Psychophysics
Psychophysics is a branch of psychology that examines the relationship between physical stimuli and the psychological responses they elicit in organisms. This field emerged in the mid-nineteenth century, largely thanks to the foundational work of pioneers like Ernst Heinrich Weber and Gustav Fechner. Psychophysics encompasses all five senses—vision, hearing, touch, taste, and smell—and primarily revolves around threshold measurements. These thresholds are critical points that indicate the minimum levels of stimulus required to provoke a sensory response.
Weber's law, formulated by Weber, highlights that the ability to notice a change in stimulus is proportional to the original intensity of that stimulus. Fechner expanded on this by seeking to quantify the connection between physical events and mental experiences, culminating in his influential book, "Elements of Psychophysics." Modern methods in psychophysics, such as the Method of Limits, Method of Adjustment, Method of Constant Stimuli, and the Staircase Method, continue to build on these original concepts. These methods strive to accurately assess how individuals perceive stimuli, recognizing that subjective experiences can vary significantly among different people.
On this Page
Psychophysics
Psychophysics is a field of psychology that studies the effects of physical stimuli on the psychological responses of an organism. The science was pioneered in the mid-nineteenth century as a way to measure sensations as perceived by the mind. Psychophysics can be applied to any of the five senses—vision, hearing, touch, taste, or smell—and primarily relies on the concept of threshold measurement—a minimum point at which a reaction is generated—to gauge results.
Origins
Prior to the nineteenth century, scientists who studied human behavior considered the body and the mind separate entities. The body was a part of the physical world and the consciousness part of the mental world. Examination of the human mind was most often left to the field of philosophy.
In the 1830s, German physician Ernst Heinrich Weber began experimenting with the concept of a difference threshold—the smallest possible difference that would be noticed between two separate stimuli. Using weights, Weber found that the difference between heavier weights would need to be greater in order to be noticed than the difference between lighter weights. For example, if a subject noticed a half-pound change in weight added to a five-pound bar, then one pound would need to be added to a ten-pound bar for the subject to notice. His experiments led to the formulation of Weber's law, which states that a change in stimulus that is just noticeable is a constant ratio of the original stimulus.
Almost three decades later, German physicist and psychologist Gustav Fechner built on Weber's work and began focusing on the effects external stimuli have on all the senses. Fechner wanted to discover how a physical event experienced by the body is received by the mind. He used his background in physics to attempt to create a mathematical equation quantifying the relationship between body and consciousness. His 1860 book, Elements of Psychophysics, established the science of psychophysics and gave it a name.
Fechner recognized measuring a sensation is a difficult task. A sensation is a subjective response to a stimulus and varies by individual. External factors can also affect how a sensation is perceived. For example, a subject whose eyes had adjusted to a dark room would perceive an amount of light differently than a subject who was standing in daylight. Fechner's solution was to introduce stimuli to a subject and determine whether or not sensations were present and if the sensations were perceived as the same or not. From these judgments, he was able to develop various methods to measure the response.
Methods of Psychophysics
Much of modern psychophysics is still based on Fechner's work and uses thresholds to measure the relationship between stimuli and perception. In addition to measuring the difference threshold, researchers also gauge the value of an absolute threshold. An absolute threshold is the smallest perceptible amount of stimulus that will produce a response. For example, the dimmest amount of light or weakest amount of sound a subject can detect is the absolute threshold. Fechner devised three methods to determine threshold values; later researchers added others. Results from these methods can vary depending on the time it takes for a particular subject's nervous system to register a response, the intensity of the stimulus, or differing criteria used by the researchers.
Method of Limits: To measure absolute threshold using this method, a subject is presented with a series of stimuli in either ascending or descending order and is asked via a yes-or-no question to determine the smallest amount that is detectible. If the test begins with the brightest amount of light, for example, the light would be decreased incrementally until the subject determines he or she can no longer perceive it. One of the drawbacks of this method is that subjects can begin to anticipate a value and "predict" when they can perceive a stimulus.
Method of Adjustment: In this method, the subject controls the amount of stimulus and continually adjusts it until he or she finds the amount that is "just barely detectible." With sound, for example, a subject would turn a knob until the point when he or she can or cannot hear a sound. This method can pose problems for researchers because the level of perception can differ from person to person.
Method of Constant Stimuli: The method presents a series of five to nine stimuli in a random order and the subject is asked to detect the desired threshold value. A subject may be asked to choose the brightest in a series of shaded colored circles shown in a certain order. The test would be repeated with the circles shown in a different order. This method is generally considered the most accurate because it removes the possibility the subject can try to predict the outcome.
Staircase Method: This method was developed from later research and is most often used by modern psychologists. The Staircase Method is based on the Method of Limits in which a series of stimuli is presented in an alternating ascending or descending order. When the subject can detect the desired variable, the test is stopped and the "direction" of the staircase is reversed and the process repeated. The threshold is considered to be the intensity level at the point the staircase is stopped and reversed.
Bibliography
Baker, Daniel. "Visual Psychophysics for Beginners." Daniel's Visionarium. Daniel's Visionarium. Web. 11 Mar. 2016. https://bakerdh.wordpress.com/2011/04/28/visual-psychophysics-for-beginners/
"Chapter 7: Using Psychophysics to Study Perception." University of Washington. PDF. Web. 11 Mar. 2016. http://courses.washington.edu/psych333/handouts/coursepack/ch07-Using‗psychophysics.pdf
"Classical Psychophysical Methods." University of Calgary. University of Calgary. Web. 11 Mar. 2016. http://ucalgary.ca/pip369/mod1/measuring/classical
Gescheider, George A. Psychophysics: The Fundamentals. Mahwah: Lawrence Erlbaum Associates, 1997. Print.
"Psychophysics—Concepts in Psychophysics." Psychology Encyclopedia. Net Industries. Web. 11 Mar. 2016. http://psychology.jrank.org/pages/514/Psychophysics.html
Woodruff, Burrton. "Introduction to Psychophysics." Appalachian State University. PDF. Web. 11 Mar. 2016. http://www1.appstate.edu/~kms/classes/psy3203/Psychophysics/Intropsychophysics.html