An Aldean musical instrument
The Aldean musical instrument was an advanced device controlled by thoughts. The player put his fingers on certain pads on the instrument and simply felt the notes in his head. If done correctly, the instrument would start to glow in different colors and produce a melody that was similar in mood to the player's feelings and thoughts.
Melian, an aged Aldean musician, taught Katie, a child aboard the USS Enterprise-D, how to play the instrument when she was abducted by the Aldeans. (TNG: "When The Bough Breaks")