Acquisition of Sign Languages.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing research on sign language acquisition without systematic review or meta-analysis methodology.
PubMed 34746335 · doi:10.1146/annurev-linguistics-043020-092357
What was done
This is a narrative review synthesizing literature on how children acquire natural sign languages. It examines developmental timelines, modality-specific features (phonology, visual iconicity, and spatial representations), and the consequences of early language deprivation in deaf children.
What was found
The abstract reports no quantitative data or effect sizes. It qualitatively describes that deaf children exposed to fluent signers from birth acquire sign language on the same developmental time scale as spoken language acquisition. It notes that visual iconicity, sign phonology, and spatial reference reflect modality-specific aspects of acquisition. Delayed first-language acquisition due to inaccessible linguistic input results in negative language outcomes, whereas earlier access to sign language correlates with superior language and academic achievement.
Why it matters
It highlights that human language acquisition operates on equivalent developmental timelines regardless of sensory modality and underscores the critical developmental risks of language deprivation when deaf infants lack early accessible input.
Limits
The abstract provides no quantitative metrics, sample sizes, search strategy, or systematic inclusion criteria. The review notes that existing literature is limited by participant diversity and requires broader study populations.