Discover magazine has a fantastic Carl Zimmer piece about a man who lost the ability to see things in his mind’s eye after a minor neurological procedure.
Zimmer covers a recently published study on patient MX who lost his conscious visual imagery but could still do tests, like mental rotation, that were assumed to need the ability to mentally picture the procedure to work it out.
All the exams the scientists gave MX confirmed his claim that he was missing his mind’s eye. And yet he could do lots of things that would seem impossible without one. Without any effort he could give the scientists detailed descriptions of landmarks around Edinburgh, for example. He could remember visual details, but he couldn’t “see” them. Della Sala and Zeman asked MX to say whether each letter of the alphabet had a low-hanging tail (like g and j). He got every one right. They asked him about specific details of the faces of famous people (“Does Tony Blair have light-colored eyes?”). He did just as well as the architects.
The key insight came with a test derived from a classic psychological experiment invented in the 1970s by Stanford University psychologist Roger Shepherd. Della Sala and Zeman showed MX pairs of pictures, each one consisting of an object made up of 10 cubes. MX had to say whether the pairs of objects were different things or actually the same thing shown from two different perspectives. Normal people solve this puzzle in a strikingly consistent way, with their response time depending on how much the angle of perspective differs between the two objects: The bigger the difference, the longer it takes people to decide whether the objects are the same…
MX’s results flew in the face of that explanation. When he solved the puzzles, he always took about the same amount of time to answer—and he got every one right.
We still understand relatively little about the role and importance of visual mental imagery or what role it takes in problems or impairments.
A study I was part of found that people with congenital prosopagnosia, a genetic inability to recognise faces, had virtually absent visual imagery despite having no signs of brain damage or neurological abnormalities.
Patients who acquire prosopagnosia after brain damage often report that they can no longer imagine what faces look like, but in MX’s case, he seems to have lost his ability to mentally ‘see’ faces but has no problem recognising people.
The Discover article is a concise yet comprehensive take on this new study that helps us understand the link between how we experience the world and how we construct it inside our heads.
Link to Discover article ‘Look Deep Into the Mind’s Eye’.