  Without explicit feedback, humans can rapidly learn the meaning of words.
Children can acquire a new word after just a few passive exposures, a process
known as fast mapping. This word learning capability is believed to be the most
fundamental building block of multimodal understanding and reasoning. Despite
recent advancements in multimodal learning, a systematic and rigorous
evaluation is still missing for human-like word learning in machines. To fill
in this gap, we introduce the MachinE Word Learning (MEWL) benchmark to assess
how machines learn word meaning in grounded visual scenes. MEWL covers human's
core cognitive toolkits in word learning: cross-situational reasoning,
bootstrapping, and pragmatic learning. Specifically, MEWL is a few-shot
benchmark suite consisting of nine tasks for probing various word learning
capabilities. These tasks are carefully designed to be aligned with the
children's core abilities in word learning and echo the theories in the
developmental literature. By evaluating multimodal and unimodal agents'
performance with a comparative analysis of human performance, we notice a sharp
divergence in human and machine word learning. We further discuss these
differences between humans and machines and call for human-like few-shot word
learning in machines.
