Final answer:
The smallest difference between two stimuli detectable 50% of the time is termed the 'just noticeable difference' or 'difference threshold'. It differs from the 'absolute threshold', which is the minimum stimulus energy detected half of the time.
Step-by-step explanation:
The smallest difference between two stimuli that can be detected 50 percent of the time it is present is called the just noticeable difference (jnd) or difference threshold. The absolute threshold refers to the minimum amount of stimulus energy required to be detected half of the time, but when it comes to detecting differences between stimuli, the concept of just noticeable difference becomes relevant. This is consistent with Weber's law, which suggests that the difference threshold is a constant fraction relative to the magnitude of the original stimulus. The sensitivity of our sensory systems to various stimuli is measured under controlled conditions, with the absolute and difference thresholds playing key roles in determining our sensory experiences.