My guess is they are mid-layer activations in the brain that your consciousness (attention?) is connecting to, or which are being directed to the lower layers and interpreted as input.
> It turns out that hallucinations comprising spirals, circles, and rays that emanate from the centre correspond to stripes of neural activity in V1 that are inclined at given angles. Lattices like honeycombs or chequer-boards correspond to hexagonal activity patterns in V1.
