1. Control methods used in a study of the vowels;G.E. Peterson;Journal of the Acoustical Society of America,1952
2. Talker Variability in Speech Processing;H. C. Nusbaum,1997
3. Models for the perception of speech and visual form;A. M. Liberman,1967
4. Perturbation of vowel articulations by consonantal context: An acoustical study;K. N. Stevens;Journal of Speech & Hearing Research,1963
5. Invariance and Variability in Speech Processes;J.L. Elman,1986