Psychophysical - SpeedyLook encyclopedia

History

It is considered that Gustav Fechner, author of the Elemente der Psychophysik in 1860, is the founder of the psychophysical one. Even if one can make go up his influences with the German physicists like Johann Friedrich Herbart, Fechner were the first to have undertaken a systematic mathematisation of the relation between stimulation and Sensation starting from work of Ernst Weber.

Raise of Fechner, influenced by work of Hermann von Helmholtz and the theories of the Experimental method in the Natural science, the German physiologist Wilhelm Wundt will give to psychophysical its methodological and theoretical bases. Appointed professor at the university of Leipzig, it creates the first laboratory of experimental Psychologie in which will come to study many European and American psychologists. On the American continent, a turning took place at the end of the years 1950 with work of Stanley Stevens, then psychologist at the laboratory of Harvard. By being interested in the physiological properties of the acoustic transduction of the sounds by the ear, it replaça on the front of the scene the role of the peripheral bodies in the feeling. As from the years 1960, the comparison of psychophysical measurements with neurophysiological observations largely took part in the convergence of the experimental Psychologie with the Neurosciences.

Concepts & methods

The experimental step into psychophysical in general consists in isolating a physical size in order to determine how it is connected to a feeling. For example, to study how the frequency of a sound is perceived, the psychophysical approach will consist in handling the height of the sound (physical size) and collecting the judgments of the subject taking part in the experiment.

The psychophysical one rests primarily on the concept of Seuil of detection . It is about the limit from which an individual is not able any more to say if a stimulation is present or not. By extension, it is also the threshold with the lower part of which he does not manage to distinguish two stimulations. In this case, one then uses rather the expression differential Seuil .

The methods used to determine this Seuil of detection are multiple. Progress of experimental methodology into psychophysical, on the whole, consisted in eliminating skews in the mode from presentation of stimulations which could distort the evaluation of the threshold of detection. The principal methods are:

the method of the adjustments : the experimental subject varies itself stimulation in order to place it on the level which he judges being the limit of his threshold of detection
the method of the limits : the experimenter presents about the experiment a series of stimuli of decreasing or increasing intensity and records the level from which the experimental subject does not manage any more to detect the stimulus.
the method of the constant stimuli : with the difference of the method of the limits, the level of stimulation varies in a nonprédictible way by the experimental subject. This last must each time say so yes or not a stimulus was present.

These same measurements applied to the experimental determination of the differential Seuil led Weber then Fechner to propose the Loi of Weber-Fechner which stipulates as for the same type of stimulations the differential threshold is proportional to the physical size. For example, to discriminate according to their tonal Height, two sounds around 1000 Hz, the differential threshold will be twice higher than the differential threshold with 500 Hz.

The law of Weber is indeed valid in many fields of perception (like the perception of the sound intensity, the Perception of time, the perception of the Température) however one observes deviations compared to this law when one widens the range of variation of the physical parameters. In 1961, Stanley Stevens proposed a generalization of it known as Loi of Stevens according to which the feeling is related to stimulation by a Loi of power of which it could give the exhibitors for a great number of sensory fields.

In addition, Stevens introduced a fundamental distinction between physical the parameters which reflect a continuum sensory, known as prosthetic and those for which a quantitative variation of the physical parameter results in a qualitatively different perceptive change, metathetic feeling . Thus, if the tonal height is well a sensory continuum, it is not the same for the Couleur: it is not by increasing the Wavelength of a luminous stimulation of a certain color, red for example, that one gives a more intense feeling (" more rouge" in fact).

During years 1960, the Théorie of the detection of the signal was applied in a very fertile way to psychophysical measurements of the sensitivity. Developed within the framework of the engineering of the Telecommunications, this mathematical theory seeks to determine the reliability of a system of detection when there is noise in measurements. The interest of this theory was rather quickly charged by the psychologists insofar as the experimental subject when one presents to him stimulations close to his threshold of detection finds in a situation similar to a measure to a disturbed context. By measuring not only the performance by the number of correct detections but by also entering missed detections and them false alarms (cases where the subjects believed to detect a stimulus or a difference between two stimuli whereas there was not) one obtains an index of the sensitivity ratio/specificity of the capacities of discrimination of a given individual. That makes it possible to compare the purely perceptive capacity of a subject that it is preserving (i.e. reticent to report that it saw a signal of which it is not sure) or liberal (tending to say " I have vu" even if it is not sure of him). The theory of the detection of the signal remains the principal methodological framework used into psychophysical.

References

Random links:

Montegnée | Khaled Hosseini | Hamlet (opera) | Jean-Felix Infant | Gary Caldwell (footballer)