early plural comprehension?

[Brian MacWhinney]

Dear Info-CHILDES,
    During class discussion on Monday, one of my students asked
whether there were any experiments that have told us the age at which
a child can comprehend the plural marker.  We were discussing the
findings of research in the picture preference task (perhaps with
reinforcement) that have demonstrated comprehension at perhaps 12
months.  If this paradigm can be used to see if children can
distinguish "cat" from "dog" early on, has it also been used to see
if children can distinguish "cat" from "cats?"
    We were particularly interested in information on the plural
marker, simply because it is so early in production, so semantically
transparent, and so easily demonstrated pictorially.  However,
evidence for the early learning of other grammatical markers would
also be interesting. We are hoping that such information could shed
further light on the comprehension-production lag during this
period.  Can anyone please point us to the relevant reference?  Many
thanks.

--Brian MacWhinney, CMU