Answer:
JNd/difference threshold
Step-by-step explanation:
The answer is "JNd/difference threshold"
JND means Just Noticeable difference. It is also know as difference threshold.
It is the amount of anything that must be changed to detect or observe a difference. This is the smallest level of excitement that people sometimes can detect fifty percent of the time.
Thus the reason why Lisa's mother could not notice the difference in ht evolume of the music is because of the difference threshold or the Just Noticeable difference.
Thus the answer is
"JNd/difference threshold."