Psychophysics is the study of the relationship between stimuli and perception. A lot of it is perceptual thresholds, so how much sound or light is needed for someone to hear or see something (fun fact: people can reliably detect a single photon in a dark room at better than chance). Thus much of the experimental protocols boil down to asking “can you hear this?” after playing a sound which is what the Verizon ads always made me think of.

The other half of the discipline is figuring out the wiring on low level perception. For instance we have massive parallel processing in the early visual system that does things like highlight lines and edges, which is what makes the Mach dot/band illusions work:

https://en.wikipedia.org/wiki/Mach_bands

It’s what I studied in undergrad as it was a nice overlap in my interests in cognitive science, psychology and computer science. I basically just like knowing how everything works :)

More info:

https://en.wikipedia.org/wiki/Psychophysics