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These are excerpts and elaborations from my book "The Nature of Consciousness"
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The Partitioning of Memory The works of George Miller(The Magical Number Seven,
Plus or Minus Two, 1956), DonaldBroadbent(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 Simonand Alan Newellargued that the human mind is a
symbolic processor and Noam Chomskyadvanced 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 DonaldBroadbentand 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 Ribots 1882 experiments on
amnesia (the loss of memory is inversely proportional to the time elapsed
between the event and the injury), but Broadbentalso hypothesized that
short-term memory may just be a set of pointers to blocks of information
located in long-term memory. Broadbentalso 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
Millers 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 wasnt 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 Broadbents 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. Back to the beginning of the chapter "Memory" | Back to the index of all chapters |
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