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Session Overview
How does the brain filter and focus? This discussion session complements the prior lecture session Attention.
Discussion
Today we're also going to talk about attention. How we engage with the world, but only a small part of it at a time. Why we can't engage with the whole thing, and what it would be like to engage with the whole thing. Limits on our attention: why we can't perceive everything at once. But at the same time, the benefits of attention: what happens when we apply our attention to something. How does that help perception; how does that help us with cognition, with these kinds of things?
Attention is very important, especially when things are moving around. So we'll talk about attention, and what's it good for.
Think About
Why do we need attention? What's it good for? What problem does it solve? How come we can't just pay attention to everything all the time? How come we can't be aware of all the things that we see in the room, all the sounds that we hear?
› Sample Answer
Demonstrations
Object Tracking
How good is your visual attention? Try out the following object tracking exercise. Keep your eyes on the fixation cross in the middle of the screen. You'll see one of the circles flash – keep an eye on it as the circles move around the screen.
Courtesy of Harvard Science Vision Lab. Used with permission.
Were you able it to follow it the whole time?
Now, try tracking multiple objects. Four circles will flash – can you track them all?
Courtesy of Harvard Science Vision Lab. Used with permission.
What if they're moving quickly?
Courtesy of Harvard Science Vision Lab. Used with permission.
The limitations of our visual attention become evident in this demonstration, especially as the number of objects to keep track of increases.
Visual Search
Feature Search: searching for a target that differs from all distracters by a unique feature.
Figure 1.
This is easy! The target seems to pop out at you. This is an example of bottom-up processing, in which your attention is captured by salient sensory information.
Figure 2.
In fact, your search is just as fast even with twice as many distracters. Can you explain how bottom-up processing may be evolutionarily advantageous?
Conjunction Search: searching for a target that has a particular combination of the distracters' features.
Figure 3.
These objects have two features: color (red or green) and orientation (vertical or horizontal). You deploy top-down attentional strategies to integrate these two features when you search for the horizontal green T.
Figure 4.
The more distracters there are, the harder it is.
Check Yourself
In the popular book series Where's Waldo?, children look for a character named Waldo – who always wears a red and white sweater and hat – in crowded scenes. What kind of processing is this? Explain your answer.
Change Blindness
Watch the following PBS video blog to see an experiment and explanation of the phenomenon of change blindness.
Inside NOVA: Change Blindness
Inattentional Blindness
To experience another limitation of your attention, watch this video clip. Can you figure out how the two scenes differ?
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Attentional Blink
While change blindness and inattentional blindness reveal the spatial limitations of our attention (i.e., we can't focus on everything in our field of vision, and we often don't notice things that we're not attending to), attentional blink is a temporal limitation. Follow this link to an experiment on attentional blink, in which you'll be able to manipulate some of the variables and see your results.
The idea is that, with things that come rapidly in time, we tend not to notice something that happens shortly after something else happens. So, for example, if something happens, and then something happens immediately after, you're likely to notice it too, but if it happens slightly afterwards, you're likely to miss it. You're almost at chance for saying whether it happened or not. And then as things spread out in time you begin to notice them more and more.
The idea is that, with things that come rapidly in time, we tend not to notice something that happens shortly after something else happens. So, for example, if something happens, and then something happens immediately after, you're likely to notice it too, but if it happens slightly afterwards, you're likely to miss it. You're almost at chance for saying whether it happened or not. And then as things spread out in time you begin to notice them more and more.
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As this graph shows, if the first target and the second target are 100ms apart, the probability of seeing the second (after seeing the first) is relatively high. However, with a separation of 200-300ms, your chances drop. Accuracy improves with greater separation in time.
Think About
What are some real-life situations where attentional blink might come into play?
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Discussion
It's recently become illegal in Massachusetts to text and drive. When I was in Chicago, it became illegal to talk on the phone and drive at the same time, and if the police saw you, they could pull you over for that and give you a pretty substantial ticket. And in some ways, that's a pretty good idea, right, because we know, after all these examples today, that attention is limited and it's weak and we just don't have a lot of it, and the world is a big, scary, frightening place with tigers coming at us everywhere. But what about doing other things in the car? Adjusting the radio, or talking to the person in the passenger seat? Are these just as dangerous as talking on a cell phone, texting, reading a book? What do you think?
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