The Dreamachine is a rotating cylinder with slits and with a light bulb inside which acts as a sort-of strobe light. It was invented by Beat generation members painter and writer Brion Gysin and mathematician (yep!) Ian Sommerville in 1959.
The frequency of the light lies in the range of brainwaves, which leads to psychadelic effects. I cite from wikipedia:
The Dreamachine is “viewed” with the eyes closed: the pulsating light stimulates the optical nerve and alters the brain’s electrical oscillations. The “viewer” experiences increasingly bright, complex patterns of color behind their closed eyelids. The patterns become shapes and symbols, swirling around, until the “viewer” feels surrounded by colors. It is claimed that viewing a Dreamachine allows one to enter a hypnagogic state. This experience may sometimes be quite intense, but to escape from it, one needs only to open one’s eyes.
According to Wikipedia the dream machine is used as an alternative audio-visual entrainment treatment for ADD. However as I am not a neuroscientist I can’t judge wether this is really true or wether this is rather a case for citizendium.
You can try out yourself what effects the stimulus has on your brain, as there is a toy online dreamachine here. With the arrow-buttons in this online application you can change the frequency of the stimulus which can lead to very different effects.
Looking at the effects it is may be scary to extrapolate what can happen if one does not only use just these simple flashlights but complex imagery like in subliminal advertising.
As for the life of mathematician Ian Sommerville, I could not find much information, just these two scary accounts from a finnish literature site citing Paul McCartney and a weired discussion post at Genevas Centre for contemporary image.