Psychophysics is a branch of psychology that studies the relationship between physical stimuli and the sensations and perceptions they produce. It aims to quantify how changes in physical properties, such as intensity or frequency, affect our sensory experiences. For example, it explores how much louder a sound must be for us to notice a difference in volume. The field was pioneered by Gustav Fechner in the 19th century, who developed methods to measure sensory thresholds and the perception of stimuli. Psychophysics has applications in various areas, including neuroscience, audiology, and visual perception, helping us understand how we interpret the world around us.