Linkage? Not sure, except on some earlier types of electronic fuel injection/throttle control.
I do know in the early 80's to early 90's when cars first had throttle body injection and then early multi port (not sequential) injection, there was a cable that connected to a TPS (Throttle Position Sensor) at the base of the throttle body itself. The cable actually opened and closed the physical throttle plate, but the ECM controlled the fuel injected into the throttle or fuel injectors themselves. What is interesting, is about the same time, stepper motor operated cruise controls were implemented on car engines. The motor ran in tandem with the gas pedal. It was just a matter of time before they started using a stepper motor to control the throttle plate all the time and placed the TPS close to, attached, or linked to the accelerator pedal.
So that is what we have today. A pedal with TPS, fed to the ECM, which operates and controls both the air (throttle) and fuel (injectors) on the engine. This way, the computer in the ECM can monitor and control through various other sensors, what the engine needs depending on load, ambient temperature, is the engine in "warm up" mode, altitude, and many other parameters.