  Current signing avatars are often described as unnatural as they cannot
accurately reproduce all the subtleties of synchronized body behaviors of a
human signer. In this paper, we propose a new dynamic approach for transitions
between signs, focusing on mouthing animations for Portuguese Sign Language.
Although native signers preferred animations with dynamic transitions, we did
not find significant differences in comprehension and perceived naturalness
scores. On the other hand, we show that including mouthing behaviors improved
comprehension and perceived naturalness for novice sign language learners.
Results have implications in computational linguistics, human-computer
interaction, and synthetic animation of signing avatars.
