Chapter 8. Attentional Capture

8.1 Title slide

Demonstration 8.5
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You must read each slide, and complete any questions on the slide, in sequence.
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title

Attentional Capture

Participate in a simulated experiment showing that stimuli with abrupt onsets tend to capture your attention.

CLICK ANYWHERE TO BEGIN

Attention can be deliberate and under your control, as now when you're deliberately paying attention to these words but could deliberately switch your attention to something else. However, in many situations, your attention isn’t under your control, as illustrated in this photo: the driver and passenger can't avoid having their attention captured by the sudden appearance of something in front of the car.
Photo: Andersen Ross/Digital Vision/Getty Images.

What Is Bottom-Up Attentional Control?

Top-down attentional control involves deliberately paying attention to something in order to get information needed to achieve a goal. But bottom-up attentional control—which involves the involuntary, unavoidable capture of attention by a salient perceptual stimulus—is just as important, and in some situations more so. Sudden changes in the environment are often accompanied by salient perceptual stimuli and might well require a rapid response—for example, to avoid an approaching predator or to seize some passing prey. This kind of rapid, automatic response bypasses the relatively slow mechanisms for deliberately directing attention via top-down control.

The difference in speed between top-down and bottom-up attentional control was assessed in an experiment in which participants searched a display containing an array of letters for a particular target letter. In each display, one letter had an abrupt onset and was therefore perceptually salient. The other items were less salient because they didn’t have abrupt onsets. The participant had to press a button as quickly as possible after either finding the target or determining that is was absent. In each trial, the participant’s response time was measured. Figure 1 illustrates the three types of trials. Each trial begins with an initial display of block eights, which changes to a search display of letters in the same positions, but with an additional letter called the abrupt-onset item. The participant searches this display for a target letter (H), which can be (1) absent, (2) present but not the abrupt-onset item, or (3) the abrupt-onset item.

When the target was present but wasn’t the abrupt-onset item, the response time increased as the number of letters to search increased (the search display could contain 3, 5, or 7 letters). This is what you’d expect if the participant has to evaluate each item separately, shifting attention from one to the next, until the target is found. In contrast, when the target was the abrupt-onset item, the response time was fast and didn’t increase as the number of letters to search increased. This suggests that the abrupt-onset item is frequently the first item to be searched, because its abrupt onset automatically captures the participant’s attention. Responses are slowest when the target is absent, because the participant has to check every item in the display to confirm that fact. These results show how bottom-up attentional control can produce a quick response to sudden events.



When the target was present but wasn't the abrupt-onset item, the response time increased as the number of letters to search increased (the search display could contain 3, 5, or 7 letters). This is what you'd expect if the participant has to evaluate each item separately, shifting attention from one to the next, until the target is found. In contrast, when the target was the abrupt-onset item, the response time was fast and didn't increase as the number of letters to search increased. This suggests that the abrupt-onset item is frequently the first item to be searched, because its abrupt onset automatically captures the participant's attention. Responses are slowest when the target is absent, because the participant has to check every item in the display to confirm that fact. These results show how bottom-up attentional control can produce a quick response to sudden events.

8.2 Explain

activity_8_5_slide_2

In this demonstration, you'll be a participant in a visual search experiment. In each trial, you'll view an initial display with some block 8s, followed by a search display in which the 8s are replaced by block letters; in addition, another block letter—called the abrupt-onset item—will also appear in the search display. Here's an example in which the abrupt-onset item is the H:

Search display

Initial display

Your task in each trial will be to determine as quickly as possible whether the search display contains an E (the target). An E will be present in half the trials and absent in half the trials. The abrupt-onset item is no more likely than the other letters to be an E. As soon as you determine whether an E is present:

Press

Press

If an E is present

If an E is absent

The computer will be measuring your response time in each trial (the time from the appearance of the search display to the time when you press P or A). At the end of the experiment, you'll see your results.

Now press the spacebar for a few practice trials.

8.3 Explain

activity_8_5_slide_3

Remember, you're looking for an E in the search display.

Press

Press

If an E is present

If an E is absent

Keep one finger on the P key and another finger on the A key, so you can press the correct key as quickly as possible. In each
trial, you'll see an initial display for 1 second, and then you'll see the search display. After you press P or A, the next trial will begin.

Press the spacebar to continue.

8.4 Explain

activity_8_5_slide_4

Press the spacebar to begin the trials.

8.5 Explain

You must select an answer and then click SUBMIT before you can click proceed to the next screen.
activity_8_5_slide_5

Now it's time to begin the actual experiment — 170 trials like the practice trials. But now the computer will be measuring your response time.

You must complete all 170 trials, which should take 10-15 minutes. If you don't complete all the trials, you won't be able to see your results.

Remember to respond as quickly as possible after you determine whether an E is present or absent in the search display:

Press

Press

If an E is present

If an E is absent

NOW PRESS THE SPACEBAR TO BEGIN THE EXPERIMENT.

8.6 Explain

activity_8_5_slide_6
You haven't completed all 170 trials. If you don't complete all the trials, you won't be able to see your results. Are you sure you want to leave?

Press the spacebar to begin the trials.

170 trials remain

8.7 Explain - Trial results

You must select an answer and then click SUBMIT before you can click proceed to the next screen.
activity_8_5_slide_7

RESULTS AND DISCUSSION
The graphs below compare your results to the typical results for groups of participants under controlled experimental conditions. The lower the response time, the faster the response and the easier the search. Note that each curve is defined by two plotted points, showing the median response times for search displays consisting of 3 or 7 letters:
• When the display didn't contain an E.
• When the display contained an E that wasn't the abrupt-onset item.
• When the display contained an E that was the abrupt-onset item.

Typical group results
Median response time (msec)
Number of items search display
Your results
Median response time (msec)
Number of items search display

Typically, response times are fastest when the target (E) is the abrupt-onset item, which suggests that the abrupt onset captures attention. Also, the response time tends not to increase as the number of items in the display increases. When the target is present but isn’t the abrupt-onset item, response time is longer and increases with the number of items. Response times are longest when the target is absent.

How do your results compare to the typical group results:
• Were response times shortest when the target had an abrupt onset? And was there any difference depending on the number of items?
• Were response times longer when the target was present but wasn’t the abrupt-onset item? Did the response time increase with the number of items? And were response times longest when the target was absent?

Your results cannot be displayed because you didn't complete all the trials. If you want to finish the trials and see your results, click FINISH.

8.8 Explain

explain_text

What Is Bottom-Up Attentional Control?

Top-down attentional control involves deliberately paying attention to something in order to get information needed to achieve a goal. But bottom-up attentional control—which involves the involuntary, unavoidable capture of attention by a salient perceptual stimulus—is just as important, and in some situations more so. Sudden changes in the environment are often accompanied by salient perceptual stimuli and might well require a rapid response—for example, to avoid an approaching predator or to seize some passing prey. This kind of rapid, automatic response bypasses the relatively slow mechanisms for deliberately directing attention via top-down control.

The difference in speed between top-down and bottom-up attentional control was assessed in an experiment in which participants searched a display containing an array of letters for a particular target letter. In each display, one letter had an abrupt onset and was therefore perceptually salient. The other items were less salient because they didn’t have abrupt onsets. The participant had to press a button as quickly as possible after either finding the target or determining that is was absent. In each trial, the participant’s response time was measured.

Figure 1 illustrates the three types of trials. Each trial begins with an initial display of block eights, which changes to a search display of letters in the same positions, but with an additional letter called the abrupt-onset item. The participant searches this display for a target letter (H), which can be (1) absent, (2) present but not the abrupt-onset item, or (3) the abrupt-onset item.

When the target was present but wasn’t the abrupt-onset item, the response time increased as the number of letters to search increased (the search display could contain 3, 5, or 7 letters). This is what you’d expect if the participant has to evaluate each item separately, shifting attention from one to the next, until the target is found. In contrast, when the target was the abrupt-onset item, the response time was fast and didn’t increase as the number of letters to search increased. This suggests that the abrupt-onset item is frequently the first item to be searched, because its abrupt onset automatically captures the participant’s attention. Responses are slowest when the target is absent, because the participant has to check every item in the display to confirm that fact. These results show how bottom-up attentional control can produce a quick response to sudden events.

8.9 Test - single choice

You must select an answer and then click SUBMIT before you can click proceed to the next screen.
test_single_choice

Select your answer to the question below. Then click SUBMIT.

Question

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
Correct! Click EXPLAIN if you want to review this topic.
Incorrect.
The correct answer is B.
Click EXPLAIN if you want to review this topic.

8.10 Test - single choice

You must select an answer and then click SUBMIT before you can click proceed to the next screen.
test_single_choice

Select your answer to the question below. Then click SUBMIT.

Question

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
Correct! Click EXPLAIN if you want to review this topic.
Incorrect.
The correct answer is C.
Click EXPLAIN if you want to review this topic.

8.11 Test - single choice

You must select an answer and then click SUBMIT before you can click proceed to the next screen.
test_single_choice

Select your answer to the question below. Then click SUBMIT.

Question

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
Correct! Click EXPLAIN if you want to review this topic.
Incorrect.
The correct answer is A.
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