Law of similarity
Similar objects are interpreted as same.
The image at hand demonstrates the law of similarity. This law describes the ability of our brains to view objects with similar qualities (shape, size, ...) that are in close proximity as a whole.
The righthand image is interpreted as an accumulation of similar objects, even though they are not similar. Our brain detects that the objects are of the same size, and that is enough to be interpreted as similar objects by our brain.