If you go to Wikipedia, and type the words mind's eye, you will get a definition of the same, where its states that human's have the "ability to visualize, i.e., to experience visual mental imagery...one's ability to "see" things with the mind." It goes on to expand on what it is, where it says that it is not fully understood...and then starts to get into terms like lateral geniculate nucleus, neocortex and neuroplasticiity....all subjects I didn't learn in Biology 101...
I suspect people like me, who rely on their creativity as part of their lively hood, have the ability to picture things in their mind better than others who don't. I can't speak for all inventors, artists, writers and the like. But I have always been able to mentally construct things in my brain. Imagine having brain CAD software, where you can construct things or figure out other ways to build something, all without lifting a finger, and just using the synapses located deep in your cerebellum.
Graphic designers do the same thing...they create something in their brain, and just use a computer and software to make it come to life...The lines of a logo don't seem cool enough, or maybe everything looks great but the color doesn't seem right? The designer just imagines the logo cooler looking or with the right color in their mind's eye, and then puts it into the computer software to bring it to life...that does the trick!
Writers weave the plot of their soon to be best-seller novel in their brain...Then, they construct carefully worded sentences to parlay their vision of the story to others...It may not come out perfect the first time, but through new drafts, reworked plots and further refinements (including opinions from their soul mate, family or even publisher), the story finally becomes final and is s ready for book binding or e-books...who can you attribute did the bulk of the work for the writer? The mind's eye, of course..
For inventors...if one iteration is built in the mind, but has a flaw? Try another avenue, maybe this iteration will solve the flaw in the previous. Need to solve a complex engineering problem for a never before made product (and soon to be invention)? Create different versions in your brain, all on the fly, using all the engineering and material tools you have available...the ones that you have been stashing away in your brain from the day you were born, waiting to use some rainy day.
Still can't figure out a difficult problem? Many times, a deep sleep can bring an answer to an engineering conundrum up to the surface..hopefully you will write it down or make a note to remember it, so the dream tide doesn't pull the solution back into the ocean of ideas not yet used or uncovered. (See my earlier blog on April 26, 2011 entitled Your Brain - Working Overtime, All The Time).
The mind's eye can even be fully functioning even when numbed by stress, drugs and alcohol, and depression, which is why you see recording artists able to put out highly creative and pinnacle songs of their career when they are barely able to function when not creating...The mind's eye is working like an obedient dog for them, to be able to bring it to the forefront on command and then let it recede back to a state where it is compromised beyond use.
How does your mind's eye work for you? Are you able to use it to your advantage in your daily work or personal life? Or are you inhibited when trying to picture something in your mind, and need to see it in real life first? Either way, it doesn't matter, brains are one amazing tool...if one doesn't have a good mind's eye, I can guarantee it makes up for it in other, in super complex, high functioning ways!