Vowel harmony in Klao linear and nonlinear analyses

Klao, a Kru language spoken in Liberia, has a nine-vowel system. Like most other Kru languages, it displays harmony sensitive to pharyngeal constriction (tongue-root retraction). What gives the Klao vowel-harmony system special interest is the fact that a great deal of variation occurs, suggesting that vowel harmony is in some way optional. This provides a counter-example to the claim (made in Clements [1977l) that root-controlled vowel harmony is always obligatory. Given this optionality, the question arises as to which model best captures the facts of Klao vowel harmony. 'l,w frameworks are considered: one, along the lines of Anderson [1930], treats vowel harmony as one more assimilation rule, and the other, following the model found in Clements [1981] handles vowel harmony autosegmentally.