We group together objects that are connected.

We fill in gaps to create continuous edges, allowing us to perceive an object as a whole.

We tend to look for smooth, continuous patterns in objects. Similarly, while having a conversation we can partially ignore any interruptions and understand the sentences in a continuous manner.

We group together things that look alike.

We perceive features as grouped when they are close together.

We group items together that move at the same time. In audition, a similar effect takes place which is referred to as grouping by onset.