Psychophysics

Psychophysics is one of the oldest psychological history of science research areas; they refers to the lawful correlations between subjective psychic ( mental ) experience and quantifiable, so objective physical stimuli as the triggering processes. Psychophysics was established in 1860 as a branch of experimental psychology Fechner and based on the preliminary work of Ernst Heinrich Weber. It is sometimes also considered as a branch of sensory physiology, perception psychology or psychophysiology and deals partly with aesthetic questions of taste.

In Fechner, the distinction between external and internal psychophysics goes back. While the outer psychophysics measures the relationship between sensory irritation and experience, the inner psychophysics deals with the relations between neural processes and experience. Usually, the study of stimulus- experience contexts is the " psychophysics " primarily understood, while the area of the inner psychophysics is assigned to the cognitive neuroscience today. These assignments result from the fact that Fechner the inner psychophysics postulate only theoretically, but due to lack of neuroscientific methods could not do research on it.

History

The Pythagoras (ca. 570-510 BC), attributed the discovery of a constant ratio between the length of the strings of a lyre and the basic chords of the music is based on the legend of Pythagoras in the forge. Nevertheless, has received the designation for the Pythagorean based on the fifth as the most harmonious mood interval, vgl.a. Circle of fifths. The tone intervals, referred to as harmonic oscillation conditions are as follows: octave 1:2, fifth 2:3, fourth 3:4 and 4:5 Major third. With these remarks, the sheet is already stretched to aesthetic issues, such as those of the golden section to which Fechner has also written empirical studies.

One of the earliest approaches to psychophysical scaling comes from Claudius Ptolemy (ca. 100-175 AD) around 150 AD It has a useful measure of the size of the stars proposed based on the apparent brightness of the stars.

Subregions

Apart from the distinction between inner and outer psychophysics can differentiate the areas of work in relation to the sensory modalities. Many psychophysical work on a sense - ie about the visual or auditory perception (see a psychoacoustics ), the smell or touch - specialized. Moreover, one can distinguish four different issue areas:

Psychophysical laws

In psychophysics three classic laws have been formulated. Weber's law describes the observation that the difference threshold is in an almost direct proportion to stimulus intensity: the stronger the stimulus, the greater must be the stimulus difference to notice this difference. The formal description is:

This represents the stimulus difference and for the stimulus. The quotient is also called a Weber's fraction. An example: For k = 1/10 you need for a stimulus of 10 units a stimulus difference of one unit in order to notice him. With a weight of 20 g would therefore need 2 g to register a difference. With a weight of 20 kg, however, it would be 2 kg stimulus fluctuation.

Fechner law ( Fechner - scale) describes the relationship between stimulus intensity and experience:

E represents in the formula, the sensation strength, R is the stimulus intensity. It corresponds to the logarithm of the stimulation intensity multiplied by a constant, to which a further (small ) constant is added. In other words, says Fechner law that sensation strength ( approximately and in a suitable range ) grows with the logarithm of the stimulus intensity. A doubling of the stimulus intensity so do not be a doubling of sensation strength, but only about an increase of k * 30% result. Fechner derived his scale from the Weber 's law from means of the postulate that (depending on the different stimulus intensity ) difference threshold corresponds to a constant increase sensation. The sensation strength is then the integral of Weber's collapse. Like all of neurophysiological / psychological perception laws Fechner law applies only within a certain scope. Fechner scales are, for example, the volume measurement ( as sound pressure level in dB) and brightness measurement is based.

Middle of the 20th century, it was Stanley S. Stevens ( 1957), a way to measure sensation strengths directly. It led to a different method of so-called Magnitude Estimation. The sensation strengths found by these methods can be well over a wide range by a power function describe ( Stevens's power function ):

The exponent is represented here modality power which is less than one for the majority of the sense (with the exception of the pain sensation and the length ) and the estimated size of a subjective attribute. After Stevens meets the average estimate of the size of an attribute to be about as a power function of the intensity of the stimulus. The Stevens' law is often shown in a double logarithmic representation; in it, the relationship is a straight line, whose slope is determined by the exponent.

In most representations of the Steven'sche law is presented as the opposite the Fechner'schen truer. This popular textbook opinion is, however, contradicted.

Science and philosophy historical significance

The psychophysics has developed in relation to other cognitive science disciplines very early. Weber's and Fechner's central work fall on the middle of the 19th century. Their systematic and empirical investigation of stimulus - experience - contexts has had a great influence on many scientists and philosophers. Examples are Hermann von Helmholtz and Ernst Mach, Max Weber and Wilhelm Wirth. Sigmund Freud introduced the introduced by Fechner principle of psychic energy on ( psychodynamics ). Fechner sensation touches the central doctrine in the philosophy of mind mind-body problem. Psychophysics was thus one of the science historically significant pioneers of a scientific study of consciousness processes.

At the same time the work of Fechner also provides a critical and skeptical perspective on the natural sciences. Fechner did not think that mental events can be reduced to physical events as a critic of materialism. Nevertheless, he tried to make with the psychophysics relationships between these events. Fechner methodological setting is partially reflected even today when neuroscientists again, the search for neural correlates of consciousness, without wishing to make a metaphysical statement about the nature of consciousness.

After it appeared for several decades to include almost de rigueur to keep the classical psychophysics for obsolete and therefore not to take their methods of knowledge, a strong growth of interest is noted in the present.