Have you been at a restaurant and heard a bell ring in the kitchen to notify servers that a plate of food was ready to be served?  Most likely, hearing that bell made you feel stomach growl; you probably salivated at the thought of the server bringing that plate of food to your table!  How does the sound of this bell bring out such feeling and behavior?

Earlier this week, the work of Arzi et al., posted by Kate, showed that humans could learn while they are asleep.  The researchers paired pleasant and unpleasant odors with audible sounds while the volunteers were asleep, and showed that the volunteers learned these pairings in their sleep!  These experiments were based on classical conditioning, the oldest and one of the most often cited models of learning.

Russian scientist, Ivan Pavlov developed the concept of classical conditioning while he was studying the digestive system in dogs.  In 1904, he won the Nobel Prize “in recognition of his work on the physiology of digestion, through which knowledge on vital aspects of the subject has been transformed and enlarged.”  Pavlov is best known, however, for his model of non-conscious, instinctive type of learning.  This all started when Pavlov opened his creaky cabinet door to get dog food.  He noticed that his dog would start to salivate just by hearing the sounds of the cabinet door.  It seemed that the dog had learned to associate that sound with food!

To test his hypothesis, Pavlov brought a bell (actually a tuning fork) and rang it.  Seeing that the ringing of the bell failed to elicit any response from the dog, Pavlov deemed the bell a ‘neutral stimulus.’  When food was presented to the dog, it naturally responded to the smell by salivating (an unconditioned response, UCR).  Then, Pavlov paired the ringing of the bell with the presentation of dog food.  This was repeated many times, so that the dog could learn to associate the sound of the bell with the presentation of food.  Later, Pavlov only rang the bell, and the dog would salivate even if no food were present!  In more scientific terms, the dog learned that the ringing of the bell (conditioned stimulus, CS) meant that it could eat, so the dog salivated (conditioned response, CR).

In reality, it may not take such a long learning period for us to become classically conditioned to a stimulus.  For instance, it only takes one time of getting sick after eating something to become nauseous after smelling it again!  Earlier this month, my dog had a treat from the refrigerator.  Now, every time I open the refrigerator, she runs to the kitchen in the hopes of getting a treat!  Can you think of other real-life examples of classical conditioning?

Image adapted from Flickr/Frank Jacobi
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Jooyeun Lee

Jooyeun (JL) dreamt about being an artist and yet she is now in her fifth year as a Neuroscience Ph.D. student at USC.As she studied art in college, it opened up a whole new world beyond her perspective and turned out earning a Bachelor’s degree in Biology.Thereafter, she joined a neuroscience lab at California State University, Northridge, studying wound healing response in diabetic neuropathy as her Master’s thesis project.Currently, she studies neurological disorders, such as Down syndrome and Alzheimer’s disease, using Drosophila as a model system.
Profile photo of Jooyeun Lee

Jooyeun Lee

View posts by Jooyeun Lee
Jooyeun (JL) dreamt about being an artist and yet she is now in her fifth year as a Neuroscience Ph.D. student at USC. As she studied art in college, it opened up a whole new world beyond her perspective and turned out earning a Bachelor’s degree in Biology. Thereafter, she joined a neuroscience lab at California State University, Northridge, studying wound healing response in diabetic neuropathy as her Master’s thesis project. Currently, she studies neurological disorders, such as Down syndrome and Alzheimer’s disease, using Drosophila as a model system.

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  1. Early in my teaching career, trying to be seen as a positive role model, I got in the habit of praising just about every piece of work my students turned in. After a short while it became apparent to me that I was actually training them to turn in garbage. These days, the praise is more measured, by the way :>)

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