This extension for EventIDE software allows designing experiments, where stimulus presentation is accurately locked to a selected phase of the online EEG signal. The extension consists of a hardware driver and a phase prediction module. The hardware driver performs real-time acquisition of single-channel data from an EEG amplifier. Based on that data, the phase prediction module continuously estimates a time interval to the next predicted occurrence of the selected phase in an online neural signal. The estimated time interval is then used by EventIDE to initiate a locked stimulus presentation.
Real-time pattern forecast of alpha oscillations (~10 Hz) in an EEG signal. The present time moment corresponds to the ‘zero time’ mark on the X-axis. Signal forecast is shown with a green line. The signal contained between two white bars is used for prediction of the future signal.
Real-time phase forecast and stimulus presentation locked to the upper phase of alpha oscillations (~10 Hz) in an EEG signal. The present time moment corresponds to the ‘zero time’ mark on the X-axis. Phase forecasts are shown with the green vertical bars.
The phase prediction module performs the following steps in a moving signal window:
- Estimation of the frequency power in the chosen frequency range;
- Instantaneous phase estimation;
- Adaptive bandpass filtering of the signal;
- Time-series forward prediction;
- Real-time plotting of the signal window, frequency power and signal forward prediction;
- Collection of numerical signal statistics, e.g. the current dominant frequency;
- Estimation of the time interval to the next phase-locked stimulus presentation;
- Evaluation of the past predictions in respect to the real signal.
The phase prediction module is optimized for ultra-fast data analysis and stimulus delivery. The module was tested both with real-time EEG recordings and in an EEG emulation mode, in which a large amount of the offline EEG data were used. The results of the testing revealed that the module:
- makes accurate phase predictions even in a noisy and frequency-unstable signal;
- can make prediction for any signal phase (not only signal peaks);
- can be used for a wide range of oscillation rhythms after minimal tuning;
- provides comprehensive and detailed statistics for real-time monitoring;
- allows a researcher to control and adjust the estimation procedure in real-time;
- allows presentation of an arbitrary stimulus locked to a signal phase with 1ms accuracy;
- can easily be adapted to the existing experimental setups;
- demonstrates good performance on a standard PC.
Real-time signal processing can be helpful in designing experiments with a direct neurofeedback control, where you use certain signal characteristics to adjust an ongoing stimulus presentation. Another possible application of signal processing would be designing of mental games and activities, in which the bio-signals are registered as a form of participant response. The signal sources in EventIDE are not bound to the bio-amplifiers only. A wide range of recording bio-sensors can be engaged for signal processing.
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- Ilia Korjoukov, Lucia M. Talamini, Eva van Poppel, Maria Molodova, Roy Cox (2016) Stimulus presentation locked to arbitrary patterns and oscillatory phases in a real-time EEG signal. Conference: Sleep and Cognition Event. Amsterdam, the Netherlands. DOI: 10.13140/RG.2.1.4123.3527.
- Eva van Poppel, Ilia Korjoukov, Lucia M Talamini (2016) A new closed-loop stimulation procedure: The influence of slow oscillation up-state cueing on vocabulary memory, Conference: European Sleep Research Society 23rd Congress, Bologna, Italy, September 2016. DOI: 10.13140/RG.2.2.11020.72328.
- Cox R, Korjoukov I, de Boer M, Talamini L.M. (2014) Sound asleep: processing and retention of slow oscillation phase-targeted stimuli. PLoS One. 2014 Jul 7;9(7):e101567. DOI: 10.1371/journal.pone.0101567.