Messing With Information in Short-Term Memory

Source: American Psychological Association

Sometimes the world around you is busy. Other times, it is fairly stable. As I write this, my desktop is stable. There is nothing moving around except for the characters on my computer screen as I type. The other day, though, as I walked along a busy street through a market, there were people, dogs, and objects everywhere. It felt as though everything was in motion.

At any given moment, you are able to keep track of the locations and properties of some of the items in the world around you. That can be helpful if you suddenly need to reach for something or to look at an object nearby. The more stable the world around you, the more you might expect that you are able to keep track of the properties of the objects in your world.

This question was addressed in a paper by Sol Sun, Celia Fidalgo, Morgan Barense, Andy Lee, Jonathan Cant, and Susanne Ferber in the November 2017 issue of the Journal of Experimental Psychology: General.

In order to do carefully controlled studies, the researchers focused on the participants’ memory for the color of a target object. The method is a little complicated, but I’ll do my best to explain it.

In each trial, participants first saw a picture of a familiar object drawn from a set (like an umbrella, pen, or spool of thread) that is not associated with any particular color. The object was shown in a color for 800 milliseconds (four-fifths of a second), and participants were told to remember the color of the object. I’ll call the color to be remembered the target color.

After that, participants saw a sequence of five pictures of the same object in different colors. These pictures each appeared for 360 milliseconds (a little over one-third of a second). The researchers got people to pay attention to the sequence of objects by telling them they would have to press a button if two objects in a row in this sequence had the same color. Participants were good at identifying the repeated color. I will call the colors of these five objects the distractor colors.

Finally, participants had to identify the color of the original object by selecting it from a color wheel shown on the screen. The question is whether these five objects interfered with participants’ memory of the colors.

The researchers varied the relationship of the target color to the distractor colors. In some conditions, the distractor colors were very similar to the target. In this case, memory for the target color was basically unaffected.

In some conditions, the distractor colors were very different from the target color. In this case, memory for the target color was bad. In fact, it was so bad, people had to just guess at the target color. It was as if the target color were completely erased from memory.

In some conditions, the distractor colors were moderately similar to the target color. In this case, memory for the target was also bad, but now people were not guessing randomly. Instead, their memory for the target color was close to the actual but more variable. In this case, it was as if the distractors blurred the original memory.

Another condition varied whether the distractors had the same shape as the target. So, the target might have been an umbrella, and the distractors might have been spools of thread. Changing the identity of the object did not influence the effect of the distractor colors on the memory for the target.

What does all of this mean?

Short-term memory helps us to identify objects that we might need again soon. When we see a similar color repeatedly, short-term memory just assumes we are seeing the same object many times. The small variations in color don’t matter much. When the colors are very different, then memory assumes that there are many different objects around and so it is not worth trying to keep track of what is there.

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An interesting thing happens when the colors are only moderately similar. In this case, short-term memory seems to decide that perhaps the first look you got at the object wasn’t completely accurate. And so, it assumes that the same object is out there, but that your memory for the exact color is not accurate. That is why it feels as though the memory for the original color is blurred.

In this way, your short-term memory is making calculations of when it is worth holding on to information about what is in the environment. In chaotic environments, there is no need to hold on to information, because chances are things will change quickly. Only when things are fairly stable do you keep track of what is there.