ABSTRACT
One of the most remarkable properties of the sensory systems is their extreme sensitivity as measured by the absolute threshold. The ability to tell one intensity from another—the just noticeable difference or differential threshold—is also very good, but not nearly so astonishing as the fine ability to tell whether a faint stimulus is present or absent. The minute amount of stimulation needed to initiate a sensation makes it appear that nature has pushed close to the theoretical limits in providing us with receptors to detect chemical, mechanical, and electromagnetic events in the environment. Such acute sensitivity no doubt has served a decisive role in evolution and has made it possible for complex, mobile animals to survive in ecological competition. The study of sensory thresholds has become a central concern of psychophysics.
