I never knew this existed until someone mentioned to me that Brad Wardell had recently described how he found out he could not visualize things with his mind:
My wife and I recently came across a show that referenced a person who had the inability to visualize images in their minds.
My immediate reaciton was, “Of course they can’t, nobody can. We call those hallucinations.” I thought it was absurd to suggest that people could just conjure up an image in their minds.
Turn out, I’m the defective one
He links to a NYT article describing the condition. The BBC reported on this last year as well, and they have a mini-test you can take to determine if you might have the condition. According to the researcher they interviewed, aphantasia is not a disorder, just a different way the brain works. The opposite condition also exists, "hyperphantasia," in which one has extremely vivid mental imagery.
As a very visual thinker, this condition amazes me. I almost can't conceive of how people manage to cope, but apparently people with aphantasia can somewhat work around it by memorizing numerical or other details of things.
Amazing how we're always learning new things about the brain.
Those of you who think you may have either aphantasia or hyperphantasia really should contact Dr. Adam Zeman in the UK: firstname.lastname@example.org - I'm sure the research group can use all the data they can get.
Thanks to concentric, here is a link to information about a conference scheduled for May 2016 which will examine the findings of Dr. Zeman's team.