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phonetic units (unique to signed languages), (ii) syllabic organization, and it was (iii) usedwithout meaning or reference. This hand activity was also wholly distinct from all infants'rhythmic hand activity, be they deaf or hearing. Even its structure was wholly distinct from allinfants' communicative gestures. The discovery of babbling in another modality was exciting. Itconfirmed the hypothesis that babbling represents a distinct and critical stage in the ontogeny ofhuman language. However, it disconfirmed existing hypotheses about why babbling occurs: Itdisconfirmed the view that babbling is neurologically determined by the maturation of thespeech-production mechanisms, per se. Specifically, it was thought that the "baba," CV(consonant-vowel) alternation that infants produce is determined by the rhythmic opening andclosing of the mandible (jaw). But manual babbling is also produced with rhythmic, syllabic(open-close, hold-movement hand) alternations. How can we explain this? Where does thiscommon structure come from? A new series of studies is currently under way to examine thephysical basis of this extraordinary phenomenon (see Optotrak studies below, "The Physics ofManual Babbling").The Physics of Manual BabblingWhere does the common structures in vocal and manual babbling come from? Is manualbabbling really different from all babies' other rhythmic hand movements? I have hypothesizedthat the common structure observed across manual and vocal babbling is due to the existence of"supra-modal constraints," with the rhythmic oscillations of babbling being key. Both manualand vocal babbling, alone, are produced in rhythmic, temporally-oscillating bundles, which Ihave hypothesized may, in turn, be yoked to constraints on the infant's perceptual systems. Thenext challenge then was to figure out how to study it. I recently conducted a new study of manualbabbling with my colleague at McGill, David Ostry, and students Siobhan Holowka de Belle,Lauren Sergio, and Bronna Levy. We used the powerful "OPTOTRAK Computer Visual-Graphic Analysis System. The precise physical properties of all infants' manual activity weremeasured by placing tiny Light-Emitting Diodes (LEDs) on infants' hands and feet. The LEDstransmitted light impulses to cameras that, in turn, sent signals into the OPTOTRAK system.This information was then fed into the computer software that we designed to provide us withinformation analogous to the spectrographic representation of speech, but adapted here for thespectrographic representation of sign. Thus, for the first time, we were able to obtain recordingsof the timing, rate, path movement, velocity, and "info" for all infant hand activity, and to obtainsophisticated, 3-D graphic displays of each. This work is presently in press in Nature (2001).Bilingualism and Early Brain DevelopmentI. Bi-lingual hearing babies acquiring a signed and a spoken language from birth, and bi-lingualhearing babies acquiring two different signed languages from birth (and no speech): Presently, anadditional test of the hypothesis that speech is critical to the acquisition process is underinvestigation in my laboratory, testing two critical populations: (1) "bi-lingual" hearing infantswho are being exposed to signed and spoken languages (i.e., one parent signs, one parentspeaks), and (2) "bi-lingual" hearing infants who are being exposed to two distinct signedlanguages (ASL and LSQ), but who are receiving no spoken language input whatsoever. Withregard to group (1), bi-lingual, signing/speaking children achieve all linguistic milestones in bothmodalities at the same time (e.g., vocal and manual babbling, first words and first signs, firstgrammatical combinations of words and signs, respectively, and beyond; see Petitto et al., in© 2008 Dr. Catherine CollierAll Rights Reserved115