Part 1: Chapter 2
The biological switch
Hebbian learning
As we are considering abstract conceptual frameworks, rather than detailed biological structures, the exact mechanisms involved in learning and memory will not be covered here other than to provide brief descriptions, where necessary, and references to appropriate technical papers.
The learning mechanism used in the brain is a case in point. This is a highly technical subject, which would require a full book to explain in detail. Suffice to say that the identification and memorizing of patterns of sensory inputs is a well studied subject area, backed up by many years of research.
The general idea is that a combination of sensory inputs will energize a particular area (or areas) of the brain. If such a sensory experience is associated with a particular word installed in memory, a neural link is established between the area energized by the sensory inputs and the area of memory energized by the sound of the word.
For example, a small child might be shown a picture of a tiger for the first time. The child will experience neural activity corresponding to the visual input but would have no means of giving that neural activity a name until someone tells the child it is called a "tiger". The energized area (or areas) of the brain energized by the visual image will then be connected to the area of the brain that has been energized by the sound of someone saying "tiger".
Once this neural connection has been made, the sound of "tiger" will also energize the area of the brain enegrgized by the visual image. Conversely, the area of the brain energized by the visual image of a tiger would energize the area of the brain that is energized by the sound of the word "tiger".
This is a gross oversimplification of the actual mechanisms involved in this process, but it gives you a general idea. For more detail, you can search on the Web for the term Hebbian Learning
The idea of different areas of the brain stimulating activity in each other during a learning process was first proposed by the Canadian neuropsychologist, Donald O. Hebb (1904-1985). His book, The Organization of Behaviour described how synaptic connections, between neural assemblies stimulated simultaneously, could be strengthened.
The most important concept to emerge from Hebb's work was his formal statement (known as Hebb's postulate) of how learning could occur. Learning was based on the modification of synaptic connections between neurons. As he wrote:
ÒWhen an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased.Ó (p.62)
His ideas, known as Hebbian Learning, form the basis of modern cognitive psychobiology and the principles are used in the design of neural networks for artificial intelligence systems.