (action) and "pow" (power), in this order. Then you will receive some mental command samples. They look like this:

The values in the array com match the labels in the array cols. So "push" is the value for "act" , and 0.376 is the value for "pow".

Below is the description of the labels used in each data stream.

EEG

The stream "eeg" uses these labels:

The maker objects include these fields:

Example for an INSIGHT:

Example for an EPOC+ or EPOC X:

Motion

The stream "mot" uses these labels:

Depending on the headset, the labels for the gyroscope will be GYROX, GYROY, GYROZ or the quaternions. You will never get both these labels.

Example for a newer INSIGHT:

Example for an older INSIGHT:

To understand the meaning of motion data, you can refer .

Device information

The stream "dev" uses these labels:

Example with INSIGHT:

Example with EPOC+ or EPOC X:

EEG Quality

Please read this to understand the difference between the contact quality and the EEG quality.

The stream "eq" uses these labels:

This stream was added in Cortex 2.7.0

Example with INSIGHT:

Band power

This stream gives you the power of the EEG data. The values are absolute, the unit is uV^2 / Hz. Each sample is calculated based on the last 2 seconds of EEG data.

The labels of the stream "pow" use the format "SENSOR/BAND", when SENSOR is the name of the EEG sensor and BAND is the name of the band power. Cortex provides these bands:

• theta (4-8Hz)

• alpha (8-12Hz)

• betaL (low beta, 12-16Hz)

So the low beta for AF3 has the label "AF3/betaL". The gamma for Pz has the label "Pz/gamma".

Example with INSIGHT:

Example with EPOC+ or EPOC X:

Performance metric

Each performance metric is a decimal number between 0 and 1. Zero means "low power", 1 means "high power". So for example, a value of 0.1 for "eng" means that the user is not engaged, a value of 1.0 means the user is very engaged. If the detection cannot run because of a poor EEG signal quality then the value is null.

For each performance metrics, the flag isActive is true if the detection of this metrics is running properly. It is false if the detection cannot run. This can happen if the EEG signal from the headset is of poor quality. This flag was added in Cortex 2.2.1

The "met" stream labels vary depending on the headset type, as shown in the tables below:

The "met" Stream Labels of MN8

Example

The "met" Stream Labels of EPOC / INSIGHT / FLEX - (with EPOC config only)

Example

To understand the meaning of each performance metrics, you can refer .

Mental command

The stream "com" uses these labels:

Facial expression

The stream "fac" uses these labels:

Use the method to get the possible actions.

System events

The stream "sys" is used for the of the mental command and facial expression. It uses these labels:

For example, just after you start a training for the mental command detection, you receive a system event like this:

This method is to cancel a subscription that was previously created by the subscribe method.

Parameters

The parameter streams must contain one or more values, chosen from this list: "eeg", "mot", "dev", "pow", "met", "com", "fac", "sys". See for details.

Result

The result is an object that includes these fields:

In case of success, you get an object with these fields:

In case of failure, you get an object with these fields:

Examples

Unsubscribe successfully from the performance metrics and motion streams.

This method is to subscribe to one or more data streams. You can call unsubscribe to cancel a subscription. After you successfully subscribe to a stream, Cortex will keep sending you data sample objects.

See Data Subscription for details.

Parameters

The parameter streams must contain one or more values, chosen from this list: "eeg", "mot", "dev", "eq", "pow", "met", "com", "fac", "sys". See for details.

Result

The result is an object that includes these fields:

In case of success, you get an object with these fields:

Please note that the field cols is especially important. This field tells you which values you will get in the data stream, and in which order. See for details.

In case of failure, you get an object with these fields:

Examples

Subscribe successfully to motion and performance metrics.

Subscribe successfully to performance metrics, but fail to subscribe to raw EEG.