The two test an urban legend that claims that there is frequency around 19 Hz that can produce feelings of discomfort, dread and, yes, even fear. But the thing is, 19 Hz is below the threshold of human hearing, so these feelings are produced without anyone being able to hear the note.
Read moreWhat sound frequency makes you hallucinate?
The standing waves/hallucinations arise when flicker frequencies are approximately twice the natural frequency of the damped oscillations in the neural dynamics (Rule et al., 2011). The resonant frequency of simple cells in the primary visual cortex of cat typically peaks near 5 Hz (Movshon et al., 1978).
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