Effects of practice variability on learning of relaxed phonation in vocally hyperfunctional speakers.

The present study investigated the effects of practice variability on the learning of relaxed phonation using a motor learning perspective. Twenty-one individuals with hyperfunctional voice problems were evenly and randomly assigned to three groups of practice conditions: constant, blocked, and random practice conditions. During training, participants in the constant practice condition were asked to read aloud sentence stimuli with four Chinese characters. Participants in the blocked practice condition were asked to read aloud sentence stimuli with increasing sentence length, starting from sets of two characters to five characters. Participants in the random practice condition were asked to practice reading sentence stimuli of variable length from two to five characters presented in a random fashion. Surface electromyographic feedback (sEMG) from the thyrohyoid muscle site was given to each participant after reading every two sentence stimuli. Results demonstrated that for all the participants, voice motor learning was evidenced by the decreased sEMG levels in delayed retention test. Generalization to untrained passage was shown as well. However, results did not reveal any difference in the learning among the three practice conditions. The findings from the present study did not support the hypothesis of contextual interference, which states that practice using variable items presented in a random mode is more beneficial to learning than practice using constant items.