The question then arises, ``optimal in what sense?'' We propose that optimality be defined by a balance between the ability to communicate accurately and the effort required to communicate. This concept was described by Ohala (1992) who called speech a compromise between effort and communication clarity.
Specifically that the optimal pitch curve is the one that minimizes the sum of effort plus a scaled error term. Certainly, when we speak, we wish to be understood, so the speaker must consider the error rate on the speech channel to the listener. Likewise, much of what we do physically is done smoothly, with minimum muscular energy expenditure, so minimizing effort in speech is also a plausible goal.