Observation and What You Perceive With Your Senses

Perception is the process of making sense of the information we take in with our senses. We identify, organize and interpret this sensory information to in order understand and represent environmental stimuli.
Perception involves signals that go through the nervous system, which in turn result from physical or chemical stimulation of the sensory system. Seeing involves light hitting the retina; smell involves odor molecules; and hearing is a response to pressure waves.
Our individual perception is determined by our past experiences - what we learned about the world, our memories, and our expectations. Perception is also influenced by culture, ethnicities values, and beliefs.
Because each person assigns different value to each of these influences, the same object or event is perceived differently by different people. Although our eyes may see the same thing, we filter, focus, and perceive it differently. This is why multiple eye witnesses to the same crime often have very different descriptions of the same suspect or event.
Source (https://ccmit.mit.edu/observation/ page 4)