The truth assessment, also known as a Dalek lie detector (AUDIO: The Five Companions) or monitoring array, (AUDIO: The Conquest of Far) was the Dalek form of lie-detector, where an individual placed their hands on spherical sensors while being questioned.
A similar device was used to extract the truth from a subject. The subject was hooked up to a machine, facing away from a large, typically circular, screen. They were then interrogated, with their truthfulness assessed on the screen behind them. If they told a lie, a truthful image would replace the lie they had originally been trying to tell. Thus the device not only determined falsehoods, it extracted and revealed the truth that the subject was seeing in their own mind.
- "Statement: You are working against the Daleks. True or false?"
Several of the Doctor's companions underwent the truth assessment, including Romana I, (AUDIO: The Dalek Contract) Romana II or the Doctor's TARDIS, (TV: Destiny of the Daleks, PROSE: The Lying Old Witch in the Wardrobe) Nyssa, (AUDIO: The Five Companions) Charley Pollard, (AUDIO: Brotherhood of the Daleks) Amy Pond, (COMIC: The Only Good Dalek) Jo Grant, (AUDIO: The Conquest of Far) and Peri Brown. (AUDIO: Emissary of the Daleks)
Jeff Stone observed a Dalek being interrogated with one after the Dalek had spotted Stone creeping around the Dalek city, and his fellow Daleks were incredulous that such a thing might be possible. The fact that the Daleks hooked one of their own up to the device implied that Daleks were quite capable of lying. When his colleagues determined that he was telling the truth, they sounded an intruder alarm, forcing Stone to hurriedly leave the planet. (COMIC: City of the Daleks)
Romana I was also hooked up to one whilst on a Dalek ship in the Proxima System. She worked out that it worked in reverse. She could ask a Dalek a question and it gave a response to its answer. (AUDIO: The Dalek Contract)
Jo Grant was interrogated after being captured by the Daleks on Far. They asked her which incarnation she travelled with, and if she knew of their plans. This version of the machine they used was able to inflict great pain on her. (AUDIO: The Conquest of Far) A similar version was used to interrogate Peri Brown as it inflicted pain on her, but this version could visualise Peri's thoughts. (AUDIO: Emissary of the Daleks)