If popular online platforms systematically expose their users to partisan and unreliable news, they could potentially contribute to societal issues such as rising political polarization^1,2. This concern is central to the ‘echo chamber’^3,4,5 and ‘filter bubble’^6,7 debates, which critique the roles that user choice and algorithmic curation play in guiding users to different online information sources^8,9,10. These roles can be measured as exposure, defined as the URLs shown to users by online platforms, and engagement, defined as the URLs selected by users. However, owing to the challenges of obtaining ecologically valid exposure data—what real users were shown during their typical platform use—research in this vein typically relies on engagement data^{4,8,11,12,13,14,15,16} or estimates of hypothetical exposure^{17,18,19,20,21,22,23}. Studies involving ecological exposure have therefore been rare, and largely limited to social media platforms^7,24, leaving open questions about web search engines. To address these gaps, we conducted a two-wave study pairing surveys with ecologically valid measures of both exposure and engagement on Google Search during the 2018 and 2020 US elections. In both waves, we found more identity-congruent and unreliable news sources in participants’ engagement choices, both within Google Search and overall, than they were exposed to in their Google Search results. These results indicate that exposure to and engagement with partisan or unreliable news on Google Search are driven not primarily by algorithmic curation but by users’ own choices.

如果流行的在线平台系统地让用户接触党派和不可靠的新闻，它们可能会助长社会问题，例如日益加剧的政治两极分化^1,2。这种担忧是“回音室” ^3,4,5和“过滤气泡” ^6,7辩论的核心，这些辩论批评用户选择和算法管理在引导用户访问不同在线信息源^{8,9,10方面的作用}. 这些角色可以通过曝光（定义为在线平台向用户显示的 URL）和参与度（定义为用户选择的 URL）来衡量。然而，由于获得生态学上有效的曝光数据（真实用户在他们的典型平台使用期间显示的内容）的挑战，这方面的研究通常依赖于参与数据^{4,8,11,12,13,14,15,16}或估计假设暴露^{17,18,19,20,21,22,23}。因此，涉及生态暴露的研究很少见，而且主要限于社交媒体平台^7,24，留下关于网络搜索引擎的悬而未决的问题。为了解决这些差距，我们在 2018 年和 2020 年美国大选期间进行了两波研究配对调查，并采用了生态上有效的谷歌搜索曝光率和参与度衡量指标。在这两波浪潮中，我们发现参与者在谷歌搜索和整体参与选择中的身份一致性和不可靠新闻来源比他们在谷歌搜索结果中看到的要多。这些结果表明，在 Google 搜索上接触和参与党派或不可靠的新闻主要不是由算法管理驱动的，而是由用户自己的选择驱动的。