Which psychophysicist's major contribution was to demonstrate that the relationship between incoming stimuli and corresponding perceptions was not one-to-one?

The psycho-physicist we are talking about here is Fechner.

Thus,

the answer is none other than Gustav Fechner.

Gustav Theodor Fechner was indeed the founder of the experimental psychology. This experimental psychology is the one that applied the scientific method to the research of behavior and mind. And the question above is also one of the contributions of Gustav Fechner and his works.

nigger, that word was originated for white folks   to keep black people under

and when black people use it, they know that's just how they greet each other

and when white folks use it, they know there's a double meaning under

answer; analytical,creative and practical;