6.7 Signal Detection Theory: Definition & Examples
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. No, it’s not that you’re going crazy, and yes, I am aware that this is the first explanation that goes through everyone’s mind.
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. So, it turns out that some of those noises you’ve been hearing really are all in your head, and I guess that’s okay.
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.
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