What does psychophysics study? unusual discoveries in laboratory experimentations
the laws of physics and how believable they are
people's reactions and perceptions to stimuli

people's reactions and perceptions to stimuli.

Explanation:

Psychophysics can be defined as the scientific study of people's reactions and perceptions to stimuli.

Stimulus can be defined as an obvious change in either the chemical or physical structure of an organism' environment (either external or internal). Thus, all living organisms (humans) respond to changes in their environment and consequently, an appropriate response or reaction is made. Also, stimulus arising from within the organism is known as internal stimulus while those from its environment are known as the external stimulus.

In organisms, the specialized cells that detect stimulus are generally known as sensory receptors while a group of these receptors is referred to as sense organ.

Hence, psychophysics is a branch of psychology and it is typically focused on determining the effects of stimuli on the mental health or processes of humans.