All of these interfaces (Sonic Transducer, Medusa, and de-Medusa) are similar in interaction and instructive to compare, so I’ll be reviewing them together in this post.

After the terrifying dinner party and subsequent chase around the castle, Janet, Brad, and Dr. Scott wind up on a raised platform facing Frank-N-Furter in the laboratory, and, fed up with their nonsense, he activates the Sonic Transducer.

Sonic Transducer

To do this, he pulls a large double-pole knife switch mounted to the panel between the Reactor Power Input and Monitor from an up to a down position.

This has the effect of “freezing in place” the people on the platform. One must presume that the effect lasts as long as the switch is down.

That’s it. That’s the interaction.

The Transducer will seduce ya

Dr. Scott guesses on hearing the name that, “It is, I suppose, some kind of audio-vibratory physio-molecular transport device?” Brad grips his shoulder and says, “You mean…!” Dr. Scott confirms it, “A device which is capable of breaking down solid matter and then projecting it through space and—who knows—maybe even time itself.”

Narrator: It wasn’t.

I mean, in the show it is, but I think that term “sonic transducer” was included in the script because it sounded pseudoscientific, mocking the B-movie shows from which this movie draws some inspiration. But that term does mean a real thing in the real world, and I don’t want any engineers reading to be confused.

Map it, Janet

The mapping here is upside-down. As I noted in the prior post, for vertical controls, up naturally maps to on. There is a competing map here, that [switch down == feet down]. (Yes, yes. Vheels, too.) And if this were the only control of its sort in the panel, I might agree.

But given that this is part of a panel of controls, some of which are also knife switches (see below), consistency wins. In a high-pressure situation, like, say, a monster rampaging out of a vivification vat, Transsexuals (as in from the planet Transsexual, not my awesome trans readers, shout out yo 👋🏻🏳️‍⚧️) shouldn’t have to remember which knife switch is up for on and which one is down for on. That’s far too error prone.

Add gravity threatening to turn it on accidentally, and the case is closed.

Medusa and de-Medusa

Following a bit of dialogue, Magenta, Riff Raff, Rocky, and Columbia all enter the lab through the wheelchair hole. After some more dialogue and song, Frank-N-Furter glances at Magenta, who stands by a control on the panel labeled Medusa. It’s a large-handled double-pole knife switch mounted to the control panel, covered in the same powder coat red as the rest. When we first see it, the handle is up. During Brad’s threat to Frank, Magenta raises her hand to the handle. When Frank nods her way, she throws it to the down position and immediately back to the up position.

At the moment the switch is at the lowest point, a lightning-bolt-shaped light illuminates green on the front of the switch for a moment, we hear a pewp sound, and Brad turns to stone. Dr. Scott, Janet, Columbia, and even Rocky are turned to stone in the same way.

Quick consistency aside: Why is Dr. Scott’s lap blanket turned to stone when the rest of his clothes disappear, and when Brad’s robe and Janet’s undergarments just fall to their feet? Is there a missing set of controls for what to do with the clothing, and how to make modesty exceptions?

Later,—after Frank dresses them, puts makeup on them, and places them on a proscenium stage (Dr. Scott is left backstage for some reason)—a hand reaches to a control which has a chalk label of “de-Medusa” written on the brick wall to which it is mounted. When it is pulled down and pushed back up again, Columbia turns back to her regular flesh-and-blood self, and the floor show musical number begins.

One by one, the switch is flipped and the other characters are de-Medusa-ed as well, right when their number is up. It is a reminder of the gonzo nature of this movie that not only is a diegetic rationale for the whole floor show never given, but we must accept that somehow when they are turned back from stone, they exhibit no disorientation and immediately begin singing and dancing their parts in a diegetic musical number they have never heard of, much less rehearsed, before that moment. Were the lyrics and choreography somehow beamed into their heads? But let’s not ponder these things, as the (floor) show must go on.

The de-Medusa is very similar to the Medusa control and has the same problems: A double-pole knife switch, which does its thing when at the bottom of its extent. It also targets a single person at a time but there’s no interface to indicate which one. The only thing I can see that’s different is that it is painted powder coat black instead of red. Since they are functionally the same, we can talk about them together.

Missing control

How do the Transsexuals target individual people to Medusa? Using today’s tech, you can imagine an audio classifier determining who spoke most recently (or sung most recently? insulted Frank most recently? who Frank was looking at? Any of these could work.) and a visual classifier identifing where that person was. Then the weapon could automatically aim there.

The makers of the film in 1975 didn’t have access to those technologies. But they could have solved it manually. Riff Raff—who is right there, not doing anything—could have aimed a pivoting barrel, like a spotlight, or fiddled with a joystick to aim one of the overhead lights. Something to convey this is how they set the area of effect.

Mapping. Again with the bad mapping.

For very similar reasons to the Sonic Transducer, this is the wrong mapping. Up maps more naturally to on. Gravity threatens to activate it accidentally. And what happens if it did fall and just hangs there at the bottom? This leads us to the next section, where I try to convince you that it’s exactly the wrong control.

A knife switch is the wrong control

It is an axiom of interaction design that the control should map as well as possible to its effect. To illustrate this, consider two common household controls.

Doorbell buzzer: Push this and it rings a bell inside the house for as long as you keep it pushed. The moment you let up, the ringing stops. This is called a momentary switch.	Light switch: Flip this up and see the light it controls illuminate. It’ll stay that way until the switch is flipped down again. Continuing to press up does nothing. This is called a toggle switch.

Now consider what happens if you switch these two.

Doorbell switch: Flip this up, and the bell rings for as long as it remains up. The opportunity for abuse is nightmare fuel.	Light buzzer: Press this and the light comes on, but only as long as you stand there and hold the thing. The lamp is dim because you refuse to stand there and press it constantly. Because you only think of yourself.

These examples serve to illustrate the point: Some controls fit their effect, others don’t.

Where it works

In the case of the Sonic Transducer, Medusa, and de-Medusa, the control is a toggle switch like the light switch, which fits persistent states. That’s exactly right for the Sonic Transducer effect. It is a state that the Transsexuals want to control, and have it be persistent as long as that control stays on.

Where it don’t

But in the case of the Medusa and de-Medusa, it is being used to say “turn them to stone now”. The event is instant, but the control is not. I mean, sure, that point at the bottom can be considered a momentary switch the way Magenta uses it, but it’s not germanely so. And she doesn’t have to treat it like a momentary switch. She could just leave it at the bottom, and it’s unclear exactly what would happen if she did. So it’s just wrong.

Clever readers will note that the stone/flesh states are persistent and reversible, just like light on/off. So doesn’t that befit a toggle? It would, if there were one thing to toggle. But the state lives in the people, not the panel, and there are five of them petrified at different times. A single toggle can’t Medusa the next person without de‑Medusa‑ing the prior, even with some selection mechanism. You can imagine one toggle per victim, somehow “imprinted” on each as they’re turned, but then you have to explain how that association gets made, and that’s its own pain. Targeting plus activation is narratively simplest.

Much more fitting than a toggle switch or a knife switch would be a big button on the panel, which, like the lever on a toaster or the “start” button on a microwave, sets a process in motion. So better would have been: Riff Raff works the joystick to target the spotlight on the victim and at Frank’s nod, Magenta slams the giant button on the panel. If a button wouldn’t deliver the dramatic motion, then a spring-return lever—like on a punch clock or slot machine—would work better than the knife switch. That would preserve the drama without being nonsensical, and preserve the design principle at the heart of this post:

Controls should match their effects as best they can.