In 2016, Jeremy Yeaton moved to a city of 40,000 in southeastern Bulgaria. "It was intense," says Yeaton, who grew up in Ho-Ho-Kus, New Jersey. They went to Haskovo as a Fulbright English Teaching Assistant and were the sole native speaker at a foreign-language high school. The teenage students in their classes were nearly the only people with whom they could converse during their year-long stint living there.

"My only option to communicate was to learn Bulgarian," says Yeaton, putting it bluntly. "I did not speak much when I arrived, and I spoke pretty well when I left."

Yeaton, who had studied linguistics, French, and Chinese during undergrad at Rutgers, always loved language. "It's so central to the human experience," they say. "There's something very special about being able to communicate with other people, in any capacity."

But that extreme immersion experience in Bulgaria pushed them back toward research as a career path. "I wanted to do more than just teach language," they said. "I wanted to understand the mechanisms that allow language to work."

To research the brain, they needed more hands-on experience in either neuroscience or psychology. When they found a Parisian masters program in cognitive science that had a linguistics track, it felt like a good fit. "I had been learning French for years and years," says Yeaton, who had also spent time in France previously. They took the plunge and enrolled at the École Normale Supérieure in 2017.

Two years later, they moved south to Marseille, masters diploma in hand. While working there, they applied to be part of the first Ph.D. cohort in UCI's Department of Language Science, a uniquely interdisciplinary program. Whereas their work might fall into departments including cognitive science, neuroscience, linguistics, communication sciences, and even psychology at other schools, UCI's language science program puts all of those people under one roof.

However, it was 2020 and the pandemic shaped Yeaton's journey from the start. "I applied to UCI with plans to do a whole bunch of experiments on human subjects. And then covid happened," says Yeaton, who completed the first full year of their program remotely, from Marseille. Doing in-person experiments was no longer an option. Their advisor, Greg Hickok, Distinguished Professor of cognitive sciences & language science, was involved with a large consortium centered on aphasia, or language loss (common after strokes). Hickok had access to a large behavioral and neuroimaging dataset and suggested that it might be of interest.

Yeaton was intrigued. "There's been a lot of work on aphasia over the years, but very little, relatively speaking, looking at the level of syntax," or the way in which words are arranged to express a thought. "Rather than looking at, you know, did they pronounce a word wrong or did they mean to say 'princess,' and they said 'queen,' for example—that's out of the scope of what I do. I'm looking specifically at the structure of sentences."

Yeaton dove into the literature and found that it often lumped together the two main types of expressive syntactic disorders: agrammatism and paragrammatism. Agrammatism is characterized by omissions and simplification. "You'll get things like, 'Boy kick ball,'" says Yeaton. "You have the content words, but then nothing else." Paragrammatism, on the other hand, results in what early 20th-century neurologist Karl Kleist called sentence monsters: He sent to everyone to tell people you're everybody around. "Basically, it's these long, confused things that don't make a lot of sense," says Yeaton. "I can kind of get a sense for what you were trying to say, but that was not a well formed sentence."

In addition to the brain mechanisms that allow us to produce such sentences, we know that there is also a mechanism that allows us to understand sentences. What was unclear was whether production and comprehension are tied together. Existing evidence showed that people with agrammatism do not seem to have comprehension deficits and also tend to present with frontal-lobe lesions in their brains in MRI scans. In addition, there was some research demonstrating that both people with paragrammatism and people with comprehension deficits have lesions in the posterior temporal lobe. "The fact that those were close together kind of led us all to assume, slash hope, that there was some sort of underlying mechanism that would support both," says Yeaton.

Their dissertation, which they defended in June, suggests that comprehension and production do indeed seem to be tied together, at least when it comes to paragrammatism. It's not necessarily the case that everyone with paragrammatism has a comprehension deficit, but they do seem to be much more closely related than agrammatism and comprehension deficits, says Yeaton. Moreover, their dissertation underscores the value in not only studying different syntactic disorders separately but also taking a multifaceted approach to this type of research.

"UCI’s Department of Language Science is highly interdisciplinary, seeking to understand how human language ability works by integrating and cross-fertilizing with other areas of cognition, neurobiology, biomedical research, statistics, and computer science (AI, for example). Jeremy’s research does exactly this through focus on how syntax—a core component of language science—is enabled and processed by the brain through the study of clinical populations and using analytical tools from neuroscience and statistical modeling," says Hickok, who also chairs the Department of Language Science. "It’s not easy taking such an integrated approach, because it requires mastery of multiple fields of research. But Jeremy’s work shows that the payoff can be significant."

Funded through the Undergraduate Research Opportunities Program (UROP), several of Yeaton's undergraduate research assistants have even presented or will present at conferences including ones hosted by the American Speech-Language-Hearing Association in Seattle, the Society for the Neurobiology of Language in DC, and the Academy of Aphasia in San Diego.

Yeaton credits their own mentor, Hickok, for directing them while also fostering their agency as a researcher. "What you will see sometimes with grad students is that they fall into the research interests of their advisor, not necessarily their own," Yeaton says. "Greg very much allowed me to choose my own path, to have a lot of autonomy, which means that I've produced a dissertation that I'm very proud of."

They've found mentorship in one form or another throughout language science. "The department as a whole was very supportive," says Yeaton, noting that they've interacted with every faculty member. "​I've ​come to each of them independently at different points for different kinds of advice or guidance. They've all been willing to provide their insight, to provide guidance, to point me in the right direction." It's a path that has ultimately led them toward the bleeding edge of the neurotechnology field.

"With recent advances in microelectrode arrays and machine learning, there have been a few labs in the country that have been able to decode speech motor plans from people with ALS," Yeaton says. People with ALS, or amyotrophic lateral sclerosis (sometimes called Lou Gehrig's disease), experience a breakdown in motor neuron function, which can affect one's physical ability to speak. By implanting electrodes into the brains of people affected by ALS, scientists have been able to identify what they're trying to express with enough accuracy that they can go back to work full time.

Yeaton recently accepted a position as a postdoctoral fellow at the UC Davis Neuroprosthetics lab and is confident that the Department of Language Science was a good choice. "There's no doubt in my mind that this Ph.D. program and this department were the right ones for me."

-Alison Van Houten for UCI Social Sciences
-photo by Luis Fonseca, UCI Social Sciences