What is the Absolute Threshold?

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The term absolute threshold is often used in neuroscience and experimental research. An absolute threshold is the smallest detectable level of a stimulus. For example, in an experiment on sound detention, researchers may present a sound with varying levels of volume. The smallest level that a participant is able to hear is the absolute threshold.

However, it is important to note that at such low levels, participants may only detect the stimulus part of the time.

Because of this, the absolute threshold is usually defined as the smallest level of a stimulus that a person is able to detect 50 percent of the time.

Examples of Absolute Thresholds

  • Hearing
    In hearing, the absolute threshold refers to the smallest level of a tone that can be detected by normal hearing when there are no other interfering sounds present. An example of this might be measuring at what levels a participants can detect the ticking sound of clock.

    Young children generally have a lower absolute threshold for sounds since the ability to detect sounds at the lowest and highest ranges tends to decrease with age. Researchers suggest that the quietest sound that children with normal hearing can detect is around 1,000 Hz.
  • Vision
    In vision, the absolute threshold refers to the smallest level of light that a participant can detect. For example, determining the absolute threshold for vision might involve measuring the distance at which a participant can detect the presence of a candle flame in the dark.

    In one classic experiment, researchers found that after controlling for dark adaptation, wavelength, location and stimulus size, the human eye was able to detect a stimulus of 90 photons.
  • Smell
    For odors, the absolute threshold involves the smallest concentration that a participant is able to smell. An example of this would be to measure what the smallest amount of perfume that a subject is able to smell in a large room.

While the absolute threshold is often thought of purely in terms of sensation and perception, a number of factors can play a role including expectations, motivations, and thoughts.

For example, if you are expecting to hear a noise, you might be more likely to detect it at lower levels than you would if you do not expect to hear the noise.

The absolute threshold should not be confused with the difference threshold, which is the smallest possible detectable difference between two stimuli.

References

"Absolute Threshold." (2001). Gale Encyclopedia of Psychology. Found at http://www.encyclopedia.com/doc/1G2-3406000012.html

Gelfand, S A., 1990. Hearing: An introduction to psychological and physiological acoustics. 2nd edition. New York and Basel: Marcel Dekker, Inc/

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