1. A device for introducing control words by speech said words being pronounced by a speaker and belonging to a predetermined vocabulary of n words, said device comprising: means for coding each word pronounced by the speaker in accordance with a first predetermined algorithm, which gives a coded word; means for memorizing (a) n coded references each corresponding to the coding of one of the n words of said vocabulary in accordance with the said first algorithm and (b) at least one word pronounced by said speaker in coded form; means for displaying one of said n words; means for initiating a change in coded references to provide a different code corresponding to a word; and a control circuit connected to the memorizing means and to the display means, comprising: (a) repetition detection means for comparing a presently pronounced coded word to the previous coded pronounced word, if it exists, in dependence on a second predetermined algorithm, to detect whether or not the presently pronounced word is a repetition of the previously pronounced word; (b) means responsive to the detection means for comparing a coded pronounced word when there is no repetition, to the n references, and to allocate to each reference a level of resemblance with the coded pronounced word in dependence on a third predetermined algorithm; (c) means for causing the display of the memorized reference having a first level of resemblance when no repetition has been detected, and for causing, if repetition has been detected, the display of the word associated with the reference occupying the level of resemblance which immediately follows that of the reference associated with the word displayed immediately previously; and (d) means for replacing in said memorizing means the reference associated with the word displayed last, said reference being replaced by the information corresponding to the coding of the word repeated, said replacement being in response to activation by the speaker of the means for initiating a change of reference, when the speaker has found that the word displayed is the word that he actually pronounced, thereby providing a fresh coded reference for the word.