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Cohort model

PHONETICS: A theory of auditory word recognition. When the first 200 ms of a word is heard, a cohort of possible word candidates is activated. When more of the word becomes audible, candidates that no longer match the incoming information are deactivated, until only one candidate remains. This model is a strictly bottom-up model in that candidates can only be activated on the basis of acoustic information, not on the basis of e.g. context information (Marslen-Wilson 1984). The later hybrid versions of the cohort model allowed context to play a role during the later stages of word recognition whereas the initial stage remained autonomous (i.e. uninfluenced by e.g. sentence context). The latest version is the distributed Cohort model (Gaskell & Marslen-Wilson 1997). In this model, lexical units are points in a multidimensional space, represented by vectors of phonological and semantic output nodes. The phonological nodes contain information about the phonemes in a word, whereas the semantic nodes contain information about the meaning of the words. The speech input maps directly and continuously onto this lexical knowledge. As more bottom-up information comes in, the network moves towards a point in lexical space corresponding to the presented word. Activation of a word candidate is thus inversely related to the distance between the output of the network and the word representation in lexical space. A constraining sentence context functions as a bias: the network shifts through the lexical space in the direction of the lexical hypotheses that fit the context. However, there is little advantage of a contextually appropriate word over its competitors early on in the processing of a word. Only later, when a small number of candidates still fits the sensory input, context starts to affect the activation levels of the remaining candidates more significantly. There is also a mechanism of bottom-up inhibition, which means that in case the incoming sensory information no longer fits that of the candidate, the effects of the sentence context are overridden.
LIT. Gaskell, M.G. & Marslen-Wilson, W.D. (1997)
Marslen-Wilson, W.D. (1984)