formants of the pure vowels of British English Written by J. C. Wells contains information, diagrams and tables.
Different pitches are derived by shifting the fundamental and overtones while leaving the vowel formants relatively untouched.
The frequency of F4 generally shows larger and more stable effects than lower formants.
It is concluded that this " continuity illusion " helped the auditory system to combine information from physically non-simultaneous formants.
frequency modulation detection interference (FMDI) was larger for formants with shallow than for those with steep spectral slopes.