I have created the scenario with 4 red LEDs flickering with different frequencies separated by minimum 20 cm (at the side of monitor). The selected flickering frequencies sets were (6.25, 6.66, 7.14 and 7.69 Hz), (11.36, 11.9, 12.5 and 13.15 Hz) and (7, 8, 9 and 11 Hz) in different trials.
At the time of analysis, the FFT is consisting a noise and peaks near 10 Hz frequencies. I used the BioSemi Actiview amplifier with 64 channels, to record signal at 2048 Hz sampling frequency. I asked subject to look to a particular LED for 10 sec and then look to other. Trigger was provided for segmentation accordingly. I recorded the data for maximum duration of 5 min to avoid sleepiness of subject.
I have seen the peaks at desired frequency for other online available data sets but I am not getting it for my recorded data. The FFTs for LED flickering frequencies (6.25, 6.66, 7.14 and 7.69 Hz) is attached with this question. Please help me to understand the proper recording conditions.
Hi,
How accurate is your stimuli frequency? As you have mentioned that you are using LED's, confirm the flash frequency with an oscilloscope.
For SSVEP you'll get the exact frequency from O1 or O2 even with low sampling frequencies (64 or 128).
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