Final answer:
The upper boundary of the auditory response area is called the threshold of pain, representing the point at which sound intensity reaches a level that is painfully loud and potentially damaging to the ear.
Step-by-step explanation:
The upper boundary of the auditory response area is called the threshold of pain. This is the point at which sound becomes painfully loud and can cause damage to the ear after brief exposure. In an audiogram, which graphs the threshold of hearing in intensity level versus frequency, the threshold of pain would be represented at the top end of the graph, well above the normal range of hearing and near the levels that can cause immediate hearing damage. The ear's range of sensitivity to sound intensity is truly remarkable, covering a trillion-fold range from the quietest perceivable sounds to those that can cause pain and hearing loss, sometimes summarized as extending from the threshold of hearing to the threshold of pain.