"Lives without imagery - Congenital aphantasia", Zeman et al 2015

In 2010 we reported a particularly 'pure' case of imagery generation disorder, in a 65 year old man who became unable to summon images to the mind's eye after coronary angioplasty (Zeman et al., 2010). Following a popular description of our paper (Zimmer, 2010), we were contacted by over twenty individuals who recognised themselves in the article's account of 'blind imagination', with the important difference that their imagery impairment had been lifelong. Here we describe the features of their condition, elicited by a questionnaire, and suggest a name - aphantasia - for this poorly recognised phenomenon...We explored the features of their condition with a questionnaire devised for the purpose and the Vividness of Visual Imagery Questionnaire (VVIQ) (Marks, 1973) (see supplementary material for further details). Participants typically became aware of their condition in their teens or twenties when, through conversation or reading, they realised that most people who 'saw things in the mind's eye', unlike our participants, enjoyed a quasi-visual experience. 19/21 were male. 5/21 reported affected relatives. 10/21 told us that all modalities of imagery were affected. Our participants rating of imagery vividness was significantly lower than that of 121 controls (p<.001, Mann Whitney U test - see Figure 1). Despite their substantial (9/21) or complete (12/21) deficit in voluntary visual imagery, as judged by the VVIQ, the majority of participants described involuntary imagery. This could occur during wakefulness, usually in the form of 'flashes' (10/21) and/or during dreams (17/21)...14/21 participants reported difficulties with autobiographical memory. The same number identified compensatory strengths in verbal, mathematical and logical domains.

"The Brain: Look Deep Into the Mind's Eye; We take visual imagination for granted. But the blank inner world of a patient called MX demonstrates the rich neural processes needed to create the images in our heads." & "Picture This? Some Just Can't", describing "Loss of imagery phenomenology with intact visuo-spatial task performance: A case of 'blind imagination'", Zeman et al 2010 (mirror):

MX agreed to a series of examinations. He proved to have a good memory for a man of his age, and he performed well on problem-solving tests. His only unusual mental feature was an inability to see mental images. Dr. Zeman and his colleagues then scanned MX's brain as he performed certain tasks. First, MX looked at faces of famous people and named them. The scientists found that certain regions of his brain became active, the same ones that become active in other people who look at faces. Then the scientists showed names to MX and asked him to picture their faces. In normal brains, some of those face-recognition regions again become active. In MX's brain, none of them did. Paradoxically, though, MX could answer questions that would seem to require a working mind's eye. He could tell the scientists the color of Tony Blair's eyes, for example, and name the letters of the alphabet that have low-hanging tails, like g and j. These tests suggested his brain used some alternate strategy to solve visual problems....When the scientists asked their [21 later surveyed] subjects to mentally count the windows in their house or apartment, 14 succeeded. They seem to share MX’s ability to use alternate strategies to get around the lack of a mind’s eye.

...Thomas Ebeyer, a 25-year-old Canadian student, discovered his condition four years ago while talking with a girlfriend. He was shocked that she could remember what a friend had been wearing a year before. She replied that she could see a picture of it in her mind. “I had no idea what she was talking about,” he said in an interview. Mr. Ebeyer was surprised to discover that everyone he knew could summon images to their minds. Last year, someone showed him my article about MX...Dr. Zeman now wonders just how common aphantasia is. “Moderately rare” is his guess, but to follow up, he has sent the questionnaire to thousands of people in Exeter. He hopes to find enough people with the condition to begin a bigger scanning study, comparing their brains with those of people who see vivid mental images. Together, they may reveal more than MX could on his own.