A cadaverousness of complexion; an eye large, liquid, and luminous beyond comparison… (8)
The special quality of Usher’s eyes suggests that he has special abilities of perception. And, indeed, he can recognize elements of the supernatural that take the narrator longer to recognize.
We painted and read together; or I listened, as if in a dream, to the wild improvisations of his speaking guitar. (15)
This is another case of doubling; reality is reflected, though distorted, in the worlds of fiction and music.