How does proximity create unity? this is a psychology question

Proximity occurs when elements are placed close together. Without proximity, objects may be perceived only as separate shapes. It is when then are given close proximity that unity transpires. This proximity allows the figures to be seen as a unified whole. 

I know this question was asked long ago, but there might be someone else hoping to find the answer. I hope this can be of some help :)

An independent variable that the student controls during the experiment. (i'm not 100% sure this is correct, so i'm sorry if it's wrong)