Semantic memory

Caffeine improves performance on tests of semantic memory, free recall, and recognition memory (Smith et al. 1994 Warburton 1995). However, the effects are both dose and task dependent. In some studies, higher doses produced greater improvement, while in others subjects receiving caffeine performed slightly worse than placebo (Loke 1988 ... 

Incongruities such as the dream character who has the physical attributes of one person that we know and the face of another illustrate an indiscriminate but perhaps functionally significant over-inclusiveness in the categories of unconscious memory systems. We can get at this process by using semantic memory tests of subjects awakened from REM and tested both immediately and later when the sleep inertia is over. Compared to waking and to NREM sleep, we find the expected REM enhancement of weak primes (i.e., loose associations) but, to our surprise, not of strong primes (strong associations). 

Effects of ketamine on thought disorder, working memory, and semantic memory in healthy volunteers. Biol Psychiat 43 811-816. 

Collins, A. M., and Quillian, M. R. (1969). Retrieval time from semantic memory. Journal of Verbal Learning and Verbal Behaviour, 9, 432-438. 

Montgomery C, Fisk JE, Newcombe R, Murphy PN. The differential effects of ecstasy/polydrug use on executive components shifting, inhibition, updating and access to semantic memory. Psychopharmacology 2005 182 262-76. 

A placebo-controlled study of low-dose ketamine infusion in ten volunteers showed formal thought disorder and impairments in working and semantic memory (428). The degree of thought disorder correlated with the impairment in working memory. 

Long-term memory then stores and operates on very diverse types of information, and there are many theories as to how the different types of information are represented and organized within it. Research shows that long-term memory operates according to a number of different systems, and researchers disagree as to exactly how it should be divided up. Yet there are some very influential theoretical divisions of long-term memory that are now widely accepted. These are the divisions between procedural memory, episodic memory, and semantic memory. 

Episodic memory is the conscious recollection or remembering of specific experiences from a person s life. These memories often include the time and place of the experience, as well as a representation of the role the individual remembering played in it. An example of an episodic memory would be recalling the first time you operated a computer, including where and with whom, in contrast to how to operate a computer. Episodic memories seem to be more affected by the passage of time than are procedural or semantic memories such that if the... 

Exactly how the immense amount of information we acquire throughout life is stored or organized in semantic memory is still an active area of research. Most experts believe that, in general, information is stored in networks of related concepts. The more similar various concepts are, the more closely associated they will be in memory. Research in semantic memory does in fact indicate that it is organized such that when a certain idea is activated or brought to mind, related or similar items will be identified faster. For instance, if one is discussing roses, knowledge of other flowers and plants will be recalled faster and with more ease. 

Two specific types of mental representations hypothesized to be used by the semantic memory system to organize information are schemas and categories. Schemas are ordered frameworks or outlines of world knowledge that help us organize and interpret new information. They are like maps or blueprints into which new related information will be fitted. Knowledge of your home town or city, with its streets, various buildings, and neighborhoods is an example of a schema. 

Semantic memory—Memory system holding all the easily articulated knowledge of the world an individual has that does not refer to particular events in their life. 

Smith, E., Shoben, E. J., Rips, L. J. (1974). Structure and process in semantic memory A feature model for semantic decisions. Psychological Review, 81, 214-241. 

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