In neuroscience and psychophysics, an absolute threshold was originally defined as the lowest level of a stimulus – light, sound, touch, etc.
However, only about half of these entered the retina, due to reflection (from the cornea), absorption, and other factors relating to transmittance of the ocular media.
In this case the light covers a wide field over an extended period of time instead of being concentrated on one spot on the retina in a short burst.
Knowing the pupil diameter and the wavelength of the light, the result can be described in terms of luminance (~0.000001 candela per square meter or 10−6 cd/m2) or retinal illuminance (~0.00002 Trolands).
[7] In terms of total absolute power sensitivity, Denton and Pirenne in the Journal of Physiology in 1954 found that for diffuse, extended sources i.e. a relatively large (~ 45-degree wide source, as viewed by the subject) frosted glass aperture, and a long (5 second) observation and decision time, the human eye could begin to reliably distinguish the lit from unlit glass at a power level of approximately 7.6 × 10−14 watts / steradian-cm2 at the eye for green (510 nm) light.
[14] The threshold of hearing is generally reported as the RMS sound pressure of 20 μPa (micropascals) = 2×10−5 pascal (Pa).
The threshold of a chemical compound is determined in part by its shape, polarity, partial charges and molecular mass.
A WaveTek stimulator was used to measure absolute threshold of touch by "tapping" a participant's finger pad with a 2 mm diameter probe.
Lindblom found that on average, there was a 27% difference in threshold level between slow and fast mechanical pulses on a participant's finger pad.
[22] Being deprived of calories for a short time increases sensitivity to and decreases absolute threshold for sweet and salty foods.
[24][25] Main article: Sensory processing disorder Some people have an abnormally high or low absolute threshold for one or more senses that interferes with their quality of life.