A study of stimulus range effects in free modulus magnitude estimation of contrast

The exponents of perceived contrast functions determined for sine wave gratings varied from 1.1, when perceived contrasts were estimated over a 0.6 log unit range of stimulus contrast, to 0.56 when perceived contrasts were estimated over a 1.9 log unit range of stimulus contrast. Intermediate stimulus contrast ranges produced intermediate exponents. This contrast range effect appears to account for the different exponents reported in previous magnitude estimation studies and for the fact that some studies show an exponent increasing with increasing spatial frequency while others do not.