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threshold (thresh´old)

1. The point at which a stimulus first produces a sensation. 2. The lower limit of perception of a stimulus. 3. The minimal stimulus that produces excitation of any structure; e.g., the minimal stimulus eliciting a motor response. 4. limen [A.S. therxold]
absolute t. the lowest limit of any perception whatever. Cf. differential t. stimulus t;
achromatic t. visual t
auditory t. the intensity of any barely perceptible sound.
brightness difference t. the smallest difference that can be perceived as a difference in brightness.light difference (2);
t. of consciousness the lowest point at which a stimulus sensation can be perceived.
convulsant t. the smallest amount of stimulation, electric current, or drug required to induce a convulsion.
differential t. the lowest limit at which two stimuli can be differentiated.threshold differential;
displacement t. the least distinguishable break in the contour of a line.
double-point t. the least degree of separation of two points applied to the body surface that permits of their being felt as two.
erythema t. the dose at which erythema of the skin is produced by irradiation with ultraviolet, gamma, or x-rays.
fibrillation t. least intensity of an electrical stimulus that will initiate fibrillation.
galvanic t. rheobase
t. of island of Reil limen insulae
light differential t. the smallest difference in light intensity that can be appreciated.
minimum light t. visual t
t. of nose limen nasi
pain t. the smallest intensity of a painful stimulus at which the subject perceives pain.
phenotypic t. a quantitative genetic trait with a continuous distribution termed its liability may generate two kinds of phenotype, according to whether the liability lies above or below some critical t. at about which a radical change in behavior occurs. For instance, blood uric acid level is a liability with an approximately gaussian distribution. At a critical point of chemical saturation (the t. crystallization occurs and the resulting gout or nongout is a t. trait.
relational t. the smallest degree of difference between two stimuli that permits them to be perceived as different.
renal t. concentration of plasma substance above which the substance appears in the urine.
stimulus t. absolute t
swallowing t. 1. the moment that the act of swallowing begins after the mastication of food; 2. the critical moment of reflex action initiated by minimum stimulation, prior to the act of deglutition.
visual t. , t. of visual sensation the minimal light intensity evoking a visual sensation.achromatic t., minimum light t;


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