Blind in the mind: why some people can’t see pictures in their imagination
theconversation.com
theconversation.com
The best advice I've seen about the condition is to learn how to relax first. Some people prefer their other senses - auditory or kinesthetic - and it's only when they're fully relaxed that they can start to incorporate 'visuals' into their imagination.
People whose inner world is basically non-sensory are 'Digitals', rather than the usual VAK.