In the soon to be released book POINT from the Work Book Series 
Closure is cited as one of the Gestalt attributes of the Elements of Design.
As a simple exercise to show the kids that the mind seeks to close imagery so that it makes sense in context, have them make one of their images into a jigsaw puzzle. How To Make an Online Jigsaw.
The workbook will soon be released on Teachers Pay Teachers.
Global Citizens Art 