The Nature of Consciousness

Piero Scaruffi

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

The Partitioning of Memory

The works of George Miller (“The Magical Number Seven, Plus or Minus Two”, 1956), Donald Broadbent (1957), Allen Newell (1958) and Noam Chomsky (1957), that all came out in the second half of the 1950s, established a new paradigm in Psychology, broadly referred to as "cognitivism", that ended the supremacy of behaviorism. Where behaviorism was only interested in the relationship between input (stimuli) and output (behavior), cognitivism focused on the processing that occurs between the input and the output

Herbert Simon and Alan Newell argued that the human mind is a symbolic processor and Noam Chomsky advanced a theory of language based on modules inside the mind which are capable of symbolic processing.

The standard model that became popular in the late 1950s, due particularly to the work of the British psychologist Donald Broadbent and the US psychologist George Miller, was based on the existence of two types of memory: a "short-term memory", limited to few pieces of information, capable of retrieving them very quickly and subject to decaying also very quickly; and a "long-term memory", capable of large storage and much slower in both retrieving and decaying. Items of the short-term memory move to the long-term memory after they have been "rehearsed" long enough.

The idea was already implicit in William James’ writings (he called them “primary” and “secondary” memory), and in Theodore Ribot’s 1882 experiments on amnesia (the loss of memory is inversely proportional to the time elapsed between the event and the injury), but Broadbent also hypothesized that short-term memory may just be a set of pointers to blocks of information located in long-term memory. 

Broadbent also stated the principle of "limited capacity" to explain how the brain can focus on one specific object out of the thousands perceived by the retina at the same time. The selective character of attention is due to the limited capacity of processing by the brain. In other words, the brain can only be conscious of so many events at the same time. What actually gets the attention is complicated to establish, because Broadbent found out that attention originates from a multitude of attentional functions in different subsystems of the brain. 

Broadbent's model of memory (also known as the "filter theory") reflected at least two well-known features of memory: information about stimuli is temporarily retained but it will fade unless attention is turned quickly to it; the unattended information is "filtered out" without being analyzed.  He drew a distinction between a sensory store of virtually unlimited capacity and a “categorical” short-term store of limited capacity.  The latter is the way that a limited-capacity system such as human memory can cope with the overwhelming amount of information available in the world. 

At the same time, George Miller’s experiments proved that our short-term memory can hold only up to seven “chunks” of information and therefore provided an order of magnitude for it. It wasn’t clear, though, what was the “size” of a chunk: is the entire car a chunk of information, or is each wheel a chunk, or...? In Broadbent’s model, a chunk is a pointer to something that already exists. Therefore a chunk can be even very “big”, as long as it is already in memory. Its “size” is not important (in short-term memory, it is only a pointer). This is consistent with experiments in which short-term memory proves to be capable of holding familiar images, but not of images never seen before.

The British psychologist Alan Baddeley (“Working Memory”, 1974) showed that a unitary short-term memory does not account for memory disorders and replaced short-term memory with a "working memory" that has basically three components: a short-term memory for verbal information, a short-term memory for visual information, and a control system.

In fact, neural regions in the prefrontal cortex (the newest part of the brain, from an evolutionary standpoint) can draw data from other regions of the brain and hold them for as long as needed. The prefrontal cortex is unique in having a huge number of connections with the sensory system and with lower brain centers.  The prefrontal cortex could be the locus of a "working memory", in which decisions, planning and behavior take place.

 


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