The absolute threshold is the minimal amount of energy necessary to stimulate the sensory receptors.
While the absolute threshold is a useful concept, it does not exist in reality. One individual might be unable to detect a certain faint light during one trial but at a later time may detect it. In addition, scientists cannot determine with absolute certainty how much energy is present in a light because of limits to the physics of measurement. As a result, psychologists often define the threshold as the lowest intensity that a person can detect 50% of the time.
A number of different factors influence the absolute threshold, including the observer's motivations and expectations, and whether the person has adapted to the stimulus. Scientists have discovered that cognitive processes can influence the measurement of the threshold and that it is more complex than previously believed. Psychologists have also studied the degree of dissimilarity two stimuli must have in order to be noticed as being different. Such an approach involves what are called difference thresholds.
Absolute threshold measurements are used in experimental research and in diagnostic testing because they reveal the degree of sensitivity of the sense perception being tested.
See also Ames room ; Helmholtz, Hermann Von; Perception ; Sensory modalities ; Vision .
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