Gustav Theodor Fechner Robert H. All rights reserved. Previously published in Wozniak, R. Classics in Psychology, Historical Essays.
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History[ edit ] Many of the classical techniques and theories of psychophysics were formulated in when Gustav Theodor Fechner in Leipzig published Elemente der Psychophysik Elements of Psychophysics. From this, Fechner derived his well-known logarithmic scale, now known as Fechner scale.
During the s, when psychological research in Nazi Germany essentially came to a halt, both approaches eventually began to be replaced by use of stimulus-response relationships as evidence for conscious or unconscious processing in the mind. Peirce , who was aided by his student Joseph Jastrow , who soon became a distinguished experimental psychologist in his own right.
In their experiment, Peirce and Jastrow in fact invented randomized experiments: They randomly assigned volunteers to a blinded , repeated-measures design to evaluate their ability to discriminate weights. Though I promptly took to the laboratory of psychology when that was established by Stanley Hall , it was Peirce who gave me my first training in the handling of a psychological problem, and at the same time stimulated my self-esteem by entrusting me, then fairly innocent of any laboratory habits, with a real bit of research.
He borrowed the apparatus for me, which I took to my room, installed at my window, and with which, when conditions of illumination were right, I took the observations.
The results were published over our joint names in the Proceedings of the National Academy of Sciences. The demonstration that traces of sensory effect too slight to make any registry in consciousness could none the less influence judgment, may itself have been a persistent motive that induced me years later to undertake a book on The Subconscious.
One leading method is based on signal detection theory , developed for cases of very weak stimuli. However, the subjectivist approach persists among those in the tradition of Stanley Smith Stevens — He also advocated the assignment of numbers in ratio to the strengths of stimuli, called magnitude estimation. Stevens added techniques such as magnitude production and cross-modality matching.
He opposed the assignment of stimulus strengths to points on a line that are labeled in order of strength. Nevertheless, that sort of response has remained popular in applied psychophysics. Such multiple-category layouts are often misnamed Likert scaling after the question items used by Likert to create multi-item psychometric scales, e. Omar Khaleefa  has argued that the medieval scientist Alhazen should be considered the founder of psychophysics.
Although al-Haytham made many subjective reports regarding vision, there is no evidence that he used quantitative psychophysical techniques and such claims have been rebuffed. All the senses have been studied: vision , hearing , touch including skin and enteric perception , taste , smell and the sense of time.
Regardless of the sensory domain, there are three main areas of investigation: absolute thresholds, discrimination thresholds and scaling. A threshold or limen is the point of intensity at which the participant can just detect the presence of a stimulus absolute threshold  or the presence of a difference between two stimuli difference threshold .
Stimuli with intensities below the threshold are considered not detectable hence: sub-liminal. Stimuli at values close enough to a threshold will often be detectable some proportion of occasions; therefore, a threshold is considered to be the point at which a stimulus, or change in a stimulus, is detected some proportion p of occasions.
Absolute threshold is also often referred to as detection threshold. Several different methods are used for measuring absolute thresholds as with discrimination thresholds; see below. Discrimination[ edit ] A difference threshold or just-noticeable difference , JND is the magnitude of the smallest difference between two stimuli of differing intensities that the participant is able to detect some proportion of the time the percentage depending on the kind of task. To test this threshold, several different methods are used.
The subject may be asked to adjust one stimulus until it is perceived as the same as the other method of adjustment , may be asked to describe the direction and magnitude of the difference between two stimuli, or may be asked to decide whether intensities in a pair of stimuli are the same or not forced choice.
The just-noticeable difference JND is not a fixed quantity; rather, it depends on how intense the stimuli being measured are and the particular sense being measured. The subject is presented with one stimulus, for example a weight, and is asked to say whether another weight is heavier or lighter in some experiments, the subject may also say the two weights are the same. At the point of subjective equality PSE , the subject perceives the two weights to be the same.
Absolute and difference thresholds are sometimes considered similar in principle because there is always background noise interfering with our ability to detect stimuli. For example, if the experiment is testing the minimum amplitude of sound that can be detected, the sound begins too quietly to be perceived, and is made gradually louder.
In the descending method of limits, this is reversed. In each case, the threshold is considered to be the level of the stimulus property at which the stimuli are just detected. A possible disadvantage of these methods is that the subject may become accustomed to reporting that they perceive a stimulus and may continue reporting the same way even beyond the threshold the error of habituation. Conversely, the subject may also anticipate that the stimulus is about to become detectable or undetectable and may make a premature judgment the error of anticipation.
At that point, the sound is made louder at each step, until the subject reports hearing it, at which point it is made quieter in steps again. This way the experimenter is able to "zero in" on the threshold. This prevents the subject from being able to predict the level of the next stimulus, and therefore reduces errors of habituation and expectation. Friedrich Hegelmaier described the method of constant stimuli in an paper. Method of adjustment[ edit ] The method of adjustment asks the subject to control the level of the stimulus, instructs them to alter it until it is just barely detectable against the background noise, or is the same as the level of another stimulus.
This is repeated many times. This is also called the method of average error. The difference between the variable stimuli and the standard one is recorded after each adjustment and the error is tabulated for a considerable series. At the end mean is calculated giving the average error which can be taken as the measure of sensitivity. Adaptive psychophysical methods[ edit ] The classic methods of experimentation are often argued to be inefficient. This is because, in advance of testing, the psychometric threshold is usually unknown and much data is collected at points on the psychometric function that provide little information about the parameter of interest, usually the threshold.
Adaptive staircase procedures or the classical method of adjustment can be used such that the points sampled are clustered around the psychometric threshold. Adaptive methods can be optimized for estimating the threshold only, or threshold and slope. Adaptive methods are classified into staircase procedures see below and Bayesian or maximum-likelihood methods.
Staircase methods rely on the previous response only and are easier to implement. Bayesian methods take the whole set of previous stimulus-response pairs into account and are believed to be more robust against lapses in attention.
Staircases usually begin with a high intensity stimulus, which is easy to detect. There are many different types of staircase procedures, using different decision and termination rules. Many different staircase algorithms have been modeled and some practical recommendations suggested by Garcia-Perez. If the participant makes the correct response N times in a row, the stimulus intensity is reduced by one step size.
If the participant makes an incorrect response the stimulus intensity is increased by the one size. A threshold is estimated from the mean midpoint of all runs. This estimate approaches, asymptotically, the correct threshold. The point of maximum likelihood is then chosen as the best estimate for the threshold, and the next stimulus is presented at that level since a decision at that level will add the most information. In a Bayesian procedure, a prior likelihood is further included in the calculation.
This psychometric function of the geometric means of their numbers is often a power law with stable, replicable exponent. Instead of numbers, other sensory or cognitive dimensions can be used to match a stimulus and the method then becomes "magnitude production" or "cross-modality matching". The exponents of those dimensions found in numerical magnitude estimation predict the exponents found in magnitude production. Magnitude estimation generally finds lower exponents for the psychophysical function than multiple-category responses, because of the restricted range of the categorical anchors, such as those used by Likert as items in attitude scales.
Elements of Psychophysics
Despite being raised by his religious father, Fechner became an atheist in later life. In he was appointed professor of physics at Leipzig. But in , he contracted an eye disorder while studying the phenomena of color and vision , and, after much suffering, resigned. Subsequently, recovering, he turned to the study of the mind and its relations with the body, giving public lectures on the subjects dealt with in his books. Whilst lying in bed Fechner had an insight into the relationship between mental sensations and material sensations. This insight proved to be significant in the development of psychology as there was now a quantitative relationship between the mental and physical worlds. A different but essential side of his character is seen in his poems and humorous pieces, such as the Vergleichende Anatomie der Engel , written under the pseudonym of "Dr.
ELEMENTS OF PSYCHOPHYSICS FECHNER PDF
The Classical Psychologists pp. A Source Book in the History of Psychology pp. The page numbers included her are from the Rand edition. There are, however, limits to its validity as well as complications, which we shall have carefully to examine later. In the case of simple lens refraction we abstract from optical aberration. In fact they may become invalid as soon as the simple hypotheses for which they are true no longer exist. Yet they will always remain [p.
History[ edit ] Many of the classical techniques and theories of psychophysics were formulated in when Gustav Theodor Fechner in Leipzig published Elemente der Psychophysik Elements of Psychophysics. From this, Fechner derived his well-known logarithmic scale, now known as Fechner scale. During the s, when psychological research in Nazi Germany essentially came to a halt, both approaches eventually began to be replaced by use of stimulus-response relationships as evidence for conscious or unconscious processing in the mind. Peirce , who was aided by his student Joseph Jastrow , who soon became a distinguished experimental psychologist in his own right. In their experiment, Peirce and Jastrow in fact invented randomized experiments: They randomly assigned volunteers to a blinded , repeated-measures design to evaluate their ability to discriminate weights.
Tugrel And it also has that simplicity which we are accustomed to find in fundamental laws of nature. Though holding good within certain limits only, the law has been found to be immensely useful. Fechner speculated that if the corpus callosum were splittwo separate streams of consciousness would result — the mind would become two. In other projects Wikimedia Commons Wikisource. Hegel and the monadism of Rudolf Hermann Lotze.