Absolute Threshold: Examples, Definition & Quiz
In this lesson, we'll talk about what absolute threshold is and explore some examples of absolute threshold for the human senses - specifically for vision and hearing. In the end, test your knowledge with a quiz.
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Absolute Threshold Defined
Have you ever heard the story of the Pea and the Princess? In this fairy tale, a prince is seeking a princess to take for his wife and, as luck would have it, a young woman claiming to be a princess seeks shelter from the rain at his castle. The prince's mother conducts a test to determine the authenticity of the woman's royal status - she is a princess if she can feel the presence of a pea in the bed she spends the night in, which is covered by 20 mattresses and as many featherbeds. The woman wakes in the morning complaining of a sore back from a lump in the bed, and the prince is overjoyed to have finally found a princess to marry.
It's safe to assume that the princess has a very sensitive back to be able to feel a stimulus with such a low absolute threshold. Absolute threshold is the smallest level of energy required by an external stimulus to be detectable by the human senses, including vision, hearing, taste, smell and touch. It is more precisely defined as the degree of intensity of a stimulus necessary to correctly detect that stimulus 50% of the time. Stimuli at or above the absolute threshold - those which can be detected - are called supraliminal.
Since we use our senses all the time, absolute threshold plays a part in everything we do. Here are examples of absolute threshold for each of the five senses:
Let's delve further into two of these senses - vision and hearing.
Absolute threshold concerning vision is the smallest amount of light that you can detect. Imagine, for instance, a car with its headlights on is driving toward you in the dark night. At first, you can't see the car, because it is too far away (the headlights are not intense enough) for you to detect. But, at some point, you are able to see the headlights, because it reached your absolute threshold.
In 1942, three researchers, Hecht, Schlaer and Pirenne, conducted a groundbreaking experiment in absolute threshold in vision. They displayed flashing lights of different intensities to human subjects in order to determine the lowest level of light that humans could detect. This experiment revealed that the human eye can detect a stimulus of as little as 90 photons.
In hearing, absolute threshold is the smallest level of tone that you can detect, considering you have normal hearing and there are no interfering sounds. For example, you might not be able to hear someone whispering from 20 feet away, but if that person speaks up to a normal voice, it may reach your absolute threshold. Children tend to have lower absolute thresholds than adults - a child can detect a sound as low as 1,000 Hz.
Absolute threshold is the lowest level of energy necessary from a stimulus for it to be detectable by the human senses. More specifically, it is the smallest degree of intensity of a stimulus needed to detect that stimulus half of the time. In vision, for instance, absolute threshold is the lowest level of light the human eye can detect. In hearing, it is the lowest level of tone the human ear can detect.
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