Source: Laboratory of Jonathan Flombaum—Johns Hopkins University
In order for recognition of a certain stimulus to take place, visual attention needs to be directed towards said stimulus. To the earliest parts of the visual system, objects are not objects, they are collections of visual features-lines, corners, changes in texture, color, and light. Attention is the resource that is necessary for later processing in order to recognize what a given bundle of features adds up to. This makes attention a central focus of research. One especially important set of questions concerns how people sustain attention, that is, the extent to which they can continuously maintain a focus of attention from moment-to-moment. It is now known that sustained attention takes great effort. When attention needs to be focused very rapidly on something that is moving or changing very quickly, the effort involved causes a momentary lapse in attention once it is disengaged. This kind of lapse in attention is called an attentional blink. It is like the brain blinks for a moment, shutting down attention for a rest. Stimuli that appear during an attentional blink will not be perceived.
In 1992, a group of researchers devised a paradigm to study the attentional blink, and the paradigm has come to be known by the same name.1 It demonstrates some of the challenges to maintaining focused attention. This video demonstrates how to implement the attentional blink paradigm in order to study sustained visual attention.
- The experiment requires a computer and experiment implementation software such as E-Prime, or a programming environment such as MATLAB or PsychoPy.
2. Stimulus and experiment design
- This experiment relies on a general experimental procedure called Rapid Serial Visual Presentation, RSVP for short.
- The basics of RSVP involve experimental trials in which a series of images is shown rapidly, one after the other. Images usually remain in a display for less than 200 ms, before being replaced by another image, making extensive processing of the images difficult.
- Start by making a basic RSVP program. Set it to present streams of large black lowercase letters (Helvetica font) in the center of the display, each one lasting only 50 ms. The letters should take up about 2.5 in. vertically and 1.5 in. horizontally. Figure 1 schematizes an RSVP sequence.
Figure 1: The basics of rapid serial visual presentation (RSVP). A series of images is shown in rapid succession, in this case, lowercase letters each remaining for only 50 ms before becoming replaced by the subsequent letter.
- Now, to make this an attentional blink program, do as follows:
- Make trials that are 30 images long-i.e. there will be 30 characters displayed, each for 50 ms, making each trial 1.5 s total.
- 28 of the characters in each trial are lowercase letters as just described, but two are numbers.
- In each trial, randomly select the two numbers between 1 and 9 to show, but also ensure that the two numbers in a trial are always different.
- Randomly select the place in which the first number appears within the boundary of the 8th item presented and the 20th item presented. In other words, in each trial, place one number somewhere between the 8th and 20th RSVP position.
- The second number appears anywhere between immediately after the first and six positions after it. Since the position of the second number is defined relative to the first, these are called lag positions. The second number can have a lag position ranging between 1 and 6. In fact, over the course of the whole experiment there will be an equal number of each of the lag positions between 1 and 6. Figure 2 schematizes the concept of a lag position.
- Program the experiment to include 180 trials total, 30 each for each lag position, 1-6.
- At the end of each trial, the screen should read "First? Second?", as shown in Figure 2, to prompt the observer to report the numbers they saw during the trial.
- Finally, set up the program to produce an output spreadsheet that reports all the relevant data. Each row in the file corresponds to the contents of a single trial, and should include the following information, as shown in Figure 3: the trial number, the position of the first number in the RSVP stream, the lag position of the second number, the true identity of the first number, the true identity of the second number, and the key press made by the participant to identify the first number, and the same for the second.
Figure 2: Methods for the attentional blink. A ready screen is followed by an RSVP stream consisting mainly of letters, 30 images in total. Embedded among the letters are two numbers. The first number appears anywhere between the 8th and the 20th positions in the stream. The position of the second number is called a lag and defined relative to the appearance of the first number such that following the first immediately is called lag 1, the next position lag 2, and so on. The experiment consists of 30 trials at each of lags 1-6.
Figure 3: Organization of a data output table for an attentional blink experiment. Each row corresponds to a trial of the experiment. The important parameters to record are the position of the first number in the stream (a value between 8 and 20), the lag until the second number (a value between 1 and 6), the identity of the two numbers shown, and the responses given by the participant at the end of the trial.
3. Running the experiment
- For a complete experiment, it is ideal to test between 10-20 participants, but the result of this experiment should be apparent in the data of most individual participants.
- To test a participant, seat them in front of the computer monitor so that the back of their chair is about 60 cm away.
- Explain the instructions to them as follows:
- "This experiment is designed to investigate the speed of human attention. Each trial will be more or less the same. You will see a screen with the word 'Ready?' on it. The screen will remain so until you press the spacebar to initiate a trial. Once a trial is initiated, you will see a series of lowercase letters appear rapidly in the center of the screen over the course of 1.5 seconds. Two numbers will appear embedded between the letters. They will appear in random positions, and not necessarily immediately after one another. Your task is to pay close attention to the sequence of letters, and to try to recognize the two letters that appear. At the end of a trial, you will be prompted to input the numbers that you think appeared, and in the order that you think you saw them, the first one first, followed by the second. There will be 180 trials total, so the experiment should only last 5-10 minutes. It is very important, however, that you do your best. If you are uncertain about the identity of a number in any trial, just guess. Any questions?"
- After answering any questions, start the experiment for the participant, watching as they completes a few trials in case any further questions arise. Then leave the participant to complete the experiment.
4. Analyzing Results
- The first thing to do in order to analyze the results is to add two columns to the now populated data spreadsheet, a column called Accuracy 1, and one called Accuracy 2, meant to indicate whether the participant correctly identified the number in each position in that trial. Compare the actual number that appeared in each trial with the response given, filling the column with a 1 for a correct response, and a 0 for an incorrect response. Figure 4 shows how the table should look at this point.
Figure 4: Populated data output for an attentional blink experiment. The columns Accuracy 1 and Accuracy 2 report whether the response entered by a participant matched the actual identities of the number presented during each trial. 1 indicates a correct response, and 0 indicates an incorrect response.
- Now compute the overall response accuracy for the participant for the first number. Do this by averaging the numbers in the Accuracy 1 column of the spreadsheet. This should be very high, between 0.90 and 1.
- Finally compute the average response accuracy for each of the six lag positions for the second number.
Processing information in a rapidly changing environment is demanding, and visual attention is necessary for object recognition to occur.
For example, to recognize how a group of features comprises an object, like this football, visual attention is required, and sustaining it takes considerable effort.
In dynamic situations where items move rapidly—like a football and players on the field during a game—the attentional effort involved causes a momentary lapse in attention once it is disengaged, such as when the quarterback is looking for a receiver.
This lapse is referred to as an attentional blink—as if the brain blinks for a moment, shutting down attention for a rest—in which stimuli, such as an opponent, are not perceived.
Based on the methods pioneered by Raymond, Shapiro and Arnell in 1992, this video demonstrates how to implement the phenomenon of Attentional Blink by discussing the steps required to design the stimuli and execute the paradigm, as well as how to analyze the data and interpret the results describing the accuracy of responses across trials with varying levels of attentional engagement.
In this experiment, a series of images, such as large black lower case letters and numbers in Helvetica font, are presented for 50 ms one after the other—an experimental procedure called Rapid Serial Visual Presentation, RSVP for short.
Each trial is programmed to display 30 characters in total, whereby two of the images are different numbers between 1 and 9.
The first is randomly placed somewhere between the eighth and twentieth RSVP position, while the second digit is randomly inserted in a spot immediately after the first number, to six places after it. This spacing is called the lag position, which can range from 1 to 6.
Over the course of the experiment, there are 180 trials, 30 at each of the 6 lag positions.
After each trial, participants are asked to report the numbers, in the order that they appeared, during the RSVP. The dependent variable is recorded as the number of correct responses across lag positions.
The logic behind the paradigm is that the first number will grab the participant’s attention, leading to a very high accuracy in naming the first ones. However, depending on the lag position, performance is expected to vary when reporting the second number.
If it appears immediately after the first, performance should still be very high—a concept called lag 1 sparing.
Accuracy should be affected most dramatically when the second number is in the second and third lag positions—because of the attentional blink phenomenon—and accuracy will be less affected at the later lag positions, those that occur after the short attentional blink window.
Before the experiment, set up the program to generate an output spreadsheet that reports all of the relevant data for subsequent analysis, including the trial number, the position of the first digit in the RSVP stream and the lag, the true identity of the first and second numbers, and the responses given.
To begin, greet the participant in the lab and guide them into the experimental room. Have them sit comfortably in front of the computer, with their chair back approximately 60 cm away.
Now, explain the task instructions: The screen will display the word "Ready?"until the space bar is pressed, after which a series of letters and numbers will immediately and rapidly appear.
Direct the participant to indicate what numbers they saw by pressing the corresponding keys in the same order they saw them. Remind them that if they are not sure what numbers they saw, to just guess.
After answering any questions, leave the room and allow them to complete the 30 trials at all lag positions, for a total of 180. When they are finished, thank them for taking part in the experiment.
To begin data analysis, open the spreadsheet with the data output from the experiment. Add two columns, named 'Accuracy 1' and 'Accuracy 2', to indicate whether the participant correctly identified the number in each position.
For each trial, in the column labeled 'Accuracy 1', indicate whether or not they identified the first number correctly by placing a 1 or incorrectly by assigning a 0. Duplicate this for the column labeled 'Accuracy 2'.
Next graph the mean accuracy across all trials for the first, along with the averages for the second numbers reported—'Accuracy 2'—by lag positions.
Notice that the response for the first number—'Accuracy 1'—was very high, which demonstrates that even though the number appears very briefly, in an unpredictable location and embedded between letters, focused attention can support detailed processing and recognition.
As predicted, when the second number immediately followed the first, accuracy remained high due to lag 1 sparing. Thus, focused attention triggered by the first number remains engaged, allowing for the capture of the second number.
However, for lag positions 2 and 3, mean accuracy values decreased dramatically, reflecting the phenomenon of attentional blink. That is, after processing the first number, attention becomes temporarily disengaged, thereby reducing processing and recognition.
Though, the attentional blink did not last long, as shown by the improved performance for lag positions 4, 5, and 6.
Now that you are familiar with the phenomenon, let’s look at how the paradigm is used to investigate the basic limitations of visual attention in more detail, including the kinds of things that may capture it automatically, and even how anxiety and other mental health problems may divert it.
In a similar RSVP task using photographs, participants were asked to identify a target image—one that was rotated in an unusual position. For example, an upside-down room was included as the target, and participants reported if it was an indoor or an outdoor scene.
In some trials, researchers added a picture of a spider to the stream in a position preceding the target. They hypothesized that this might automatically capture attention because of the fear it induces. In this case, they reasoned that it should produce an attentional blink—leading the rotated target to be missed.
Indeed, participants responded inaccurately when a spider preceded the target, demonstrating that fear-inducing objects can automatically capture attention and produce attentional blinks.
Researchers have also used the same paradigm to investigate differences between people with severe phobias and those with just a typical dislike of spiders.
In this instance, the task is reversed: the rotated room is shown beforehand, presenting the spider in the lag 2 position. For most participants then, the perception of the spider is blocked by the attentional blink.
Interestingly, individuals with severe arachnophobia did not show an attentional blink, as they reported seeing the spider—suggesting that at times, emotional stimuli have a very strong pull on attention, when it would otherwise be disengaged.
You’ve just watched JoVE’s introduction to the attentional blink. Now you should have a good understanding of how to design and execute an attention-engagement task, as well as analyze and assess the results.
Thanks for watching!
Graph average response accuracy for the first number, along with response accuracy for the second number as a function of lag position. Figure 5 shows an example.
Figure 5: Results of an attentional blink experiment. As shown, participants are generally able to report the first number in a sequence with very high accuracy, here about 0.97. When a second number appears immediately, performance is not as good, but still very high-a phenomenon called lag 1 sparing. In the second and third lag positions, performance tends to be very poor however. This is called the attentional blink, the idea being that attention is mustered to process the first number rapidly, and then becomes momentarily unavailable-like blinking one's eyes- before it can be engaged again to recognize a second number. The results suggest that heavily focused attention can be sustained, but only with brief interruptions following bouts of intensive processing.
The graph can be generated for each participant, or averaged across a group of participants. As shown in the figure, the pattern of performance is that participants tend to be very accurate reporting the identity of the first number in each trial. This demonstrates that even though the number appears very briefly, in an unpredictable location, and embedded between letters, focused attention can support detailed processing and recognition. Immediately following numbers are processed accurately as well, as shown by the relatively high performance for lag 1 numbers. This is known as lag 1 sparing. It is thought that as the focused attention remains engaged during this time, the rapid appearance of the next number allows it to be processed. However, at lags 2 and 3, performance is considerably impaired. This is the phenomenon that is known as the attentional blink.
The idea is that following the processing of the first number, attention becomes temporarily disengaged-like blinking one's eyes. Remember, the numbers shown in lags 2 and 3 last for all of 50 ms each, not a very long time. They just happen to appear during a brief period in which attention disengages. It quickly re-engages however, to support rapidly improving performance during for lags 4, 5, and 6. Taken together these results demonstrate the power and limitations of sustained visual attention. Attention can be sustained to find and identify brief and unpredictably positioned stimuli-numbers. Intensive processing is followed by a brief respite, temporarily limiting the ability to recognize objects.
Applications and Summary
Like many other laboratory tasks for studying attention, the attentional blink has become a common tool in studies of brain damage, as well as in studies that use neuroimaging techniques to investigate the brain areas involved in controlling and coordinating attention.
The attentional blink paradigm has also been used to investigate the kinds of things that may capture attention automatically, and even how anxiety and other mental health problems may cause diverted attention. These studies use the same paradigm just described, only with pictures of real-world images instead of letters. A participant's task would be to detect any image that is rotated in an unusual position, reporting at the end of the trial whether the rotated image was an indoor or an outdoor scene. Figure 6A shows an example of this basic paradigm, and Figure 6B then shows how the paradigm is used to ask whether something automatically captures attention.
Figure 6. Methods for the emotion-induced attentional blink. Panel A shows a general RSVP procedure with photographic images. The task is to detect the image in the stream that is rotated (called the target), and at the end of the trial, to report whether that image was an indoor or an outdoor scene. Panel B shows how these methods are used to produce an emotion-induced attentional blink. Prior to the appearance of the target, an emotional-inducer is shown, here a spider, an object about which many people express fear and anxiety and which tends to grab attention. The target is then shown at lag 2 relative to the emotional-inducer. Although the inducer is task-irrelevant, if it is sufficiently attention-grabbing, it will produce an attentional blink, and participants will have difficulty detecting the rotated target, evidenced by inaccurate indoor/outdoor reports.
In Figure 6B, a spider is shown in the RSVP stream prior to the target. In fact, the target is shown at lag 2 relative to the spider image. The spider is not task relevant, but fear of spiders is common. If the visual system is tuned to automatically detect and process spiders, then the presence of that image in the stream would produce an attentional blink. Indeed, that is what has been found-spiders, snakes, and other threatening images automatically capture attention, producing an emotion-induced attentional blink.
Researchers have also used this paradigm to investigate differences between people with severe phobias, and those with just the usual antipathy towards spiders. In this case, the paradigm is reversed. A target is presented and a spider is shown at lag 2. Is the spider seen, or is it rendered invisible because of the attentional blink? For most people, perception of the spider is blocked by the attentional blink. But for individuals with arachnophobia, the spider is seen, even in lag positions that should suffer from a blink. This suggests that a phobia causes certain stimuli to have a very strong pull on attention, even when attention would otherwise be disengaged.
- Raymond, J. E., Shapiro, K. L., & Arnell, K. M. (1992). Temporary suppression of visual processing in an RSVP task: An attentional blink?. Journal of Experimental Psychology: Human Perception and Performance, 18(3), 849