Closure describes our tendency to look for unity in objects and to see lines as a single unit. Therefore, given the mere suggestion of an object, we will tend to fill in the details. For exmple, it is likely that you perceive the series of disconnected lines represened below as a square, and the series of disconnected dots as forming a single circle.
Closure explains why we see the following isntructional image, depicting the parts of the brain involved in creating long-term memory, as a whole head.
Note, however, that the box enclosing the image and textual lables gives it the closure we require. Moore and Fitz (1993) caution against using shapes and designs that lack closure because learners are "likely to waste tiem trying to complete it or wondering why it is not completed" (p. 142).