Perseption filter

A perception filter is a device that will cloak something (EG: a spacehip, being etc...). A person/thing with a perseption filter can disguise himself as anything.

History
In venice, 1580, the Saturnynians used perseption filters to disguise themselves as normal humans, only with sharp vampire-lie teeth. The Doctor managed to deactivate the perseption filters with his sonic screwdriver.

In Leadworth, 1996, Prisoner Zero was able to escape his prison via a crack in time. He was transported to a young Amelia Pond's house. He hid in a room and put a perseption filter on it, so that it was only visible from the corner of ones eye. It can only be assumed that the doctor removed the perseption filter with the capture of Prisoner Zero.

In 2010, a spaceship crahsed on top of Craig Owens' bungalow, and disguised itself as the top floor of the house. The autopilot then needed the correct person to pilot the ship. The Doctor and Craig caused the spaceship to implode, causing the perseption filter to stop working.

Behind the Scenes

 * The Doctor Who Confidential accompaniment for Human Nature suggests that Timothy Latimer, the boy who was immune to the perception filter, was a genetic mutant born with an extra piece in his brain. The final script makes no mention of this, although the Doctor does note that he has an extra telepathic synapse in his brain, accounting for his strange abilities.
 * The series has yet to establish when the perception filter was installed or activated in the TARDIS for the first time. It would appear to be a relatively recent innovation (possibly Time War-related?), as there are many occasions in the original series and 1996 telefilm where no perception filter effect is in evidence.
 * The perception filter is very similar to the "Someone Else's Problem field", as mentioned in the Hitch-Hiker's Guide to the Galaxy books by former Doctor Who writer and story editor Douglas Adams.