Lucid dream research done in the 1970s had subjects signalling from within a dream using eye movement. https://www.researchgate.net/publication/258201870_Lucid

Lucid dream research done in the 1970s had subjects signalling from within a dream using eye movement. https://www.researchgate.net/publication/258201870_Lucid_dream_verified_by_volitional_communication_during_REM_sleep https://www.researchgate.net/publication/258201870_Lucid_dre...