The absolute threshold is the minimum level of stimulus intensity needed for a stimulus to be detected 50% of the time.
Also known as "just noticeable difference", it's the smallest amount by which a stimulus must be changed in order to differentiate between it and an original stimulus.
This law states that the change in a stimulus that will be just noticeable is a constant ratio of the original stimulus.
As mentioned earlier, this theory predicts how and when we detect a faint stimulus amid background noise.