Delayed language access hampers but does not hinder visual statistical learning in deaf and hard of hearing children

Statistical learning in deaf and hard of hearing (DHH) children is poorly understood and the impact of age of sign language acquisition has not been systematically investigated. In the present study, we examined visual statistical learning and transfer effects in early (age of sign language acquisition before the age of three years) and late (age of sign language acquisition after the age of three years) DHH child signers (aged 6-8 years) of German Sign Language, compared to age-matched hearing children. The children completed a visual artificial grammar learning task across three learning sessions, each consisting of alternating learning and test phases. In a fourth session, a new stimulus set was introduced using the same underlying artificial grammar to assess transfer abilities. Early signers tended to show higher learning performance in the first session, while no difference between early and late signers was observed in the third session. Compared to age-matched hearing children, both DHH groups were indistinguishable in the first session but performed lower in the third session. Crucially, only early signers successfully transferred the learned sequence rules to the new stimulus set comparable to hearing children. Correlation analyses indicated that higher visuo-spatial working memory capacity in DHH children was associated with higher performance during transfer and in late signers during learning as well. Overall, the findings suggest that early exposure to natural language input affects visual statistical learning abilities in DHH children.