The Discovery of Babbling on the Human Hand
In the course of conducting research on deaf infants’ transition from pre-linguistic gesturing to first signs (9-12 months), Petitto first discovered a class of hand activity that contained linguistically-relevant units that was different from all other hand activity at this time. Her data showed that deaf infants appeared to be babbling with their hands. Additional studies were undertaken to understand the basis of this extraordinary behavior. The findings that were reported in Science revealed unambiguously a discrete class of hand activity in deaf infants that was structurally identical to vocal babbling observed in hearing infants.Like vocal babbling, manual babbling was found to possess:(i) Have a restricted set of phonetic units (unique to signed languages)(ii) Possess syllabic organization(iii) Be used without meaning or reference.This hand activity was also wholly distinct from all infants’ rhythmic hand activity, be they deaf or hearing.