Seeking Psychophysics Answers

[Michael Sean Davis]

As part of some graduate research I am doing, I need a function that 
describes the relationship between the intensity of a physical stimulus 
and subjective psychological magnitude.  The outdated  Introductory 
Psychology material that I have (from the 1970s) talks about Fechner’s 
Law and Stevens Power Function.  It indicates these laws as follows: 

Fechner’s Law:  S = K log I

Steven’s Power Function: S = I (to the K exponent)

where S is psychological magnitude, K is a constant particular to the 
continuum, and I is the intensity of the physical stimulus.

The text says that there are problems with both of these functions, but 
that the evidence is leaning toward Steven’s Power Function.

My question is: what is the current thinking about the relationship 
between physical and psychological magnitude of stimuli?  Has either of 
these functions been accepted?  Are there new ways of thinking about 
this relationship? 

Any feedback from knowledgeable people or psychophysics gurus will be 
regarded as near live saving information!

My e-mail is davis at intr.net.  My fax is (202) 965-7879.

Many thanks in advance!!

--Michael Sean Davis