Where in the brain are concepts located?

Some researchers believe to have found the brain region where concepts are represented, for example in the anterior temporal lobe (Thomson, 2006). Others claim that semantic knowledge is distributed throughout the whole brain. If we think of a cat for example we think of the smooth fur, the sound of purring, the smell and the shape of a cat in the respective brain regions for sensual, visual and auditive information. (Pulvermüller, 2001)

Many models have been created in order to understand the functioning of the brain but also to enable computers to partly understand meaning of words.

Teachable Language Comprehender Model

The concepts in our brain are in a hierarchical order. Canaries are part of the category birds. It would be too much to store that canaries, starlings, blackbirds can sing. We rather know that birds can sing and that canaries are birds. (Quillian & Collins, 1969)

However, the concepts are not in a hierarchical order in the sense that they belong to only one category. A lemon belongs to the category food but also to grows on trees. And grows on trees is not a subcategory of food since not everything that grows on trees is eatable. This rather suggests the organisation of a network where everything can be connected to everything.

Associative Models

Donald Hebb postulated that every time when two neurons are active, the connection between them grows. Associative models use a matrix of size n*n, where n is the number of words in the lexicon. A matrix is simply a collection of numbers, in this case there is a number for every known word that describes the connection strength to every other word. Similar to the Hebbian process in the brain the associative model increases this number every time two words occur together. (Semantic Memory, 2012)

A baby first does not connect words to meaning. “Lemon” and “apple” are just sounds like “lalala” and “bububu”. Then someone points at a lemon and says “lemon”. The baby connects the two things and overgeneralizes: it thinks all these round things are called “lemon”. It points on a lemon, an apple, an orange, a mandarin and says “lemon, lemon, lemon, lemon”. Then someone points on the apple and says “apple” and the baby learns the details: apparently not all round things are lemons but all round things that are yellow… until it makes more experiences and sees another round thing that is yellow but not a lemon and so on. (Spitzer, 2002)

We don’t remember everything that we’ve seen or experienced but every experience refines our representations of the world. Therefore the representation of the meaning of a word is the product of all experiences that are somehow connected to that word. We know a lot about lemons, that they are yellow, eatable, grow on trees but we don’t remember when we learned that. The part of the memory that remembers autobiographic details is the episodic memory. The semantic memory is in contrast to that abstract and free from single experiences. (Semantic Memory, 2012)

References

Pulvermüller, F. (2001, December). Brain reflections of words and their meaning. Trends in Cognitive Sciences, 5(12).

Quillian, M. R., & Collins, A. M. (1969). Retrieval Time from Semantic Memory. Journal of Verbal Learning and Verbal Behaviour, 8, 240--247.

Semantic Memory. (2012, March 14). Retrieved from Wikipedia: http://en.wikipedia.org/wiki/Semantic_memory

Spitzer, M. (2002). Lernen. Gehirnforschung und die Schule des Lebens.Heidelberg: Spektrum Akademischer Verlag.

Thomson, H. (2006, September 7). Semantic memory pinpointed in the brain. Retrieved from New Scientist: http://www.newscientist.com/article/dn10012