  Children typically learn the meanings of nouns earlier than the meanings of
verbs. However, it is unclear whether this asymmetry is a result of complexity
in the visual structure of categories in the world to which language refers,
the structure of language itself, or the interplay between the two sources of
information. We quantitatively test these three hypotheses regarding early verb
learning by employing visual and linguistic representations of words sourced
from large-scale pre-trained artificial neural networks. Examining the
structure of both visual and linguistic embedding spaces, we find, first, that
the representation of verbs is generally more variable and less discriminable
within domain than the representation of nouns. Second, we find that if only
one learning instance per category is available, visual and linguistic
representations are less well aligned in the verb system than in the noun
system. However, in parallel with the course of human language development, if
multiple learning instances per category are available, visual and linguistic
representations become almost as well aligned in the verb system as in the noun
system. Third, we compare the relative contributions of factors that may
predict learning difficulty for individual words. A regression analysis reveals
that visual variability is the strongest factor that internally drives verb
learning, followed by visual-linguistic alignment and linguistic variability.
Based on these results, we conclude that verb acquisition is influenced by all
three sources of complexity, but that the variability of visual structure poses
the most significant challenge for verb learning.

Computation and Language;Artificial Intelligence;Machine Learning