Sihan Chen's fascination with languages began when he was a teenager in his high school choir in his hometown of Shenzhen, China. "We sang religious and folk songs in different languages like Mandarin, English, Albanian, and Latin, and I would look up how to pronounce words in different languages," he says.
These early experiences planted the seed for his current research interests in cognition and language as a third-year PhD student in MIT's Department of Brain and Cognitive Sciences (BCS). Under the guidance of Professor Edward "Ted" Gibson, Chen studies how different languages have developed into what we see today, with a particular emphasis on environmental and social factors. "I was always interested in the invisible pressures that shape our languages over time," he says.
Despite Chen's ongoing interest in language, he started on a different academic path. After completing the demanding entrance exams for Chinese universities, he made a last-minute decision to apply to U.S. colleges. With just three months to prepare for the SAT and language test, he says his resume paled compared to his American peers' extensive extracurricular activities. He took the chance and landed at the University of Miami, where he pursued a major in mechanical engineering.
Alongside his engineering studies, Chen dedicated several elective courses to his interest in linguistics. In one of these courses, he stumbled upon a thought-provoking paper, coincidentally written by a student from BCS, exploring how language influences our perception of color. "It fascinated me and made quite an impression," he recalls. Now, he is working on a paper challenging some of those findings.
Chen says reading such papers in college helped him discover the perfect match between his intellectual interests and abilities, augmented by the skills he had acquired through his mechanical engineering training. Although the topics addressed in these papers were quite different from what he encountered in his major, the underlying thought process to solve the problems are similar. "You identify the process, break it down into different steps, and think about how you can model each mathematically and implement the model computationally." He decided to reach out to Gibson, who further encouraged him to continue his work.
Approaching graduation, Chen faced a tough decision between the more familiar path of biomedical engineering and pursuing his deepening passion for language and cognition. "I think it was clear this is where I wanted to go, but it was a tough decision." He decided to apply.
Chen's current work with Gibson revolves around a central thesis of his lab: Since we often use language to communicate, we have the incentive to use it efficiently. Chen and his colleagues are looking into how different languages convey spatial information with spatial deictic demonstratives — words or phrases such as "here" and "from there" in English. "Efficiency here means communicating spatial information as accurately as possible, with a system involving as few demonstratives as possible," says Chen.
In communication, there is a trade-off between two factors: accuracy and simplicity, as one cannot fully achieve both at the same time. If one wants to pursue accuracy, the resulting spatial deictic system must be very complex. In contrast, if one intends to pursue simplicity, the resulting system won't be able to convey any information. Using tools in information theory and a database of 220 languages from various parts of the world, Chen and his collaborators show that existing spatial deictic systems are very close to the optimal systems predicted by information theory. In addition, they also show that human languages prefer spatial demonstrative systems that have a consistent pattern.
Seeking how societal characteristics might shape language features, Chen and his colleagues analyze data from diverse languages. They hypothesize two types of societies: exoteric societies, marked by mobility, large population size, and a significant number of second language speakers, and esoteric societies, characterized by being more close-knit, having less migration, and fewer second-language speakers. Exoteric languages, such as English, are widely spoken and have more complex syntax but simplified morphology. Conversely, esoteric societies tend to have languages with more complex morphology, such as more noun cases.
"English, for example, rarely has cases, except in pronouns where it distinguishes between nominative and accusative cases with pronouns like 'I' and 'me' and uses the genitive case with 'my,' indicating a relationship, and that's about it. But other, more esoteric languages have up to 15 cases, including cases for objects, direction, and location. We think that this difference in noun cases arises from word learning processes, where second-language learners focus on rules, while native speakers memorize these specific variations."
Trying to see what influences the way humans speak, Chen's research also extends to acoustics. A waveform is a visual representation of a sound you might be familiar with from your audio player. Waveforms depict the amplitude of a wave over time, comprising delicate and minuscule oscillations that amalgamate into a broader pattern known as the modulation envelope. "We want to determine the frequency of this broader oscillation, which can also be described as the rhythm of speech," Chen explains. Previous research revealed that in eight languages, this rhythm of speech typically exhibits a frequency peaking at 4 hertz — a rhythm that researchers believe is related to the coordination between speech production and comprehension. "We expanded this research to 94 languages, and we are now analyzing 4 million recordings to determine further the prevalence of this phenomenon across different regions of the globe," says Chen.
Reflecting on his research and studies in the last three years, Chen says MIT's Department of Brain and Cognitive Sciences is a highly supportive environment, fostering collaboration among individuals from diverse backgrounds. "There is always someone available to offer assistance and guidance," he says. "it's so cool to see people from different backgrounds with their own expertise coming together collaboratively to uncover fascinating secrets of the human mind."