  A number of studies carried out on different languages have found that tongue
movements in speech are made along two primary degrees of freedom (d.f.s): the
high-front to low-back axis and the high-back to low-front axis. We explore the
hypothesis that these two main d.f.s could find their origins in the physical
properties of the vocal tract. A large set of tongue shapes was generated with
a biomechanical tongue model using a Monte-Carlo method to thoroughly sample
the muscle control space. The resulting shapes were analyzed with PCA. The
first two factors explain 84% of the variance, and they are similar to the two
experimentally observed d.f.s. This finding suggests that the d.f.s. are not
speech-specific, and that speech takes advantage of biomechanically based
tongue properties to form different sounds.
