Telepathic humanoids who communicate mind to mind and, with Lwaxana Troi as their teacher, began learning spoken language.
The Cairn have no spoken language of their own because they communicate entirely through telepathy. Contact with their vivid, image-filled minds can be draining even for an experienced telepath. They wanted to learn speech so they could deal with other species.
In Dark Page, Lwaxana Troi taught Ambassador Maques and his young daughter Hedril to speak. The strain of the work brought a long-buried memory to the surface and left Lwaxana in a coma, and Maques helped Deanna Troi enter her mother's mind, where she discovered Lwaxana's grief over her elder daughter Kestra, Deanna's sister, who had drowned as a child.