Seth volunteered to participate in a taste test for a new soup. the testers want to know when the participants notice a reduction in salt in the soup. after seth tastes several bowls of soup he notices that the last bowl has less salt than the others. seth's detection of the difference in salt content is an example of detecting the:

The just noticeable difference (JND).

Explanation:

The just noticeable difference (JND) or difference threshold is the minimum level of stimulation that someone is able to perceive 50 percent of the time. This concept can be applied to all perception areas: smell, taste, sight, touch, and hearing.  

It is important to differentiate it from the absolute threshold. The latest refers to the smallest detectable level of stimulation. For instance, the lowest volume of a song that a person can detect represents the absolute threshold. While the lowest change in volume of a song would represent the difference threshold.