Both writers were inspired by images.
In this article, Creating Content the Frankenstein Way, Mark Levy says of Mary Shelley (at that time, she was Mary Godwin):
“One night, as she lay in bed with eyes closed but unable to sleep, a scene appeared in her mind. She saw, in her own words, a ‘pale student of unhallowed arts kneeling beside the thing he had put together,’ which she soon recognized as a ‘hideous phantasm of a man stretched out.’ Then, ‘on the working of some powerful engine,’ the phantasm showed ‘signs of life.’
Mary Shelley wrote Frankenstein as a result of the images in her mind.
Stevenson drew a map, which he called “Treasure Island”, Treasure Island by Robert Louis Stevenson:
The more Stevenson studied this map of his creation, the more his imagination expanded. First, he could see the vegetation of the island. Then the island became peopled in his mind’s eye, and their stories began to appear. “It was to be a story for boys,” Stevenson wrote; and with excitement and ease, he produced the first fifteen chapters in as many days.
Images are powerful
One of my writing students was stuck on a project. I asked her to close her eyes, and relax, while musing about the project. Then I asked her to wait for an image to float into her mind. As soon as something appeared, no matter how silly, she was to tell me what it was.
After a minute or two, she told me she saw a clock. At first the clock meant nothing to her. I let her complain about how silly the exercise was for a minute. Finally she stopped talking. I said: “Write down what you’re thinking.”
To cut a long story short, the image of the clock solved the problem she was having very neatly.
Everyone is creative. You can become as creative as you want to be, if you pay attention to the images which float through your mind. “Split brain” theory suggests that your right brain “thinks” in images. These images are then interpreted by the logical left brain.
Therefore, if you’re stuck on a problem, or want to be more creative, any images which float through your mind may provide a creation solution. Just pay attention to them, and see what happens.