What is Psychophysics - What is Psychophysics?...

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What is Psychophysics? Psychophysics is concerned with describing how an organism uses its sensory systems to detect events in its environment. This description is functional, because the processes of the sensory systems are of interest, rather than their structure (physiology). One psychophysical theory, the Theory of Signal Detectability (TSD), uses a combination of statistical decision theory and the concept of the ideal observer to model an observer's sensitivity to events in its environment. TSD is stimulus-oriented, because properties of the stimuli are used to determine the theoretically best, or ideal, observer for a given detection task. This observer may then be used to compare the performance of human, and other, observers. For instance, the ability of humans to detect Psychophysical methods Methods for the quantitative study of the relations between physical stimulus magnitudes and the corresponding magnitudes of sensation, for example, between the physical intensity of a light and its perceived brightness or the concentration of a sugar solution and its observed sweetness. To establish these relations, measurement scales are needed, not only for physical magnitudes but also for subjective magnitudes. Subjective scales are not obtained directly from observation but are theoretical models which summarize observed relations between stimuli and responses. See Sensation The term psychophysical methods is sometimes extended to include certain scaling techniques which are most often used with subjective dimensions to which there correspond no simple physical dimensions, for example, food preferences. In 1860, G. Fechner designed psychophysical methods to measure the absolute threshold, defined as the minimum stimulus energy that an organism can detect, and the differential threshold, defined as the minimum detectable change in a stimulus. Both quantities had to be defined as statistical averages. To obtain reliable measurements for these averages, Fechner devised the method of limits (also called the method of minimal changes) and the method of constant stimuli. In the method of limits, the experimenter begins with a stimulus which is too weak for the subject to detect. In successive presentations, the stimulus intensity is increased in small, equal steps, the subject reporting after each presentation whether the stimulus was perceived until it has been detected. The descending series is then begun, the stimulus intensity beginning at an above-threshold value and decreasing in steps until the subject signals the disappearance of the stimulus. Many such series are given. In measuring the difference threshold, essentially the same procedure is involved, except that the subject now signals the relation of a comparison stimulus to a standard stimulus. After a large number of such trials, the average of each of these four threshold values is computed. To measure the absolute threshold by the method of constant stimuli, the experimenter selects a small number of stimulus values
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What is Psychophysics - What is Psychophysics?...

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