Telepathy Tile

Telepathic Tiles are the means by which Sahasrahla, and occasionally Princess Zelda, keep in touch with Link throughout his quest in A Link to the Past. When Link approaches one of these tiles, he is able to communicate telepathically with his distant allies, at which point they will express a hint about the current dungeon to him. It's unknown whether or not Sahasrahla or Zelda need a Telepathic Tile of their own to communicate with Link, but certain circumstances, such as Princess Zelda being captured by Ganon and imprisoned in a crystal when Link is speaking to her, would suggest not.

Trivia
A Telepathic Tile can be found in Chris Houlihan's Top Secret Room that allows Link to hear a message from the contest winner.