What is incidental encoding and how does it differ from intentional learning?

Incidental encoding occurs when memories form naturally during daily experiences without explicit effort to remember. Unlike intentional learning where people study content deliberately, incidental encoding happens passively as life unfolds. For example, people remember meeting a friend not because they tried to memorize the moment, but because the experience was encoded automatically into long-term memory.

What is a cover task and why is it used in incidental encoding experiments?

A cover task is an activity participants complete without knowing their memory for the stimuli will be tested later. Researchers use cover tasks to expose individuals to stimuli while disguising the true purpose of the study. This allows researchers to investigate how different types of engagement—personal versus impersonal—affect memory formation without participants consciously trying to remember.

How do personal and impersonal cover tasks affect memory performance differently?

Personal engagement with stimuli strengthens memory formation compared to impersonal evaluation. In experiments, participants who evaluate whether they've touched an object show better memory performance than those who simply determine if the object's name contains a letter. This demonstrates that deeper, more personal processing during incidental encoding produces stronger long-term memories.

What are the two main phases of a typical incidental encoding experiment?

The encoding phase exposes participants to images of everyday objects for 2 seconds each while they complete a cover task. The second phase is a surprise memory recall test where participants view paired images and select which one they previously saw. This two-phase design allows researchers to measure how well memories formed incidentally during the cover task.

How is memory performance measured and analyzed in incidental encoding studies?

Researchers compute the proportion of correct responses during the surprise memory test and compare it to chance level, which is 50% since participants choose between two images. Results are graphed to visualize differences between conditions. Memory performance greater than 50% indicates successful incidental encoding, with higher scores reflecting stronger memory formation.

How has incidental encoding research contributed to understanding memory deficits in Alzheimer's disease?

Studies show Alzheimer's patients remember very little when asked to study images intentionally, but perform much better with incidental encoding using personal or emotional cover tasks. This suggests that activation of emotion areas in the brain fosters memory encoding even in patients with memory deficits. Researchers have combined incidental encoding paradigms with functional imaging to identify brain regions like the amygdala and hippocampus involved in emotional memory formation.

Why is the incidental encoding paradigm valuable for studying real-world memory formation?

In daily life, people form lasting memories incidentally without deliberate study, such as remembering magazine content or a partner's first meeting. The incidental encoding paradigm mirrors this natural process, making it ideal for investigating how everyday experiences produce strong long-term memories. This approach reveals which types of engagement—personal, intellectual, deep, or shallow—tend to produce robust memories in real-world contexts.

Incidental Encoding

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1. Stimulus and apparatus.

Run the experiment on a computer.
Collect a set of pictures of real-world, everyday objects (Figure 1).

Figure 1. Sample stimuli for incidental encoding. Typical experiments utilize color photographs of everyday objects, like the five shown here. Many labs make such stimulus sets publicly available. These examples are from a group at MIT: http://cvcl.mit.edu/MM/uniqueObjects.html.
For each such image, create a paired case in which the object in the picture is the same, but in a different state (Figure 2).

Figure 2. Examples of paired images in different states.

2. Procedure.

The experiment has two phases. The first is the incidental-encoding phase.
Expose the participant to a large set of images without their knowing that they will be tested later. This is the goal of the encoding phase, so for this reason, give the participant a cover task. In this case, use a letter judgment task.
1. Ask the participant to name each object they see and to report whether the object’s name has the letter ‘C’ in it.
When the participant arrives for the experiment, explain the instructions for the incidental-encoding phase of the experiment and the cover task, as follows:
1. “The experiment you are about to participate in was designed to investigate human language, and in particular, how our brains relate visual inputs to the names of common nouns. On each trial of the experiment, you will be shown a common object for 2 seconds. Your task is to report whether that object has a letter ‘C’ in its name. For example, if you see a coffee machine, you would press the ‘Y’ key to indicate that ‘coffee machine’ does include the letter ‘C’. But if you were to see a tennis ball, you would press the ‘N’ key. Please make your response as quickly as possible. After you make a response, the image will remain on the screen for a total duration of 2 seconds, and then the screen will be empty for 1 second, after which the next image will appear. You will be asked to judge a total of 100 images.” (Figure 3).

Incidental encoding procedure diagram with objects: abacus, tomato, books for cognitive processing.
Figure 3. Procedure for incidental encoding. An object is shown in isolation for 2 s, during which the participant needs to press a key to indicate whether the name for that object includes the letter ‘C.’ In the examples shown, a “yes” response would be given for the first object (an “ABACUS”), but not for the second two (“TOMATO” and “BOOKS”). This is a cover task, to ensure that the participant is exposed to the stimuli incidentally, without knowing that memory will be tested later. Between images, the observer sees a blank 1 s display. This experiment includes 100 distinct objects following this procedure.

Cover Task Variation. The basic incidental encoding procedure has been used to ask many different kinds of questions about the nature of long-term memory. In order to do this, contrast the performances with different cover tasks. This allows a researcher to ask about the kinds of engagement that support better (or worse) incidental encoding into long-term memory.
One classic effect deals with levels of processing. To investigate the effects of levels of processing on memory encoding, test half the participants using the letter cover task described already (“Does the name of this object have a letter ‘C’ in it?”). This is an impersonal, and relatively superficial way, to evaluate an object.
Have the other half of the participants do a different cover task designed to engage personal and more detailed processing. Explain the following instructions to the participant:
1. “On each trial of the experiment, you will be shown a common object for 2 seconds. Your task is to report whether you have ever touched an object like the one shown. Think for a moment, and then press the ‘Y’ key if you can think of a time that you have touched such an object, or press the ‘N’ key if you cannot think of such a time. We are using this experiment to quantify how frequently people interact with basic objects. This is a process known as ‘norming.’ We will use the results of this experiment to analyze the results of future experiments that use these images as a stimulus set.”
2. Note that the last part of the instructions is there to convince the participant of the “cover.” It supplies a reason for asking them to complete a somewhat odd task, just like the suggestion that the experiment is designed to investigate language supplies a reason for the letter ‘C’ task.
Just as the instructions describe, have the participant complete 100 trials with one of the cover tasks, which expose them to the sample stimuli. A participant only does one of the cover tasks.
After the incidental-exposure phase is complete, conduct the test phase immediately or after a break. For this experiment, use a 20 min break.
1. Let the participant know that they will have a break before continuing on to additional experiments.
When the break is over, conduct the surprise memory test. Explain the instructions to the participant as follows:
1. “Thank you for your participation. I’d now like you to do a second task designed to investigate how well you remember the objects you saw earlier. On each trial, you will see two pictures of the same object. One will be a picture of the object you saw when you were doing the letter judgment task. The other will be a picture of that object in a different state—it could be rotated, opened, closed, and so on. Your job is to identify the image you saw before. In each trial, one of the pictures will be on the right side of the screen and the other will be on the left. Press the right or left arrow key to indicate the image you think is the one you saw before. If you are unsure, just guess.”
As the instructions describe, each trial of the test phase includes an image from the encoding phase along with its paired state image. Present the images in a different random order from the encoding phase (Figure 4).

Figure 4. Procedure for the surprise memory test. Each trial includes one of the images the participant saw during incidental exposure along with its state pair. The participant’s task is to indicate which image they saw previously (the one on the right or left side of the screen).
To analyze the results, compute the proportion of correct responses made by the participant during the test phase. With 100 images, participants should correctly identify between 65 and 95, on average. Note that 50 would be the expected outcome (on average) if one simply guessed and actually remembered nothing about the images. So performances better than 50% indicate that images were encoded into long-term memory during the cover task.

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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