The transmission deficit model is based on a multi-component theory of memory representation that suggests that semantic and phonological information is stored in memory and retrieved separately. The transmission deficit model posits that TOTs occur when there is activation of the semantic component of the target word memory but this activation does not pass on to the phonological level of the memory of the target word. Thus, TOTs are caused by the deficit in transmission of activation from the semantic memory store to the phonological memory store.