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Cognitive Psychology

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Incidental Encoding



A great deal of our daily experiences gets encoded into long-term memory incidentally, as life goes by, without us explicitly trying to encode it.

For example, people do not remember the moment they first met a friend because they try to; rather, they just do.

Such implicit long-term memory is studied with an incidental encoding paradigm, which enables memories to be formed without the participant being asked to specifically remember a series of images.

This encoding is accomplished through the use of a cover task, where images are shown, but individuals are not explicitly told to remember them. At a later time, they are surprised with a memory test of the images.

This video demonstrates methods for investigating implicit long-term memory, including how to design stimuli and perform an experiment involving an incidental encoding paradigm, as well as how to analyze the data and interpret the results.

A typical incidental encoding experiment has two phases. The first consists of the encoding phase, where participants are exposed to a large set of pictures of real-world, everyday objects.

During this session, images are individually shown on the screen for 2 sec, with an inter-image interval of 1 sec. Half the participants are asked to do a cover task where they evaluate the object in an impersonal, and relatively superficial way by determining if there is a letter 'c' in its name.

The other half of the participants are asked to complete a more personal and detailed evaluation of the object by determining if they have ever touched the object on the screen. Note that including two cover tasks allows researchers to investigate whether the type of object engagement differentially affects incidental encoding into long-term memory.

The second phase of the experiment is the surprise memory recall test. All participants are randomly shown two images of the same object: one is the same as what was presented during the cover task, while the other is slightly different. Participants are asked to choose the image they think they previously saw.

In this case, the dependent variable is the number of correct choices during the recall test. Memory performance is expected to be greater for those who completed the more personal cover task, compared to the impersonal one.

To begin the experiment, greet the participant in the lab and explain the general procedures that will be used for the task.

During the experiment, have the participant sit comfortably in front of the screen and keyboard. Randomly assign participants to one of the two cover tasks, and instruct them to press the 'Y' key to respond yes or the 'N' key for no after the image is presented.

After judging 100 objects in the initial encoding phase, allow the participant to have a 20-min break.

When the break is over, explain to the participant that there is a final memory recall test, where two objects will appear and they must choose the one they think they saw during the initial phase by pressing the left or right arrow keys this time.

During this final recall phase, have each participant complete 100 paired trials, with the incidental objects presented in random order.

To analyze the results, compute the proportion of correct responses made by all of the participants during the surprise memory test phase and graph the results. Note that chance level is 50%, since there were only two choices.

Notice that incidental encoding into memory occurred during both cover tasks; however, having a more personal engagement with the presented items strengthened the formation of memories.

Now that you are familiar with an incidental encoding paradigm, let's take a look at other ways experimental psychologists use the task to investigate long-term memory formation.

The incidental encoding paradigm is used to investigate the memory deficits caused by diseases such as Alzheimer's. Patients remember very little compared with healthy controls when they are asked to study and remember images.

However, if an incidental encoding paradigm with a personal or emotional cover task is used, patients have a much better memory, suggesting that activation of emotion areas in the brain may foster memory encoding.

Other researchers have combined incidental encoding paradigms with functional magnetic resonance imaging to elucidate the brain regions involved in memory formation of emotional items, including the amygdala, hippocampus, and other medial temporal lobe structures.

You've just watched JoVE's introduction to incidental encoding. Now you should have a good understanding of how to setup and perform an experiment, as well as analyze and assess the results.

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