With help from an artificial language network, MIT neuroscientists have discovered what kind of sentences are most likely to fire up the brain’s key language processing centers.

The new study reveals that sentences that are more complex, either because of unusual grammar or unexpected meaning, generate stronger responses in these language processing centers. Sentences that are very straightforward barely engage these regions, and nonsensical sequences of words don’t do much for them either.

For example, the researchers found this brain network was most active when reading unusual sentences such as “Buy sell signals remains a particular,” taken from a publicly available language dataset called C4. However, it went quiet when reading something very straightforward, such as “We were sitting on the couch.”

“The input has to be language-like enough to engage the system,” says Evelina Fedorenko, Associate Professor of Neuroscience at MIT and a member of MIT’s McGovern Institute for Brain Research. “And then within that space, if things are really easy to process, then you don’t have much of a response. But if things get difficult, or surprising, if there’s an unusual construction or an unusual set of words that you’re maybe not very familiar with, then the network has to work harder.”

Fedorenko is the senior author of the study, which appears today in Nature Human Behavior. MIT graduate student Greta Tuckute is the lead author of the paper.

Processing language

In this study, the researchers focused on language-processing regions found in the left hemisphere of the brain, which includes Broca’s area as well as other parts of the left frontal and temporal lobes of the brain.

“This language network is highly selective to language, but it’s been harder to actually figure out what is going on in these language regions,” Tuckute says. “We wanted to discover what kinds of sentences, what kinds of linguistic input, drive the left hemisphere language network.”

The researchers began by compiling a set of 1,000 sentences taken from a wide variety of sources — fiction, transcriptions of spoken words, web text, and scientific articles, among many others.

Five human participants read each of the sentences while the researchers measured their language network activity using functional magnetic resonance imaging (fMRI). The researchers then fed those same 1,000 sentences into a large language model — a model similar to ChatGPT, which learns to generate and understand language from predicting the next word in huge amounts of text — and measured the activation patterns of the model in response to each sentence.

Once they had all of those data, the researchers trained a mapping model, known as an “encoding model,” which relates the activation patterns seen in the human brain with those observed in the artificial language model. Once trained, the model could predict how the human language network would respond to any new sentence based on how the artificial language network responded to these 1,000 sentences.

The researchers then used the encoding model to identify 500 new sentences that would generate maximal activity in the human brain (the “drive” sentences), as well as sentences that would elicit minimal activity in the brain’s language network (the “suppress” sentences).

In a group of three new human participants, the researchers found these new sentences did indeed drive and suppress brain activity as predicted.

“This ‘closed-loop’ modulation of brain activity during language processing is novel,” Tuckute says. “Our study shows that the model we’re using (that maps between language-model activations and brain responses) is accurate enough to do this. This is the first demonstration of this approach in brain areas implicated in higher-level cognition, such as the language network.”

Linguistic complexity

To figure out what made certain sentences drive activity more than others, the researchers analyzed the sentences based on 11 different linguistic properties, including grammaticality, plausibility, emotional valence (positive or negative), and how easy it is to visualize the sentence content.

For each of those properties, the researchers asked participants from crowd-sourcing platforms to rate the sentences. They also used a computational technique to quantify each sentence’s “surprisal,” or how uncommon it is compared to other sentences.

This analysis revealed that sentences with higher surprisal generate higher responses in the brain. This is consistent with previous studies showing people have more difficulty processing sentences with higher surprisal, the researchers say.

Another linguistic property that correlated with the language network’s responses was linguistic complexity, which is measured by how much a sentence adheres to the rules of English grammar and how plausible it is, meaning how much sense the content makes, apart from the grammar.

Sentences at either end of the spectrum — either extremely simple, or so complex that they make no sense at all — evoked very little activation in the language network. The largest responses came from sentences that make some sense but require work to figure them out, such as “Jiffy Lube of — of therapies, yes,” which came from the Corpus of Contemporary American English dataset.

“We found that the sentences that elicit the highest brain response have a weird grammatical thing and/or a weird meaning,” Fedorenko says. “There’s something slightly unusual about these sentences.”

The researchers now plan to see if they can extend these findings in speakers of languages other than English. They also hope to explore what type of stimuli may activate language processing regions in the brain’s right hemisphere.

The research was funded by an Amazon Fellowship from the Science Hub, an International Doctoral Fellowship from the American Association of University Women, the MIT-IBM Watson AI Lab, the National Institutes of Health, the McGovern Institute, the Simons Center for the Social Brain, and MIT’s Department of Brain and Cognitive Sciences.

Kwesi Afrifa came to MIT from his hometown of Accra, Ghana, in 2020 to pursue an interdisciplinary major in urban planning and computer science. Growing up amid the many moving parts of a large, densely populated city, he had often observed aspects of urban life that could be made more efficient. He decided to apply his interest in computing and coding to address these problems by creating software tools for city planners.

Now a senior, Afrifa works at the City Form Lab led by Andres Sevstuk, collaborating on an open-source, Python-based tool that allows researchers and policymakers to analyze pedestrians’ behaviors. The package, which launches next month, will make it more feasible for researchers and city planners to investigate how changes to a city’s structural characteristics impact walkability and the pedestrian experience.

During his first two years at MIT, Afrifa worked in the Civic Data Design Lab led by Associate Professor Sarah Williams, where he helped build sensing tools and created an online portal for people living in Kibera, Nairobi, to access the internet and participate in survey research.

After graduation, he will go on to work as a software engineer at a startup in New York. After several years, he hopes to start his own company, building urban data tools for integration into mapping and location-based software applications.

“I see it as my duty to make city systems more efficient, deepen the connection between residents and their communities, and make existing in them better for everyone, including groups which have often been marginalized,” he says.

“Cities are special places”

Afrifa believes that in urban settings, technology has a unique power to both accelerate development and empower citizens.

He witnessed such unifying power in high school, when he created the website ghanabills.com, which aggregated bills of parliament in Ghana, providing easy access to this information as well as a place for people to engage in discussion on the bills. He describes the effect of this technology as a “democratizing force.”

Afrifa also explored the connection between cities and community as an executive member of Code for Good, a program that connects MIT students interested in software with nonprofits throughout the Boston area. He served as a mentor for students and worked on finding nonprofits to match them up with.

Language and visibility

Sharing African languages and cultures is also important to Afrifa. In his first two years at MIT, he and other African students across the country started the Mandla app, which he describes as a Duolingo for African languages. It had gamified lessons, voice translations, and other interactive features for learning. “We wanted to solve the problem of language revitalization and bring African languages to the broader diaspora,” he says. At its peak a year ago, the app had 50,000 daily active users.

Although the Mandla App was discontinued due to lack of funding, Afrifa has found other ways to promote African culture at MIT. He is currently collaborating with architecture graduate students TJ Bayowa and Courage Kpodo on a “A Tale of Two Coasts,” an upcoming short film and multimedia installation that delves into the intricate connections between perceptions of African art and identity spanning two coasts of the Atlantic Ocean. This ongoing collaboration, which Afrifa says is still taking shape, is something he hopes to expand beyond MIT.

Discovering arts

As a child, Afrifa enjoyed writing poetry. Growing up with parents who loved literature, Afrifa was encouraged to become involved with the theater and art scene of Accra. He didn’t expect to continue this interest at MIT, but then he discovered the Black Theater Guild (BTG).

The theater group had been active at MIT from the 1990s to around 2005. It was revived by Afrifa in his sophomore year when Professor Jay Scheib, head of Music and Theater Arts at MIT, encouraged him to write, direct, and produce more of his work after his final project for 21M.710 (Script Analysis), a dramaturgy class taught by Scheib.

Since then, the BTG has held two productions in the past two years: “Nkrumah’s Last Day,” in spring 2022, and “Shooting the Sheriff,” in spring 2023, both of which were written and directed by Afrifa. “It’s been very rewarding to conceptualize ideas, write stories and have this amazing community of people come together and produce it,” he says.

When asked if he will continue to pursue theater post-grad, Afrifa says: “That’s 100 percent the goal.”

Pedro Reynolds-Cuéllar, an MIT PhD student in both media arts and sciences and art, culture, and technology (ACT), explores how technology and culture intersect in spaces often overlooked by mainstream society, stretching beyond the usual scope of design research.

A former lecturer and researcher at MIT D-Lab with experience in robotics, Reynolds-Cuéllar is an ACT Future Heritage Lab affiliate, a member of the Space Enabled Group within the MIT Media Lab, and a MAD Fellow who hails from rural Colombia, where resourcefulness isn't a skill but a way of life. “I grew up seeing impressive ingenuity in solving a lot of problems, building contraptions, tools, and infrastructure … all sorts of things. Investigating this ingenuity has been the question driving my entire PhD,” he reflects.

Emphasizing the importance of cultural elements in how people collaborate, his work encourages a more localized, culturally informed perspective on technology design. “I am interested in investigating how technology takes place in geographies and spaces that are outside of mainstream society, mostly rural places,” he says.

At the heart of South America, Colombia is home to over 80 distinct groups of Indigenous tribes known to exist, each carrying unique customs, beliefs, and practices. This contributes to Colombia's cultural mosaic and linguistic diversity, with more than 68 spoken languages. This meant plenty of opportunities for Reynolds-Cuéllar to engage with communities without trying to reshape or “fix” them, but rather to amplify their intrinsic strengths and amplify their voices.

“My colleagues and I developed a digital platform meticulously documenting collaborative processes when designing technology. This platform, called Retos, captures the invaluable social capital that blooms from these interactions,” Reynolds-Cuéllar explains. Born from a need to foster cross-pollination, the platform serves as a bridge between universities, companies, and rural Colombian organizations, enhancing their existing initiatives and facilitating processes such as funding applications. It received an award from MIT Solve and the 2022 MIT Prize for Open Data from MIT Libraries. 

Designing with culture in mind

Reynolds-Cuéllar's approach isn’t formulaic. “Culture is pivotal in shaping collaboration dynamics,” he emphasizes. “Reading about collaboration can make it seem like something universal, but I don’t think it works that way. This means common research methods are not always effective. You must ‘tune in,’ and build upon existing methods in the local fabric.” This understanding fuels Reynolds-Cuéllar’s work, allowing him to sculpt each project to resonate with a community's distinct cultural context. At the heart of his doctoral research, he integrates Indigenous knowledge and what he calls “ancestral technology into design practices — a form of world-making (design) that primarily supports cultural cohesion, rooted in bounded geography and with a history that lives through collective memory. “I'm prompting designers, who may lack direct access to Indigenous scholarship, to recalibrate their design approaches,” Reynolds-Cuéllar articulates.

This appeal to look into multiple perspectives and methodologies broadens the horizons of conventional design thinking. Beyond designing things for a specific function or solution, Reynolds-Cuéllar looks at practices that also help maintain the cultural fabric of a place. He gives the example of weaving looms, which are not only the result of ingenious design, but also allow Indigenous communities to build artifacts with great cultural meaning and economic benefit: “When I work on the loom … I feel differently. I have access to a different state of mind and can easily get into a flow. I am building things where I can tell the story of my life within my culture. I'm making something that is meaningful for people around me, and I'm not doing it alone, we're doing it all together,” adds Reynolds-Cuéllar.

Among his ventures, Reynolds-Cuéllar's work with coffee farmers stands out. His projects in collaboration with these communities are all about empowering coffee farmers to refine their processes and gain agency over their livelihood and economic undertakings.

“The coffee industry in Colombia is intricate, with various layers influencing farmers’ lives, from bioengineered seeds to chemical fertilizers, and centralized roasting operations. It’s political and even philosophical,” Reynolds-Cuéllar states. Coffee farmers could sell the raw beans for a low price to the powerful Federación Nacional de Cafeteros (the National Federation of Coffee Growers of Colombia), but there are other alternatives to foster agency and self-determination. “We collaborate with coffee growing collectives, helping them to achieve consistency in roasting procedures, improve equipment designs, and set up packaging infrastructure,” which means farmers can produce higher-value specialty coffee which they can choose to sell directly to consumers. Reynolds-Cuéllar's work creates ripple effects, bolstering autonomy and local economies.

Too many questions

Throughout his research, Reynolds-Cuéllar describes a turning point in meeting an Indigenous cultural and social leader: “We were collaborating with a group of fishermen on Colombia's Atlantic coast, within an Indigenous community. Our initial curriculum mirrored conventional design methods. Yet, the leader's insight shifted my perspective profoundly. It was the first time my methods were being challenged.” The encounter prompted Reynolds-Cuéllar to scrutinize his methodology: “This leader told me: ‘You guys ask a lot of questions.’ I started explaining the benefit of questions, and methods in the usual design jargon. He replied: ‘I still think you ask too many questions. We ask the most important questions, and then we spend a lot of time reflecting on them,” remembers Reynolds-Cuéllar. This shift underscored the realization that there is no such thing as universal design, and that standardized methodologies don’t universally translate. They sometimes inadvertently strip away cultural nuances, where they could instead cultivate their dynamic expression.

For Reynolds-Cuéllar, his participation in MAD’s design fellowship has been instrumental. The fellowship not only provided essential funding but also offered a sense of community. “The fellowship facilitated meaningful conversations, especially talks like Dori Tunstall's on ‘Decolonizing Design,’” Reynolds-Cuéllar reflects. The financial support also translated into practical aid, allowing him to advance his projects, including compensating field researchers in Colombia.

Beyond academic pursuits, Reynolds-Cuéllar envisions writing a book titled “The Atlas of Ancestral Technology of Colombia.” More than mere documentation, this large atlas format would be a compendium of the myriad stories Reynolds-Cuéllar has unearthed, with illustrating images crafted in Colombia — visual representations from each culture, descriptions, and local stories about these artifacts. “I want a book that could counter some of the predominant narratives on design,” asserts Reynolds-Cuéllar. Through his work, Reynolds-Cuéllar already started to craft a blueprint for approaching design with cultural significance and intention, laying the foundation for a more inclusive and purposeful approach to technology and innovation.

A few years ago, David Hsu started taking a keen interest in some apartment buildings in Brooklyn and the Bronx — but not because he was looking for a place to live. Hsu, an associate professor at MIT, works on urban climate change solutions. The property owners were retrofitting their buildings to make them net-zero emitters of carbon dioxide via better insulation, ventilation, and electric heating and appliances. They also wanted to see the effect on interior air quality.

In the process, the owners started working with Hsu and an MIT team to assess the results using top-grade air quality sensors. They found that beyond its climate benefits, retrofitting lowered indoor pollutants from high levels to almost-undetectable levels. It is a win-win outcome.

“Not only are those buildings cleaner and use less energy and do not emit greenhouse gases, they also have better air quality,” Hsu says. “The hopeful thing is that as we remake our buildings for decarbonization, a lot of technologies are so superior that our lives will be better, too.”

Hsu’s projects frequently yield practical, concrete steps for climate action. In New York City, Hsu found, mandating the measurement of energy use lowered consumption 13 to 14 percent over four years. In a 2017 paper, he and his co-authors studied which climate actions would most reduce carbon emissions in 11 major U.S. cities. Cleveland and Denver can greatly reduce use of fossil fuels, for example, while better energy efficiency in new homes would make a big difference in Houston and Phoenix.

“You have to figure out what works and doesn’t work,” Hsu says. “I try to figure out how we can have cleaner and healthier cities that will be more sustainable, equitable, and more just.”

Significantly, Hsu does not just prescribe climate action elsewhere, he also works for change at MIT. He helped create a zero-emissions roadmap for MIT’s School of Architecture and Planning as well as the Department of Urban Studies and Planning, where he is an associate professor of urban and environmental planning and is part of Fast Forward: MIT’s Climate Action Plan for the Decade, serving in the Climate Education Working Group.

“People can get depressed about how you tackle this large, civilization-wide problem, and then you realize lots of other people care about this. Lots of smart people at MIT and other places are working on it, and there are lots of things we can do, individually and collectively,” Hsu says.

And as Hsu’s work shows, lots of people tackle the climate crisis by working on local issues. For his research and teaching, Hsu was granted tenure at MIT this year.

Urban planning by way of Amherst

Hsu studies cities, but is not from one. Growing up in the college town of Amherst, Massachusetts, Hsu could walk out of his home and “be in the woods in a minute.” He attended Yale University as an undergraduate, majoring in physics, and started venturing into New York City with friends. After graduation, Hsu moved there and got a job.

Or three jobs, really. Over the next 10 years, Hsu worked as an engineer, in real estate finance, and for the New York City government as a vice president at the NYC Economic Development Corporation, where he helped manage the city’s post-September 11 redevelopment of the East River waterfront. Eventually, he decided to pursue graduate studies in urban planning, building on his experience.

“Engineering, finance, and government, you put those three things together and they’re basically urban planning,” Hsu says. “It took me a decade after school to realize urban planning is a thing I could do. I say to students, ‘You’re lucky, you have this major. I never had this in college.’”

As a graduate student, Hsu received an MS from Cornell University in applied and engineering physics, then an MSc from the London School of Economics and Political Science in city design and social science, before getting his PhD in urban design and planning at the University of Washington in Seattle. He served on the faculty at the University of Pennsylvania before moving to MIT in 2015.

Hsu studies an array of topics involving local governments and climate policy. He has published multiple papers on Philadelphia’s attempts to refurbish its stormwater infrastructure, for example. His studies about retrofitted apartment buildings are forthcoming as three papers. A 2022 Hsu paper, “Straight out of Cape Cod,” looked at the origins of Community Choice Aggregation, an approach to purchasing clean energy that started in a few Massachusetts communities and now involves 11 percent of the U.S. population.

“I joke that the ideal reader of my articles is not a mayor and it’s not an academic, it’s a midcareer bureaucrat trying to implement a policy,” Hsu says.

Actually, that’s no mere joke. At MIT, City of Cambridge officials have contacted Hsu to discuss his studies of New York and Philadelphia, something he welcomes. Even if not in local government himself, Hsu says, “I know I can do research that might move some of those projects along. It’s my way of trying to contribute to the world outside of academia.”

“It’s all important”

There is still another way Hsu contributes to climate action: by influencing what MIT does. He helped craft the climate policies of the School of Architecture and Planning and the Department of Urban Studies and Planning, which aim to produce net zero emissions for the department through the use of tools like carbon offsets for travel. As part of the Institute-wide Climate Education Working Group convened under the Fast Forward plan, Hsu is busy thinking about how to integrate climate studies into MIT education.

“Our Fast Forward team does great work together. David McGee, Lisa Ghaffari, Kate Trimble, Antje Danielson, Curt Newton, they’re so engaged,” says Hsu. “Our students are terrifically hard-working and skilled and care about climate change, but don’t know how to affect it necessarily. We want to give them on-ramps and skills.”

He is also chair of the fast-growing 11-6 major that combines urban studies and planning with computer science.

“Climate change is happening so fast, and is so big, that every job could be climate-change related,” Hsu says. “If people leave MIT with a higher base understanding of climate change, then you can be a lawyer or consultant or work in finance or computer science and address the unsolved problems.”

Indeed, Hsu thinks many students, who he believes increasingly recognize the severity of climate change, need to prioritize the battle against it when shaping their careers.

“Our fight against climate change is not going to be over by 2050, but 25 years from now, we’re going to know if we transitioned to a net-zero-emitting society for the sake of humanity,” Hsu says. “The students are more aware than ever that climate change is going to dominate their lives. I want students to look back with satisfaction that they helped society.”

More bluntly, he says: “Are you going to say, ‘Oh, I made some money and enhanced my career, but the planet’s going to be destroyed? Or ideally will you find a job that’s satisfying and can support your future hopes for yourself and your family, and also save the planet? Because I think there are a lot of [job] options like that out there.”

Hsu adds, “We’re going to need people pulling in different directions. It’s all important. That’s the message to our students. Go find something you think is important and use your skills. We’re going to need that many people to work on climate change.”