Wikipedia
Aphantasia
Aphantasia is a hypothesized neurological condition where a person does not possess a functioning mind's eye. The phenomenon was first described by Francis Galton in 1880, but remained largely unstudied until 2015, when it was termed aphantasia by a team led by Adam Zeman of the University of Exeter Medical School. Further studies are being planned.
In April 2016 an essay by Blake Ross, co-creator of the Mozilla Firefox web browser, was published, describing his own aphantasia and his realisation that not everyone experiences it. It gained wide circulation in social media.