Production fluency in spoken language users acquiring a sign language as an L2 in adulthood

A study was conducted to examine production variability in American Sign Language (ASL) in order to gain insight into the development of manual fluency. Production variability was characterized through the spatiotemporal index (STI), which represents production stability in whole-utterances and is a function of variability in effector displacement waveforms (Smith et al., 1995). Motion capture cameras were used to acquire hand and limb displacement data across a set of eight target signs embedded in carrier phrases. The STI values of Deaf signers and hearing learners at three different ASL experience levels were compared to determine whether production stability varied as a function of time spent acquiring ASL, as it is for spoken English (Kleinow and Smith, 2000). We hypothesized that higher production variability as indexed by higher STI values would be evident for beginning ASL learners, with variability decreasing as ASL language experience increased. As predicted, Deaf signers showed significantly lower STI values than the hearing learners, suggesting that stability of production is indeed characteristic of increased ASL use. A linear trend across experience levels of hearing learners was not statistically significant, indicating that improvement in production fluency across relatively short time scales was not observed. This novel approach to characterizing fluency in ASL utterances has relevance for assessing L2 acquisition of sign languages and possibly for the characterization of sign production disorders.published or submitted for publicationnot peer reviewe