The following is a summary of “Linking perceived to physical contrast: Comparing results from discrimination and difference-scaling experiments,” published in the January 2022 issue of Ophthalmology by Shooner, et al.

To study how stimulus contrast is encoded in achromatic and chromatic pathways using simple grating stimuli, psychophysical approaches were employed to estimate the relationship between perceived stimulus intensity and physical intensity. Researchers compared two experimental approaches for a study: contrast discrimination and maximum likelihood difference scaling (MLDS). 

The results of both experiments were modeled using a transducer function that maps physical contrast to an internal signal and an estimate of the variability of this representation (internal “noise”). The transducers derived from both experiments had a similar form but occupied different ranges of physical contrast, reflecting differences in contrast sensitivity. It supported the idea that suprathreshold chromatic and achromatic contrast are processed similarly once differences in contrast sensitivity are considered. However, model estimates of internal noise were higher in the MLDS experiment than in the discrimination experiment, which could be attributed to a difference in task complexity. 

An alternative version of the MLDS model was tested, in which internal noise increased with response level, but the alternative did not perform better than the original constant-variance model in predicting holdout data in a cross-validation analysis.

Reference: jov.arvojournals.org/article.aspx?articleid=2778295