SAP - Principles of Sensation Lesson

Learning Targets:

  • Describe general principles of organizing and integrating sensation to promote stable awareness of the external world. 
  • Discuss basic principles of sensory transduction, including absolute threshold, difference threshold, signal detection, and sensory adaptation. 
  • Identify the research contributions of major historical figures in sensation and perception. 

AP psychology course and exam description, effective fall 2020. (n.d.). https://apcentral.collegeboard.org/media/pdf/ap-psychology-course-and-exam-description.pdf

Principles of Sensation

Sensory Thresholds

If we were to sense everything around us, it would be overstimulating and even painful. Think of when you have a headache and light, smell, and sound affect it. Fortunately, we do not have the ability to sense everything all the time. A stimulus must first be strong enough to be detected. This means it must have enough flavor to taste, be loud enough to hear, and so forth. When a stimulus reaches such a point (in which it can be detected) we call it a threshold. In sensation, there are two kinds of thresholds: absolute and difference.

Absolute Thresholds

Absolute thresholds are the minimum amount of stimulus that is needed to be detected by the senses 50% of the time. You may be asking why only half the time. This is because the ability to detect a stimulus will vary from person to person and from case to case. Two problems have been cited regarding absolute thresholds. The first has to do with signal detection. Subjects want to be part of the norm and may claim to have sensed a stimulus falsely. The second has to do with sensory adaptation (we will talk about this more in a moment).

Psychologist Eugene Galanter proposed a list of classic examples of absolute thresholds. You can view them in the interactive below.

Difference Thresholds

Difference thresholds describe the minimum difference in stimuli needed for a person to detect a difference between two stimuli at least half of the time. It is sometimes called "just noticeable difference" or JND. Just noticeable differences will vary depending on the nature of the original stimulus. A way of describing the JND was proposed by Ernst Weber and is called Weber's Law. It states that the size of a JND is a constant proportion of the size of the original stimulus. So, the ability to detect a change in a stimulus depends on the intensity of the original stimulus. They must differ by a constant percentage and not a constant amount.

Subliminal Stimulation

James Vicary claimed to have increased popcorn and coke sales in a New Jersey movie theater by flashing the words "Eat Popcorn" and "Drink Coke"Subliminal stimulation or perception refers to the perception of sensory stimuli that is below one's absolute threshold. Examples include sounds that are too faint to hear, images too fast to record, etc. Subliminal stimulation was first studied by James Vicary, a marketing executive in 1957. He claimed to have increased popcorn and coke sales in a New Jersey movie theater by flashing the words "Eat Popcorn" and "Drink Coke". Both were flashed so quickly that they were below one's absolute threshold. Since then, many have claimed that subliminal messaging has the power to change or control behavior. They have been used both positively and negatively and conjured up much debate.

So, what is the effect of subliminal messages? Do they have the power to change our behavior? Research has found that subliminal messages can indeed influence perception, but they cannot make you commit an act you normally would not do. They are what clinicians call "prime a response".   The effects of these messages are very subtle and don't last exceptionally long.

Sensory Adaptation

Sometimes our responsiveness to a stimulus becomes decreased because of constant sensory stimulation. When this happens, we no longer perceive that stimulus. We become accustomed to constant stimuli, allowing us to notice a change in stimuli. For example, do you feel the socks or the smartwatch that you are wearing all day? No, probably not. You will feel them when you put them on first thing in the morning, but the sensation is lost as you wear them throughout the day. Sensory adaptation applies to all the senses.

Please take a moment to view the video on Sensory Adaptation:

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