The primary purpose of this investigation was to explore the effects of varying degrees of vocal tract semi-occlusion in Vocal Function Exercises (VFEs) on attainment of pre- established maximum phonation time (MPT) goals in individuals between the ages of 18 and 45 with normal voice. Individuals were randomized into three experimental groups: the traditional VFE with a semi-occluded vocal tract (SOVT), modified /o/ with partial occlusion, and modified /a/ without significant occlusion. For six weeks, the participants completed the four exercises two times each, twice daily on corresponding vocal tract postures assigned by group. Results indicated significant change in percent of MPT goal attained for the traditional VFE group. Neither modified vocal tract group resulted in significant change. Decreased occlusion appears insufficient in producing substantial change in voice production despite increased compliance compared to the traditional VFE group.