We had slightly different readings.
As he was writing he became aware that he was being watched, and a figure slowly emerged to his left. It was indistinct and on the periphery of his vision but it moved as V.T. would expect a person to. The apparition was grey and made no sound… V.T. was unable to see any detail and finally built up the courage to turn and face the thing. As he turned the apparition faded and disappeared.
He experienced a visual disturbance in his periphery manifesting as the false perception of a person. Even without it being interpreted as a person, that’s a textbook mild hallucination.
Once V.T. knew this he calculated the frequency of the standing sound wave … 18.97Hz … plus or minus 10%
Table IV on page 212 of this book shows frequencies causing disturbance to the eyes and vision to be within the band 12 to 27 Hz.
Most interestingly, a NASA technical report mentions a resonant frequency for the eye as 18 Hz (NASA Technical Report 19770013810).
He cited two sources inline with ranges narrower than 8-40Hz which indicate that vision can be affected at the same frequencies he measured in the lab. He even noted that everyone would have slightly different resonant frequencies.
No, it’s not a full research paper, but it is the citation you requested.
I’m not sure I understand. Peripheral hallucinations are a recognized type of hallucination, and hallucinations can involve anything from shadows or flashes of light through to full vivid imagery. It only requires perceiving anything that isn’t really there and but it feels real. The patterns or colors you see when you close your eyes are considered hallucinations too.