A brief introduction to Psychophysics
Psychophysics is the study of human perception, or how the physics of the outside world (photons, sound waves, etc) are represented in the human mind and brain. The understanding of this domain is important to a variety of modern technologies including sound and image compression, evaluation of auditory and visual impariments, and the design of virtual and augmented reality systems.
Standard questions in psychophysics include finding perceptual thresholds (a level set estimation problem) and estimating just-noticeable differences (a global exploration problem).
For more information on this field of study, see Psychophysics on Wikipedia or this short intro to psychophysics from Neuromatch Academy.