When deep learning models are deployed in the true world, perhaps to detect financial fraud from bank card activity or discover cancer in medical images, they are sometimes in a position to outperform humans.
But what exactly are these deep learning models learning? Does a model trained to identify skin cancer in clinical images, for instance, actually learn the colours and textures of cancerous tissue, or is it flagging another features or patterns?
These powerful machine-learning models are typically based on artificial neural networks that may have hundreds of thousands of nodes that process data to make predictions. Attributable to their complexity, researchers often call these models “black boxes” because even the scientists who construct them don’t understand all the things that is occurring under the hood.
Stefanie Jegelka isn’t satisfied with that “black box” explanation. A newly tenured associate professor within the MIT Department of Electrical Engineering and Computer Science, Jegelka is digging deep into deep learning to know what these models can learn and the way they behave, and how you can construct certain prior information into these models.
“At the top of the day, what a deep-learning model will learn depends upon so many aspects. But constructing an understanding that’s relevant in practice will help us design higher models, and likewise help us understand what is occurring inside them so we all know when we will deploy a model and when we will’t. That’s critically necessary,” says Jegelka, who can be a member of the Computer Science and Artificial Intelligence Laboratory (CSAIL) and the Institute for Data, Systems, and Society (IDSS).
Jegelka is especially fascinated about optimizing machine-learning models when input data are in the shape of graphs. Graph data pose specific challenges: As an example, information in the information consists of each details about individual nodes and edges, in addition to the structure — what’s connected to what. As well as, graphs have mathematical symmetries that should be respected by the machine-learning model in order that, as an example, the identical graph at all times results in the identical prediction. Constructing such symmetries right into a machine-learning model will likely be difficult.
Take molecules, as an example. Molecules may be represented as graphs, with vertices that correspond to atoms and edges that correspond to chemical bonds between them. Drug firms will probably want to use deep learning to rapidly predict the properties of many molecules, narrowing down the number they have to physically test within the lab.
Jegelka studies methods to construct mathematical machine-learning models that may effectively take graph data as an input and output something else, on this case a prediction of a molecule’s chemical properties. This is especially difficult since a molecule’s properties are determined not only by the atoms inside it, but in addition by the connections between them.
Other examples of machine learning on graphs include traffic routing, chip design, and recommender systems.
Designing these models is made even harder by the incontrovertible fact that data used to coach them are sometimes different from data the models see in practice. Perhaps the model was trained using small molecular graphs or traffic networks, however the graphs it sees once deployed are larger or more complex.
On this case, what can researchers expect this model to learn, and can it still work in practice if the real-world data are different?
“Your model will not be going to give you the option to learn all the things due to some hardness problems in computer science, but what you may learn and what you may’t learn depends upon the way you set the model up,” Jegelka says.
She approaches this query by combining her passion for algorithms and discrete mathematics along with her excitement for machine learning.
From butterflies to bioinformatics
Jegelka grew up in a small town in Germany and have become fascinated about science when she was a highschool student; a supportive teacher encouraged her to take part in a global science competition. She and her teammates from the U.S. and Hong Kong won an award for a web site they created about butterflies, in three languages.
“For our project, we took images of wings with a scanning electron microscope at a neighborhood university of applied sciences. I also got the chance to make use of a high-speed camera at Mercedes Benz — this camera often filmed combustion engines — which I used to capture a slow-motion video of the movement of a butterfly’s wings. That was the primary time I actually got in contact with science and exploration,” she recalls.
Intrigued by each biology and arithmetic, Jegelka decided to review bioinformatics on the University of Tübingen and the University of Texas at Austin. She had just a few opportunities to conduct research as an undergraduate, including an internship in computational neuroscience at Georgetown University, but wasn’t sure what profession to follow.
When she returned for her final 12 months of faculty, Jegelka moved in with two roommates who were working as research assistants on the Max Planck Institute in Tübingen.
“They were working on machine learning, and that sounded really cool to me. I had to write down my bachelor’s thesis, so I asked on the institute in the event that they had a project for me. I began working on machine learning on the Max Planck Institute and I loved it. I learned a lot there, and it was a terrific place for research,” she says.
She stayed on on the Max Planck Institute to finish a master’s thesis, after which launched into a PhD in machine learning on the Max Planck Institute and the Swiss Federal Institute of Technology.
During her PhD, she explored how concepts from discrete mathematics may help improve machine-learning techniques.
Teaching models to learn
The more Jegelka learned about machine learning, the more intrigued she became by the challenges of understanding how models behave, and how you can steer this behavior.
“You possibly can achieve this much with machine learning, but provided that you’ve the precise model and data. It will not be only a black-box thing where you throw it at the information and it really works. You truly need to give it some thought, its properties, and what you wish the model to learn and do,” she says.
After completing a postdoc on the University of California at Berkeley, Jegelka was hooked on research and decided to pursue a profession in academia. She joined the school at MIT in 2015 as an assistant professor.
“What I actually loved about MIT, from the very starting, was that the people really care deeply about research and creativity. That’s what I appreciate essentially the most about MIT. The people here really value originality and depth in research,” she says.
That concentrate on creativity has enabled Jegelka to explore a broad range of topics.
In collaboration with other faculty at MIT, she studies machine-learning applications in biology, imaging, computer vision, and materials science.
But what really drives Jegelka is probing the basics of machine learning, and most recently, the difficulty of robustness. Often, a model performs well on training data, but its performance deteriorates when it’s deployed on barely different data. Constructing prior knowledge right into a model could make it more reliable, but understanding what information the model needs to achieve success and how you can construct it in will not be so easy, she says.
She can be exploring methods to enhance the performance of machine-learning models for image classification.
Image classification models are all over the place, from the facial recognition systems on mobile phones to tools that discover fake accounts on social media. These models need massive amounts of knowledge for training, but because it is dear for humans to hand-label hundreds of thousands of images, researchers often use unlabeled datasets to pretrain models as a substitute.
These models then reuse the representations they’ve learned after they are fine-tuned later for a selected task.
Ideally, researchers want the model to learn as much as it could possibly during pretraining, so it could possibly apply that knowledge to its downstream task. But in practice, these models often learn only just a few easy correlations — like that one image has sunshine and one has shade — and use these “shortcuts” to categorise images.
“We showed that this can be a problem in ‘contrastive learning,’ which is a normal technique for pre-training, each theoretically and empirically. But we also show that you may influence the kinds of data the model will learn to represent by modifying the varieties of data you show the model. That is one step toward understanding what models are literally going to do in practice,” she says.
Researchers still don’t understand all the things that goes on inside a deep-learning model, or details about how they’ll influence what a model learns and the way it behaves, but Jegelka looks forward to proceed exploring these topics.
“Often in machine learning, we see something occur in practice and we try to know it theoretically. This can be a huge challenge. You desire to construct an understanding that matches what you see in practice, so that you may do higher. We’re still just firstly of understanding this,” she says.
Outside the lab, Jegelka is a fan of music, art, traveling, and cycling. But today, she enjoys spending most of her free time along with her preschool-aged daughter.