Meaning, memory structure, and mental processes.
Although people experience little difficulty in recognizing printed words and comprehending sentences, they cannot do it instantaneously. Experimental psychologists have recently measured the speed of these mental processes by applying a reaction-time method. The method provides new data concerning the organization and retrieval of familiar semantic information in human memory. It has been found that close relations between the meanings of words help people to recognize and pronounce the words faster, especially when the words are hard to see because of visual distortions. Close relations between word meanings also facilitate the comprehension of some sentences, as indicated by how long a person takes to decide whether the sentences are true or false. The facilitation is not universal, however. When the relation between the meanings of two words must be analyzed carefully, their proximity may actually inhibit mental processing. These results, along with additional findings, support the hypothesis that human memory includes a semantic network that represents various categories of objects at distinct locations linked to specify their relations with each other. The memory structure probably influences a number of different mental processes that use it. One possible access route to the network is through a set of detectors designed to accumulate sensory information and signal the presence of particular words. There also appear to be processes for searching and comparing pieces of knowledge after a person finds the memory locations of designated categories. Further research using the reaction-time method may provide a more detailed inventory of what facts are retrieved directly from memory and what are computed from other stored information (36).