Synthesizing photo-realistic images is of crucial importance for a large variety of applications, including movies, telepresence, design visualizations, or training simulators. New technologies such as virtual and augmented reality require high-quality renderings at high frame rates, which poses a tremendous challenge for the design of rendering algorithms. Traditionally, this challenge has been attacked either by simulating light transport from physical first principles, or by re-using existing images to create new views. In recent years, data-driven techniques have risen as a third pillar in the space of rendering algorithms. All approaches have their distinct pros and cons, giving rise to a continuum of hybrid algorithms trying to merge the best of the three worlds. In this talk, I will give an overview over this continuum, with an emphasis on our more recent work, which seeks to reconcile image quality, rendering efficiency, and controllability.

In this presentation, I will talk about some of the recent work we did on new methods for reconstructing computer graphics models of real world scenes from sparse or even monocular video data. These methods are based of bringing together neural network-based and explicit model-based approaches.

I will also talk about new neural rendering approaches that combine explicit model-based and neural network based concepts for image formation in new ways. They enable new means to synthesize highly realistic imagery and videos of real work scenes under user control.

Indisputably, the Web has revolutionized the way people receive, consume, and interact with information. At the same time, unfortunately, the Web offers a fertile ground for amplifying socio-technical issues like the spread of hateful content and false information; hence there is a pressing need to develop techniques and tools to understand, detect, and mitigate these issues on the Web. In this talk, I will present our data-driven quantitative approach towards understanding such emerging socio-technical problems, focusing on the spread of hateful content targeting specific demographic groups. Also, I will present our work on understanding mitigation strategies employed by social networks (i.e., moderation interventions) and assessing their effectiveness towards reducing the prevalence and impact of these issues on the Web.

Computational social choice is an interdisciplinary field that studies collective decision making from an algorithmic perspective. Determining the winners under various voting rules is a mainstream area of research in computational social choice. Many such rules assume that the voters provide complete information about their preferences, an assumption that is often unrealistic because typically only partial preference information is available.  This state of affairs has motivated the study of the notions of the necessary winners and the possible winners with respect to a variety of voting rules.

The main aim of this talk is to present an overview of winner determination under incomplete information and to highlight some recent advances in this area, including the development of a framework that aims to create bridges between computational social choice and data management. This framework infuses relational database context into social choice and allows for the formulation of sophisticated queries about voting rules, candidates, winners, issues, and positions on issues. We will introduce the necessary answer semantics and the possible answer semantics to queries and will explore the computational complexity of query evaluation under these semantics.

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Program termination is a key question in program verification. This talk considers the termination of probabilistic programs, programs that can describe e.g., randomized algorithms, security algorithms and Bayesian learning.

Probabilistic termination has several nuances. Diverging program runs may occur with probability zero. Such programs are almost surely terminating (AST). If the expected duration until termination is finite, they are positive AST.

This talk presents a simple though powerful proof rule for deciding AST, reports on recent approaches towards automation, and sketches a Dijkstra-like weakest precondition calculus for proving positive AST in a compositional way.

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Cyber-physical systems (CPSs) combine cyber capabilities, such as computation or communication, with physical capabilities, such as motion or other physical processes. Cars, aircraft, and robots are prime examples, because they move physically in space in a way that is determined by discrete computerized control algorithms. Designing these algorithms is challenging due to their tight coupling with physical behavior, while it is vital that these algorithms be correct because we rely on them for safety-critical tasks.

This talk highlights some of the most fascinating aspects of the logical foundations for developing cyber-physical systems with the mathematical rigor that their safety-critical nature demands. The underlying logic, differential dynamic logic, provides an integrated specification and verification language for dynamical systems, such as hybrid systems that combine discrete transitions and continuous evolution along differential equations.

In addition to providing a strong theoretical foundation for CPS, differential dynamic logics have been instrumental in verifying many applications, including the Airborne Collision Avoidance System ACAS X, the European Train Control System ETCS, automotive systems, mobile robot navigation, and a surgical robotic system for skull-base surgery. Logic is the foundation to provably transfer safety guarantees about models to CPS implementations. This technology is also the key ingredient behind Safe AI for CPS.

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An ever-increasing amount of data to be analyzed raises novel challenges for the theory of computation. How can we prove computational difficulty of a seemingly simple task when facing enormous data sets? Developing such methods is essential for determining which problems can or cannot be solved at a large scale.

Fine-grained complexity theory in P provides corresponding methods by establishing tight connections between fundamental algorithmic problems. In particular, we show that many natural sequence comparison problems cannot be solved in truly subquadratic time, assuming a stronger version of the famous P ≠ NP conjecture. These results give rigorous insights into the challenges encountered, e.g., in the context of genome comparison, and even aid in developing novel efficient algorithms.

Despite such early successes, this young theory is still in its infancy: In particular, most of the current results establish connections between isolated algorithmic problems, rather than between classes of problems. Can we establish a more encompassing theory and turn the current problem-centric state of the art to a full-fledged structural complexity theory for large data sets? Towards this end, we discuss a quest for completeness and classification theorems (inspired by a finite-model-theoretic approach and the Dichotomy Theorem for constraint satisfaction problems), and present promising initial results.

The Internet was meant to be neutral: treat all traffic the same, without discriminating in favor of specific apps, sites, or services. As commercial interests threaten this ideal, many countries have introduced neutrality regulations. Unfortunately, none of them are actually enforceable. In this talk, I will first discuss the challenge of inferring whether a network is neutral or not using solely external observations. Then, I will show that we can go beyond neutrality inference and reach network transparency, in which networks provide explicit hints that enable their users to reliably assess network behavior, including neutrality. Network transparency, however, requires exposing information about what traffic is seen where and when, which can hurt user privacy. I will close by looking at the important question of whether network transparency indeed must come at the cost of reduced anonymity for Internet users.

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Don't we all dream of the perfect assistant whom we can just tell what to do and the assistant can figure out how to accomplish the tasks? Formally, given a specification F(X,Y) over the set of input variables X and output variables Y, we want the assistant, aka functional synthesis engine, to design a function G such that (X,Y=G(X)) satisfies F. Functional synthesis has been studied for over 150 years, dating back Boole in 1850's and yet scalability remains a core challenge. Motivated by progress in machine learning, we design a new algorithmic framework Manthan, which views functional synthesis as a classification problem, relying on advances in constrained sampling for data generation, and advances in automated reasoning for a novel proof-guided refinement and provable verification. On an extensive and rigorous evaluation over 609 benchmarks, we demonstrate that Manthan significantly improves upon the current state of the art, solving 356 benchmarks in comparison to 280, which is the most solved by a state of the art technique; thereby, we demonstrate an increase of 76 benchmarks over the current state of the art. The significant performance improvements, along with our detailed analysis, highlights several interesting avenues of future work at the intersection of machine learning, constrained sampling, and automated reasoning.

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We are seeing a persistent gap between the theoretical security of e.g. cryptographic algorithms and real world vulnerabilities, data-breaches and possible attacks. Software developers – despite being computer experts – are rarely security experts, and security and privacy are usually, at best, of secondary importance for them. They may not have training in security and privacy or even be aware of the possible implications, and they may be unable to allocate time or effort to ensure that security and privacy best practices and design principles are upheld for their end users. Understanding their education and mindsets, their processes, the tools that they use, and their pitfalls are the foundation for shifting development practices to be more secure. This talk will give an overview of security challenges for developers, and interdisciplinary research avenues to address these.

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To establish software security at scale, we need efficient automated vulnerability discovery techniques that can run on thousands of machines. In this talk, we will discuss the abundant opportunities and fundamental limitations of fuzzing, one of the most successful vulnerability discovery techniques. We will explore why only an exponential number of machines will allow us to discover software bugs at a linear rate. We will discuss the kind of correctness guarantees that we can expect from automatic vulnerability discovery, anywhere from formally proving the absence of bugs to statistical claims about program correctness. We shall touch upon unexpected connections to ecological biostatistics and information theory which allow us to address long-standing scientific and practical problems in automatic software testing. Finally, we will take a forward looking view and discuss our larger vision for the field of software security.

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Software is everywhere, and almost everywhere, software is broken. Some bugs just crash your printer; others hand an identity thief your bank account number; still others let nation-states spy on dissidents and persecute minorities. This talk outlines my work preventing bugs using a blend of programming languages techniques and systems design. First, I'll talk about securing massive, security-critical codebases without clean slate rewrites. This means rooting out hard-to-find bugs---as in Sys, which scales symbolic execution to find exploitable bugs in systems like the twenty-million line Chrome browser. It also means proving correctness of especially vulnerable pieces of code---as in VeRA, which automatically verifies part of the Firefox JavaScript engine. Finally, I'll discuss work on stronger foundations for new systems---as in CirC, a recent project unifying compiler infrastructure for program verification, cryptographic proofs, optimization problems, and more.

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Building intelligent visual systems is essential for the next generation of artificial intelligence systems. It is a fundamental tool for many disciplines and beneficial to various potential applications such as autonomous driving, robotics, surveillance, augmented reality, to name a few. An accurate and efficient intelligent visual system has a deep understanding of the scene, objects, and humans. It can automatically understand the surrounding scenes. In general, 2D images and 3D point clouds are the two most common data representations in our daily life. Designing powerful image understanding and point cloud processing systems are two pillars of visual intelligence, enabling the artificial intelligence systems to understand and interact with the current status of the environment automatically. In this talk, I will first present our efforts in designing modern neural systems for 2D image understanding, including high-accuracy and high-efficiency semantic parsing structures, and unified panoptic parsing architecture. Then, we go one step further to design neural systems for processing complex 3D scenes, including semantic-level and instance-level understanding. Further, we show our latest works for unified 2D-3D reasoning frameworks, which are fully based on self-attention mechanisms. In the end, the challenges, up-to-date progress, and promising future directions for building advanced intelligent visual systems will be discussed.

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Satisfying the growing demand for more compute as processor performance continues to stagnate in the post-Moore era requires radical changes throughout the systems stack. A proven strategy is to move from today’s general purpose platforms to post-Moore systems, specialized systems comprising tightly integrated and co-designed hardware and software components. Currently, designing and implementing these systems is a complex, laborious, and risky process, accessible to few and only practical for the most computing intensive applications. In this talk, I discuss the nascent challenges in building post-Moore systems and illustrate them through specific systems I have built. As a first step to address these challenges, I present Simbricks, a modular simulation framework that flexibly combines existing simulators for computers, custom hardware, and networks, into complete virtual post-Moore systems, enabling developers to compare and evaluate designs earlier and quicker. I conclude with a look towards future opportunities in abstractions, tooling, and methodology to further simplify the development of post-Moore systems.



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Model checking is an automatic approach for testing and verifying programs, and has proven to be very effective in a number of settings ranging from hardware designs to intricate low-level systems software. In this talk, I will present our recent research on applying model checking to weakly consistent concurrent programs. I will explain the key challenges involved in making model checking effective in this setting and how to address them.

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In this talk, I will describe a distributionally robust learning framework that offers accurate uncertainty quantification and rigorous guarantees under data distribution shift. This framework yields appropriately conservative yet still accurate predictions to guide real-world decision-making and is easily integrated with modern deep learning. I will showcase the practicality of this framework in applications on agile robotic control and computer vision. I will also introduce a survey of other real-world applications that would benefit from this framework for future work.

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To create trustworthy AI systems, we must safeguard machine learning methods from catastrophic failures. For example, we must account for the uncertainty and guarantee the performance for safety-critical systems, like in autonomous driving and health care, before deploying them in the real world. A key challenge in such real-world applications is that the test cases are not well represented by the pre-collected training data. To properly leverage learning in such domains, we must go beyond the conventional learning paradigm of maximizing average prediction accuracy with generalization guarantees that rely on strong distributional relationships between training and test examples. In this talk, I will describe a distributionally robust learning framework that offers accurate uncertainty quantification and rigorous guarantees under data distribution shift. This framework yields appropriately conservative yet still accurate predictions to guide real-world decision-making and is easily integrated with modern deep learning. I will showcase the practicality of this framework in applications on agile robotic control and computer vision. I will also introduce a survey of other real-world applications that would benefit from this framework for future work.

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Despite the phenomenal empirical successes of deep learning in many application domains, its underlying mathematical mechanisms remain poorly understood. Mysteriously, deep neural networks in practice can often fit training data perfectly and generalize remarkably well to unseen test data, despite highly non-convex optimization landscapes and significant over-parameterization. Moreover, deep neural networks show extraordinary ability to perform representation learning: feature representation extracted from a trained neural network can be useful for other related tasks.

In this talk, I will present our recent progress on building the theoretical foundations of deep learning, by opening the black box of the interactions among data, model architecture, and training algorithm. First, I will show that gradient descent on deep linear neural networks induces an implicit regularization effect towards low rank, which explains the surprising generalization behavior of deep linear networks for the low-rank matrix completion problem. Next, turning to nonlinear deep neural networks, I will talk about a line of studies on wide neural networks, where by drawing a connection to the neural tangent kernels, we can answer various questions such as how training loss is minimized, why trained network can generalize, and why certain component in the network architecture is useful; we also use theoretical insights to design a new simple and effective method for training on noisily labeled datasets. Finally, I will analyze the statistical aspect of representation learning, and identify key data conditions that enable efficient use of training data, bypassing a known hurdle in the i.i.d. tasks setting.

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Failures of machine learning systems can threaten both the security and privacy of their users. My research studies these failures from an adversarial perspective, by building new attacks that highlight critical vulnerabilities in the machine learning pipeline, and designing new defenses that protect users against identified threats. In the first part of this talk, I'll explain why machine learning models are so vulnerable to adversarially chosen inputs. I'll show that many proposed defenses are ineffective and cannot protect models deployed in overtly adversarial settings, such as for content moderation on the Web. In the second part of the talk, I'll focus on the issue of data privacy in machine learning systems, and I'll demonstrate how to enhance privacy by combining techniques from cryptography, statistics, and computer security.

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Software bugs are pervasive and costly.  As a result, developers spend the majority of their time debugging their software.  Traditionally, debugging involves inspecting and tracking the runtime behavior of a program.  Alas, program inspection is computationally expensive, especially when employing powerful techniques such as dynamic information flow tracking, data-race detection, and data structure invariant checks.  Moreover, debugging logic is difficult to specify correctly.  Current tools (e.g., gdb, Intel Pin) allow developers to write debugging logic in an imperative inline programming model that mirrors the programming style of traditional software.  So, debugging logic faces the same challenges as traditional software, including concurrency, fault handling, dynamic memory, and extensibility.  In general, specifying debugging logic can be as difficult as writing the program being debugged!

In this talk, I will describe a new data-centric debugging framework that alleviates the performance and specification limitations of current debugging models.  The key idea is to use deterministic record and replay to treat a program execution as a massive data object consisting of all program states reached during the execution.  In this framework, developers can express common debugging tasks (e.g., tracking the value of a variable) and dynamic analyses (e.g., data-race detection) as queries over an execution's data object.  My research explores how a data-centric model enables large-scale parallelism to accelerate debugging queries (JetStream and SledgeHammer) and relational query models to simplify the specification of debugging logic (SledgeHammer and the OmniTable Query Model).

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Conversations are central to our social systems. Understanding how conversationalists navigate through them could unlock great improvements in domains like public health, where the provision of social support is crucial. To this end, I develop computational frameworks that can capture and systematically examine aspects of conversations that are difficult, interesting and meaningful for conversationalists and the jobs they do. Importantly, these frameworks aim to yield actionable understandings—ones that reflect the choices that conversationalists make and their consequences, beyond the inert linguistic patterns that are produced in the interaction.

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Graphs are widespread models for relations between entities. One of the fundamental problems when dealing with graphs is to decide isomorphism, i.e., to check whether two graphs are structurally identical. Even after decades of research, the quest for an efficient graph-isomorphism test still continues. In this talk, I will discuss the Weisfeiler-Leman (WL) algorithm as a powerful combinatorial procedure to approach the graph-isomorphism problem. The algorithm can be seen as a link between many research areas (the ""WL net""), including, for example, descriptive complexity theory, propositional proof complexity, and machine learning. I will present work regarding the two central parameters of the algorithm – its dimension and the number of iterations – and explore their connection to finite-model theory. I will also touch on some past and ongoing projects in other areas from the WL net.

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Deep learning today is successful in almost any domain of computer vision. The talk will revisit the seminal work of FlowNet to show how deep learning was applied to optical flow and led to a paradigm shift in this domain. Optical flow, disparity, motion and depth boundaries as well as uncertainty estimation with multi-hypothesis networks will be covered and it will be discussed how deep learned models could surpass traditional methods. Asking the more fundamental question what models we need in computer vision, the talk will then progress to recent deep-learned scene representation approaches such as the ones obtained by learned signed distance functions and NeRF and provide a perspective on how computer vision might change in the future.

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The success of today's hardware and software systems is due in part to a mature toolbox of techniques, like abstraction, that systems designers use to manage complexity. While powerful, these techniques are also subtly dangerous: they induce implicit trust relationships among system components and between related systems, presenting attackers with many opportunities to undermine the integrity of our hardware and software. This talk discusses an approach to building systems with precise control over trust, drawing on techniques from theoretical computer science. Making this approach practical is a challenge that requires innovation across the entire technology stack, from hardware to theory. I will present several examples of such innovations from my research and describe a few potential directions for future work.

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Data is now everywhere: enormous amounts of data are produced and processed every day. Data is gathered,exchanged, and used extensively in computations that serve many purposes: e.g., computing statistics on populations, refining bidding strategies in ad auctions, improving recommendation systems, and making loan or hiring decisions. Yet, data is not always transacted and processed in a responsible manner. Data collection often happens without the data holders' consent, who may also not be compensated for their data. Privacy leaks are numerous, exhibiting a need for better privacy protections on personal and sensitive data. Data-driven machine learning and decision making algorithms have been shown to both mimic past bias and to introduce additional bias in their predictions, leading to inequalities and discrimination. In this talk, I will focus on my research on using data in a more responsible manner. The main focus of the talk will be on my work on the privacy issues that arise in data transactions and data-driven analysis, under the lens of a framework known as differential privacy. I will go over my work on designing transactions for data where we provide differential privacy guarantees to the individuals whose sensitive data we are buying and using in computations, and will focus on my recent work on providing differential privacy to agents in auction settings, where it is natural to want to protect the valuations and bids of said agents. I will also give a brief overview of the other directions that I have followed in my research, both on the optimization and economic challenges that arise when letting agents opt in and out of data sharing and compensating them sufficiently for their data contributions, and on how to reduce the disparate and discriminatory impact of data-driven decision-making.

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The network stack in today's operating systems is a remnant from a time when a server had a handful of cores and processed requests from a few thousand clients. It simply cannot keep up with the scale of modern servers and the requirements of modern applications. Specifically, real-time applications and high user expectations enforce strict performance requirements on the infrastructure. Further, there is a fundamental shift in the way hardware capacity scales from simply relying on Moore's law to deliver faster hardware every couple of years to leveraging parallel processing and task-specific accelerators. This talk covers innovations in three key components of the network stack. First, I will cover my work on scalable packet scheduling in software network stacks, improving the control of traffic outgoing from large-scale servers. Second, I will move on to my work on improving overload control for servers handling microsecond-scale remote procedure calls, providing better control over incoming traffic to large-scale servers. Then, the talk covers my work on Wide Area Network (WAN) congestion control, focusing on network-assisted congestion control schemes, where end-to-end solutions fail. The talk will conclude with a discussion of plans for future research in this area.

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Several major innovations in artificial intelligence (AI) (e.g. convolutional neural networks, experience replay) are based on findings about the brain. However, the underlying brain findings took many years to first consolidate and many more to transfer to AI. Moreover, these findings were made using invasive methods in non-human species. For cognitive functions that are uniquely human, such as natural language processing, there is no suitable model organism and a mechanistic understanding is that much farther away. In this talk, I will present my research program that circumvents these limitations by establishing a direct connection between the human brain and AI systems with two main goals: 1) to improve the generalization performance of AI systems and 2) to improve our mechanistic understanding of cognitive functions. Lastly, I will discuss future directions that build on these approaches to investigate the role of memory in meaning composition, both in the brain and AI. This investigation will lead to methods that can be applied to a wide range of AI domains, in which it is important to adapt to new data distributions, continually learn to perform new tasks, and learn from few samples.

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This talk reports Facebook's experience of managing the backbone network during the COVID-19 crisis. Our philosophy centers around "risk prevention" to identify potential failures in the network and mitigate their effects. We define metrics for network risk and quantify the impact of COVID-19 with them. We also describe a risk assessment system that has been in production for three years, which involves accurate failure modeling and efficient risk simulation. With ten months of assessment results, we claim our backbone to be robust against the COVID-19 stress test, achieving high service availability and low routing dilation. We share our operational measures to minimize possible traffic loss. Surprising findings during this period give us insights to further improve our approach. First, we observe a substantial reduction of optical failures because of less human activity, which inspires failure prediction to trade model stability for agility by considering short-term failure statistics when necessary. Second, we find a negative correlation between network traffic and human mobility, indicating non- networking signals traditionally ignored can be used for better network management.

LLVM is an industrial-strength compiler that's used for everything from day-to-day iOS development (in Swift) to pie-in-the-sky academic research projects. This makes the LLVM framework a sweet spot for bug-finding and verification technologies--any improvements to it are amplified across its many applications.

This talk asks the question: what does LLVM code _mean_, and, how can we ensure that LLVM-based tools (compilers, optimizers, code instrumentation passes, etc.) do what they're supposed to -- especially for safety- or security-critical applications? The Verified LLVM project (Vellvm) is our attempt to provide an answer. Vellvm gives a semantics to LLVM IR programs in the Coq interactive theorem prover, which can be used for developing machine-checkable formal properties about LLVM IR programs and transformation passes.

Our approach to modeling LLVM IR semantics uses _interaction trees_, a data structure that is suitable for representing impure, possibly nonterminating programs in dependent type theory. Interaction trees support compositional and modular reasoning about program semantics but are also executable, and hence useful for implementation and testing. We'll see how interaction trees are used in Vellvm and, along the way, we'll get a taste of what LLVM code looks like including some of its trickier semantic aspects. We'll also see (at a high level) how modern interactive theorem provers--in this case, Coq--can be used to verify compiler transformations.

No experience with LLVM or formal verification technologies will be assumed.

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The pivotal role of software in our modern world imposes strong requirements on quality, correctness, and reliability of software systems. The ability to understand program code plays a key role for programmers to fulfill these requirements. Despite significant progress, research on program comprehension has had a fundamental limitation: program comprehension is a cognitive process that cannot be directly observed, which leaves considerable room for (mis)interpretation, uncertainty, and confounding factors. Thus, central questions such as "What makes a good programmer?" and "How should we program?" are surprisingly difficult to answer based on the state of the art.

In this talk, I will report on recent attempts to lift research on program comprehension to a new level. The key idea is to leverage methods from cognitive neuroscience to obtain insights into the cognitive processes involved in program comprehension. Opening the "black box" of human cognition will lead to a breakthrough in understanding the why and how of program comprehension and to a completely new perspective and methodology of measuring program comprehension, with direct implications for programming methodology, language design, and education.