This study investigated how caregivers modulate their
speaking rate according to children’s lexical knowledge and
the context of the interaction, and how such adjustments
affect children’s word learning. We studied a seminaturalistic corpus where caregivers talked about different
toys with their 3-4 years old children. The toys were known
or unknown to the child, and present or absent from the
environment. We found that caregivers talked about
unknown toys with a slower speaking rate than known ones.
When toys were absent, caregivers also tended to slow down
for the toy’s name, although they produced the whole
utterance faster. Crucially, the results of a subsequent
recognition task for children showed that caregivers’ greater
adjustment in speaking rate between known and unknown
words predicted better immediate learning. Our findings
suggest that caregivers modify their speaking rate in a
helpful manner when the situation is more demanding,
which assists children in word learning