| absolute threshold | The minimum stimulus intensity that a person can detect. See difference threshold.
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| criterion | The implicit rule used by an observer in order to convert sensory information into overt responses. See d'.
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| cross-modality matching | A psychophysical procedure in which one sort of stimulus (for instance, a light) is adjusted so that the sensation the stimulus produces matches the sensation produced by a different sort of stimulus (for instance, a sound).
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| d' | In signal detection theory, a measure of sensitivity. See criterion.
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| dark light | See intrinsic light.
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| difference threshold | The minimum amount by which stimulus intensity must be changed in order to produce a just noticeable change in sensation. See absolute threshold.
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| direct scaling techniques | A set of psychophysical procedures for measuring subjective sensory experiences such as loudness or brightness; these procedures are based on the assumption that people can rate sensory magnitude.
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| forced-choice method | A psychophysical procedure in which a person must identify the interval during which a stimulus occurred; in an alternative version, the person must identify the spatial location at which a stimulus was presented.
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| intrinsic light (dark light) | Spontaneous sense of dim light caused by residual retinal signals arising in the complete absence of light stimulation.
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| just noticeable difference (JND) | The smallest discriminable difference between two stimuli that differ along one dimension.
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| method of adjustment | A psychophysical procedure in which a person adjusts a stimulus so that it is just detectable (absolute threshold) or until a just noticeable change is produced (difference threshold).
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| method of constant stimuli | A psychophysical procedure in which each of a fixed set of stimuli is presented in random order.
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| method of limits | A psychophysical procedure in which the stimulus intensity changes progressively in small steps until the person's response changes, for example, from "No, I don't see it" to "Yes, I do see it."
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| multidimensional scaling (MDS) | A quantitative technique for geometrically representing similarity among stimuli.
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| power law | The psychophysical principle that sensation magnitude tends to grow as a power function of stimulus intensity.
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| psychometric function | A graph showing the frequency with which each stimulus elicits each of two possible responses.
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| psychophysical function | A graph showing the threshold as a function of some stimulus variable.
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| psychophysics | The branch of perception that is concerned with establishing quantitative relations between physical stimulation and perceptual events.
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| signal detection theory | A quantitative treatment of detection and discrimination performance, in which the observer is characterized as a maker of statistical decisions; the system also prescribes techniques that allow the observer's sensitivity to the stimulus to be estimated independently of the observer's criterion, or preference for particular responses. See d' and beta.
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| staircase method | A psychophysical procedure in which the stimulus presentations, governed by a person's responses, are made to bracket the threshold; an interactive variant of the method of limits.
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| Weber's Law | The principle that for various stimulus intensities the difference threshold tends to be a constant fraction of the stimulus.
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| beta | In signal detection theory, a measure of the observer's bias.
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