Final answer:
The smallest amount of stimulus that can be detected at least 50% of the time is referred to as the absolute threshold, which is the minimal stimulus energy required for detection.
Step-by-step explanation:
The smallest amount of stimulus that can be detected at least 50% of the time is known as the absolute threshold. The absolute threshold refers to the minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time. The incredible sensitivity of our sensory systems can be exemplified by the fact that, given optimal conditions, the human eye can detect a candle flame from 30 miles away, and the ear can hear the tick of a clock from 20 feet away.