That's exactly what you're feeling. A solenoid (controlled by the ECU) opens up a throttle blade that's internal to the intake manifold, causing a shorter path for the air charge to follow. Higher rpm's demand quick air (just get it in there, NOW!) for power. Lower r's demand speedy air (which is what the longer intake runners provide, velocity into the combustion chamber).

The variable timing is always adjusting, so it's not something that you'll feel 'kick in'. But the computer controls the timing through the individual coils, the mixture through the injectors, and now even the air that's introduced into the engine (not to mention cam timing!).

Sure beats the ol' days of the Chevy V8 with 1 cam and 2 barrels, huh?