Book definition: Explains how we detect "signals," consisting of stimulation affecting our eyes, ears, nose, skin, and other sense organs.

Signal Detection Theory explains how we detect "signals:, consisting of stimulation from all of our sense organs. This theory uses the same concepts to explain both the electronic sensing of stimuli by devices such as an IPod or TV, and human senses such as vision and hearing.
Signal Detection Theory or SDT for short theorizes that sensation is affected by the characteristics of a stimulus, the background stimulation, and the detector. For example, one might pay more attention during a test if he/she drinks a five hour energy right beforehand; and a person's bias and personal interests might affect the information they remember when they watch a documentary or a school assembly.
SDT helps to shed some light on why thresholds are variable; or why you may be able to detect something such as a sound one time and you won't be able to notice it the next. An observer's physical and mental status is always changing. So when an observer experiences sensation, the observer must compare the sensory experience with constantly changing expectations and biological conditions. When you hear someone behind you, what you perceive it to be depends on what you may be expecting to hear, such as a friend or an attacker, the extent of your hearing, and the other sounds going on around you. Because SDT takes into account all of the different variables, it is much more of an accurate portrayal of sensation than was classical psychophyisics.

It explains how we detect "signals," consisting of stimulation affecting our eyes, ears, nose, skin, and other sense organs. Signal Detection Theory says that sensation is a judgment the sensory system makes about incoming stimulation. Often, it occurs outside of consciousness. In contrast to older theories from psychophysics, Signal detection theory takes observer characteristics into account.

Sensation depends on the characteristics of the stimulus, the background stimulation, and the detector


  • You are less likely to hear someone talking to you when you're in a crowd than when you are in a quiet room. (background stimulation)
  • You are more likely to hear someone say your name than someone elses name because you are more used to hearing and responding to it (characteristics of the stimulus / detector?)

Additional Resources

  • Four researchers by the names of John A. Swets, David M. Green, Joel B. Swets, and David J. Getty conducted an expirement way back in 1979. The expirement was done in multipe trials; usually having the expirementees pour water in beakers each time a stimulus may or may not have appeared. What they found was that smaller stimuli that does NOT pass our absolute threshold usually prompt a false alarm or a miss. They then created multiple mathmatical graphs in order to explain how certain stimuli alerts humans while others don't. These graphs also incorporated/explained why sometimes we miss usually obvious stimuli.
Getty, D. J., Swets, J. A., Swets, J. B., & Green, D. M. (1979). On the prediction of confusion matrices from similarity judgments. Attention, Perception, & Psychophysics, 26(1), 1-19.

  • An experiment concerning wine tasting was done to test out Signal Detection Theory. A wine taster was placed with the task of tasting Pinot Noir wine and detect if an inferior grape, Gamay, was added. The taster tried 20 glasses of wine. The results were nine hits, two false alarms, one miss, and eight correct rejections. Most of the time the taster could correctly identify if the wine had been tampered with, also the results show that when in doubt, the taster rather say the wine was tampered with then not.
Abdi, H. (2007). Signal detection theory (SDT). Encyclopedia of measurement and statistics, 866-889.

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