Psychophysics
The purpose of this chapter is to provide the reader with some tools for studying and understanding the sensory systems in general. The notions of absolute threshold and difference threshold are defined, and a series of classic methods for estimating thes
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Psychophysics
A field of psychology, psychophysics has as main concern the understanding of the passage of a physical event into a psychological reality. Researchers in psychophysics examine the link between the physical measurement of a stimulation and the psychological measurement of this stimulation. Psychophysicists are primarily interested in three types of capabilities: detecting stimuli, discriminating them, and estimating their value (scaling). The first two types are associated with the fundamental concepts of absolute threshold and differential threshold, respectively.
1.1 Detection The different sensory systems provide information on the physical and chemical changes that may occur in the environment. A fundamental objective of psychophysics is to assess the minimum amplitude that these changes must have so that an individual can be notified. This minimum amplitude, that is to say the smallest amount of energy that can be detected in the absence of any stimulation, is called absolute threshold. Below this threshold, sensation is not possible. However, this threshold is a point whose identification corresponds to an operational definition for a given method. Traditional psychophysics offers several methods for estimating a threshold. The most conventional are the method of constant stimuli, the method of limits, and the method of adjustment. For now, only the constant method is presented: Gustav Fechner One could say that psychophysics started in 1860 with the publication of the book Elements of psychophysics by the German researcher Gustav Theodor Fechner (1801–1887). Philosopher and physicist, the founder of psychophysics wanted to study the links between the inner world and the outer world. Also known under the pseudonym of “Dr. Mise”, Fechner, who worked in Leipzig, had quite a special mind. We owe him various experimental methods still used in psychophysics, but he was also interested in, for example, the properties of the electric current, experimental aesthetics, and even life after death. Note © Springer International Publishing Switzerland 2016 S. Grondin, Psychology of Perception, DOI 10.1007/978-3-319-31791-5_1
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1 Psychophysics that there is an annual meeting of psychophysics, usually held in October, called Fechner Day (October 22). This meeting is held in different locations around the world under the supervision of the International Society for Psychophysics (http://www.ispsychophysics. org/), founded in 1985 in southern France.
1.1.1 Absolute Threshold and Method of Constant Stimuli For measuring an absolute threshold with the method of constant stimuli, also called the constant method, one must first determine the threshold roughly by locating a region for which a stimulus is almost never perceived and for which a stimulus is almost always perceived. Then, we generally select from five to nine stimuli located between these regions. After this selection, the selected stimuli are presented repeatedly in random order. The method requires an observer to make at least a hundred ju
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