Depending upon how much time people take in responding to questions, the nature of organisation in long-term memory, has been inferred.

The most important unit of representation of knowledge in long-term memory is a concept. Concepts are mental categories for objects and events, which are similar to each other in one or in more than one way. Concepts may also get organised in schemas which are mental frameworks which represent our knowledge and assumptions about the world.

In the year 1969, Allann Collins and Ross Quillian suggested that knowledge in long-term memory is organised hierarchically and assumes a network structure. Elements of this structure are called nodes. Nodes are concepts while connections between nodes are labelled relationships, which indicate category membership or concept attributes.

Fig: The Hierarchical Network Model