Psychophysics is the study of how stimuli are perceived by organisms, notably humans. In simple terms, when you touch a lit stove, you feel that it is hot. The broader implications aim to study all aspects of how we perceive the world, and how our perception affects how we navigate through life. The field covers all five senses, as well as the sense of the passage of time.

Psychophysics has its roots in the 1800s. Gustav Theodor Fechner, a German psychologist, is credited with coining the term. He contributed many valuable hypotheses to the field, such as the fact that if the right hemisphere of the brain were separated from the left one, it would result in a subject with a split consciousness. This theory was validated nearly 100 years later, and this method is used today to treat some forms of epilepsy.

One of Fechner's most important contributions to science and medicine is proving that the processes of the human mind can be measured accurately in a laboratory. In fact, he's so important that psychophysicists celebrate October 22^nd as Fechner Day.

Much of the work in this field is done through experimental psychology. This simply means posing a series of tasks to human volunteers and recording their actions. There are various methods to conduct psychophysical tests. For instance, there is the Method of Limits, exemplified in a common test given to assess hearing. A sound (or other stimuli being tested) starts out so low that it cannot be perceived, and gradually made louder until the subject reports they notice it. This and other methods are ruled by the principles of thresholds-levels at which subjects can feel stimuli. A crucial threshold is one where the stimuli is barely-noticeable, or noticeable only some of the time.

Extrapolating meaning from these actions, however, can be a challenge, and competing teams of scientists can reach different conclusions from the same results.

Since Psychophysics relies on the subject of the experiment to accurately report on what they are sensing, study can be difficult. Experimenters must be mindful of several subject errors which could skew their experiments. Common errors include 'habituation,' in which the subjects report that they can perceive a stimulus they cannot perceive, out of habit, or 'anticipation', in which the subject expects the stimulus, and reports it early. Georg von Bekesy combated these errors with the 'staircase method,' in which the stimulus is made fainter until the subject can't perceive it, and then slowly louder until they can, allowing researchers to pinpoint the subject's true threshold.

Psychophysics have allowed various humans conditions to be studied properly, including benign ones like synesthesia, where the subject sees colors that correspond with certain sounds, to dangerous ones like epilepsy, in which abnormal electrical patterns in the brain lead to sensory disturbance. Some forms of epilepsy can be triggered by visual stimuli, such as flashing lights. Studying this link can is vital, as it may ultimately help many people lead a normal life.

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