Final answer:
The smallest amount of a stimulus needed to detect its presence is known as the absolute threshold, which is the minimum amount of stimulus energy that must be present to be detected 50% of the time.
Step-by-step explanation:
The term for the smallest amount of a stimulus needed to detect its presence is known as the absolute threshold. This refers to the minimum amount of stimulus energy required to be detected 50% of the time. For example, the absolute threshold for vision could be the smallest amount of light detectable by the eye. This concept is crucial in understanding the limits of human sensation and perception. The absolute threshold highlights the sensitivity of our sensory receptors, like being able to detect a candle flame from 30 miles away on a clear night, or the tick of a clock from 20 feet away in a silent room.