Home | People | Papers | Projects | Methods | Links | Graduate Programs | Subjects
The Co-Occurrence Hypothesis. Having established the existence of a letter-specific visual area, the obvious question is how did it arise? We have been pursuing a hypothesis that is motivated by the observation that neural learning is fundamentally correlation-based. A fundamental insight underlying Hebb's pioneering work on cell assemblies (Hebb, 1949) was the idea that neural learning is based on strengthening the connections between simultaneously firing (i.e., correlated) neurons. Put simply, the idea is that neurons that fire together, wire together.
Given that neural learning is correlation-based, what environmental factors would be most likely to lead to changes in brain organization such as the emergence of a letter area? One obvious possibility is correlations in the environment. Furthermore, the nature of text and reading imposes some very strong spatial and temporal correlations on letters and words. An obvious characteristic of text is that letters appear together in space. Words are composed of spatial clusters of letters, sentences are made up of spatial clusters of words, and text is made up of spatial clusters of sentences. These spatial correlations also lead to temporal correlations during reading: Groups of letters are processed together followed immediately by the processing of other groups of letters. Digits, shapes and other stimuli occur occasionally, but they are the exception; the rule is letters upon letters upon letters.
We hypothesized that this statistical organization of the environment could lead to changes in the spatial organization of the neural architecture underlying visual word recognition, specifically that spatial and temporal clustering of letters could interact with the brain's correlation-based learning mechanisms (Hebbian learning) to lead to the segregation of letter recognition. The feasibility and explicitness of this co-occurrence hypothesis was confirmed by means of a neural network model and one of its predictions was borne out in a behavioral study.
Neuroimaging | Theory | Cognitive Modeling | Behavioral Studies | Discussion | Papers