2020’s Top AI & Machine Learning Research Papers

Despite the challenges of 2020, the AI research community produced a number of meaningful technical breakthroughs. GPT-3 by OpenAI may be the most famous, but there are definitely many other research papers worth your attention. 

For example, teams from Google introduced a revolutionary chatbot, Meena, and EfficientDet object detectors in image recognition. Researchers from Yale introduced a novel AdaBelief optimizer that combines many benefits of existing optimization methods. OpenAI researchers demonstrated how deep reinforcement learning techniques can achieve superhuman performance in Dota 2.

To help you catch up on essential reading, we’ve summarized 10 important machine learning research papers from 2020. These papers will give you a broad overview of AI research advancements this year. Of course, there are many more breakthrough papers worth reading as well.

We have also published the top 10 lists of key research papers in natural language processing and computer vision. In addition, you can read our premium research summaries, where we feature the top 25 conversational AI research papers introduced recently.

Subscribe to our AI Research mailing list at the bottom of this article to be alerted when we release new summaries.

If you’d like to skip around, here are the papers we featured:

1. A Distributed Multi-Sensor Machine Learning Approach to Earthquake Early Warning
2. Efficiently Sampling Functions from Gaussian Process Posteriors
3. Dota 2 with Large Scale Deep Reinforcement Learning
4. Towards a Human-like Open-Domain Chatbot
5. Language Models are Few-Shot Learners
6. Beyond Accuracy: Behavioral Testing of NLP models with CheckList
7. EfficientDet: Scalable and Efficient Object Detection
8. Unsupervised Learning of Probably Symmetric Deformable 3D Objects from Images in the Wild
9. An Image is Worth 16×16 Words: Transformers for Image Recognition at Scale
10. AdaBelief Optimizer: Adapting Stepsizes by the Belief in Observed Gradients

Best AI & ML Research Papers 2020

1. A Distributed Multi-Sensor Machine Learning Approach to Earthquake Early Warning, by Kévin Fauvel, Daniel Balouek-Thomert, Diego Melgar, Pedro Silva, Anthony Simonet, Gabriel Antoniu, Alexandru Costan, Véronique Masson, Manish Parashar, Ivan Rodero, and Alexandre Termier

Original Abstract 

Our research aims to improve the accuracy of Earthquake Early Warning (EEW) systems by means of machine learning. EEW systems are designed to detect and characterize medium and large earthquakes before their damaging effects reach a certain location. Traditional EEW methods based on seismometers fail to accurately identify large earthquakes due to their sensitivity to the ground motion velocity. The recently introduced high-precision GPS stations, on the other hand, are ineffective to identify medium earthquakes due to their propensity to produce noisy data. In addition, GPS stations and seismometers may be deployed in large numbers across different locations and may produce a significant volume of data, consequently affecting the response time and the robustness of EEW systems. 

In practice, EEW can be seen as a typical classification problem in the machine learning field: multi-sensor data are given in input, and earthquake severity is the classification result. In this paper, we introduce the Distributed Multi-Sensor Earthquake Early Warning (DMSEEW) system, a novel machine learning-based approach that combines data from both types of sensors (GPS stations and seismometers) to detect medium and large earthquakes. DMSEEW is based on a new stacking ensemble method which has been evaluated on a real-world dataset validated with geoscientists. The system builds on a geographically distributed infrastructure, ensuring an efficient computation in terms of response time and robustness to partial infrastructure failures. Our experiments show that DMSEEW is more accurate than the traditional seismometer-only approach and the combined-sensors (GPS and seismometers) approach that adopts the rule of relative strength.

Our Summary 

The authors claim that traditional Earthquake Early Warning (EEW) systems that are based on seismometers, as well as recently introduced GPS systems, have their disadvantages with regards to predicting large and medium earthquakes respectively. Thus, the researchers suggest approaching an early earthquake prediction problem with machine learning by using the data from seismometers and GPS stations as input data. In particular, they introduce the Distributed Multi-Sensor Earthquake Early Warning (DMSEEW) system, which is specifically tailored for efficient computation on large-scale distributed cyberinfrastructures. The evaluation demonstrates that the DMSEEW system is more accurate than other baseline approaches with regard to real-time earthquake detection.

What’s the core idea of this paper?

• The existing solutions to early earthquake warning (EEW) do not work well enough:
  • Seismometers have difficulty detecting large earthquakes because of their sensitivity to ground motion velocity.
  • GPS stations are ineffective in detecting medium earthquakes, as they are prone to producing lots of noisy data.
• The authors present the Distributed Multi-Sensor Earthquake Early Warning (DMSEEW) algorithm, which:
  • takes sensor-level class predictions from seismometers and GPS stations (i.e. normal activity, medium earthquake, large earthquake);
  • aggregates these predictions using a bag-of-words representation and defines a final prediction for the earthquake category.
• Furthermore, they introduce a distributed cyberinfrastructure that can support the processing of high volumes of data in real time and allows the redirection of data to other processing data centers in case of disaster situations.

What’s the key achievement?

• The experiments demonstrate that the DMSEEW algorithm outperforms other baseline approaches (i.e. the seismometer-only baseline approach and the combined sensors baseline approach that adopts the rule of relative strength) in predicting:
  • large earthquakes:
    • precision – 100% vs. 63.2%;
    • recall – 100% vs. 85.7%;
    • F1 score – 100% vs. 72.7%.
  • medium earthquakes:
    • precision – 76.7% vs. 70.7%;
    • recall – 38.8% vs. 34.1%;
    • F1 score – 51.6% vs. 45.0%.

What does the AI community think?

• The paper received an Outstanding Paper award at AAAI 2020 (special track on AI for Social Impact).

What are future research areas?

• Evaluating DMSEEW response time and robustness via simulation of different scenarios in an existing EEW execution platform. 
• Evaluating the DMSEEW system on another seismic network.

2. Efficiently Sampling Functions from Gaussian Process Posteriors, by James T. Wilson, Viacheslav Borovitskiy, Alexander Terenin, Peter Mostowsky, Marc Peter Deisenroth

Original Abstract 

Gaussian processes are the gold standard for many real-world modeling problems, especially in cases where a model’s success hinges upon its ability to faithfully represent predictive uncertainty. These problems typically exist as parts of larger frameworks, wherein quantities of interest are ultimately defined by integrating over posterior distributions. These quantities are frequently intractable, motivating the use of Monte Carlo methods. Despite substantial progress in scaling up Gaussian processes to large training sets, methods for accurately generating draws from their posterior distributions still scale cubically in the number of test locations. We identify a decomposition of Gaussian processes that naturally lends itself to scalable sampling by separating out the prior from the data. Building off of this factorization, we propose an easy-to-use and general-purpose approach for fast posterior sampling, which seamlessly pairs with sparse approximations to afford scalability both during training and at test time. In a series of experiments designed to test competing sampling schemes’ statistical properties and practical ramifications, we demonstrate how decoupled sample paths accurately represent Gaussian process posteriors at a fraction of the usual cost.

Our Summary 

In this paper, the authors explore techniques for efficiently sampling from Gaussian process (GP) posteriors. After investigating the behaviors of naive approaches to sampling and fast approximation strategies using Fourier features, they find that many of these strategies are complementary. They, therefore, introduce an approach that incorporates the best of different sampling approaches. First, they suggest decomposing the posterior as the sum of a prior and an update. Then they combine this idea with techniques from literature on approximate GPs and obtain an easy-to-use general-purpose approach for fast posterior sampling. The experiments demonstrate that decoupled sample paths accurately represent GP posteriors at a much lower cost.

What’s the core idea of this paper?

• The introduced approach to sampling functions from GP posteriors centers on the observation that it is possible to implicitly condition Gaussian random variables by combining them with an explicit corrective term.
• The authors translate this intuition to Gaussian processes and suggest decomposing the posterior as the sum of a prior and an update.
• Building on this factorization, the researchers suggest an efficient approach for fast posterior sampling that seamlessly pairs with sparse approximations to achieve scalability both during training and at test time.

What’s the key achievement?

• Introducing an easy-to-use and general-purpose approach to sampling from GP posteriors.
• Demonstrating, with a series of experiments, that decoupled sample paths:
  • avoid many shortcomings of the alternative sampling strategies;
  • accurately represent GP posteriors at a much lower cost; for example, simulation of a well-known model of a biological neuron required only 20 seconds using decoupled sampling, while the iterative approach required 10 hours.

What does the AI community think?

• The paper received an Honorable Mention at ICML 2020. 

Where can you get implementation code?

• The authors released the implementation of this paper on GitHub.

3. Dota 2 with Large Scale Deep Reinforcement Learning, by Christopher Berner, Greg Brockman, Brooke Chan, Vicki Cheung, Przemysław “Psyho” Dębiak, Christy Dennison, David Farhi, Quirin Fischer, Shariq Hashme, Chris Hesse, Rafal Józefowicz, Scott Gray, Catherine Olsson, Jakub Pachocki, Michael Petrov, Henrique Pondé de Oliveira Pinto, Jonathan Raiman, Tim Salimans, Jeremy Schlatter, Jonas Schneider, Szymon Sidor, Ilya Sutskever, Jie Tang, Filip Wolski, Susan Zhang

Original Abstract 

On April 13th, 2019, OpenAI Five became the first AI system to defeat the world champions at an esports game. The game of Dota 2 presents novel challenges for AI systems such as long time horizons, imperfect information, and complex, continuous state-action spaces, all challenges which will become increasingly central to more capable AI systems. OpenAI Five leveraged existing reinforcement learning techniques, scaled to learn from batches of approximately 2 million frames every 2 seconds. We developed a distributed training system and tools for continual training which allowed us to train OpenAI Five for 10 months. By defeating the Dota 2 world champion (Team OG), OpenAI Five demonstrates that self-play reinforcement learning can achieve superhuman performance on a difficult task.

Our Summary 

The OpenAI research team demonstrates that modern reinforcement learning techniques can achieve superhuman performance in such a challenging esports game as Dota 2. The challenges of this particular task for the AI system lies in the long time horizons, partial observability, and high dimensionality of observation and action spaces. To tackle this game, the researchers scaled existing RL systems to unprecedented levels with thousands of GPUs utilized for 10 months. The resulting OpenAI Five model was able to defeat the Dota 2 world champions and won 99.4% of over 7000 games played during the multi-day showcase.

What’s the core idea of this paper?

• The goal of the introduced OpenAI Five model is to find the policy that maximizes the probability of winning the game against professional human players, which in practice implies maximizing the reward function with some additional signals like characters dying, resources collected, etc.
• The researchers approach this goal in the following way:
  • While the Dota 2 engine runs at 30 frames per second, the OpenAI Five only acts on every 4th frame.
  • At each timestep, the model receives an observation with all the information available to human players (approximated in a set of data arrays) and returns a discrete action, which encodes the desired movement, attack, etc.
  • A policy is defined as a function from the history of observations to a probability distribution over actions that are parameterized as an LSTM with ~159M parameters.
  • The policy is trained using a variant of advantage actor critic, Proximal Policy Optimization.
• The OpenAI Five model was trained for 180 days spread over 10 months of real time.

What’s the key achievement?

• OpenAI Five:
  • defeated the Dota 2 world champions in a best-of-three match (2–0);
  • won 99.4% of over 7000 games during a multi-day online showcase.

What are future research areas?

• Applying introduced methods to other zero-sum two-team continuous environments.

What are possible business applications?

• Tackling challenging esports games like Dota 2 can be a promising step towards solving advanced real-world problems using reinforcement learning techniques.

4. Towards a Human-like Open-Domain Chatbot, by Daniel Adiwardana, Minh-Thang Luong, David R. So, Jamie Hall, Noah Fiedel, Romal Thoppilan, Zi Yang, Apoorv Kulshreshtha, Gaurav Nemade, Yifeng Lu, Quoc V. Le

Original Abstract 

We present Meena, a multi-turn open-domain chatbot trained end-to-end on data mined and filtered from public domain social media conversations. This 2.6B parameter neural network is simply trained to minimize perplexity of the next token. We also propose a human evaluation metric called Sensibleness and Specificity Average (SSA), which captures key elements of a human-like multi-turn conversation. Our experiments show strong correlation between perplexity and SSA. The fact that the best perplexity end-to-end trained Meena scores high on SSA (72% on multi-turn evaluation) suggests that a human-level SSA of 86% is potentially within reach if we can better optimize perplexity. Additionally, the full version of Meena (with a filtering mechanism and tuned decoding) scores 79% SSA, 23% higher in absolute SSA than the existing chatbots we evaluated. 

Our Summary 

In contrast to most modern conversational agents, which are highly specialized, the Google research team introduces a chatbot Meena that can chat about virtually anything. It’s built on a large neural network with 2.6B parameters trained on 341 GB of text. The researchers also propose a new human evaluation metric for open-domain chatbots, called Sensibleness and Specificity Average (SSA), which can capture important attributes for human conversation. They demonstrate that this metric correlates highly with perplexity, an automatic metric that is readily available. Thus, the Meena chatbot, which is trained to minimize perplexity, can conduct conversations that are more sensible and specific compared to other chatbots. Particularly, the experiments demonstrate that Meena outperforms existing state-of-the-art chatbots by a large margin in terms of the SSA score (79% vs. 56%) and is closing the gap with human performance (86%).

What’s the core idea of this paper?

• Despite recent progress, open-domain chatbots still have significant weaknesses: their responses often do not make sense or are too vague or generic.
• To address these issues, the Google research team introduces Meena, a generative conversational model with 2.6B parameters trained on 40B words mined from public social media conversations:
  • Meena is built on a seq2seq model with Evolved Transformer (ET) that includes 1 ET encoder block and 13 ET decoder blocks.
  • The model is trained on multi-turn conversations with the input sequence including all turns of the context (up to 7) and the output sequence being the response.
• To measure the quality of open-domain chatbots, such as Meena, the researchers introduce a new human-evaluation metric, called Sensibleness and Sensitivity Average (SSA), that measures two fundamental aspects of a chatbot:
  • making sense,
  • being specific.
• The research team discovered that the SSA metric shows high negative correlation (R2 = 0.93) with perplexity, a readily available automatic metric that Meena is trained to minimize.

What’s the key achievement?

• Proposing a simple human-evaluation metric for open-domain chatbots.
• Demonstrating that a large-scale low-perplexity model can be a good conversationalist:
  • The best end-to-end trained Meena model outperforms existing state-of-the-art open-domain chatbots by a large margin, achieving an SSA score of 72% (vs. 56%).
  • Furthermore, the full version of Meena, with a filtering mechanism and tuned decoding, further advances the SSA score to 79%, which is not far from the 86% SSA achieved by the average human.

What does the AI community think?

• “Google’s “Meena” chatbot was trained on a full TPUv3 pod (2048 TPU cores) for 30 full days – that’s more than $1,400,000 of compute time to train this chatbot model.” – Elliot Turner, CEO and founder of Hyperia.
• “So I was browsing the results for the new Google chatbot Meena, and they look pretty OK (if boring sometimes). However, every once in a while it enters ‘scary sociopath mode,’ which is, shall we say, sub-optimal” – Graham Neubig, Associate professor at Carnegie Mellon University.

What are future research areas?

• Lowering the perplexity through improvements in algorithms, architectures, data, and compute.
• Considering other aspects of conversations beyond sensibleness and specificity, such as, for example, personality and factuality.
• Tackling safety and bias in the models.

What are possible business applications?

• The authors suggest some interesting applications for open-domain chatbots such as Meena:
  • further humanizing computer interactions; 
  • improving foreign language practice; 
  • making interactive movie and videogame characters relatable.

Where can you get implementation code?

• Considering the challenges related to safety and bias in the models, the authors haven’t released the Meena model yet. However, they are still evaluating the risks and benefits and may decide otherwise in the coming months.

5. Language Models are Few-Shot Learners, by Tom B. Brown, Benjamin Mann, Nick Ryder, Melanie Subbiah, Jared Kaplan, Prafulla Dhariwal, Arvind Neelakantan, Pranav Shyam, Girish Sastry, Amanda Askell, Sandhini Agarwal, Ariel Herbert-Voss, Gretchen Krueger, Tom Henighan, Rewon Child, Aditya Ramesh, Daniel M. Ziegler, Jeffrey Wu, Clemens Winter, Christopher Hesse, Mark Chen, Eric Sigler, Mateusz Litwin, Scott Gray, Benjamin Chess, Jack Clark, Christopher Berner, Sam McCandlish, Alec Radford, Ilya Sutskever, Dario Amodei

Original Abstract 

Recent work has demonstrated substantial gains on many NLP tasks and benchmarks by pre-training on a large corpus of text followed by fine-tuning on a specific task. While typically task-agnostic in architecture, this method still requires task-specific fine-tuning datasets of thousands or tens of thousands of examples. By contrast, humans can generally perform a new language task from only a few examples or from simple instructions – something which current NLP systems still largely struggle to do. Here we show that scaling up language models greatly improves task-agnostic, few-shot performance, sometimes even reaching competitiveness with prior state-of-the-art fine-tuning approaches. Specifically, we train GPT-3, an autoregressive language model with 175 billion parameters, 10× more than any previous non-sparse language model, and test its performance in the few-shot setting. For all tasks, GPT-3 is applied without any gradient updates or fine-tuning, with tasks and few-shot demonstrations specified purely via text interaction with the model. GPT-3 achieves strong performance on many NLP datasets, including translation, question-answering, and cloze tasks, as well as several tasks that require on-the-fly reasoning or domain adaptation, such as unscrambling words, using a novel word in a sentence, or performing 3-digit arithmetic. At the same time, we also identify some datasets where GPT-3’s few-shot learning still struggles, as well as some datasets where GPT-3 faces methodological issues related to training on large web corpora. Finally, we find that GPT-3 can generate samples of news articles which human evaluators have difficulty distinguishing from articles written by humans. We discuss broader societal impacts of this finding and of GPT-3 in general.

Our Summary 

The OpenAI research team draws attention to the fact that the need for a labeled dataset for every new language task limits the applicability of language models. Considering that there is a wide range of possible tasks and it’s often difficult to collect a large labeled training dataset, the researchers suggest an alternative solution, which is scaling up language models to improve task-agnostic few-shot performance. They test their solution by training a 175B-parameter autoregressive language model, called GPT-3, and evaluating its performance on over two dozen NLP tasks. The evaluation under few-shot learning, one-shot learning, and zero-shot learning demonstrates that GPT-3 achieves promising results and even occasionally outperforms the state of the art achieved by fine-tuned models.

What’s the core idea of this paper?

• The GPT-3 model uses the same model and architecture as GPT-2, including the modified initialization, pre-normalization, and reversible tokenization.
• However, in contrast to GPT-2, it uses alternating dense and locally banded sparse attention patterns in the layers of the transformer, as in the Sparse Transformer.
• The model is evaluated in three different settings:
  • Few-shot learning, when the model is given a few demonstrations of the task (typically, 10 to 100) at inference time but with no weight updates allowed.
  • One-shot learning, when only one demonstration is allowed, together with a natural language description of the task.
  • Zero-shot learning, when no demonstrations are allowed and the model has access only to a natural language description of the task.

What’s the key achievement?

• The GPT-3 model without fine-tuning achieves promising results on a number of NLP tasks, and even occasionally surpasses state-of-the-art models that were fine-tuned for that specific task:
  • On the CoQA benchmark, 81.5 F1 in the zero-shot setting, 84.0 F1 in the one-shot setting, and 85.0 F1 in the few-shot setting, compared to the 90.7 F1 score achieved by fine-tuned SOTA.
  • On the TriviaQA benchmark, 64.3% accuracy in the zero-shot setting, 68.0% in the one-shot setting, and 71.2% in the few-shot setting, surpassing the state of the art (68%) by 3.2%.
  • On the LAMBADA dataset, 76.2 % accuracy in the zero-shot setting, 72.5% in the one-shot setting, and 86.4% in the few-shot setting, surpassing the state of the art (68%) by 18%.
• The news articles generated by the 175B-parameter GPT-3 model are hard to distinguish from real ones, according to human evaluations (with accuracy barely above the chance level at ~52%).

What does the AI community think?

• “The GPT-3 hype is way too much. It’s impressive (thanks for the nice compliments!) but it still has serious weaknesses and sometimes makes very silly mistakes. AI is going to change the world, but GPT-3 is just a very early glimpse. We have a lot still to figure out.” – Sam Altman, CEO and co-founder of OpenAI.
• “I’m shocked how hard it is to generate text about Muslims from GPT-3 that has nothing to do with violence… or being killed…” – Abubakar Abid, CEO and founder of Gradio.
• “No. GPT-3 fundamentally does not understand the world that it talks about. Increasing corpus further will allow it to generate a more credible pastiche but not fix its fundamental lack of comprehension of the world. Demos of GPT-4 will still require human cherry picking.” – Gary Marcus, CEO and founder of Robust.ai.
• “Extrapolating the spectacular performance of GPT3 into the future suggests that the answer to life, the universe and everything is just 4.398 trillion parameters.” – Geoffrey Hinton, Turing Award winner.

What are future research areas?

• Improving pre-training sample efficiency.
• Exploring how few-shot learning works.
• Distillation of large models down to a manageable size for real-world applications.

What are possible business applications?

• The model with 175B parameters is hard to apply to real business problems due to its impractical resource requirements, but if the researchers manage to distill this model down to a workable size, it could be applied to a wide range of language tasks, including question answering, dialog agents, and ad copy generation.

Where can you get implementation code?

• The code itself is not available, but some dataset statistics together with unconditional, unfiltered 2048-token samples from GPT-3 are released on GitHub.

6. Beyond Accuracy: Behavioral Testing of NLP models with CheckList, by Marco Tulio Ribeiro, Tongshuang Wu, Carlos Guestrin, Sameer Singh

Original Abstract 

Although measuring held-out accuracy has been the primary approach to evaluate generalization, it often overestimates the performance of NLP models, while alternative approaches for evaluating models either focus on individual tasks or on specific behaviors. Inspired by principles of behavioral testing in software engineering, we introduce CheckList, a task-agnostic methodology for testing NLP models. CheckList includes a matrix of general linguistic capabilities and test types that facilitate comprehensive test ideation, as well as a software tool to generate a large and diverse number of test cases quickly. We illustrate the utility of CheckList with tests for three tasks, identifying critical failures in both commercial and state-of-art models. In a user study, a team responsible for a commercial sentiment analysis model found new and actionable bugs in an extensively tested model. In another user study, NLP practitioners with CheckList created twice as many tests, and found almost three times as many bugs as users without it.

Our Summary 

The authors point out the shortcomings of existing approaches to evaluating performance of NLP models. A single aggregate statistic, like accuracy, makes it difficult to estimate where the model is failing and how to fix it. The alternative evaluation approaches usually focus on individual tasks or specific capabilities. To address the lack of comprehensive evaluation approaches, the researchers introduce CheckList, a new evaluation methodology for testing of NLP models. The approach is inspired by principles of behavioral testing in software engineering. Basically, CheckList is a matrix of linguistic capabilities and test types that facilitates test ideation. Multiple user studies demonstrate that CheckList is very effective at discovering actionable bugs, even in extensively tested NLP models.

What’s the core idea of this paper?

• Existing approaches to evaluation of NLP models have many significant shortcomings:
  • The primary approach to the evaluation of models’ generalization capabilities, which is accuracy on held-out data, may lead to performance overestimation, as the held-out data often contains the same biases as the training data. Moreover, this single aggregate statistic doesn’t help much in figuring out where the NLP model is failing and how to fix these bugs.
  • The alternative approaches are usually designed for evaluation of specific behaviors on individual tasks and thus, lack comprehensiveness.
• To address this problem, the research team introduces CheckList, a new methodology for evaluating NLP models, inspired by the behavioral testing in software engineering:
  • CheckList provides users with a list of linguistic capabilities to be tested, like vocabulary, named entity recognition, and negation.
  • Then, to break down potential capability failures into specific behaviors, CheckList suggests different test types, such as prediction invariance or directional expectation tests in case of certain perturbations.
  • Potential tests are structured as a matrix, with capabilities as rows and test types as columns.
• The suggested implementation of CheckList also introduces a variety of abstractions to help users generate large numbers of test cases easily.

What’s the key achievement?

• Evaluation of state-of-the-art models with CheckList demonstrated that even though some NLP tasks are considered “solved” based on accuracy results, the behavioral testing highlights many areas for improvement.
• Applying CheckList to an extensively tested public-facing system for sentiment analysis showed that this methodology:
  • helps to identify and test for capabilities not previously considered;
  • results in more thorough and comprehensive testing for previously considered capabilities;
  • helps to discover many more actionable bugs.

What does the AI community think?

• The paper received the Best Paper Award at ACL 2020, the leading conference in natural language processing.

What are possible business applications?

• CheckList can be used to create more exhaustive testing for a variety of NLP tasks.
• Such comprehensive testing that helps in identifying many actionable bugs is likely to lead to more robust NLP systems.

Where can you get implementation code?

• The code for testing NLP models with CheckList is available on GitHub.

7. EfficientDet: Scalable and Efficient Object Detection, by Mingxing Tan, Ruoming Pang, Quoc V. Le

Original Abstract 

Model efficiency has become increasingly important in computer vision. In this paper, we systematically study neural network architecture design choices for object detection and propose several key optimizations to improve efficiency. First, we propose a weighted bi-directional feature pyramid network (BiFPN), which allows easy and fast multi-scale feature fusion; Second, we propose a compound scaling method that uniformly scales the resolution, depth, and width for all backbone, feature network, and box/class prediction networks at the same time. Based on these optimizations and EfficientNet backbones, we have developed a new family of object detectors, called EfficientDet, which consistently achieve much better efficiency than prior art across a wide spectrum of resource constraints. In particular, with single-model and single-scale, our EfficientDet-D7 achieves state-of-the-art 52.2 AP on COCO test-dev with 52M parameters and 325B FLOPs, being 4×–9× smaller and using 13×–42× fewer FLOPs than previous detectors. Code is available on https://github.com/google/automl/tree/master/efficientdet.

Our Summary 

The large size of object detection models deters their deployment in real-world applications such as self-driving cars and robotics. To address this problem, the Google Research team introduces two optimizations, namely (1) a weighted bi-directional feature pyramid network (BiFPN) for efficient multi-scale feature fusion and (2) a novel compound scaling method. By combining these optimizations with the EfficientNet backbones, the authors develop a family of object detectors, called EfficientDet. The experiments demonstrate that these object detectors consistently achieve higher accuracy with far fewer parameters and multiply-adds (FLOPs).

What’s the core idea of this paper?

• To improve the efficiency of object detection models, the authors suggest:
  • A weighted bi-directional feature pyramid network (BiFPN) for easy and fast multi-scale feature fusion. It learns the importance of different input features and repeatedly applies top-down and bottom-up multi-scale feature fusion.
  • A new compound scaling method for simultaneous scaling of the resolution, depth, and width for all backbone, feature network, and box/class prediction networks.
• These optimizations, together with the EfficientNet backbones, allow the development of a new family of object detectors, called EfficientDet.

What’s the key achievement?

• The evaluation demonstrates that EfficientDet object detectors achieve better accuracy than previous state-of-the-art detectors while having far fewer parameters, in particular:
  • the EfficientDet model with 52M parameters gets state-of-the-art 52.2 AP on the COCO test-dev dataset, outperforming the previous best detector with 1.5 AP while being 4× smaller and using 13× fewer FLOPs;
  • with simple modifications, the EfficientDet model achieves 81.74% mIOU accuracy, outperforming DeepLabV3+ by 1.7% on Pascal VOC 2012 semantic segmentation with 9.8x fewer FLOPs;
  • the EfficientDet models are up to 3× to 8× faster on GPU/CPU than previous detectors.

What does the AI community think?

• The paper was accepted to CVPR 2020, the leading conference in computer vision.
• The high level of interest in the code implementations of this paper makes this research one of the highest-trending papers introduced recently.

What are possible business applications?

• The high accuracy and efficiency of the EfficientDet detectors may enable their application for real-world tasks, including self-driving cars and robotics.

Where can you get implementation code?

• The authors released the official TensorFlow implementation of EfficientDet.
• The PyTorch implementation of this paper can be found here and here.

8. Unsupervised Learning of Probably Symmetric Deformable 3D Objects from Images in the Wild, by Shangzhe Wu, Christian Rupprecht, Andrea Vedaldi

Original Abstract 

We propose a method to learn 3D deformable object categories from raw single-view images, without external supervision. The method is based on an autoencoder that factors each input image into depth, albedo, viewpoint and illumination. In order to disentangle these components without supervision, we use the fact that many object categories have, at least in principle, a symmetric structure. We show that reasoning about illumination allows us to exploit the underlying object symmetry even if the appearance is not symmetric due to shading. Furthermore, we model objects that are probably, but not certainly, symmetric by predicting a symmetry probability map, learned end-to-end with the other components of the model. Our experiments show that this method can recover very accurately the 3D shape of human faces, cat faces and cars from single-view images, without any supervision or a prior shape model. On benchmarks, we demonstrate superior accuracy compared to another method that uses supervision at the level of 2D image correspondences.

Our Summary 

The research group from the University of Oxford studies the problem of learning 3D deformable object categories from single-view RGB images without additional supervision. To decompose the image into depth, albedo, illumination, and viewpoint without direct supervision for these factors, they suggest starting by assuming objects to be symmetric. Then, considering that real-world objects are never fully symmetrical, at least due to variations in pose and illumination, the researchers augment the model by explicitly modeling illumination and predicting a dense map with probabilities that any given pixel has a symmetric counterpart. The experiments demonstrate that the introduced approach achieves better reconstruction results than other unsupervised methods. Moreover, it outperforms the recent state-of-the-art method that leverages keypoint supervision.

What’s the core idea of this paper?

• The goal of the introduced approach is to reconstruct the 3D pose, shape, albedo, and illumination of a deformable object from a single RGB image under two challenging conditions:
  • no access to 2D or 3D ground truth information such as keypoints, segmentation, depth maps, or prior knowledge of a 3D model;
  • using an unconstrained collection of single-view images without having multiple views of the same instance.
• To achieve this goal, the researchers suggest:
  • leveraging symmetry as a geometric cue to constrain the decomposition;
  • explicitly modeling illumination and using it as an additional cue for recovering the shape;
  • augmenting the model to account for potential lack of symmetry – particularly, predicting a dense map that contains the probability of a given pixel having a symmetric counterpart in the image.

What’s the key achievement?

• Qualitative evaluation of the suggested approach demonstrates that it reconstructs 3D faces of humans and cats with high fidelity, containing fine details of the nose, eyes, and mouth.
• The method reconstructs higher-quality shapes compared to other state-of-the-art unsupervised methods, and even outperforms the DepthNet model, which uses 2D keypoint annotations for depth prediction.

What does the AI community think?

• The paper received the Best Paper Award at CVPR 2020, the leading conference in computer vision.

What are future research areas?

• Reconstructing more complex objects by extending the model to use either multiple canonical views or a different 3D representation, such as a mesh or a voxel map.
• Improving model performance under extreme lighting conditions and for extreme poses.

Where can you get implementation code?

• The implementation code and demo are available on GitHub.

9. An Image is Worth 16×16 Words: Transformers for Image Recognition at Scale, by Alexey Dosovitskiy, Lucas Beyer, Alexander Kolesnikov, Dirk Weissenborn, Xiaohua Zhai, Thomas Unterthiner, Mostafa Dehghani, Matthias Minderer, Georg Heigold, Sylvain Gelly, Jakob Uszkoreit, Neil Houlsby

Original Abstract 

While the Transformer architecture has become the de-facto standard for natural language processing tasks, its applications to computer vision remain limited. In vision, attention is either applied in conjunction with convolutional networks, or used to replace certain components of convolutional networks while keeping their overall structure in place. We show that this reliance on CNNs is not necessary and a pure transformer can perform very well on image classification tasks when applied directly to sequences of image patches. When pre-trained on large amounts of data and transferred to multiple recognition benchmarks (ImageNet, CIFAR-100, VTAB, etc.), Vision Transformer attain excellent results compared to state-of-the-art convolutional networks while requiring substantially fewer computational resources to train.

Our Summary 

The authors of this paper show that a pure Transformer can perform very well on image classification tasks. They introduce Vision Transformer (ViT), which is applied directly to sequences of image patches by analogy with tokens (words) in NLP. When trained on large datasets of 14M–300M images, Vision Transformer approaches or beats state-of-the-art CNN-based models on image recognition tasks. In particular, it achieves an accuracy of 88.36% on ImageNet, 90.77% on ImageNet-ReaL, 94.55% on CIFAR-100, and 77.16% on the VTAB suite of 19 tasks.

What’s the core idea of this paper?

• When applying Transformer architecture to images, the authors follow as closely as possible the design of the original Transformer designed for NLP.
• The introduced Transformer-based approach to image classification includes the following steps:
  • splitting images into fixed-size patches;
  • linearly embedding each of them;
  • adding position embeddings to the resulting sequence of vectors;
  • feeding the patches to a standard Transformer encoder;
  • adding an extra learnable ‘classification token’ to the sequence.
• Similarly to Transformers in NLP, Vision Transformer is typically pre-trained on large datasets and fine-tuned to downstream tasks.

What’s the key achievement?

• Vision Transformer pre-trained on the JFT300M dataset matches or outperforms ResNet-based baselines while requiring substantially less computational resources to pre-train. It achieves an accuracy of:
  • 88.36% on ImageNet; 
  • 90.77% on ImageNet-ReaL; 
  • 94.55% on CIFAR-100; 
  • 97.56% on Oxford-IIIT Pets;
  • 99.74% on Oxford Flowers-102;
  • 77.16% on the VTAB suite of 19 tasks.

What does the AI community think?

• The paper is trending in the AI research community, as evident from the repository stats on GitHub.
• It is also under review for ICLR 2021, one of the key conferences in deep learning.

What are future research areas?

• Applying Vision Transformer to other computer vision tasks, such as detection and segmentation.
• Exploring self-supervised pre-training methods.
• Analyzing the few-shot properties of Vision Transformer.
• Exploring contrastive pre-training.
• Further scaling ViT.

What are possible business applications?

• Thanks to their efficient pre-training and high performance, Transformers may substitute convolutional networks in many computer vision applications, including navigation, automatic inspection, and visual surveillance.

Where can you get implementation code?

• The PyTorch implementation of Vision Transformer is available on GitHub.

10. AdaBelief Optimizer: Adapting Stepsizes by the Belief in Observed Gradients, by Juntang Zhuang, Tommy Tang, Sekhar Tatikonda, Nicha Dvornek, Yifan Ding, Xenophon Papademetris, James S. Duncan

Original Abstract 

Most popular optimizers for deep learning can be broadly categorized as adaptive methods (e.g. Adam) or accelerated schemes (e.g. stochastic gradient descent (SGD) with momentum). For many models such as convolutional neural networks (CNNs), adaptive methods typically converge faster but generalize worse compared to SGD; for complex settings such as generative adversarial networks (GANs), adaptive methods are typically the default because of their stability. We propose AdaBelief to simultaneously achieve three goals: fast convergence as in adaptive methods, good generalization as in SGD, and training stability. The intuition for AdaBelief is to adapt the step size according to the “belief” in the current gradient direction. Viewing the exponential moving average (EMA) of the noisy gradient as the prediction of the gradient at the next time step, if the observed gradient greatly deviates from the prediction, we distrust the current observation and take a small step; if the observed gradient is close to the prediction, we trust it and take a large step. We validate AdaBelief in extensive experiments, showing that it outperforms other methods with fast convergence and high accuracy on image classification and language modeling. Specifically, on ImageNet, AdaBelief achieves comparable accuracy to SGD. Furthermore, in the training of a GAN on Cifar10, AdaBelief demonstrates high stability and improves the quality of generated samples compared to a well-tuned Adam optimizer. Code is available at https://github.com/juntang-zhuang/Adabelief-Optimizer.

Our Summary 

The researchers introduce AdaBelief, a new optimizer, which combines the high convergence speed of adaptive optimization methods and good generalization capabilities of accelerated stochastic gradient descent (SGD) schemes. The core idea behind the AdaBelief optimizer is to adapt step size based on the difference between predicted gradient and observed gradient: the step is small if the observed gradient deviates significantly from the prediction, making us distrust this observation, and the step is large when the current observation is close to the prediction, making us believe in this observation. The experiments confirm that AdaBelief combines fast convergence of adaptive methods, good generalizability of the SGD family, and high stability in the training of GANs.

What’s the core idea of this paper?

• The idea of the AdaBelief optimizer is to combine the advantages of adaptive optimization methods (e.g., Adam) and accelerated SGD optimizers. Adaptive methods typically converge faster, while SGD optimizers demonstrate better generalization performance.
• The intuition for AdaBelief is to adapt the step size based on how much we can trust in the current gradient direction:
  • If the observed gradient deviates greatly from the prediction, we have a weak belief in this observation and take a small step.
  • If the observed gradient is close to the prediction, we have a strong belief in this observation and take a large step.

What’s the key achievement?

• The AdaBelief Optimizer has three key properties:
  • fast convergence, like adaptive optimization methods;
  • good generalization, like the SGD family;
  • training stability in complex settings such as GAN.
• These properties are validated with extensive experiments:
  • In image classification tasks on CIFAR and ImageNet, AdaBelief demonstrates as fast convergence as Adam and as good generalization as SGD.
  • It outperforms other methods in language modeling.
  • In the training of a WGAN, AdaBelief significantly improves the quality of generated images compared to Adam.

What does the AI community think?

• The paper was accepted to NeurIPS 2020, the top conference in artificial intelligence.
• It is also trending in the AI research community, as evident from the repository stats on GitHub.

What are possible business applications?

• AdaBelief can boost the development and application of deep learning models as it can be applied to the training of any model that numerically estimates parameter gradient. 

Where can you get implementation code?

• Both PyTorch and Tensorflow implementations are released on GitHub.

If you like these research summaries, you might be also interested in the following articles:

• GPT-3 & Beyond: 10 NLP Research Papers You Should Read
• Novel Computer Vision Research Papers From 2020
• AAAI 2021: Top Research Papers With Business Applications
• ICLR 2021: Key Research Papers

Enjoy this article? Sign up for more AI research updates.

We’ll let you know when we release more summary articles like this one.