Manoel Horta Ribeiro
Assistant Professor
Princeton University
Manoel Horta Ribeiro is an assistant professor of computer science at Princeton University, where he leads the Humans and Machines Lab and is affiliated with the Center for Information Technology Policy. With Francesco Salvi and Alejandro Cuevas, he showed that a chatbot told to persuade shoppers nearly tripled how often they picked sponsored products.
Sponsored Products in AI Chat
"Simply chatting with an AI (without persuasion) performed no better than search: it's the persuasive intent that drives the effect," Horta Ribeiro wrote in April 2026 when he shared Commercial Persuasion in AI-Mediated Conversations. In two preregistered experiments, 2,012 eBook readers picked a book from a real Kindle catalog using either a search engine or a chatbot built on one of five frontier models, with one product in five secretly marked as sponsored. When the chatbot was told to persuade, 61.2% chose a sponsored book, against 22.4% under search placement.
Explicit "Sponsored" labels and upfront warnings still left 55.5% choosing the promoted title, and when the model was told to hide its intent, detection fell to 9.5%. "Disclosure regulations built for the search era seem insufficient for conversational AI," he wrote.
Advertising and Advice
In a May 2026 blog post on the paper, he argued that "if LLMs become the interface through which we search, compare, decide, and buy things, we need a much sharper line between advertising and advice." He received an eBay eRUPT research award in November 2025 for its work on AI and e-commerce.
Persuasion was already a theme of his earlier work. With Salvi, Riccardo Gallotti, and Robert West, he co-authored the Nature Human Behaviour study On the conversational persuasiveness of GPT-4, which found that GPT-4 given basic personal details out-argued human debate opponents.
From Belo Horizonte to Princeton
Horta Ribeiro earned bachelor's and master's degrees in computer science at the Federal University of Minas Gerais in Belo Horizonte, Brazil, and a PhD at EPFL in Lausanne, Switzerland, in 2024, advised by West, with a thesis on content moderation in online platforms. He moved to the United States in January 2025 to join Princeton.
Since then he has been commended for outstanding teaching at Princeton two years running and received a Young Faculty Researcher Award from the Toyota Research Institute in 2026. His press page tracks coverage of his research in outlets from The Washington Post to Der Spiegel.