Theoretical Approaches to Speech Production :: Spreading Activation Theory SAT

Theoretical Approaches to Speech Production There are two main theories of Speech production, Spreading Activation Theory - SAT (Dell, 1986: Dell & O’Seaghdha, 1991) and Word- Form Encoding by Activation and Verification – WEAVER++ (Levelt et al., 1989: 1999). The SAT theory was devised by Dell (1986) then revised by Dell & O’Seaghda (1991). The theory works on a 4 level connectionist model: parallel and dynamic. The Semantic level is the meaning of what is going to be said. The Syntactic level is the grammatical structure of the words in the planned utterance The Morphological level is the morphemes (basic units of meaning of word forms) in the planned sentence. The Phonological level is the basic unit of sound within a sentence. In addition to the main structure of the SAT model a representation is formed at each level. Pre-Planning is more particular at the semantic level. There are categorical rules at each level, which impose constraints on item categories and category combination. The internal lexicon (dictionary) is considered to be a constructionist network it includes nodes for concepts, words, morphemes and phonemes. So when one node is activated it sends a message to activate all other nodes connected to it. The later computational model WEAVER++ was put forward by Levelt, Roelofs, and Meeyer (1999) derived from Lefvelt (1989). The model is based on the assumptions that there is a feed forward activation network spreading through the network and does not go back. There are 3 levels in the network the highest level of nodes represented are lexical the second level are lemmas which are abstract words from the mental lexicon and the lowest level are the nodes in support of morphemes the basic unit of meaning and phonemes. The network does not have any inhibitory links. The production of speech follows through the stages exactly serial. A word error will occur if the level of activity in the node does no match to the appropriate node higher up. There are 6 stages of processing in the WEAVER++ Theory 2 more than the SAT theory. First the Conceptual preparation stage where the lexical concepts are activated. Stage 2 comes the Lexical selection where an abstract word or lemma is Selected along with its syntactic features. The Morphological encoding is The basic word form derived from the lemma activated. Stage 5 is the Phonetic encoding is where the speech sounds are set. Articulation is the Final stage defines the way the word is pronounced.