absolute threshold

n. The lowest level of a sensory stimulus to which a subject can give any indication of perception of a stimulus. Originally psychophysicists believed there was some absolute level which corresponded with human consciousness which defined this limit, but close study revealed variability in subject responses which were partially random and partially dependent on the instructions given to the subject. Subsequent study revealed that there is a gradual onset of stimulus detection which is usually described using signal detection methods which give probabilities of response to a stimulus at different intensities or levels of the stimulus. ► See ABSOLUTE LIMEN