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The Precision of Visual Working Memory with Delayed Estimation

The Precision of Visual Working Memory with Delayed Estimation



Experimental psychologists use the delayed estimation paradigm to assess the precision of visual memories, and how such memories degrade the more one tries to remember at once.

On one hand, human memory is constrained by the number of pieces of information an individual can remember-like how many items they need to restock the pantry-meaning that it is quantitatively limited.

Memory can also be limited in its precision. For example, a person can recognize their mother on the phone because they remember the sound of her voice. However, an individual's "stored" memory of their mother's voice may not perfectly match its actual, physical sound. Thus, memory can also be qualitatively limited.

The delayed estimation paradigm provides a way to evaluate the relationship between these quantitative and qualitative limits of memory.

This video demonstrates methods for investigating the precision of visual working memory, including how to design the stimulus and perform an experiment involving a delayed estimation paradigm, as well as how to analyze and interpret the results.

In this experiment, color provides an ideal stimulus to evaluate the precision of visual working memory, as it can be mentally represented in a continuous, non-linear spectrum known as a color ring.

Participants are asked to perform several trials during which they must remember a color stimulus. Each of these trials consists of three phases: sample, delay, and test.

During the sample phase, a randomly colored square appears onscreen for 500 ms. The square then disappears, leaving a blank screen.

Through this delay phase, participants are asked to focus on the empty screen for 900 ms, whereby the sample color must be remembered.

In the final test phase, a probe square-outlined in black and devoid of color-appears in the same position as the colored box shown previously.

Simultaneously, participants are shown a color ring consisting of 180 different colors and asked to select the region of the color ring that most closely resembles the original sample color.

Note that the color ring always appears in a random orientation, which ensures that participants can't associate specific areas onscreen with certain colors.

To increase task difficulty, the memory load-the number of colored boxes shown in each trial-is varied from one to eight.

The dependent variable then is the precision of color working memory-how accurately participants remember the color or colors shown during the sample phase.

For a given sample color, participants are expected to vary within the "true" color range, but rarely choose colors that are drastically different.

As memory load increases, the precision of color working memory is likely to decrease.

To begin, choose a set of 180 colors with varying hues, which together form a color ring. Check that these colors demonstrate the same light intensity and contrast relative to the background color on the screen; this ensures that no single color will be more memorable to participants during the trials.

When the participant arrives, direct them to a computer and explain the procedure of the experiment.

Emphasize that when a specific region of the screen is probed, only the color of the box that appeared earlier in that same position should be chosen. In addition, instruct the participant to guess if they are unsure of a probed sample color.

To assure that participants understand the task, allow them to perform ten practice trials.

Once the participant understands the instructions, have them complete 480 experimental trials, with equal numbers of trials for memory loads between one and eight.

For each trial, record the memory load, the true colors of the sample boxes, and the colors the participant chose after the delay period.

To analyze the data independent of color, for every sample box shown and probed in a trial, calculate the angular error-the distance in degrees between the true and chosen response colors on the color ring.

If the participant remembered the exact color of the sample box after the delay period, the angular error should be zero.

For each group of trials dealing with the same memory load, create a frequency distribution curve, where the angular error is plotted on the X axis and frequency on the Y axis.

Once frequency distribution curves have been generated, calculate the standard deviation-the spread of values around the mean-for each.

Take the inverse of the standard deviation to generate a value representing memory precision. If this value is large, this is indicative of memory being precise for a group of trials.

To visualize the data, plot the calculated memory precision values as a function of memory load. Notice that as load increases, memory precision tends to decline, suggesting a tradeoff between how many things a participant can remember at once, and how precisely they can store this information.

Now that you know how to design and perform an experiment using delayed estimation, let's look at how researchers are currently using this paradigm to tease apart different aspects of visual memory.

Until now, we've discussed how delayed estimation has been used to assess short-term working memory, in which a participant only has to briefly store a piece of color information for a single a trial. However, researchers could also investigate long-term color memory with this paradigm, evaluating it over much longer periods.

Furthermore, this paradigm can also be used to compare the precision of visual memory between different individuals, for example, visual-based professionals like interior designers, and potentially less-visual subjects, such as lawyers or doctors.

Finally, although researchers typically use the delayed estimation paradigm to evaluate memory for color, it can also be employed in neurocognitive assessments of other types of visual working memory-like that pertaining to shapes.

You've just watched JoVE's introduction to delayed estimation. We've reviewed how to perform this method, as well as collect and analyze participant color memory data. Importantly, we've noted how this technique can help understand how the qualitative limits of human color memory can be influenced by quantitative factors.

Thanks for watching!

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