  High-performance neural language models have obtained state-of-the-art
results on a wide range of Natural Language Processing (NLP) tasks. However,
results for common benchmark datasets often do not reflect model reliability
and robustness when applied to noisy, real-world data. In this study, we design
and implement various types of character-level and word-level perturbation
methods to simulate realistic scenarios in which input texts may be slightly
noisy or different from the data distribution on which NLP systems were
trained. Conducting comprehensive experiments on different NLP tasks, we
investigate the ability of high-performance language models such as BERT,
XLNet, RoBERTa, and ELMo in handling different types of input perturbations.
The results suggest that language models are sensitive to input perturbations
and their performance can decrease even when small changes are introduced. We
highlight that models need to be further improved and that current benchmarks
are not reflecting model robustness well. We argue that evaluations on
perturbed inputs should routinely complement widely-used benchmarks in order to
yield a more realistic understanding of NLP systems robustness.
