Answer:
Difference threshold or also Just Noticeable Difference
Step-by-step explanation:
The above mentioned case between room mates, where one room mate was able to detect a minute change in volume shows an instance of the difference threshold.
Difference threshold can be defined as stimulation at its minimum level that can be detected by an individual almost 50 % of the times.
It is the lowest possible level of sound that is detectable by a person.
That is what happened in the mentioned case that when the volume was increased from 14 to 15, Amber was able to detect it.