Papers by Nikolaos Pappas
ABC: Attention with Bounded-memory Control (2022.acl-long)
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Hao Peng, Jungo Kasai, Nikolaos Pappas, Dani Yogatama, Zhaofeng Wu, Lingpeng Kong, Roy Schwartz, Noah A. Smith
| Challenge: | Existing approaches to attention with bounded-memory control (ABC) have a quadratic complexity in sequence lengths, making it prohibitive for long sequences. |
| Approach: | They propose a new abstraction that bounds memory size to improve efficiency . they propose bounded-memory control, which connects several efficient attention variants . |
| Outcome: | The proposed approach outperforms existing approaches on language modeling, machine translation, and masked language model finetuning. |
Rethinking LLM Uncertainty: A Multi-Agent Approach to Estimating Black-Box Model Uncertainty (2025.findings-emnlp)
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Yu Feng, Phu Mon Htut, Zheng Qi, Wei Xiao, Manuel Mager, Nikolaos Pappas, Kishaloy Halder, Yang Li, Yassine Benajiba, Dan Roth
| Challenge: | Existing methods to gauge model’s uncertainty through self-consistency in responses to the target query are misleading: an LLM may confidently provide an incorrect answer to a target query, yet give a confident and accurate answer to that same query when answering a knowledge-preserving perturbation of the query. |
| Approach: | They propose a method that uses multi-agent interaction to estimate black-box LLMs' uncertainty. |
| Outcome: | The proposed method outperforms existing self-consistency based methods and improves hallucination detection. |
Balancing Classification and Calibration Performance in Decision-Making LLMs via Calibration Aware Reinforcement Learning (2026.findings-acl)
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| Challenge: | Large language models (LLMs) are increasingly deployed in decision-making tasks where accuracy and reliable confidence estimates are essential. |
| Approach: | They propose a calibration-aware reinforcement learning formulation that directly adjusts decision-token probabilities. |
| Outcome: | The proposed model preserves RLVR’s accuracy level while mitigating overconfidence, reducing ECE scores up to 9 points. |
Journey Before Destination: On the importance of Visual Faithfulness in Slow Thinking (2026.eacl-long)
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| Challenge: | Existing evaluations for visual hallucinations are narrow. |
| Approach: | They propose a framework that decomposes reasoning chains into perception versus reasoning steps and uses off-the-shelf VLM judges for step-level faithfulness. |
| Outcome: | The proposed framework reduces Unfaithful Perception Rate while preserving final-answer accuracy. |
Grounded Compositional Outputs for Adaptive Language Modeling (2020.emnlp-main)
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| Challenge: | Language models are a key component of natural language processing, but their size is a problem because they are typically trained with a closed output vocabulary derived from the training data. |
| Approach: | They propose a fully compositional output embedding layer for language models that is grounded in semantically related words and free-text definitions. |
| Outcome: | The proposed model outperforms state-of-the-art methods and adaptation approaches on cross-domain modeling and cross-learning tasks. |
MAGID: An Automated Pipeline for Generating Synthetic Multi-modal Datasets (2024.naacl-long)
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Hossein Aboutalebi, Hwanjun Song, Yusheng Xie, Arshit Gupta, Lijia Sun, Hang Su, Igor Shalyminov, Nikolaos Pappas, Siffi Singh, Saab Mansour
| Challenge: | Existing approaches to augment textual dialogues with retrieved images pose privacy, diversity, and quality constraints. |
| Approach: | They propose a framework to augment text-only dialogues with diverse and high-quality images by using a diffusion model and a feedback loop. |
| Outcome: | The proposed framework is comparable to or better than baselines, with significant improvements in human evaluation, especially against retrieval baselines where the image database is small. |
Pre-training Intent-Aware Encoders for Zero- and Few-Shot Intent Classification (2023.emnlp-main)
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Mujeen Sung, James Gung, Elman Mansimov, Nikolaos Pappas, Raphael Shu, Salvatore Romeo, Yi Zhang, Vittorio Castelli
| Challenge: | Existing methods for IC training do not provide sufficient examples for each intent . a novel pre-training method is proposed to provide a better understanding of intents . |
| Approach: | They propose a method that uses contrastive learning with intent psuedo-labels to produce embeddings that are well-suited for IC tasks. |
| Outcome: | The proposed method achieves 5.4% and 4.0% higher accuracy than the current state-of-the-art method on four IC datasets. |
Sentence Bottleneck Autoencoders from Transformer Language Models (2021.emnlp-main)
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| Challenge: | Existing methods for pretraining a language model on text have been used for building models in NLP, but they do not work for sentence representations derived from pretrainer models based on tokens or basic pooling operations. |
| Approach: | They propose to build a sentence-level autoencoder from a pretrained transformer language model. |
| Outcome: | The proposed model achieves better quality than previous methods on text similarity and style transfer tasks while using fewer parameters than large pretrained models. |
Multilevel Text Alignment with Cross-Document Attention (2020.emnlp-main)
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| Challenge: | Existing alignment methods operate at a single, predefined level and cannot learn to align texts at sentence and document levels. |
| Approach: | They propose a learning approach that equips hierarchical attention encoders for representing documents with a cross-document attention component, enabling structural comparisons across different levels. |
| Outcome: | The proposed model outperforms existing hierarchical, attention encoders on citation recommendation and plagiarism detection tasks. |
DEM: Distribution Edited Model for Training with Mixed Data Distributions (2024.emnlp-main)
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| Challenge: | Recent fine-tuning approaches for large language models require supervised finetun on diverse datasets and follow different distributions. |
| Approach: | They propose a distribution edited model that integrates models individually trained on each data source with the base model using basic element-wise vector operations. |
| Outcome: | The proposed model outperforms baseline models on a variety of benchmarks and is cheaper than standard data mixing methods. |
Plug and Play Autoencoders for Conditional Text Generation (2020.emnlp-main)
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| Challenge: | Text autoencoders are used for conditional generation tasks such as style transfer. |
| Approach: | They propose a plug-and-play method where any pretrained autoencoder can be used and only requires learning a mapping within the embedding space. |
| Outcome: | The proposed method performs better than or comparable to strong baselines while being up to four times faster. |
Backward Compatibility During Data Updates by Weight Interpolation (2024.eacl-long)
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| Challenge: | Retraining a model with a larger amount of training data introduces negative flips . retraining the model with the updated data introduce negative flipping . |
| Approach: | They propose a backward compatible weight interpolation method to improve model predictions without regression bugs. |
| Outcome: | The proposed method reduces negative flips without sacrificing accuracy . it is straight forward to implement and does not increase inference cost. |
MEAV: Model Editing with Alignment Vectors for inference time LLM alignment in single and multidomain preference spectrum (2026.findings-acl)
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Sadat Shahriar, Zheng Qi, Nikolaos Pappas, Srikanth Doss, Kishaloy Halder, Monica Sunkara, Manuel Mager, Yassine Benajiba
| Challenge: | Existing training-time alignment methods require full retraining when a change is needed. |
| Approach: | They propose an inference-time model-editing-based alignment method that learns encoded representations of preference dimensions and allows dynamic adjusting of the model behavior. |
| Outcome: | The proposed method can be used to align large language models to human preferences . it reduces the cost of inference by half compared to the prompt engineering approach . |
Unraveling and Mitigating Safety Alignment Degradation of Vision-Language Models (2025.findings-acl)
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Qin Liu, Chao Shang, Ling Liu, Nikolaos Pappas, Jie Ma, Neha Anna John, Srikanth Doss, Lluis Marquez, Miguel Ballesteros, Yassine Benajiba
| Challenge: | LLaVA-7B demonstrated a decline in safety alignment ability on multi-modal inputs compared to its LLM backbone. |
| Approach: | They propose a method to recover alignment ability from LLM backbone while preserving functional capabilities of VLMs. |
| Outcome: | The proposed framework recovers alignment ability that is inherent in the LLM backbone with minimal impact on fluency and linguistic capabilities of pre-trained VLMs. |
Eliciting Better Multilingual Structured Reasoning from LLMs through Code (2024.acl-long)
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| Challenge: | xSTREET exposes a gap in base LLM performance between English and non-English reasoning tasks. |
| Approach: | They propose a multilingual structured reasoning and explanation dataset that covers four tasks across six languages and extends the English STREET benchmark to 5 additional diverse languages. |
| Outcome: | The proposed models show improved multilingual performance on scientific commonsense reasoning subtasks and no regression on non-reasoning tasks. |
Modeling Context With Linear Attention for Scalable Document-Level Translation (2022.findings-emnlp)
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| Challenge: | Document-level machine translation models lack quadratic complexity in the sequence length due to their attention layers. |
| Approach: | They evaluate a recent linear attention model with a sentential gate to promote a recency inductive bias and compare it to open-source document translation. |
| Outcome: | The proposed model significantly improves translation quality on IWSLT 2015 and OpenSubtitles 2018 with similar or better BLEU scores. |
Finetuning Pretrained Transformers into RNNs (2021.emnlp-main)
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Jungo Kasai, Hao Peng, Yizhe Zhang, Dani Yogatama, Gabriel Ilharco, Nikolaos Pappas, Yi Mao, Weizhu Chen, Noah A. Smith
| Challenge: | Efficient transformers outperform recurrent neural networks in natural language generation, but this comes with significant computational cost and memory footprint during generation. |
| Approach: | They propose to convert a pretrained transformer into its efficient recurrent counterpart, improving efficiency while maintaining accuracy. |
| Outcome: | The proposed transformers outperform recurrent neural networks in natural language generation but come with significant computational and memory footprint during generation. |
DeAL: Decoding-time Alignment for Large Language Models (2025.acl-long)
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James Y. Huang, Sailik Sengupta, Daniele Bonadiman, Yi-An Lai, Arshit Gupta, Nikolaos Pappas, Saab Mansour, Katrin Kirchhoff, Dan Roth
| Challenge: | Large Language Models (LLMs) are expected to generate content aligned with human preferences. |
| Approach: | They propose a framework that allows the user to customize reward functions and enables Decoding-time Alignment of LLMs (DeAL). |
| Outcome: | The proposed framework allows the user to customize reward functions and enables Decoding-time Alignment of LLMs. |
Towards Long Context Hallucination Detection (2025.findings-naacl)
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Siyi Liu, Kishaloy Halder, Zheng Qi, Wei Xiao, Nikolaos Pappas, Phu Mon Htut, Neha Anna John, Yassine Benajiba, Dan Roth
| Challenge: | Large language models are prone to contextual hallucination, generating information that is either unsubstantiated or contradictory to the given context. |
| Approach: | They propose a dataset specifically designed for long-context hallucination detection. |
| Outcome: | The proposed architecture outperforms existing models while providing faster inference. |
Self-Attentive Residual Decoder for Neural Machine Translation (N18-1)
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| Challenge: | Neural sequence-to-sequence networks with attention have been used for machine translation . however, the target-side context is limited and the model lacks the ability to capture non-syntactic dependencies among words. |
| Approach: | They propose a sequence-to-sequence network with attention that captures contextual information at each time-step prediction through an attention mechanism. |
| Outcome: | The proposed model outperforms a neural MT baseline and memory and self-attention network on three language pairs. |
Measuring and Mitigating Constraint Violations of In-Context Learning for Utterance-to-API Semantic Parsing (2023.findings-emnlp)
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| Challenge: | In task-oriented semantic parsing, the system aims to translate users’ utterances in natural language to machine-interpretable programs (API calls) However, Large Language Models (LLMs) are known to hallucinate and therefore pose a formidable challenge in constraining generated content. |
| Approach: | They propose to use large language models to translate user's utterances to machine-interpretable programs (API calls) they identify constraints violations in task-oriented utterrances and define fine-grained metrics that complement traditional ones. |
| Outcome: | The proposed methods reduce constraints violations and improve quality of the generated API calls, but require careful consideration given their implementation complexity and latency. |
Document-Level Neural Machine Translation with Hierarchical Attention Networks (D18-1)
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| Challenge: | Neural machine translation (NMT) can be improved by including document-level contextual information. |
| Approach: | They propose a hierarchical attention model that captures document-level contextual information and conditioning on the NMT model’s own hidden states. |
| Outcome: | The proposed model improves the BLEU score over a strong NMT baseline with the state-of-the-art in context-aware methods and that both the encoder and decoder benefit from context in complementary ways. |