The latency of EMOTIV data streams
Latency is the delay between a brain event and the time its effect is seen on the receiving device.
For EPOC X/+ and Insight, there is a 60ms delay in the digital filters in the headset firmware, plus a few more milliseconds of wireless transmission and processing delays in Cortex SDK. We account for those delays in Cortex when we add markers to data, but real-time EEG data passed through the API or displayed using EmotivPRO are shown about 200ms late to allow time for asynchronous API markers to be added correctly to the data stream.
For BCI the above 200ms output delay is not present – the data is processed in our detections as it arrives. The update rate for each detection and the length of the trailing data sample determines the latency in that case.
Performance Metrics are updated twice per second. Mental Commands are updated 4 times per sec. For PMs and Mental Commands, the additional latency comes from the time to detect a change in state.
We look at the last 1 sec of data for Mental Commands. The detection takes up to 250ms to see a significant change in the trailing 1-sec sample.
Typically the Performance Metrics take 0.5-1 seconds to respond to significant changes.