Representative Mike Doyle, Democrat of Pennsylvania, asked the tech chief executives to answer yes or no: Did their platforms contribute to the spread of misinformation before the riot?
Mr. Zuckerberg and Mr. Pichai dodged the question. Mr. Dorsey was more direct.
“Yes,” he said. “But you also have to take into consideration the broader ecosystem. It’s not just about the technology platforms we use.”
Mr. Doyle pressed the other executives.
“How is it possible for you not to at least admit that Facebook played a leading role in facilitating the recruitment, planning and execution of the attack on the Capitol?” he asked Mr. Zuckerberg.
“I think that the responsibility here lies with the people who took the actions to break the law and do the insurrection,” Mr. Zuckerberg said. He added that people who spread the misinformation bore responsibility as well.
“But your platforms supercharged that,” Mr. Doyle said.
Later, while still participating in the videoconference hearing, Mr. Dorsey tweeted a single question mark with a poll that had two options: “Yes” or “No.” When asked about his tweet by a lawmaker, he said “yes” was winning.
The January riot at the Capitol has made the issue of disinformation deeply personal for lawmakers. The riot was fueled by false claims from President Donald J. Trump and others that the election had been stolen, which were rampant on social media.
Some of the participants had connections to QAnon and other online conspiracy theories. And prosecutors have said that groups involved in the riot, including the Oath Keepers and the Proud Boys, coordinated some of their actions on social media.