About 50% of patients with Parkinson disease (PD) experience the sensation that someone is nearby when no one is present. Minor hallucinations including these so-called presence hallucinations often appear early in the disease course, manifesting before motor symptoms in as many as a third of patients. What’s more, PD hallucinations are associated with psychosis, cognitive decline, and death, making them a potential marker for poor clinical outcomes. Yet because many patients are reluctant to report these hallucinations and physicians may not ask about them, they often go undiagnosed. Now, a team of researchers in Europe has developed a technique to induce presence hallucinations among patients with PD in a controlled setting.