First formant (F1) trajectories of vocalic intervals were divided into positive and negative dynamics. Positive F1 dynamics were defined as the speeds of F1 increases to reach the maxima, and negative F1 dynamics as the speeds of F1 decreases away from the maxima. Mean, standard deviation, and sequential variability were measured for both dynamics. Results showed that measures of negative F1 dynamics explained more between-speaker variability, which was highly congruent with a previous study using intensity dynamics [He and Dellwo (2017). J. Acoust. Soc. Am. 141, EL488-EL494]. The results may be explained by speaker idiosyncratic articulation.