If I tell you to close your eyes and imagine an apple, what do you see? For most readers, a spherical shape will appear that may be red or green or yellow, more or less clear and more or less fleeting. But there are people who will not see anything, despite knowing what an apple is and being able to describe one. This is called aphantasia, a term coined some years ago by the neurologist Adam Zeman, who gave a name to a phenomenon that Francis Galton, cousin of Darwin and a pioneer in the study of individual differences, had already detected in 1880 when he asked several scientists to imagine the breakfast table and some replied that they did not understand the question. Aphantasia is, therefore, the inability to generate voluntary mental images, and it is not a disease, but a way of thinking that affects about 1% of the population. At the other extreme, we find hyperphantasia, which is the ability to think in images with almost perceptual vividness.