What aphantasia is

Aphantasia is the inability to voluntarily create mental images. The term was introduced by researchers in 2015. Some people have always had it (congenital) and some acquire it later, for example after an illness or injury. Researchers estimate that roughly 4 percent of people have some form of it. It also varies a lot: for some, other senses such as sound are affected too, and for others only sight is. It sits on a spectrum of imagery, and many people only find out in adulthood because there's nothing obvious to notice. This is general information, not medical advice.