Perception has Two Factors: Innate--Genetic Inheritance and Learned--Past Experiences.
The reason for two boxes is that Perception has two sides to it.
The first is the innate factor to the process. It is the ways we have of organizing impulses that we inherited because we are human. We experience the world in a way that a cat couldn't, and vica versa.
The second contributor to the process is our pool of past experiences. Learning plays a powerful role in how we organize incoming stimuli.
Because each of us have had different experiences, it should not surprise us when we experience the same situation differently.
NOTES: Some more interesting information on Perception.