Frequency-Guided Word Substitutions for Detecting Textual Adversarial Examples

Maximilian Mozes, Pontus Stenetorp, Bennett Kleinberg, Lewis Griffin


Abstract
Recent efforts have shown that neural text processing models are vulnerable to adversarial examples, but the nature of these examples is poorly understood. In this work, we show that adversarial attacks against CNN, LSTM and Transformer-based classification models perform word substitutions that are identifiable through frequency differences between replaced words and their corresponding substitutions. Based on these findings, we propose frequency-guided word substitutions (FGWS), a simple algorithm exploiting the frequency properties of adversarial word substitutions for the detection of adversarial examples. FGWS achieves strong performance by accurately detecting adversarial examples on the SST-2 and IMDb sentiment datasets, with F1 detection scores of up to 91.4% against RoBERTa-based classification models. We compare our approach against a recently proposed perturbation discrimination framework and show that we outperform it by up to 13.0% F1.
Anthology ID:
2021.eacl-main.13
Volume:
Proceedings of the 16th Conference of the European Chapter of the Association for Computational Linguistics: Main Volume
Month:
April
Year:
2021
Address:
Online
Venue:
EACL
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
171–186
Language:
URL:
https://aclanthology.org/2021.eacl-main.13
DOI:
10.18653/v1/2021.eacl-main.13
Bibkey:
Copy Citation:
PDF:
https://aclanthology.org/2021.eacl-main.13.pdf
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