Chapter 15 Distraction in the laboratory

Three Wise Monkeys

These are the “three wise monkeys” from a Buddhist legend, here depicted on a 17th-century wood carving in the Tōshō-gū shrine in Nikkō, Japan.

Occasionally, we may feel a bit like the leftmost monkey above, trying to ignore the sounds around us so that we can pay full attention to something we are looking at. Other times, we may want to concentrate on something we are listening to, in which case shutting our eyes like the monkey on the right might be a good idea.

It would be nice if we could simply turn off our hearing or vision at times and thereby avoid distractions. As we discussed in 5, however, as creatures that evolved in a dangerous world, our brains are evolved to be continually vigilant.

This may be most obvious in prey animals. Horses are one example; during their evolutionary history they were often eaten by creatures such as wolves and lions. Horses are thus easily distracted by the things they see.

Horse. Credit: Alex Proimos from Sydney, Australia, CC BY 2.0, via Wikimedia Commons

Horses have large, side-mounted eyes that give them almost 350° of vision, with only a small blind area spanning just 15°.

Schematic of a horse from above, with areas of no vision in grey.

Many working horses are fitted with blinders to restrict their field of vision to the front. Whether a horse’s owner is trying to get it to pull a carriage or to win a race, the blinders, also known as “blinkers,” help keep it on task.

Humans may have not had as much to fear from other animals as horses did, but we still faced dangers in our ancestral environment, from other people as well as from lions. Like that of horses, our brains are constantly monitoring incoming signals from all our senses for things that might be a danger. Sleep is a little different, but even during sleep a loud sound, a bright light, or a strong touch will pretty reliably wake people up. Not babies, though - they can be much harder to wake up. Why? Well, they evolved to rely on adults for their defense, so they can afford to concentrate on brain development rather than monitoring the environment.

The top-down attention chapter (5) introduced the idea of attentional capture. The experiment discussed there, by Theeuwes et al., used these sorts of displays:

Two displays, one with a distractor (right) and one without (left).

The task for participants in the experiment was to find the diamond and determine the orientation of the line within it. People took longer to do that in the presence of an odd-colored distractor like the red circle at right. It seems that on some trials, participants couldn’t help but shift their attention to the red object, and only after that did they attend to the diamond. All sorts of sensory signals can be distracting, of course, not just odd-colored items.

Odd sounds, for example, are often distracting. One reason is that hearing is especially important for “interrupt signals” (5) because hearing provides an early warning system. With vision, you need to look around, moving your eyes about, to detect any threats around you. With hearing, in contrast, you can detect things anywhere around you without even moving your ears and your head. Indeed, most of us can’t even move our ears, because we don’t need to move our ears or head to listen.

Some people can move their ears, but it’s not really necessary.

Sudden sounds in an otherwise quiet scene, then, can distract our attention, taking us off task.

In such a situation, you can think of the sound as like an odd color in a scene that otherwise is uniformly colored. Similarly if you feel a sudden touch against your body, this will also attract your attention. Indeed, preventing a touch from alerting people is the primary challenge faced by pickpocketers. The magician and pickpocketer Apollo Robbins addressed this by touching his victims throughout his routine, so that the touches corresponding to removing the victim’s watch wouldn’t be registered as anything different.

15.1 Bottleneck review

Previous chapters emphasized that many changes in a scene can go completely unnoticed. That’s true even if the changes are highly unusual, as long as they don’t stand out by being the only location associated with a flicker or motion signal. The reason for this is that because of the brain’s bottlenecks, most objects in a scene may never be identified. So, most of the unusual aspects of a scene will never have a chance to attract attention because they aren’t processed enough by the brain for the brain to determine whether they are unusual. If you show someone a cluttered scene and then tell them to find any unusual objects within, it will take them a long time to do so, just as it takes a long time to find Wally in the scenes of the Where’s Wally books. One has to move attention around the scene to recognise the objects, possibly one-by-one. The only scene-wide processing for unusual things is limited to a few features, like color and orientation.

These issues are also illustrated by the wimmelbilderbuch (literally “teeming picture book”) tradition of illustrations popular in the 16th century. Also known as a hidden picture book, the pages contained many disparate figures and objects.

Only by attending to each part of the image in turn could you recognise all the objects that were there. Just as with Where’s Wally today, children found them fun to look at. In the painting above, the artist Pieter Brueghel depicted people enacting idioms that children were meant to learn, such as “swimming against the tide,” “banging one’s head against a brick wall,” and “armed to the teeth” (“Netherlandish Proverbs 2021).

Most surprising things in a scene, then, won’t attract attention because they aren’t processed extensively. A secondary question, which we will turn to now, is which sorts of things will hold attention if they actually are processed.

15.2 Avoiding a bottleneck to test potential distractors

A common way that researchers use to ensure that objects are processed extensively is by presenting them one-by-one, right where the study participant is looking. This is called the rapid serial visual presentation method and we already saw it used to reveal a memory bottleneck in the previous chapter (14).

Asplund et al. (2010) used this technique to investigate what attracted attention in conditions where many different objects were briefly presented, but the participant’s task was to attend to just one. They used a rapid stream of letters, like those in the movies in 14. In one of the Asplund et al. (2010) experiments, participants had to identify one of the letters in the stream. On some trials, however, without warning the participants, they replaced one of the letters with a photograph of a face.

In the study schematised above, in 4 of 30 trials a surprise face stimulus popped up at various lags before a target letter.

The sudden appearance of the face was a surprise to the participants, at least at first. On those trials where it was included, performance identifying the letter often was worse. Specifically, if the letter was shown within about half a second after the face, accuracy reporting the letter was worse. The faces were proven to be effective distractors that held attention.

You might have guessed that faces would be potent distractors. After all, many of us are highly social, and it’s possible that our brains are evolved to orient toward faces (6.1). However, Asplund et al. (2010) found that the disruption of performance by an unexpected image was not specific to faces.

In the experiment, half of participants were actually shown a stream of faces rather than a stream of letters.

Schematic of a stream of faces with a surprise letter included.

The participants’ task was to identify a target face, not a target letter, but in some trials, a letter was included in the stream. The results were quite similar to those for the participants who viewed a stream of letters rather than a stream of faces. That is, when the surprise letter was presented less than half a second before the target face, participants were less likely to report that they had seen the target face.

The black squares show the data for those participants. When in four of the trials a letter was included in the stream of faces, participants did poorly if that letter was presented 130 or 390 ms before the letter, but they did fine if it was presented 780 ms later. In summary, the odd stimulus disrupted performance for approximately half a second (500 ms). During that interval, participants missed the target about half the time.

The same pattern was seen for those participants who saw the stream of letters punctuated by the surprise presentation of a face, as shown by the white circles in the data plot. You will, however, notice that performance was slightly poorer for this condition, where the surprise was a face, which could be caused by faces being inherently more distracting than letters. To investigate this possibility, Asplund et al. (2010) tried using other images besides faces in the letter stream and compared their effects to those of the faces.

The results yielded no significant difference between using any one of these images as a the surprise rather than the face, so although faces may have more distracting power (Langton et al. 2008), that didn’t make much difference in these experiments. More important was simply that the stimulus presented was different rather than being a particular kind of stimulus.

When something distracts you, if it’s something that interests you, you may simply choose to stop doing whatever you were in the process of doing. In that case, it’s obvious that this would impair performance of the task you chose to stop doing. What’s more interesting is when a distracter reduces your performance even though you are trying to completely ignore it. This is what was happening when the odd-colored items in the visual search experiment elevated response time (6.1) and in these Asplund et al. (2010) experiments with the images.

15.3 Surprise!

The first time one sees a jack-in-the-box, the sudden and unusual sensory event of the jack bursting out of the box can be highly surprising.

A major reason that attention was attracted to and held by the rare face presented among letters (Asplund et al. 2010), was because the face was simply different from the other stimuli presented in the trial. But another factor is the actual unexpectedness or surprise of seeing the face there’s also another phenomenon contributing to the results. Remember that each participant saw the unusual stimulus in four of the thirty trials they participated in. In the first trial that the unusual stimulus appeared, it must have been very surprising, but not so surprising the third or fourth time. When Asplund et al. (2010) broke down the results in this way, they saw the results were different the third or fourth time.

Most of the deficit caused by the unusual stimulus was confined to the first one or two trials. After that, participants did much better. So a lot of the problem was the surprise itself. After participants began to expect the stimulus, the unusual stimulus had much less effect; participants were much less distracted by it.

A good deal of the effect of distractions, then, comes from them being unexpected. After a particular event has repeated many times, it has less effect on reactions of many kinds, not just the kind of distraction assessed in these experiments. This is called habituation. Habituation, the decrease in response to a stimulus after repeated presentations, is a kind of learning. Neurons across much of the brain respond less to repetitions of an input than to the first exposure of an input. Habituation serves a variety of purposes for the brain, but here our point is just that it can reduce the orienting of attention to a stimulus.

Unfortunately, habituation is rarely complete. In the Asplund et al. (2010) work as well as the Theeuwes et al. experiment (5), even after many repetitions the average participant wasn’t able to entirely prevent those salient stimuli from interfering with their performance.

In summary, there are two things going on in such cases:

  • An unusual stimulus can attract attention, disrupting task performance for about half a second in these circumstances.
  • If the stimulus is a surprise, the disruption is greater.

And don’t forget, the stimulus has to be processed enough for it to be registered as unusual (which the researchers ensured by presenting them one-by-one).

Would it be possible to make a list of all the stimuli that, if processed, would attract attention? Perhaps not, because it may depend on the person. Have you ever been talking to a few people but then overheard someone else say your name in a separate conversation? When that’s happened to me at a party, I’ve found it very difficult to keep concentrating on the conversation I was in, even if it was an important conversation with my boss. I might manage to keep my eyes on my boss, when he finished his sentence I’d realise that I didn’t know what he had said.

Emotionally arousing stimuli are one stimulus class that may attract attention in most people. In the laboratory, one way that’s been studied is by presenting a rapid series of images and testing people on which ones they remembered. By inserting different sorts of images in the stream, researchers can determine which ones are the most distracting. One study done by an honours student, Katherine Saunders, in my laboratory used that procedure. Watch this movie to see an example image sequence from Katherine’s experiment.

After people were shown the movie, they were asked which of the below image(s) had been presented.

Response lineup. Participants clicked on the images they had seen We found that participants were less likely to remember the couch than the other images. The reason for this is that it was placed soon after a very arousing image of a dead body.

Distractions like emotionally-charged images can cause people to completely miss pictures that are presented soon after them. Based on hundreds of experiments investigating this and related effects, researchers believe part of the reason is that consolidating sensory signals into memory takes time, as we described in the previous chapter (14). Once your attention is attracted by something, your mind will often process it for storage in memory, hampering your mind’s ability to process other items into memory that occur around the same time. Unlike for the faces and letters used by Asplund et al. (2010), repeated presentation of such stimuli may not reduce their effect much (Onie, Donkin, and Most 2021); in other words, there may be very little habituation.

15.4 Learned and not learned

In the beginning of this chapter, and elsewhere (5), we referred to the importance of an alerting system in evolutionary history. Some of these alerts are probably hard-wired into our brains by evolutionary history, rather than learnt. Charles Darwin himself (Darwin 2009) suggested this possibility, when writing about a trip he took to the zoo.

I put my face close to the thick glass-plate in front of a puff-adder in the Zoological Gardens, with the firm determination of not starting back if the snake struck at me; but, as soon as the blow was struck, my resolution went for nothing, and I jumped a yard or two backwards with astonishing rapidity. My will and reason were powerless against the imagination of a danger which had never been experienced.

Charles Darwin, a few years after the 1872 publication of his book “The Expression of the Emotions in Man and Animals.”

Darwin believed that his fearful reaction to snakes was innate rather than learned. Subsequent evidence has provided some support for that idea, at least in other primates (Shibasaki and Kawai 2009); it is difficult to confirm this in humans. Many of the things that attract our attention, however, must be learned. Evolution could not keep up with the changing array of important things in our ancestral environments, and our environment and associated lifestyles are changing even more rapidly today.

The habituation learning evident in the Asplund et al. (2010) work helps reduce the tendency for us to be continually distracted by things. Unfortunately, however, the world today presents a constantly-changing set of distractions, so you will not habituate to everything, even if that were desirable.

15.5 Rewards make distractors more distracting

Have you ever looked after a dog? We have a dog in my household, and his name is Hugo. Most of the time, Hugo doesn’t pay a lot of attention to me or the other people in the house.

But when one of us starts shoveling wet dog food into Hugo’s bowl, the impact of the spoon against the ceramic bowl makes a characteristic ringing sound, and Hugo will leap to attention. Hugo has learned to associate the ringing sound with the reward of food.

I think that even if Hugo were trying to concentrate on another task, the ringing sound would distract him. At least, something like that does happen for humans. In a visual search experiment based on the study we discussed by Theeuwes, Le Pelley et al. (2015) gave participants the task of judging whether the little line they presented inside a diamond shape that appeared on each trial was horizontal or vertical. Le Pelley et al. (2015) also included an odd-colored distracter in the display. There were two major changes compared to the Theeuwes study. First, the participants received money for each correct response. Second, they earned a greater amount (10¢) if the distracter were one particular color, while they made less money (1¢) if it were another.

The best strategy for participants to maximise their earnings was to completely ignore the distractor and its color. But, you already know from chapter 5 that the odd-colored distractor will slow the participants down. The new issue here was whether the distractor that indicated the reward for the current trial would be 10¢ would affect people any differently than the distractor that indicated the reward would be just 1¢.

To end up with as much money as possible, if they can the participants ought to concentrate more on the target when the distractor indicates a large reward than when it indicates a small reward. However, this is not what happened! Instead, responses were slower when the distractor indicated the trial was high value than when it indicated the trial was low value.

Response times were longest in the high-value condition, a bit faster in the low-value condition, and fastest when no distractor was presented.

Evidently, the participants attended more to the distractor that was associated with a stronger reward, even though this reduced how much money they received at the end of the experiment. Stimuli that are associated with greater rewards seem to attract more attention, even when that is completely counterproductive.

This brings us to the situation we all face with modern technology and devices.

15.6 Exercises

  • What does the bottleneck on object identification have to do with what can distract you?
  • What lesson did Darwin draw from his experience with a snake at the zoo?
  • What do you find most distracting when you are trying to watch a lecture? What is most distracting when you are trying to study?


Asplund, Christopher L., J. Jay Todd, A. P. Snyder, Christopher M. Gilbert, and René Marois. 2010. “Surprise-Induced Blindness: A Stimulus-Driven Attentional Limit to Conscious Perception.” Journal of Experimental Psychology: Human Perception and Performance 36 (6): 1372.
Darwin, Charles. 2009. The Expression of the Emotions in Man and Animals, Anniversary Edition. 4th edition. Oxford ; New York: OUP USA.
Langton, S R, A S Law, A M Burton, and S R Schweinberger. 2008. “Attention Capture by Faces” 107 (1): 330–42.
Le Pelley, Mike E., Daniel Pearson, Oren Griffiths, and Tom Beesley. 2015. “When Goals Conflict with Values: Counterproductive Attentional and Oculomotor Capture by Reward-Related Stimuli.” Journal of Experimental Psychology: General 144 (1): 158.
“Netherlandish Proverbs.” 2021. Wikipedia, August.
Onie, Sandersan, Chris Donkin, and Steven Most. 2021. “Does a Single Session of Training Modify Emotion-Induced Blindness?” PsyArXiv.
Shibasaki, Masahiro, and Nobuyuki Kawai. 2009. “Rapid Detection of Snakes by Japanese Monkeys (Macaca Fuscata): An Evolutionarily Predisposed Visual System.” Journal of Comparative Psychology 123 (2): 131.