Mental imagery is associated with working memory:

Recent research suggests that visual mental imagery functions as if it were a weak form of perception.

Evidence suggests overlap between visual imagery and visual working memory – those with strong imagery tend to utilize it for mnemonic performance.

We use the term ‘mental imagery’ to refer to representations and the accompanying experience of sensory information without a direct external stimulus. Such representations are recalled from memory and lead one to re-experience a version of the original stimulus or some novel combination of stimuli.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4595480/

Well this is troubling, since Socionics doesn't have a concept of memory. Saying things like "Mental imagery is associated with Ni or Ti" is pointless, since you're just associating the concept of mental imagery with Ni or Ti, but you're not explaining how that mental imagery works. You can say "Mental imagery is Ni", but it's like so what? The only use of that is you have shortened the words to "Ni".