While I understand the reason behind it this is something I’ve always found rather odd and suspension of disbelief straining when it occurs in fiction.
Namely when two (or more) characters have swapped bodies and yet they retain their original voices. I assume accents and speech-patterns would remain the same *(ie: if the mind was English placed in an American body they would retain an English accent)*but surely different physical vocal equipment would result in different voice patterns?
This is even more jarring and obvious when the swap occurs between a male and a female.
Ironically the British comedy series has examples of both types of swap, in one episode (if I recall correctly, its been a long time since I saw it) Lister has its mind temporarily overwritten by the stored mental pattern of a crewmember of sufficient rank to shut down an automatic destruct sequence, however the crewmember they select was a woman (who is more than a little disconcerted to find herself in the slob Listers body) and they have her speaking in her original feminine tones from Listers mouth.
Granted Red Dwarf is a science-fiction comedy but oddly enough it usually stuck to plausibility within its own in-universe rules.
The second example has Rimmer (a hologram) attempting to distract Lister (for reasons that escape me) by projecting an image of Listers old crush Kristine Kochanski (who is very attractive I must say) but this time Rimmer is speaking in a feminine voice suitable for the body he is inhabitating. Its enough to temporarily fool Lister until Rimmer being Rimmer he screws it up.
Not a topic of earth-shattering importance but always something that creates a minor eye-brow raise from me when it occurs.
Heck, when Spock’s brain was removed in a Star Trek episode whose name escapes me, Kirk and company use a communicator to track an unusual signal and find it’s Spock, talking to himself in his own voice, which was odd 'cause, y’know, his brain wasn’t in his body at the time.
Face/Off never really convinced me; Travolta always sounded like Travolta and Nic Cage always sounded like Nic Cage.
There was an episode (or two) of Buffy the Vampire Slayer where Buffy and Faith swapped bodies and the two actresses really nailed one another’s quirks. But they did keep their own voices.
Farscape had a body-swap episode (which was incidentally absolutely hilarious), where they did… something… with the voices. I think that they recorded both actors saying the lines and mixed them in the studio, but the effect was that it really sounded like it was Crichton speaking with Aeryn’s voice, or whatever.
They also managed to get each others’ mannerisms and quirks spot-on, too. Which was especially impressive, given that two of the body-swappers were Muppets and two were in heavy alien makeup.
Attempting to address the psychology of a body-swap seriously for a moment: It might be disconcerting to hear oneself speaking in a substantially different voice from usual, not unlike the dissonance many people experience when hearing a recording of themselves. In an attempt to minimize the trauma attendant upon the swap, they would try to force their new voice as close as possible to their old one–a woman or child in an adult male body might speak at a much higher pitch than the body’s original inhabitant, and conversely a male in a female or child body might make his new voice hoarse or guttural in an attempt to imitate his normal tones. The portrayal of this as the transferred mind’s normal voice coming from the new body is a sort of shorthand for this that doesn’t strain the actor’s voice unnecessarily.
Real reason: it’s an easy way to remind everyone what’s going on, and occasionally really funny. (One of my favorite examples is an episode of Jackie Chan Adventures in which Jackie and his niece, Jade, get body-swapped, and Jackie actually asks, “Why is your voice coming out of my body?”)
In the episode where Kirk swapped minds with that crazy woman who was mad that Starfleet didn’t allow women to be starship captains both kept their original voices.
I vaguely remember a body-swap episode of The Avengers. It was just Patrick MacNee and Diana Rigg using much less posh accents and mannerisms. That was just when they were alone, though. The reasons for the swap was for two villains to impersonate the heroes. So now, instead of just pretending to be Steed and Peel (as in every other episode), MacNee and Rigg had to pretend to be people pretending to be Steed and Peel, which I imagine would challenge any actor.