ABSTRACT
Perception is not a passive window to the environment; it is instead a subjective construct of the mind. It all starts with the senses at a physiological level: The energy emitted or reflected by an object is stimulating sensory receptor cells. Let’s take vision as an example, although the basic process is similar for the other senses. When you look up at clear skies at night to enjoy some stargazing, the stimuli received by the receptor cells are all about physics: orientation, spatial frequency, brightness, and so on. Then, the brain processes the sensory information to make sense of it, and that process is perception (see Figure 3.1). For example, the brightest stars will be grouped into a shape that is meaningful to the individual viewing it (e.g., a saucepan). The brain is a powerful pattern recognizer, which allows us to swiftly create mental representations of the world and see meaningful shapes in our environment, sometimes mistakenly. The last step of information processing allows an access to semantics, to cognition. If you know which constellation appears to have the shape of a saucepan, then you will recognize that you are gazing at Ursa Major, the Big Dipper. At this point, information has reached your cognition. Although it could seem intuitive for this process to be bottom-up (first sensation, then perception, and lastly cognition), it is 20actually very often top-down, which means that your cognition (your knowledge and expectations about the world) will have an impact on your perception of it. Perception is therefore highly subjective because it is influenced by your past and present experiences.
