Book excerpt: An inside view of the experimental practices of cognitive psychology—and their influence on the addictive nature of social media Experimental cognitive psychology research is a hidden force in our online lives. We engage with it, often unknowingly, whenever we download a health app, complete a Facebook quiz, or rate our latest purchase. How did experimental psychology come to play an outsized role in these developments? Experiments of the Mind considers this question through a look at cognitive psychology laboratories. Emily Martin traces how psychological research methods evolved, escaped the boundaries of the discipline, and infiltrated social media and our digital universe. Martin recounts her participation in psychology labs, and she conveys their activities through the voices of principal investigators, graduate students, and subjects. Despite claims of experimental psychology’s focus on isolated individuals, Martin finds that the history of the field—from early German labs to Gestalt psychology—has led to research methods that are, in fact, highly social. She shows how these methods are deployed online: amplified by troves of data and powerful machine learning, an unprecedented model of human psychology is now widespread—one in which statistical measures are paired with algorithms to predict and influence users’ behavior. Experiments of the Mind examines how psychology research has shaped us to be perfectly suited for our networked age.