Cognition is synonymous with thinking, or the mental processes that include perceiving, knowing, remembering, communicating, and deciding. Sensation involves receiving environmental input through sense organs such as eyes and ears. It is the first awareness of an external stimulus such as light or sound. Perception transforms these sensations as the brain assembles the stream of data into a meaningful pattern or image.
The brain uses two different processing approaches. Bottom-up processing refers to how the brain uses raw sensory data to create a perception. For example, in a blind taste test, participants taste food they cannot see and must analyze it to guess what it is. Research has shown that newborn babies recognize that an object remains the same, even if its size or shape appears to change at a distance. This indicates that the brain comes "hardwired" to carry out bottom-up processing.Top-down processing (also called the constructivist approach) refers to how the brain constructs meaning from prior knowledge or experience. The brain uses what it already knows to transform incoming sensory data into a perception, or an identification or interpretation of that sensory data. For example, when one is able to read a sign even though several letters are missing, this is due to top-down processing. Optical illusions in which an image can be perceived two ways involve top-down processing. Another indication of top-down processing is people's failure to notice minor changes in the appearance of people they see regularly. Rather than seeing the true image of a familiar person, people see their previous perceptions of that person. Humans rely on concepts and schema to make sense of the world. A concept involves the mental classification of objects or ideas that share common characteristics. For example, people have a broad concept of residences. Within that broad concept, there are subordinate concepts such as apartments, mansions, and dorm rooms. Concepts depend on mental prototypes and exemplars. Prototypes are mental images based on the most noticeable characteristics of a person or thing. The mind holds an image of an "average" cat, which it uses to recognize all cats. Blue jays are prototypical birds; penguins and ostriches are not. Exemplars are mental examples of persons or things that serve as definitions. The mind scans its exemplars to identify unfamiliar objects. For example, people create in their memory the "bird" category, which consists of a collection of all the birds they have seen: blue jays, robins, cardinals. If a new stimulus is similar enough to some of these bird examples stored in memory, the person categorizes the stimulus in the "bird" category.
A schema is a framework for organizing or making sense of information or events based on past experiences. Schemas are like file folders into which the brain drops information about people, events, and concepts. Schemas, composed of both knowledge and judgments, are highly colored by personal biases. Psychologists generally refer to person schema (judgments about people or categories of people), role schema (conceptions about jobs and careers), event schema (scripts for behavior in social situations), and self-schema (ideas, beliefs, and knowledge of self).