Filtering is certainly part of it.
As is interpreting random stimulation as patterns, whether this is due to our perception making some order of it or possibly related to the ordering of the rods and cones.
Blind (or almost blind) people can sometimes get this disturbing syndrome
www.nhs.uk/conditions/charles-bonnet-syndrome/
Edit: I've had experiences a little like this when dozing
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FeralCatMan Unusual disease collector., Sat 31 Oct 2020, 0:41,
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