Absolute Threshold

In neuroscience and psychophysics, an absolute threshold is the smallest detectable level of a stimulus. However, at this low level, subjects will sometimes detect the stimulus and at other times not. Therefore, an alternative definition of absolute threshold is the lowest intensity at which a stimulus can be detected 50% of the time. The absolute threshold can be influenced by several different factors, such as the subject's motivations and expectations, cognitive processes, and whether the subject is adapted to the stimulus.
The absolute threshold can be compared to the difference threshold, which is the measure of how different two stimuli have to be in order for the subject to notice that they are not the same.