The Nature of Consciousness

Piero Scaruffi

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These are excerpts and elaborations from my book "The Nature of Consciousness"

Types of Memory

Experiments performed in the 1970s by the Canadian psychologist Endel Tulving and his associate Daniel Schacter proved that “intension” (such as concepts) and “extension” (such as episodes) are dealt with by two different types of memory.

“Episodic” memory contains specific episodes of the history of the individual, while semantic memory contains general knowledge (both concepts and facts) applicable to different situations.   Episodic memory, which receives and stores information about temporally-dated episodes and spatiotemporal relations among them, is a faithful record of a person's experience. 

“Semantic” memory, instead, is organized knowledge about the world.  Tulving believes these memory systems are physically distinct because their behavior is significantly different. In episodic memory, for example, the recall of a piece of information depends on the conditions ("cues") under which that piece of information has been learned (an explicit or implicit reference to it).

There are at least two more aspects of memory that fall neither into the intension or extension.

Procedural memory allows us to learn new skills and acquire habits. William James had been particularly interested in this kind of memory, having realized how important “habits” are to determine our behavior. He reduced habits to a sequence of “reflexes”, i.e. stimulus-response events. Basically, each stimulus-response pattern, once learned, becomes the building block for more complex patterns which are our “habits”, each of which is in turn a building block to create more complex “habits”. The French philosopher Henri Bergson explicitly separated the memory of habits from the memory of events.

As the French philosopher Maine de Biran had already observed two centuries earlier (“The Influence of Habit on the Faculty of Thinking”, 1804), habits rely on an “implicit” memory.

Implicit memory is "unconscious" memory, memory without awareness: unlike other types of memories, retrieval cues do not bring about a recollection of them. Implicit memories are weakly encoded memories which can nonetheless affect conscious thought and behavior. Implicit memories are not lost: they just cannot be retrieved. Amnesia is the standard condition of human memory: most of what happens is not recorded in a form that can be retrieved. In the first years, because of incompletely developed brain structures, most memories are lost or warped. Nonetheless, memories of childhood are preserved without awareness of remembering. Implicit memory is the one activated in "priming" events, or in the identification of words and objects.

That makes a grand total of four different types of memory: procedural, semantic, episodic and implicit.

Tulving also devised a scheme by which memory can associate a new perception or thought to an old memory: the remembering of events always depends on the interaction (or compatibility) between encoding and retrieval conditions.

It indeed appears that the brain accomodates several different memory systems, each of them involving the cortex but each characterized by different "pathways" leading from the cortex to other areas of the brain. Studies on amnesia (particularly by Neal Cohen in 1980) show that there are at least two separate memory systems: "declarative” memory (the memory that one can consciously remember, which is forgotten in an amnesia) and "procedural” memory (the skills and procedures which are usually not forgotten, as people with amnesia can still perform most actions they have learned throughout their lives). It appears that the hippocampus is the key to declarative memory, or at least the key to linking together declarative memories. Procedural memory is, instead, realized by circuits that involve the motor areas of the cortex and two loops that spread through the striatum and the cerebellum: acquiring skills is, indeed, a complex phenomenon.

“Emotional” memory, on the other hand, seems to depend on the working of the amygdala, i.e. on yet another separate memory system. These three memory systems are physically connected to the cortex along different pathways, which means that they can work in parallel.


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