Final answer:
The ability of a sensory system to detect changes or differences between two stimuli is referred to as the differential threshold or just noticeable difference (jnd). This contrasts with the absolute threshold, which is the minimum stimulus energy needed for detection.
Step-by-step explanation:
The ability of a sensory system to detect changes or differences between two stimuli refers to the differential threshold. Also known as the just noticeable difference (jnd), this term describes the minimum amount of difference in stimulus energy required to be detected about 50% of the time. The absolute threshold, in contrast, is the minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time. Sensory systems have both absolute and difference thresholds, which play a critical role in how we perceive sensory information.
For example, while the absolute threshold would refer to how faint a sound could be for us to just begin hearing it, the differential threshold would refer to how much louder a sound would need to become before we notice that increase in volume. Ernst Weber's law states that the difference threshold is a constant fraction of the original stimulus: that is, larger stimuli require larger differences to be noticed, while smaller stimuli require smaller differences.