The data presented by Geers et al are consistent with 3 mutually exclusive theories about the impact of natural sign languages on the development of English language skills: that natural sign languages (1) impede, (2) facilitate, or (3) have no impact on English development. Although Geers et al clearly favor theory 1, it is neither the only nor the best interpretation of their data.
Theory 2 is consistent with the data because although the authors quantified exposure to manual communication (including ASL), they did not measure proficiency in ASL. Children who have not acquired the grammar of ASL are not predicted to benefit from it as a foundation for subsequent mastery of English. We applaud these authors for considering variation in the amount of exposure to manual communication; however, we are dismayed to see ASL lumped together with other types of manual communication. Such coarse grouping prevents this crucial hypothesis from being adequately tested. (That is, children who are exposed mainly to English-based signing systems will not acquire the grammar of ASL; their performance is therefore uninformative about theory 2.) Contrary to their claims, the authors have not falsified the theory that mastering the grammar of a sign language helps a child master the grammar of a spoken language.
Theory 3 is consistent with the data because observed differences might be attributable to other demographic factors that likely affected initial inclusion, attrition over time, and/or performance on the assessments (eg, socioeconomic status, etiology of deafness). Because sign language use may covary with these additional factors, the reported effects might well disappear if these factors were controlled. Theory 3 therefore remains viable.
In our view, the best interpretation of this study is that families self-select their method of communication as a result of their child’s development in English. Under this view, the use of manual communication is a consequence of limited progress in English, not a cause. Both of these interpretations remain available because the study used a correlational design that was particularly vulnerable to self-selection.
To successfully discriminate among the 3 competing theories, future researchers will need to do the following: (1) distinguish ASL from other forms of manual communication, (2) assess ASL proficiency as a function of ASL exposure, (3) adopt a research design that minimizes the potential impact of reverse causality and self-selection effects (for example, studying the impact of exposure during a prespecified time window on outcomes after that time window, regardless of the family’s communication choices at the time of testing).
Finally, it is important to remember that English language skills are only 1 aspect of child development. Mastery of any natural language, signed or spoken, is expected to support healthy cognitive and psychosocial development, thereby promoting school readiness and long-term success. We must not forget that even in the group of best-performing children in this study, 49% fell below the average range on language proficiency; in hearing children, this figure would be a mere 16%. Clearly, much more work remains to be done to maximize deaf children’s developmental potential.
CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.
- Copyright © 2017 by the American Academy of Pediatrics