Abstract PDF Talk Poster Code BibTeX

Self-attention heads are characteristic of Transformer models and have been well studied for interpretability and pruning. In this work, we demonstrate an altogether different utility of attention heads, namely for adversarial detection. Specifically, we propose a method to construct input-specific attention subnetworks (IAS) from which we extract three features to discriminate between authentic and adversarial inputs. The resultant detector significantly improves (by over 7.5%) the state-of-the-art adversarial detection accuracy for the BERT encoder on 10 NLU datasets with 11 different adversarial attack types. We also demonstrate that our method (a) is more accurate for larger models which are likely to have more spurious correlations and thus vulnerable to adversarial attack, and (b) performs well even with modest training sets of adversarial examples.

@inproceedings{biju-etal-2022-input,
title = "Input-specific Attention Subnetworks for Adversarial Detection",
author = "Biju, Emil  and
	Sriram, Anirudh  and
	Kumar, Pratyush  and
	Khapra, Mitesh",
booktitle = "Findings of the Association for Computational Linguistics: ACL 2022",
month = may,
year = "2022",
address = "Dublin, Ireland",
publisher = "Association for Computational Linguistics",
url = "https://aclanthology.org/2022.findings-acl.4",
doi = "10.18653/v1/2022.findings-acl.4",
pages = "31--44"
}

Abstract PDF Webpage Code BibTeX

The Maximum Scatter Traveling Salesman Problem (MSTSP) is a variant of the famous Traveling Salesman Problem (TSP) and finds its use in several real-world applications including manufacturing, imaging and laser melting processes. The objective of this NP-hard problem is to maximize the cost of the least cost edge in a tour of an input graph. While several approximation algorithms have been proposed for this problem, many of them suffer from bad worst-case complexities and present challenges in scalability and practical use. Besides, these algorithms have often been designed and evaluated with a sole focus on theoretical approximation quality, while practical applications require detailed experimental evaluations to study the stability, quality and runtime over a large and diverse set of inputs. In this work, we describe six algorithms for MSTSP inspired by prior work in the area, along with improved formulations that enhance their utility in real-world scenarios. Further, we perform experimental studies motivated by smoothed analysis to comprehensively evaluate these algorithms on various performance metrics. We demonstrate that despite having bad worst-case complexities, certain algorithms perform exceedingly well in practical use cases. Our experiments reveal trade-offs among the runtime, quality and stability of different algorithms that must be considered when making a design choice depending on the objectives and constraints associated with the use of the algorithm.

@inbook{doi:10.1137/1.9781611977042.13,
	author = {Emil Biju and Sundar Raman P.},
	title = {Perturbation Analysis of Practical Algorithms for the Maximum Scatter Travelling Salesman Problem},
	booktitle = {2022 Proceedings of the Symposium on Algorithm Engineering and Experiments (ALENEX)},
	chapter = {},
	pages = {158-168},
	doi = {10.1137/1.9781611977042.13},
	URL = {https://epubs.siam.org/doi/abs/10.1137/1.9781611977042.13},
	eprint = {https://epubs.siam.org/doi/pdf/10.1137/1.9781611977042.13}
}
	

Abstract PDF Talk Slides BibTeX

Question generation is the task of generating questions from a text passage that can be answered using information available in the passage. Known models for question generation are trained to predict words from a large, predefined vocabulary. However, a large vocabulary increases memory usage, training and inference times and a predefined vocabulary may not include context-specific words from the input passage. In this paper, we propose a neural question generation framework that generates semantically accurate and context-specific questions using a small-size vocabulary. We break the question generation task into two subtasks namely, generating the skeletal structure of a question using common words from the vocabulary and pointing to rare words from the input passage to complete the question.

@inproceedings{10.1145/3430984.3431074,
	author = {Biju, Emil},
	title = {Vocabulary-Constrained Question Generation with Rare Word Masking and Dual Attention},
	year = {2021},
	isbn = {9781450388177},
	publisher = {Association for Computing Machinery},
	address = {New York, NY, USA},
	url = {https://doi.org/10.1145/3430984.3431074},
	doi = {10.1145/3430984.3431074},
	booktitle = {8th ACM IKDD CODS and 26th COMAD},
	pages = {431},
	numpages = {1},
	location = {Bangalore, India},
	series = {CODS COMAD 2021}
	}

Abstract PDF Slides Code

Multi-head self-attention is a vital component of the Transformer, a neural network architecture that has achieved state-of-the-art performance on various sequence learning tasks. In this work, we propose a method to induce accurate sample-specific attention masks for Transformer-based networks like BERT. We show that such masks are discrim- inative of the samples’ output class for various Natural Language Understanding (NLU) tasks. We leverage this property to improve model transparency and classify between authentic and adversarial samples. Further, we find two other properties which contribute to this classification. First, selectively mutating the masks leads to contrasting model outputs based on sample authenticity. Second, the consistency of auxiliary layer-wise outputs varies based on sample authenticity. By combining these observations, we propose a sample-efficient and generalized scheme for adversarial detection. We perform experiments on 8 NLU datasets with 11 different adversarial attack types and report state-of-the-art accuracy ranging from 80 to 90%. In summary, our work introduces an entirely new and promising approach to interpret and analyze large self-attention based networks for NLP.

Abstract PDF Poster Webpage Code BibTeX

Gesture typing is a method of typing words on a touch-based keyboard by creating a continuous trace passing through the relevant keys. This work is aimed at developing a keyboard that supports gesture typing in Indic languages. We begin by noting that when dealing with Indic languages, one needs to cater to two different sets of users: (i) users who prefer to type in the native Indic script (Devanagari, Bengali, etc.) and (ii) users who prefer to type in the English script but want the transliterated output in the native script. In both cases, we need a model that takes a trace as input and maps it to the intended word. To enable the development of these models, we create and release two datasets. First, we create a dataset containing keyboard traces for 193,658 words from 7 Indic languages. Second, we curate 104,412 English-Indic transliteration pairs from Wikidata across these languages. Using these datasets we build a model that performs path decoding, transliteration and transliteration correction. Unlike prior approaches, our proposed model does not make co-character independence assumptions during decoding. The overall accuracy of our model across the 7 languages varies from 70-95%.

@inproceedings{biju-etal-2020-joint,
	title = "Joint Transformer/{RNN} Architecture for Gesture Typing in Indic Languages",
	author = "Biju, Emil  and
		Sriram, Anirudh  and
		Khapra, Mitesh M.  and
		Kumar, Pratyush",
	booktitle = "Proceedings of the 28th International Conference on Computational Linguistics",
	month = dec,
	year = "2020",
	address = "Barcelona, Spain (Online)",
	publisher = "International Committee on Computational Linguistics",
	url = "https://aclanthology.org/2020.coling-main.87",
	doi = "10.18653/v1/2020.coling-main.87",
	pages = "999--1010"
	}