I know what you mean. I wonder whether it's useful to distinguish thinking from that "mind's eye" imaging capability that I believe you're describing. They might be separate things. It's pretty evident that a cat or a dog, or even a fish, has memory. Is memory the ability to conjure things in the mind's eye? If remembering one image reminds us of other images, then language-free thought might be moving through a chain of images. Substitute "image" with symbolic memories, and that might be the start of abstract reasoning.