Namhoon Lee

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21ranked-venue papers
5as first author
12since 2021 · last 2026
—ORCID · conflict

Domains — the database's venue-derived domains; a paper can count in several

Artificial intelligence and machine learning · 18 · 4 first-author · 12 since 2021Graphics, computer vision, multimedia, augmented reality and games · 4 · 2 first-author · 1 since 2021Applied, interdisciplinary, general and emerging computing · 2
YearPublicationVenuePosition
2026 Quantifying Aleatoric Uncertainty of In-Context Learning for Robust Measure of LLM Prediction Confidence
abstract
In-Context Learning (ICL) allows LLMs to adapt to new tasks from a few demonstrations, but its reliability remains a concern: predictions are highly sensitive to both prompt design and the model's ability to understand the context, obscuring whether failures arise from data properties or model limitations.Uncertainty decomposition-separating aleatoric from epistemic sources-is particularly crucial in this setting, yet existing methods, designed for standard generation tasks, fail to capture the unique dynamics of ICL.To address this, we introduce a concept of self-function vectors, built upon Bayesian views and the mechanistic interpretability of ICL.These vectors leverage internal model representations to model the latent concept learned during in-context prompting, thereby enabling a direct estimation of aleatoric uncertainty within a Bayesian framework and circumventing the reliance on brittle input or decoding manipulations.Given the lack of established benchmarks and suitable evaluation protocols, we also propose the first and rigorous evaluation protocol, in which data is manipulated in controlled ways so as to quantify aleatoric uncertainty precisely and separately from epistemic uncertainty.With this new evaluation framework, initially grounded in synthetic tasks for conceptual development and subsequently extended to real-world datasets, we show that our proposed methodology can measure uncertainty of LLM predictions made under ICL more reliably than existing alternative methods.Moreover, we show it can be used as a practical tool for trustworthy-related applications, such as hallucination detection.Our findings pave a new direction for connecting the quantitative view of uncertainty with the mechanistic understanding of model behavior.
Jinseok Chung, Minkyoung Song, Hyunji Jung, Namhoon Lee
ACL (1)4
2025 ZIP: An Efficient Zeroth-order Prompt Tuning for Black-box Vision-Language Models
abstract
Recent studies have introduced various approaches for prompt-tuning black-box vision-language models, referred to as black-box prompt-tuning (BBPT). While BBPT has demonstrated considerable potential, it is often found that many existing methods require an excessive number of queries (i.e., function evaluations), which poses a significant challenge in real-world scenarios where the number of allowed queries is limited. To tackle this issue, we propose Zeroth-order Intrinsic-dimensional Prompt-tuning (ZIP), a novel approach that enables efficient and robust prompt optimization in a purely black-box setting. The key idea of ZIP is to reduce the problem dimensionality and the variance of zeroth-order gradient estimates, such that the training is done fast with far less queries. We achieve this by re-parameterizing prompts in low-rank representations and designing intrinsic-dimensional clipping of estimated gradients. We evaluate ZIP on 13+ vision-language tasks in standard benchmarks and show that it achieves an average improvement of approximately 6% in few-shot accuracy and 48% in query efficiency compared to the best-performing alternative BBPT methods, establishing a new state of the art. Our ablation analysis further shows that the proposed clipping mechanism is robust and nearly optimal, without the need to manually select the clipping threshold, matching the result of expensive hyperparameter search.
Seonghwan Park 0003, Jaehyeon Jeong, Jaeho Lee 0001, Namhoon Lee
ICLR5
2025 SAFE: Finding Sparse and Flat Minima to Improve Pruning
abstract
Sparsifying neural networks often suffers from seemingly inevitable performance degradation, and it remains challenging to restore the original performance despite much recent progress. Motivated by recent studies in robust optimization, we aim to tackle this problem by finding subnetworks that are both sparse and flat at the same time. Specifically, we formulate pruning as a sparsity-constrained optimization problem where flatness is encouraged as an objective. We solve it explicitly via an augmented Lagrange dual approach and extend it further by proposing a generalized projection operation, resulting in novel pruning methods called SAFE and its extension, SAFE$^+$. Extensive evaluations on standard image classification and language modeling tasks reveal that SAFE consistently yields sparse networks with improved generalization performance, which compares competitively to well-established baselines. In addition, SAFE demonstrates resilience to noisy data, making it well-suited for real-world conditions.
Dongyeop Lee, Kwanhee Lee, Jinseok Chung, Namhoon Lee
ICML4
2025 Sassha: Sharpness-aware Adaptive Second-order Optimization with Stable Hessian Approximation
abstract
Approximate second-order optimization methods often exhibit poorer generalization compared to first-order approaches. In this work, we look into this issue through the lens of the loss landscape and find that existing second-order methods tend to converge to sharper minima compared to SGD. In response, we propose Sassha, a novel second-order method designed to enhance generalization by explicitly reducing sharpness of the solution, while stabilizing the computation of approximate Hessians along the optimization trajectory. In fact, this sharpness minimization scheme is crafted also to accommodate lazy Hessian updates, so as to secure efficiency besides flatness. To validate its effectiveness, we conduct a wide range of standard deep learning experiments where Sassha demonstrates its outstanding generalization performance that is comparable to, and mostly better than, other methods. We provide a comprehensive set of analyses including convergence, robustness, stability, efficiency, and cost.
Dahun Shin, Dongyeop Lee, Jinseok Chung, Namhoon Lee
ICML4
2025 An Analysis of Concept Bottleneck Models: Measuring, Understanding, and Mitigating the Impact of Noisy Annotations
abstract
Concept bottleneck models (CBMs) ensure interpretability by decomposing predictions into human interpretable concepts. Yet the annotations used for training CBMs that enable this transparency are often noisy, and the impact of such corruption is not well understood. In this study, we present the first systematic study of noise in CBMs and show that even moderate corruption simultaneously impairs prediction performance, interpretability, and the intervention effectiveness. Our analysis identifies a susceptible subset of concepts whose accuracy declines far more than the average gap between noisy and clean supervision and whose corruption accounts for most performance loss. To mitigate this vulnerability we propose a two-stage framework. During training, sharpness-aware minimization stabilizes the learning of noise-sensitive concepts. During inference, where clean labels are unavailable, we rank concepts by predictive entropy and correct only the most uncertain ones, using uncertainty as a proxy for susceptibility. Theoretical analysis and extensive ablations elucidate why sharpness-aware training confers robustness and why uncertainty reliably identifies susceptible concepts, providing a principled basis that preserves both interpretability and resilience in the presence of noise.
Seonghwan Park 0003, Jueun Mun, Donghyun Oh, Namhoon Lee
NeurIPS4
2025 MemEIC: A Step Toward Continual and Compositional Knowledge Editing
abstract
The dynamic nature of information necessitates continuously updating large vision-language models (LVLMs). While recent knowledge editing techniques hint at promising directions, they often focus on editing a single modality (vision or language) in isolation. This prevalent practice neglects the inherent multimodality of LVLMs and the continuous nature of knowledge updates, potentially leading to suboptimal editing outcomes when considering the interplay between modalities and the need for ongoing knowledge refinement. To address these limitations, we propose MemEIC, a novel method for Continual and Compositional Knowledge Editing (CCKE) in LVLMs. MemEIC enables compositional editing of both visual and textual knowledge sequentially. Our approach employs a hybrid external-internal editor featuring a dual external memory for cross-modal evidence retrieval and dual LoRA adapters that facilitate disentangled parameter updates for each modality. A key component is a brain-inspired knowledge connector, activated selectively for compositional reasoning, that integrates information across different modalities. Experiments demonstrate that MemEIC significantly improves performance on complex multimodal questions and effectively preserves prior edits, setting a new benchmark for CCKE in LVLMs. Our project is available at https://github.com/MemEIC/MemEIC.
Jin Seong, Jiyun Park, Wencke Liermann, Hongseok Choi, Yoonji Nam, Hyun Jun Kim, Soojong Lim, Namhoon Lee
NeurIPS8
2025 Critical Influence of Overparameterization on Sharpness-aware Minimization
abstract
Training overparameterized neural networks often yields solutions with varying generalization capabilities, even when achieving similar training losses. Recent evidence indicates a strong correlation between the sharpness of a minimum and its generalization error, leading to increased interest in optimization methods that explicitly seek flatter minima for improved generalization. Despite its contemporary relevance to overparameterization, however, this sharpness-aware minimization (SAM) strategy has not been studied much yet as to exactly how it is affected by overparameterization. In this work, we analyze SAM under varying degrees of overparameterization, presenting both empirical and theoretical findings that reveal its critical influence on SAM’s effectiveness. First, we conduct extensive numerical experiments across diverse domains and show that SAM consistently improves with overparameterization. Next, we attribute this phenomenon to the interplay between the enlarged solution space and increased implicit bias resulting from overparameterization. Furthermore, we show that this effect is particularly pronounced in practical settings involving label noise and sparsity, and yet, sufficient regularization is necessary. Last but not least, we provide other theoretical insights into how overparameterization helps SAM achieve minima with more uniform Hessian moments compared to SGD, and much faster convergence at a linear rate.
Sungbin Shin, Dongyeop Lee, Maksym Andriushchenko, Namhoon Lee
UAI4
2024 The Role of Masking for Efficient Supervised Knowledge Distillation of Vision Transformers
Seungwoo Son 0005, Jegwang Ryu, Namhoon Lee, Jaeho Lee 0001
ECCV (67)3
2024 Rethinking Pruning Large Language Models: Benefits and Pitfalls of Reconstruction Error Minimization
abstract
This work suggests fundamentally rethinking the current practice of pruning large language models (LLMs).The way it is done is by divide and conquer: split the model into submodels, sequentially prune them, and reconstruct predictions of the dense counterparts on small calibration data one at a time; the final model is obtained simply by putting the resulting sparse submodels together.While this approach enables pruning under memory constraints, it generates high reconstruction errors.In this work, we first present an array of reconstruction techniques that can significantly reduce this error by more than 90%.Unwittingly, however, we discover that minimizing reconstruction error is not always ideal and can overfit the given calibration data, resulting in rather increased language perplexity and poor performance at downstream tasks.We find out that a strategy of self-generating calibration data can mitigate this trade-off between reconstruction and generalization, suggesting new directions in the presence of both benefits and pitfalls of reconstruction for pruning LLMs. 1
Sungbin Shin, Wonpyo Park, Jaeho Lee 0001, Namhoon Lee
EMNLP4
2023 A Closer Look at the Intervention Procedure of Concept Bottleneck Models
abstract
Concept bottleneck models (CBMs) are a class of interpretable neural network models that predict the target response of a given input based on its high-level concepts. Unlike the standard end-to-end models, CBMs enable domain experts to intervene on the predicted concepts and rectify any mistakes at test time, so that more accurate task predictions can be made at the end. While such intervenability provides a powerful avenue of control, many aspects of the intervention procedure remain rather unexplored. In this work, we develop various ways of selecting intervening concepts to improve the intervention effectiveness and conduct an array of in-depth analyses as to how they evolve under different circumstances. Specifically, we find that an informed intervention strategy can reduce the task error more than ten times compared to the current baseline under the same amount of intervention counts in realistic settings, and yet, this can vary quite significantly when taking into account different intervention granularity. We verify our findings through comprehensive evaluations, not only on the standard real datasets, but also on synthetic datasets that we generate based on a set of different causal graphs. We further discover some major pitfalls of the current practices which, without a proper addressing, raise concerns on reliability and fairness of the intervention procedure.
Sungbin Shin, Yohan Jo, Sungsoo Ahn, Namhoon Lee
ICML4
2021 Understanding the effects of data parallelism and sparsity on neural network training
Namhoon Lee, Thalaiyasingam Ajanthan, Philip Torr 0001, Martin Jaggi
ICLR1
2021 Meta-Learning Sparse Implicit Neural Representations
abstract
Implicit neural representations are a promising new avenue of representing general signals by learning a continuous function that, parameterized as a neural network, maps the domain of a signal to its codomain; the mapping from spatial coordinates of an image to its pixel values, for example. Being capable of conveying fine details in a high dimensional signal, unboundedly of its domain, implicit neural representations ensure many advantages over conventional discrete representations. However, the current approach is difficult to scale for a large number of signals or a data set, since learning a neural representation---which is parameter heavy by itself---for each signal individually requires a lot of memory and computations. To address this issue, we propose to leverage a meta-learning approach in combination with network compression under a sparsity constraint, such that it renders a well-initialized sparse parameterization that evolves quickly to represent a set of unseen signals in the subsequent training. We empirically demonstrate that meta-learned sparse neural representations achieve a much smaller loss than dense meta-learned models with the same number of parameters, when trained to fit each signal using the same number of optimization steps.
Jaeho Lee 0001, Jihoon Tack, Namhoon Lee, Jinwoo Shin
NeurIPS3
2020 A Signal Propagation Perspective for Pruning Neural Networks at Initialization
Namhoon Lee, Thalaiyasingam Ajanthan, Stephen Gould, Philip Torr 0001
ICLR1
2019 Snip: single-Shot Network Pruning based on Connection sensitivity
Namhoon Lee, Thalaiyasingam Ajanthan, Philip Torr 0001
ICLR (Poster)1
2018 Learn to Pay Attention
Saumya Jetley, Nicholas A. Lord, Namhoon Lee, Philip Torr 0001
ICLR (Poster)3
2018 Synthesizing a Scene-Specific Pedestrian Detector and Pose Estimator for Static Video Surveillance - Can We Learn Pedestrian Detectors and Pose Estimators Without Real Data?
Hironori Hattori, Namhoon Lee, Vishnu Naresh Boddeti, Fares Beainy, Kris Makoto Kitani, Takeo Kanade
Int. J. Comput. Vis.2
2017 DESIRE: Distant Future Prediction in Dynamic Scenes with Interacting Agents
abstract
We introduce a Deep Stochastic IOC RNN Encoder-decoder framework, DESIRE, for the task of future predictions of multiple interacting agents in dynamic scenes. DESIRE effectively predicts future locations of objects in multiple scenes by 1) accounting for the multi-modal nature of the future prediction (i.e., given the same context, future may vary), 2) foreseeing the potential future outcomes and make a strategic prediction based on that, and 3) reasoning not only from the past motion history, but also from the scene context as well as the interactions among the agents. DESIRE achieves these in a single end-to-end trainable neural network model, while being computationally efficient. The model first obtains a diverse set of hypothetical future prediction samples employing a conditional variational auto-encoder, which are ranked and refined by the following RNN scoring-regression module. Samples are scored by accounting for accumulated future rewards, which enables better long-term strategic decisions similar to IOC frameworks. An RNN scene context fusion module jointly captures past motion histories, the semantic scene context and interactions among multiple agents. A feedback mechanism iterates over the ranking and refinement to further boost the prediction accuracy. We evaluate our model on two publicly available datasets: KITTI and Stanford Drone Dataset. Our experiments show that the proposed model significantly improves the prediction accuracy compared to other baseline methods.
Namhoon Lee, Wongun Choi, Paul Vernaza, Christopher B. Choy, Philip Torr 0001, Manmohan Krishna Chandraker
CVPR1
2017 Forecasting Interactive Dynamics of Pedestrians with Fictitious Play
abstract
We develop predictive models of pedestrian dynamics by encoding the coupled nature of multi-pedestrian interaction using game theory and deep learning-based visual analysis to estimate person-specific behavior parameters. We focus on predictive models since they are important for developing interactive autonomous systems (e.g., autonomous cars, home robots, smart homes) that can understand different human behavior and pre-emptively respond to future human actions. Building predictive models for multi-pedestrian interactions however, is very challenging due to two reasons: (1) the dynamics of interaction are complex interdependent processes, where the decision of one person can affect others, and (2) dynamics are variable, where each person may behave differently (e.g., an older person may walk slowly while the younger person may walk faster). To address these challenges, we utilize concepts from game theory to model the intertwined decision making process of multiple pedestrians and use visual classifiers to learn a mapping from pedestrian appearance to behavior parameters. We evaluate our proposed model on several public multiple pedestrian interaction video datasets. Results show that our strategic planning model predicts and explains human interactions 25% better when compared to a state-of-the-art activity forecasting method.
Wei-Chiu Ma, De-An Huang, Namhoon Lee, Kris Makoto Kitani
CVPR3
2016 Predicting wide receiver trajectories in American football
abstract
Predicting the trajectory of a wide receiver in the game of American football requires prior knowledge about the game (e.g., route trees, defensive formations) and an accurate model of how the environment will change over time (e.g., opponent reaction strategies, motion attributes of players). Our aim is to build a computational model of the wide receiver, which takes into account prior knowledge about the game and short-term predictive models of how the environment will change over time. While prior knowledge of the game is readily accessible, it is quite challenging to build predictive models of how the environment will change over time. We propose several models for predicting short-term motions of opponent players to generate dynamic input features for our wide receiver forecasting model. In particular, we model the wide receiver with a Markov Decision Process (MDP), where the reward function is a linear combination of static features (prior knowledge about the game) and dynamic features (short-term prediction of opponent players). Since the dynamic features change over time, we make recursive calls to an inference procedure over the MDP while updating the dynamic features. We validate our technique on a video dataset of American football plays. Our results show that more informed models that accurately predict the motions of the defensive players are better at forecasting wide receiver plays.
Namhoon Lee, Kris Makoto Kitani
WACV1
2005 Security Risk Vector for Quantitative Asset Assessment
Yoon Jung Chung, Injung Kim 0003, Namhoon Lee, Taek Lee, Hoh Peter In
ICCSA (2)3
2004 The Design and Development for Risk Analysis Automatic Tool
Young-Hwan Bang, Yoon-Jung Jung, Namhoon Lee
ICCSA (1)4