EEG Recording and Online Signal Processing on Android: A Multiapp Framework for Brain-Computer Interfaces on Smartphone

Figure 3

Timing test setup. (a) The varying delay between the programmatic start of a sound playback and the actual onset is evaluated with a smartphone running the Smarting application and the presentation mobile application. A marker sent by presentation indicates the onset of the sound playback and is recorded by the amplifier alongside with the voltage fluctuations fed from the audio jack into the EEG amplifier. The EEG time series is then transmitted wirelessly via Bluetooth to the receiving app on the same smartphone. (b) The difference between the marker (set as reference to 0 ms) and the sound signal (here: the filtered square wave) varies from trial to trial. The single trial latency is defined as the time between marker onset and the amplitude exceeding the half-maximum of the trial averaged response. We define latency jitter as the standard deviation of those single trial latencies. In addition to the jitter properties, the system can also be characterized by its lag, defined as the mean of the single trial latency measures.

(a) Timing test setup

(b) Timing test measurement