Chapter 15 Bottleneck - memory

What does it take to form a memory?

If I ask you about your memory, you’ll probably assume that I’m asking you about things pretty far in the past.. at least a different day. But memory is required even for you to report something you saw a few seconds ago. In the laboratory, researchers have devised situations in which you will occasionally forget things that happened just two seconds ago.

One thing researchers do in their experiments is show people random, unrelated stimuli. That way, people can’t use their knowledge of the way the world usually works to reconstruct what must have happened. In the real world, if I hear the doorbell ring and ten seconds later find myself holding a package addressed to me, I can reconstruct that probably what happened is I went to the door and got the package there. Standard sequences of events can help our brains reconstruct events in an act of remembering based on only fragments.

Besides showng people random unrelated stimuli in memory tests, another thing that researchers do is present stimuli quite briefly. Let’s say I ask you to remember a photo like this one, of a moth I photographed in a rainforest in Panamá.

As you examine the moth, you’ll notice various things. I can tell you that for me, the white and black pincer-shaped wing markings jumped out, as did the fuzzy white front edges of the feathery wings. You might start making various associations, possibly to an eagle’s open talon for the wing markings, or to a fur coat for the white edges of the wings. The longer you look at it, the more details you notice and think about, which creates more and more parts of a memory that later can help you remember the image.

If you were shown the picture of the moth only very briefly, then you’d have less chance to form strong memories for it. Brief exposure, in combination with the use of unrelated stimuli, help researchers to probe how memory works even in the time available in a laboratory exeriment, testing for a memory only seconds after someone is shown a stimulus.

A third feature of memory experiments is that the stimuli tend to be much more boring than my photo of the moth I showed you above. This is partly for standardisation purposes, so that stimuli can easily be swapped and result in similar findings. So, sometimes researchers just use individual letters, as you’ll see below.

Below is a movie that shows a rapid series of letters. While you watch it, look out for and try to remember the one letter that is circled.

If the movie didn’t work, you can watch it here.

Hopefully you were able to see which letter was circled. However, the act of trying to remember that letter can impair your memory of subsequent letters in the stream.


Goodbourn, P. T., P. Martini, M. Barnett-Cowan, I. M. Harris, E. J. Livesey, and A. O. Holcombe. 2016. “Reconsidering Temporal Selection in the Attentional Blink.” Psychological Science 27 (8): 1146–56.