Learn what signal detection theory is. Read about its origins and development and how researchers test the hypothesis. See signal detection theory examples in action.
Updated: 11/21/2023
Signal Detection Theory | Definition & Examples
Table of Contents
- What is Signal Detection Theory?
- Origins and Development of the Theory
- Testing Signal Detection Theory
- Signal Detection Theory Examples
- Mathematical Models and the Theory
- Applications for Signal Detection Theory
- Lesson Summary
Frequently Asked Questions
What is an example of the signal detection theory?
Signal detection theory is how one response to stimuli. If one were exposed to stimuli or a signal, they would either be aware or not aware of the signal. If aware of the signal, they choose to either act on the signal or ignore the signal. For example, a person is walking across the street, and a car honks, and the walker stops abruptly and looks at the car that is honked. Here, the car honk is a signal, and a person's response is stimuli.
What is signal detection theory?
Signal detection theory is how one response to stimuli. If one were exposed to stimuli or a signal, they would either be aware or not aware of the signal. If aware of the signal, they choose to either act on the signal or ignore the signal. The possible outcomes of the signal detection theory are hit, miss, false alarm, and correct rejection.
What are signal detection tasks?
In a test setting, an observer is given a task to sense the presence of a signal. The outcome of the task allows researchers to determine how sensitive a subject is to stimuli. Signal detection tasks are generally yes or no types of signals.
What is signal detection theory used for?
Signal detection theory is how one response to stimuli. If one were exposed to stimuli or a signal, they would either be aware or not aware of the signal.
Table of Contents
- What is Signal Detection Theory?
- Origins and Development of the Theory
- Testing Signal Detection Theory
- Signal Detection Theory Examples
- Mathematical Models and the Theory
- Applications for Signal Detection Theory
- Lesson Summary
Signal detection theory is about detecting stimuli (a signal) through the senses. Testing the signal detection theory exposes observers to signals. The initial study was designed to determine a threshold (minimum value) for human response to stimuli. However, it has changed from determining a threshold to testing how observers respond to signals. The threshold experiment showed the observers had nothing in common in relation to creating values for human observers as a standard threshold. The study, however, determined how observers view the signals. Observers perceive signals as generally due to the participant not paying attention or not being strong enough.
Signal detection theory is based on the decision-making process as one has to decide if they will act on the signal or not. The decision-making process is applied to the signal detection theory by one's response or sensitivity to stimuli (a signal). The brain responds to a signal that may or may not be present. In the case of the signal being present, it is up to the brain of the person to decide if it hears the signal. If the signal is not present, the brain may or may not think the signal was or was not present.
If the brain experiences a not present signal, this is called neural noise. This is caused when the brain constantly sends messages along with the peripheral nervous system. The brain then decides if the messages are really present or not. Generally, the process of signal detection theory flows from the outside environment to the brain. The brain accesses prior knowledge to decide if it senses the signal or not, or it uses perception to determine to act on the signal. When it chooses to respond, this is called criterion, using prior knowledge, which results in expectations.
The setting is in the park. A mother is with her child. The child wonders off and calls for his mom. Through all the noise in the park, the mother hears her son call for her. The signal helped them to be reunited. At the same time in the park, a man was walking and did not hear the signal of the boy calling for his mother. He was not focused on the call as he does not have any children. He continued his walk through the park.
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During World War II, the signal detection theory was used to help with radar, and the process determined radar from other background noise. Gustav Fechner developed the signal detection theory in 1860. In 1966, two psychophysics used the signal detection theory. John Swets and David Green felt how signal detection theory was better than the other options being offered at the time.
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When testing the signal detection theory, a signal is given or not, and the observer recognizes the signal or not. The outcomes of the signal detection experiment are hit, miss, false alarm, and correct rejection.
Hit
Hit refers to the observer being exposed to the stimulus and the observe recognizing the stimulus. Hit is a positive outcome of the testing as the stimulus was present and acknowledged by the observer.
Miss
Miss exposes the observer to the stimulus, but the observer does not acknowledge the present stimulus. Miss is viewed as a negative outcome, and it indicates that something in the testing was wrong. In the case of a miss, the stimulus was present but went undetected by the observer.
False Alarm
The stimulus is not present, but the observer thinks they encountered a stimulus.
Correct Rejection
The observer is not exposed to a stimulus, and they do not acknowledge a stimulus; this is called correct rejection. This is a positive outcome of the testing as the stimulus was not present, and the observer did not sense any signal.
The image in this section shows the signals organized in order to give better understanding.
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Living organisms are exposed to stimuli constantly throughout the day. Examples of the signal detection theory are unlimited. To understand Signal Detection Theory, see a few examples provided in this section.
Example of a Hit
A person is walking across the street, and a car honks. The walker stops abruptly and looks at the car that is honked. This is a hit as the observer hears the car honking (signal).
Example of a Miss
Someone is washing dishes, and as they clean the containers with the water running, they don't hear the phone ring in another room (signal). This would be an example of a miss as the observer did not hear the phone's ring as they were distracted with the dishes, and the sound of the phone was not loud enough.
Example of a False Alarm
A person is sleeping comfortably; they abruptly awake as they think of hearing the alarm to get up and get ready for school. This is a false alarm as the alarm clock did not buzz, but the person thought they heard the sound.
Example of a Correct Rejection
A family went camping, and they were bird watching. The family wanted to see a woodpecker. The woodpecker never made a sound, and the family never heard the woodpecker. This is an example of correct rejection as the woodpecker did not make a sound, and the family did not hear one.
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Psychologists use statistics to determine the outcome of a study when looking at signal detection theory. They collect data from subjects on their sensitivity to signals.
Gaussian Distribution with Equal Variance
The standard model for showing the signal detection theory is two Gaussian distributions with equal variance. This model is shown in a curve for probability. Probability is about how likely something is to occur, and equal variance is when both curves are equal in their distribution. In order to graph the statistical values of the results of the signal detection theory, one must use a mathematical equation. d' (d prime) is a standardized difference of distributions between hit and false alarm rates.
d Prime
d Prime (d') is used to calculate bias and sensitivity.
The formula for d' (d prime) is used for memory tasks is:
Sensitivity
d'=z(H)-z(F)
Here, z(H) is the hit rate, and z(F)is a false alarm
Bias
{eq}c=-\frac{1}{2(z(H)+z(F))} {/eq}
Here, c is the bias, z(H) is the hit rate, and z(F)is a false alarm.
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Signal detection theory has many applications, specifically where decision-making occurs. A few of the use areas are diagnostics, quality control, and psychology.
Determining Bias
Determining bias with signal detection theory is due to the experience, and knowledge individuals bring with them. If one were to live in a large city, they might be less likely to respond to a signal of a car honking the horn; this is due to past experience of many drivers honking. Bias can also exist with the researcher experimenting on signal detection theory as they too have their own experiences and knowledge they bring with them to the experiment.
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Signal detection theory is a theory that tests how one response to stimuli. The stimuli are called a signal. The signal is given or not given, and the observer has to make a decision if they acknowledge the signal or not. The theory has been used since the 1950s for detecting electric signals and is now used to determine how observers respond to signals. The four possibilities in signal detection theory are hit, miss, false alarm, and correct rejections. The data collected from the observers can be input into a mathematical equation to determine the relationship of the different possibilities. The data is then used to determine the statistical possibilities of signals.
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Video Transcript
Signal Detection
Have you ever done that thing where you could swear you hear your phone ringing or feel it vibrating in your pocket, but then you go to check it and nobody was calling? Of course you have. We all have. It's a common occurrence, and there's actually a scientific reason for it.
For a long time, psychologists have been interested in how our minds become aware of stimuli, of factors in the environment around us that can be detected through the five senses of sight, hearing, taste, touch, and smell. How do we notice these stimuli? Why do we sometimes not notice them, and why do we detect them when they're not really there?
The leading explanation: signal detection theory, which at its most basic, states that the detection of a stimulus depends on both the intensity of the stimulus and the physical/psychological state of the individual. Basically, we notice things based on how strong they are and on how much we're paying attention. Want to learn more about this? Well, for this lesson to be intellectually stimulating, it looks like you're going to have to pay attention.
Developing the Theory
Let's start by looking at where signal detection theory comes from. From the beginning of the discipline, psychologists were interested in measuring our sensory sensitivity, how well we detect stimuli. The leading theory was that there was a threshold, a minimum value below which people could not detect a stimulus.
The only problem was that no firm threshold could be established. Some people heard a faint background noise easily, while others completely missed loud noises nearby. The results were simply too inconsistent for there to be a standard threshold. So, researchers started looking for a new explanation. What they found was that the sensory sensitivity was a relationship between the strength of the signal and the level of alertness, and thus, signal detection theory was born.
Signal Detection & Decision Making
All right. So let's look at signal detection a little more concretely. Say you're walking to your car in a moderately crowded parking lot, in a place you know very well, and it's a bright and sunny day. Your mind may wander, making you more likely to miss certain signals. The rustling of leaves, for example, will probably just be registered in your mind as background noise. Now, say you're walking to your car all alone, at night, in a strange parking lot you don't know. Suddenly, those rustling leaves catch your attention, don't they? The volume of the leaves didn't change, but your alertness did.
That's the signal detection theory in action. Once you hear the rustling of leaves, you have to decide what that noise is. Was it a robber, or simply some dry foliage? The recognition that sensory sensitivity requires a conscious decision is one of the things that defines the signal detection theory. You see, not only do people have to detect signals, they have to identify them.
Researchers realized that when stimuli are difficult to detect, individuals rely on their cognitive abilities to consciously determine whether the signal was present or not. Basically, the individual makes a decision. Is it worse to say that no stimulus was present when it was, or to say that a stimulus was present when it wasn't?
Imagine that you are expecting a package. You are waiting for a knock at the door, and you think you hear one, but you're not sure. Either you can ignore it and risk missing your package, or you can risk opening the door to no one. Which is worse? Unless you're around a bunch of very judgmental people, it's probably worse to risk missing your package, so you open the door.
Psychologists have a simple way to test this. Subjects are exposed to a number of different stimuli, and asked to detect them. There are four possible outcomes. A hit is when the signal is present and detected. A miss is when the signal is present and not detected. A false alarm is when the signal is absent but is detected, like hearing your phone ring when no one is calling or a knock at the door when no one is there. Finally, there is correct rejection, when no signal was present and no signal was detected.
By exposing subjects to a series of stimuli and calculating the rate of each of these, researchers can explore the ways that decision making and sensory sensitivity are linked.
Lesson Summary
Why do you notice some things, and not others? The leading explanation is the signal detection theory, which at its most basic states that the detection of a stimulus depends on both the intensity of the stimulus and the physical/psychological state of the individual. Basically, whether or not you notice something is the result of your level of alertness vs. the strength of the signal. This theory emerged to explain the issues faced by threshold theories that believed that there was a minimum strength of a signal needed to be detected. Signal detection theory recognized that detection is controlled in part by conscious decision-making, especially in cases where the individual was unsure if a signal was present.
Researchers can test this by exposing individuals to various stimuli, then calculating the rates of hits, when the signal is present and detected; misses, when the signal is present and not detected; false alarms, when the signal is absent but is detected; and correct rejections, where no signal was present and no signal was detected. So, that's how your mind decides if your phone was going off or if it was just a false alarm.
Learning Outcomes
As you finish the video, you should make it a point to:
- Define stimuli and threshold
- Explain what the signal detection theory is
- Describe how the signal detection theory formed
- Acknowledge how signal detection impacts decision making
- Understand how psychologists test signal detection's impact on decision making
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Signal Detection Theory | Definition & Examples
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