I'm not certain which test Catmull used, but the article links to this one: https://wh.snapsurveys.com/s.asp?k=148940557153

This past weekend, I attended the conference he was interviewed at for this article. During his talk, he mentioned he had them complete the VVIQ from University of Exeter (which the other replies linked to), the Plymouth Sensory Imagery Questionnaire (https://www.plymouth.ac.uk/research/psychology/imagery), plus several more questions, maybe a dozen or so.

It's linked in the article but the link kind of looks like an ad so it's easy to miss: https://wh.snapsurveys.com/s.asp?k=148940557153

It may have been this one:

https://en.wikipedia.org/wiki/Vividness_of_Visual_Imagery_Qu...