The Thought Channel was a type of Time Lord technology that allowed one to access someone's mind. A Time Lord tribunal used this on the Second Doctor at his request so they could see the evils of the universe he had fought against. On the Thought Channel, images of a Quark, a Yeti, an Ice Warrior, a Cyberman and a Dalek were seen. (TV: The War Games)
The Second Doctor shows a Dalek to the Time Lord tribunal via the Thought Channel. (TV: The War Games)
The device was similar in practice to the Daleks' Mind Analysis Machine, which was used to forcibly ascertain the identity of the Third Doctor by manifesting the images of his previous incarnations. (TV: Day of the Daleks)