Avery could barely detect sweetness in a sip of water from a pitcher in which one quarter of a teaspoon of sugar was mixed into a half gallon of water. for taste, this is avery's:

The correct answer is absolute threshold.
Absolute threshold is a neurobiological term referring to the lowest level of a stimulus that a person is able to detect. The stimulus can either be touch, sound, taste or light.
Regarding taste, the absolute threshold of taste is the lowest concentration of a certain compound which can be detected by the human sense of taste. 

Where's the picture of the model?