He. Ross, ON THE POSSIBLE RELATIONS BETWEEN DISCRIMINABILITY AND APPARENT MAGNITUDE, British journal of mathematical & statistical psychology, 50, 1997, pp. 187-203
Some psychophysicists seek a unified theory in which the scaling of ap
parent sensory magnitude and the discrimination of differences in inte
nsity can be encompassed. When contextual factors are held constant, t
here is a positive correlation over many sensory continua between the
exponent of the power function for sensory scaling and the inverse of
the Weber fraction. Variations in neural efficiency also show a simila
r correlation with apparent magnitude and discrimination. The role of
other factors (such as contrast, adaptation and size scaling) remains
unclear. Both Weber and Fechner considered aspects of these issues. We
ber held that, for the same physical stimulus intensity, apparent magn
itude and discriminatory ability increased with neural efficiency. Fec
hner held that changes in apparent magnitude had no effect on discrimi
nation: a stable differential threshold was predicted by the Parallel
Law (Weber's Law applied to internal sensations). Evidence is consider
ed for the tactile sense and weight perception, and for visual size; T
he relation between apparent heaviness and weight discrimination is co
mplex, varying with the state of adaptation and with neural efficiency
. There is some evidence that both tactile and visual apparent size in
crease with a finer underlying neural structure; but it is unclear whe
ther other types of increase in apparent size lead to increased spatia
l acuity, or to differences in the Weber fraction for line length. The
variety of values of apparent magnitude and discrimination, and the l
ack of a monotonic relation between them, makes it unlikely that all k
nown relationships could be encompassed in a unified psychophysical th
eory.