The solution to coding speech so that it could be transmitted through the electro-neural “bottle neck” to the brain and be understood, came when the first patient described hearing vowels when different sites in the cochlea were stimulated. The vowels corresponded to the ones that would be heard when the frequency sites in the cochlea were the same as those excited in normal hearing listeners by special frequencies of importance for intelligibility known as formants. As illustrated on the top, the first formant (lower frequency) and second formant (higher frequency) define the vowel heard. Formant frequencies arise from resonances in the vocal tract due to variations in its shape. Together with other sounds they are also important for understanding consonants. The inaugural speech coding strategy selected the second formant and coded it as place of stimulation according to the frequency site in the cochlea (centre). The next advances coded the first formant and other frequencies as place of stimulation. The sound pressure of the speech was coded as current level, and the voicing frequency was coded as rate of stimulation (centre and bottom).