the lucid dreaming communication experiment itself is decades old now, people in lucid dreams have communicated to conscious scientists by moving their eyes in patterns to communicate with sleep scientists talking to the dreamer or playing sounds for them while in a lucid dream state to indicate their understanding of what was happening in the waking world.

The “first” they’re talking about is the same phenomenon shared between two people in a lucid dream, rather than one.

which is cool in its own right.