Perception is an internal source of redundancy that reduces the range of guesses the brain must make.
There are only a few determiners to choose from.
Concepts also provide redundancy. What is the last word in the following sentence?
"The monkey ate a b _ _ _ _ _."
Although there is little left of the last word, our knowledge of monkeys and what they eat would probably lead us to easily decode it as "banana," and not "bacon."
Remembering that perception is always a process of guessing, notice what redundancy does. It acts to reduce the range of the guesses we must make to recognize the input.
What perception does, itself is to provide an internal source of redundancy. Figure ground reduces the range of guessing by reducing the stimuli we must process; closure fills in many pieces to make a single cohesive whole; the best figure possible simplifies the figure etc. etc.
Can you recall the figure on Slide 30? Pragmatically it was a circle, but not really. It was many disjointed dots and some other short lines. But perceptually, you filled in the many little dots in the periphery to image the circle.