Knowledge

Building a knowledge base is a central task of development. Knowledge is the medium over which all cognitive functions operate; it alters perception, directs attention, underlies language comprehension, and supports the ability to derive new thoughts, ideas, and inventions. The apparent ease with which knowledge is acquired, organized, and extended across the life span may lead people to take these abilities for granted. Yet without knowledge, it would be impossible to navigate the world. Consider the example of a daily routine. A typical day begins with a sounding alarm, a signal that would carry no meaning to an individual who lacks a knowledge base. Without an understanding of a clock, an abstract number system, or a notion of time, it would be impossible for the individual to interpret the meaning of the beeping noise or to respond appropriately. And if that same individual miraculously made it to work despite not knowing how to drive a vehicle, the individual would be unable to comprehend the words conveyed in each unread e-mail. When put this way, it is easy to see the fundamental importance of knowledge representation. It is therefore critical to understand how the knowledge system emerges and changes across the life span, particularly with respect to the capacities and experiences that promote its development.

Since the 1970s and 1980s, knowledge has been divided into two separate systems: nondeclarative (or implicit) and declarative (or explicit). Nondeclarative knowledge consists largely of motor skills and abilities that guide behavior without being brought to consciousness (e.g., how to ride a bike). Yet when most people think about knowledge, they think of declarative knowledge. Declarative knowledge consists of information that can be intentionally and consciously retrieved. It is stored in semantic memory. Information stored in semantic memory ranges from knowledge about basic sensory attributes (e.g., the color yellow), to specific facts (e.g., the first president of the United States), to complex routines (e.g., what to do at a restaurant). Thus, semantic memory is the interconnected network of conceptual information that accumulates over the life span. Because it is the type of knowledge most people have in mind when they think about this subject, this entry provides a review of what is known about declarative knowledge in typically developing individuals, with an emphasis on how this system changes across the life span.