Data Distributional Properties Drive Emergent Few-Shot Learning in Transformers

Large transformer-based language models are able to perform few-shot learning (also known as in-context learning), without having been explicitly trained for it. We hypothesized that specific distributional properties of natural language might drive this emergent phenomenon, as these characteristics might lead to a kind of interpolation between few-shot meta-training (designed to elicit rapid few-shot learning) and standard supervised training (designed to elicit gradual in-weights learning). We also hypothesized that these distributional properties could lead to emergent few-shot learning in domains outside of language. Inspired by this idea, we ran a series of experiments on a standard image-based few-shot dataset. We discovered that a number of data properties did indeed promote the emergence of few-shot learning in transformer models. All of these properties are present in natural language -- burstiness, long-tailedness, and many-to-one or one-to-many label mappings. The data influenced whether models were biased towards either few-shot learning vs. memorizing information in their weights; models could generally perform well at only one or the other. However, we discovered that an additional distributional property could allow the two capabilities to co-exist in the same model -- a skewed, Zipfian distribution over classes -- which occurs in language as well. Notably, training data that could elicit few-shot learning in transformers were unable to elicit few-shot learning in recurrent models. In sum, we find that few-shot learning emerges only from applying the right architecture to the right data distribution; neither component is sufficient on its own.