The former president of Pixar and Walt Disney Animation Studios says he has a "blind mind's eye".
Most people can close their eyes and conjure up images inside their head such as counting sheep or imagining the face of a loved one.
But Ed Catmull, 74, has the condition aphantasia, in which people cannot visualise mental images at all.
And in a surprising survey of his former employees, so do some of the world's best animators.
Ed revolutionised 3D graphics, and the method he developed for animating curved surfaces became the industry standard.
He first realised his brain was different when trying to perform Tibetan meditation with a colleague.
Visualisation is a core part of the practice and he was told to picture a sphere in front of him.
Ed told the BBC: "I went home, closed my eyes… I couldn't see a thing and for an entire week I kept trying to visualise this sphere."
He spoke to colleagues and learned that some animators could form mental images so strong they would open their eyes and the image would still be there, so they could practically trace what they could see.
Ed just thought: "That's interesting, it's probably what makes them an artist."
But eventually Ed realised he was not alone and that, perhaps counter-intuitively, some of the greatest talents in animation could not visualise either.
Oscar-winner Glen Keane, who created Ariel (The Little Mermaid), also has no visual imagery.
Ed told the BBC: "He is truly extraordinary, he's one of the best animators in the history of hand-drawn animation.
"[And] he said that he could never visualise either."
Ed said: "When he first did The Little Mermaid, it's a bunch of scribbles.
"And then it converges, after he works on it for a while, into this gorgeous piece of art.
"And as far as he's concerned, that's the right way to work because it means he's looking deep down inside, for his emotions, and that's what drives his drawing."
Origins of aphantasia
The term aphantasia was coined by Prof Adam Zeman, from the University of Exeter Medical School, in 2015.
He had documented a case of a man who lost his mind's eye in his 60s following a heart operation.
Prof Zeman was then contacted by people who reported never having one and he described the condition as aphantasia in the journal Cortex.
Around one in 50 people is thought to have aphantasia, although exactly what is going on in the brain is still unclear.
Parts of the brain from the frontal and parietal lobes are involved in visualisation and differences at any point in the system could be the cause.
Ed, who co-founded Pixar, had a parting gift for his former employees when he left last year – a piece of homework.
He asked 540 members of staff to take a test of the vividness of their visual imagery.
He sorted the results into:
- All staff
- Technical artists – who have a strong background in computer programming as well as artistry
- Artists – the animators, film designers or storyboard artists
- Production managers – often people out of film school who organise the production
It showed that the artists were slightly better than technical artists at visualising, but the differences were not that huge.
"It was not a large skew, that's the real issue," said Ed.
The production managers were better than both.
The homework also revealed stark differences between two artists and good friends of Ed's who had worked on Frozen.
One can see an entire movie in his head and play it backwards and forwards and never needs to see a movie twice because he can visualise it.
The other cannot see anything at all.
Lessons from aphantasia
Some people with aphantasia find it a cause of distress.
People have described feeling isolated and alone after discovering that other people could see images in their heads and they could not.
Ed argues aphantasia is not a barrier to success.
He told the BBC: "I think the main message is, &#Read More – Source