A psychophysical method to determine the absolute threshold is the method of

The subfield of psychology that deals with the transformation from the physical to the psychological through detection, identification, discrimination, and scaling.

Psychophysics originated with the research of Gustav Fechner (1801-1887), who first studied the relationship between incoming physical stimuli and the responses to them. Psychophysicists have generally used two approaches in studying our sensitivity to stimuli around us: measuring the absolute threshold or discovering the difference threshold. In studying the absolute threshold using the method of constant stimuli, an experimenter will, for example, produce an extremely faint tone which the listener cannot hear, then gradually increase the intensity until the person can just hear it; on the next trial, the experimenter will play a sound that is clearly heard, then reduce its intensity until the listener can no longer hear it. Thresholds can also be ascertained through the method of constant stimuli. In this approach, stimuli of varying intensity are randomly presented. Although an observer's measured threshold will change depending on methodology, this technique gives an estimate of an individual's sensitivity.

A different psychophysical approach combines the concept of sensory abilities with the decisions and strategies that an observer uses to maximize performance in a difficult task. Rather than try to identify a single point for the threshold, psychophysicists who employ the signal detection theory have developed ways to measure an observer's sensitivity to stimuli in ways that go beyond the simple concept of the threshold. Some psychophysical research involves the identification of stimuli. There may be no question as to whether we can detect a stimulus, but sometimes we cannot identify it. For example, people can often detect odors but cannot identify them. Research in this area has centered on determining how much information is needed to allow a person to identify a stimulus. Identification constitutes a relatively small part of psychophysical research, although such research has important practical applications. For example, in the development of useful telephones, researchers had to assess how much "noise" or unwanted sound could accompany speech in a phone conversation so that a listener could understand what was said—that is, identify the spoken words accurately.

A third area of psychophysics involves discrimination of different stimuli, or difference thresholds. No two physical stimuli are absolutely identical, although they may seem to be. The question of interest here is how large must the difference be between two stimuli in order for us to detect it. The amount by which two stimuli must differ in order for us to detect the difference is referred to as the JND, or just noticeable difference. Research has indicated that for stimuli of low intensity, we can detect a difference that is small, as the intensity increases, we need a larger difference. Sometimes psychophysicists use reaction time as a measure of how different two stimuli are from one another. When two stimuli are very similar, it takes a longer time to decide if they are different, whereas large differences lead to fast reaction times.

Absolute threshold: as the stimulus strengthens from the undetectable, the point at which the person first detects it.

Signal detection theory: theory pertaining to the interaction of the sensory capabilities and the decision making factors in detecting a stimulus.

Difference thresholds: at which point can one differentiate between two stimuli. This point is termed just-noticeable difference.

Scaling: using rating scales to assign relative values (for example, rating on a scale of one to ten) to sensory experiences.

The final area of interest to psychophysicists is scaling, the activity of deciding how large or small something is or how much of it is present. Any sensory experience can be scaled. For instance, if the attractiveness of a painting is rated on a scale of one to ten, it is being scaled. If the painting is rated nine, it is considered more attractive than a painting rated eight. This simple example gives the concept underlying scaling, but psychologists have developed more complicated techniques and sophisticated mathematical approaches to scaling.

Goal - determine lawful relationship(s) between dimensions of the physical world and resulting aspect of sensation and/or perception.

In other words, how does changing something in a stimulus change what we experience in our perception.

What do each of these different types of curves mean about how experiences is related to perception?

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% of the time.

For 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. 

For 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.

For odors, the absolute threshold involves the smallest concentration that a participant is able to smell. An example of this would be to measure 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.

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.

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.

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.