What effect is applied to control the acceleration or deceleration of an animation in After Effects?

The effect applied to control the acceleration or deceleration of an animation in After Effects is easing. Easing allows animators to create more natural and dynamic motion by adjusting the timing of an animation. Instead of having movements that start and end at a constant speed, easing helps to smooth out the motion by gradually increasing or decreasing the velocity of the animated elements.

When using easing, you can apply different types—such as ease in, ease out, or ease in-out—each of which affects how the animation begins and ends. This creates a more engaging viewer experience, as animations that utilize easing mimic natural physical movements.

The other options pertain to different aspects of animation control in After Effects. Keyframe interpolation deals with how values between keyframes are calculated. Timing adjustment refers to shifting keyframes to change when actions occur without modifying their speed. Speed control typically refers to altering the overall speed of a layer but does not inherently address the nuances of acceleration and deceleration like easing does.