Research Controversy
Researchers have suggested the possibility of parents and experimenters being overly liberal in attributing sign or word status to early attempts at communication by children. There is not a universal consensus on the criteria for differentiating a child's sign or word from a more simple gesture or vocalization. Large differences in acquisition arise when only signs that label objects rather than request objects are considered. In this case the mean age of first sign production becomes 12.6 months and is more comparable with the mean age of first word production in speaking children (11.3 months).
It has also been found that children sometimes produce a combination of a pointing gesture and a spoken word earlier than they would produce a spoken two-word combination. As not all studies are uniform in accepting or disqualifying pointing gestures as signs, this can also lead to discrepancies depending on how the research is carried out.
Additionally, two possible explanations have been suggested for the differences shown in language acquisition between speaking and signing children.
Multiple Timing Mechanism
Under this theory, separate developmental mechanisms would control vocabulary and syntax development. Earlier maturation of the visual system as compared with the oral system would result in the first sign being easier to produce vs. the first word. This would also allow for the separate development of vocabulary and syntax.
Unitary Timing Mechanism
This developmental mechanism would be activated at the start of language learning and would result in a relatively fixed amount of time between language acquisition milestones. Alternatively, a unitary mechanism could activate at the same time in all children, irrespective of the onset of language learning. Environmental or peripheral factors, such as language modality or differences in a language's morphology and syntax could explain the differences between acquisition milestones in speaking and signing children.
Read more about this topic: Baby Sign Language
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