1Hz Unexpected Frequency in Signal

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achaiken
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Joined: Thu Jun 10, 2021 10:30 am

1Hz Unexpected Frequency in Signal

Post by achaiken »

Hi there,

I am running a frequency tagging study. The paradigm involves flashing visual stimuli on the screen at 2.5 & 3.16Hz to induce periodic neural responses. I've attached the grand averaged frequency spectrum showing the responses to our stimulation (fundamentals & harmonics highlighted) as well as peaks completely unrelated to our stimulation (unhighlighted). The source appears to be at 1Hz with the rest being its harmonics. I am not sure where this could be coming from as it doesn't align with our stimulation.

I have also included the topography of this 1Hz response which does not look visually based. It looks like it is right above CMS/DRL. Is it possible that something in the hardware is causing this?

Sidenote: there is an additional trigger in some of my files '4', that I did not code into the study. Unsure if this could be related.

topo.JPG
topo.JPG (39.29 KiB) Viewed 377 times
freqspect.JPG
freqspect.JPG (47.46 KiB) Viewed 377 times
Best,
Anna

Coen
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Re: 1Hz Unexpected Frequency in Signal

Post by Coen »

"Is it possible that something in the hardware is causing this?"

No, the BioSemi system does not generate any signal of exactly 1 Hz.

Best regards, Coen (BioSemi)

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