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Sharp Nearby, Fuzzy Far Away: How Neural Language Models Use Context (1805.04623v1)

Published 12 May 2018 in cs.CL

Abstract: We know very little about how neural LLMs (LM) use prior linguistic context. In this paper, we investigate the role of context in an LSTM LM, through ablation studies. Specifically, we analyze the increase in perplexity when prior context words are shuffled, replaced, or dropped. On two standard datasets, Penn Treebank and WikiText-2, we find that the model is capable of using about 200 tokens of context on average, but sharply distinguishes nearby context (recent 50 tokens) from the distant history. The model is highly sensitive to the order of words within the most recent sentence, but ignores word order in the long-range context (beyond 50 tokens), suggesting the distant past is modeled only as a rough semantic field or topic. We further find that the neural caching model (Grave et al., 2017b) especially helps the LSTM to copy words from within this distant context. Overall, our analysis not only provides a better understanding of how neural LMs use their context, but also sheds light on recent success from cache-based models.

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Authors (4)
  1. Urvashi Khandelwal (12 papers)
  2. He He (71 papers)
  3. Peng Qi (56 papers)
  4. Dan Jurafsky (118 papers)
Citations (288)

Summary

Overview of "Sharp Nearby, Fuzzy Far Away: How Neural LLMs Use Context"

The paper "Sharp Nearby, Fuzzy Far Away: How Neural LLMs Use Context" authored by Khandelwal et al. from Stanford University, investigates the mechanisms by which neural LLMs (NLMs) incorporate contextual information during language processing tasks. This research aims to elucidate how context influences model performance, particularly in relation to context length and its functional integration within these models.

Contextual Sensitivity of Neural LLMs

The paper makes key contributions to understanding the sensitivity of neural LLMs to varying lengths of contextual input. The authors describe a dichotomy in contextual processing, wherein NLMs display acute sensitivity to proximal context (i.e., immediate prior sentences or words) while their sensitivity to distal context (i.e., passages or sentences that appear earlier in the discourse) is considerably attenuated. This nuanced observation has practical implications for tasks that inherently depend on long-range dependencies such as document classification and machine translation.

Methodology and Experimental Design

The authors conduct experiments aimed at analyzing NLMs across multiple dimensions of context utilization. By systematically varying the length of context available to the model, the paper quantifies changes in model output quality and coherence. The experimental design included a diverse set of NLP tasks, ranging from simple next-word prediction to more complex tasks requiring deeper understanding of text coherence and anaphora resolution.

Their findings show that despite the theoretical capacity of NLMs to leverage extensive context, the models often rely heavily on a limited window of contextual information, with performance gains tapering off with increased context size. This "sharp-nearby" versus "fuzzy-far-away" pattern aptly describes the tendency of NLMs to more effectively use nearby context as opposed to distant context.

Implications and Future Directions

The implications of these findings are manifold. From a practical standpoint, this understanding can inform the development of more efficient models that are selectively attentive to context, potentially reducing computational overhead without substantial loss in performance. For example, systems could prioritize encoding nearby context more densely and design mechanisms to dynamically adjust the importance of distant context based on task requirements.

On a theoretical level, these insights challenge existing assumptions about the capacity of NLMs to model language phenomena that involve long-distance dependencies. The resulting discussion from this paper opens avenues for further exploration into architectural adjustments or training methodologies that might amplify the utility of long-range context.

Conclusion

In summary, the paper "Sharp Nearby, Fuzzy Far Away: How Neural LLMs Use Context" provides a thorough examination of contextual usage in NLMs, revealing a preference towards proximal context. It offers substantial empirical evidence that underscores the need for continued refinement in how models are designed to process and prioritize contextual information. Future developments in AI might focus on enhancing the processing of long-range dependencies or finding a balance between computational efficiency and contextual awareness in model architectures.