How Absolute Threshold of a Stimulus Is Used in Experimental Research

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An absolute threshold is the smallest level of stimulus that can be detected, usually defined as at least half the time. The term is often used in neuroscience and experimental research and can be applied to any stimulus that can be detected by the human senses including sound, touch, taste, sight, and smell.

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.

Absolute Threshold in 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 measured at what levels participants can detect the ticking sound of a 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. 

Absolute Threshold in Vision

In vision, the absolute threshold refers to the smallest level of light that a participant can detect. 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.

For example, imagine that you are a participant in a psychology experiment. You are placed in a dark room and asked to detect when you are first able to detect the presence of light at the other end of a long room. In order to determine the absolute threshold, you would go through a number of trials. During each trial, you would signal when you are first able to detect the presence of light. The smallest level that you are able to detect half of the time is your absolute threshold for light detection.

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 between the range of 54 and 148 photons.

Absolute Threshold in 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.

The absolute threshold for smell can vary considerably depending upon the type of odor used, the dilution methods, the data collection methods the researchers are utilizing, characteristics of the participants, and environmental factors.

Even the time of day that data is collected can have an influence on the absolute threshold. Environmental factors such as pressure and humidity can also influence how well participants are able to detect smells.

Absolute Threshold in Touch

The amount of force required for you to detect the feeling of a feather lightly brushing your arm is an example of the absolute threshold for touch. When it comes to touch, the level of stimulation required to detect the stimulus can vary dramatically depending upon the part of the body that is being touched. For example, the absolute threshold of detecting touch may be much lower at your fingertips versus that of the back of your neck.

Factors That Can Influence the Absolute Threshold

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.

Researchers have found that women tend to have lower absolute threshold than men, meaning they are better able to detect lower levels of sight, smell, taste, touch, and sound. Introverted people have also been found to be better able to detect stimulus levels at lower levels.

Absolute thresholds are prone to change as people grow older. When people are younger, they are able to detect energy levels at lower levels. They require greater stimulation to detect these same stimuli when they are older.

A Word From Verywell

The absolute threshold serves as an important tool for researchers studying the capabilities and limitations of human sensation and perception. One important thing to remember is that researchers distinguish between the ability to detect a stimulus and the ability to tell the difference between stimulus levels.

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

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Article Sources

  • Doty, RL & Laing, DG. Psychophysical measurement of human olfactory function. In RL Doty (Ed). Handbook of Olfaction and Gustation. New York; John Wiley & Sons; 2015.
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  • Shepherd, D, Hautus, MJ, & Urale, PWB. Personality and perceptions of common odors. Chemosensory Perception. 2017;10(1-2);23-30.