In her book, Lucid Dreams,

In her book, Lucid Dreams, Green predicted that conscious dreaming would be found only during Rapid Eye Movement (REM) sleep.
She also speculated over a two-way signaling system between a lucid dreamer and a waking observer, using pre-determined eye movements while dreaming. This was later scientifically documented by two separate lucid dreamers in their university laboratories: Alan Worsley at the University of Hull in England, and Stephen LaBerge at Stanford University in California.
- source:Lucid Dreaming – Waking Up to Alternate Realities , by Rebecca Turner from: evolution ezine