Final answer:
The absolute threshold is the minimum amount of stimulus energy required to be detected 50% of the time. It measures the sensitivity of our sensory receptors and can vary depending on the type and intensity of the stimulus. It is different from the difference threshold, which is the minimum amount of difference in stimulus energy required to be detected as a noticeable change.
Step-by-step explanation:
The absolute threshold refers to the minimum amount of stimulus energy required to be detected 50% of the time. For example, it is the minimum level of brightness or loudness that a person can detect half of the time. This concept is used to measure the sensitivity of our sensory receptors.
Under optimal conditions, our sensory receptors can detect very faint stimuli. For instance, the most sensitive sensory cells in the back of the eye can detect a candle flame 30 miles away on a clear night. Similarly, the hair cells in the inner ear can detect the tick of a clock 20 feet away under quiet conditions.
The absolute threshold is different from the difference threshold, which is the minimum amount of difference in stimulus energy required to be detected as a noticeable change. The difference threshold can vary depending on the intensity of the stimulus, as illustrated by the example of noticing a change in illumination from a cell phone screen in a dark movie theater versus a brightly lit basketball arena.