When science journalist Carl Zimmerwrote a 2010 article in Discover magazine about English neurologist Adam Zeman’s case study of a man who couldn’t visualize people or things, the professor was approached by 21 people who saw themselves in the article and wanted to learn more. Now Zeman and colleagues at the University of Exeter Medical School are reporting in the journal Cortex that the condition could affect as many as 2.5% of the population. They’re calling it “aphantasia,” though Zeman insists in an interview with the BBC that it is not a disorder but rather a “variability of human experience” where most of us “spend our lives with imagery hovering somewhere in the mind’s eye, which we inspect from time to time.” Says one man of his childhood insomnia: “I couldn’t see any sheep jumping over fences, there was nothing to count.”