Final answer:
A stimulus that is detected 20% of the time is classified as a subliminal stimulus because it falls below the absolute threshold, which is the minimum amount of stimulus energy required for detection 50% of the time.
Step-by-step explanation:
If a person detected a faint stimulus 20% of the time, a psychophysicist would consider the stimulus to be a subliminal stimulus. 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. A stimulus that is detected less frequently, such as 20% of the time, is not consistently enough to be considered at the absolute threshold. Instead, it falls below this threshold, rendering it subliminal. Subliminal stimuli are received by our sensory system, but we are not consciously aware of them, as evidenced by our inability to detect them the majority of the time.