Delay or Latency Between Sensors and On-Screen Feedback
SamB
Colorado
Hi,
Does anyone know how to test the total time it takes for an EEG amplifier to register its data on a display? I want to see what the base delay is and what factors impact it, and by how much—factors such as different BCI software, different delays, higher-order filters, or more layers of various processing elements.
I am currently using Cyton with Bluetooth and Brainbay for neurofeedback software.
I would also love to hear any suggestions for reducing delay.
Here are two studies that suggest that more delay results in poorer neurofeedback training. They both had a method to test total delay, but for the life of me, I did not grasp it from their explanations.
https://pubmed.ncbi.nlm.nih.gov/33166941/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8913511/
Comments
Hi Sam,
I believe you can assume MOST of the neurofeedback (NFB) session latency factor, occurs during the signal processing operations in the laptop app that you are using. By keeping the order of your filters say in the range of 4 (instead of higher orders 6,7 etc.) your delay factor is only a couple hundred milliseconds. I do know that many of these apps (Bioexplorer, BioEra, BrainBay, etc.) have a way to display the graph of delay vs frequency for each filter that you implement. The digital filter delay is unavoidable and is just the way these filters operate on time series.
https://www.google.com/search?q=dsp+filter+delay
The latency caused by the firmware and buffering (radio packets, usb delays, OS buffering) are minimal and only a few milliseconds. In the case of Cyton, it is operating at 250 Hz and thus samples every 4 ms. The OS, radio and usb buffering might add some additional few ms, but that is all.
The second link you referenced inserts very LARGE delays of 1 second or 20 seconds. So certainly understandable that this would generate poor coupling for the trainee. As a counter example regarding latency, consider the type of infra-low frequency neurofeedback offered by the Othmers (ILF) or Mark Smith (ISF). Those infra-low waves are well below .1 Hz and take many seconds to complete a cycle. Yet those systems still produce results consistently.
Regards, William
As an addendum, if you are working with ERP projects and need very precise timing, then the External Trigger pages are relevant. But almost all neurofeedback is not working with that paradigm.
https://docs.openbci.com/Cyton/CytonExternal/
[using a photoresistor to tightly couple monitor visual stimuli with the data stream trigger channel]
https://docs.openbci.com/Examples/VideoExperiment/