I do not see it," so he seems to have supposed that nobody else did.
When he made inquiries in general society, Mr.Galton found plenty of people who "saw" mental imagery with every degree of brilliance or dimness, from "quite comparable to the real object" to "I recollect the table, but do not see it"-- my own position.
Mr.Galton was next "greatly struck by the frequency of the replies in which my correspondents" (sane and healthy) "described themselves as subject to 'visions'".

These varied in degree, "some were so vivid as actually to deceive the judgment".

Finally, "a notable proportion of sane persons have had not only visions, but actual hallucinations of sight at one or more periods of their life.

I have a considerable packet of instances contributed by my personal friends." Thus one "distinguished authoress" saw "the principal character of one of her novels glide through the door straight up to her.

It was about the size of a large doll." Another heard unreal music, and opened the door to hear it better.