Attention
April 1, 2008
Category: Attention • Music • Research
Imagine yourself walking on a treadmill that starts at a reasonable pace: say, two and a half miles per hour. Every two minutes, the treadmill increases its speed by 0.2 mph: 2.7 mph, 2.9 mph, 3.1 mph, and so on. If you're in good physical condition, at some point -- usually between about 3.0 and 4.5 mph -- you'll find it more comfortable to start running instead of walking. Different individuals have different thresholds based on their fitness level and other factors, but even taking these things into account, it's difficult to explain exactly why people start running when they do. Do different people have different thresholds for pain?
Gregory Daniels and Karl Newell paid 12 physically fit college students to walk on a treadmill as it gradually increased in speed. To disguise the real purpose of the study, the students were fitted with fake oxygen consumption meters and cardiographs. They were told to walk, but to begin running as soon as it felt more comfortable. They also rated their physical exertion every two minutes by pointing to a numeric chart on the wall (remember, their mouths were covered with the oxygen consumption meters so they couldn't talk).
But most importantly, the walkers were also sometimes asked to complete simple addition and subtraction problems. Every 10 seconds, a new tape-recorded problem and answer was played, and the walkers had to raise their right hand to indicate a correct answer and raise their left hand for an incorrect answer. They repeated the experiment four times: two times with no math problems, and once each with easy (single-digit) and hard (double-digit) math problems. Here are the results:
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Posted by Dave Munger at 2:23 PM • Comments (18)
March 26, 2008
Category: Attention • Movement and exercise • Research • Video Games / Technology
[This article was originally published in January of 2007]
Many many studies have repeatedly shown the dangers of driving while using a cell phone. Yesterday, while discussing a new law in Britain imposing heavy penalties not only for driving using a handheld phone, but also while using phones with hands-free kits, commenter Jan claimed that talking to a passenger was less dangerous than talking on a phone. I replied that I hadn't seen a study demonstrating that talking with passengers was any different from talking on a phone, and Jan provided a link to one such study.
Greta and I have both read over the study, and while we can't say from these results that talking with a passenger is unequivocally safer than talking on a phone, the research is impressive. The study comes from David Strayer's laboratory, the same group that has conducted a number of studies demonstrating the danger of driving while talking on the phone.
The researchers, led by Frank Drews, recruited 48 pairs of licensed drivers to participate in a driving / talking task. Drivers were selected randomly, and were paired with people they were friends with outside of the study. Each pair was told to talk about about a "close call" -- a time when their life was threatened -- either on a cell phone or in person, while one of the people drove an eight-mile course on a driving simulator.
The conversation topic was the critical portion of the task, because previous studies comparing conversations with passengers versus on cell phones have found driving ability to be equally impaired. In these tasks, typically the passenger and driver had to complete a difficult task such as thinking of a word that starts with the last letter of the word their partner said, often under competitive circumstances: arguably this is not analogous to a real conversation in a car. The "close calls" topic was chosen because other studies had revealed that it leads to naturalistic conversations.
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Posted by Dave Munger at 8:49 AM • Comments (21)
March 11, 2008
Category: Attention • Face perception • Research
It shouldn't take you long to notice what's wrong with this picture:
Obviously Nora is defying gravity in this shot -- you can't help but notice it. But in your first glance at the photo, how quickly do you notice what's wrong? Do you spot the oddity faster than you'd notice Nora in the original, unaltered picture?
A 1978 study by Geoffrey Loftus and Norman Mackworth found that people respond quicker to unusual or inappropriate objects in line drawings, such as an octopus instead of a tractor in a farm scene. They moved their eyes an average of 7 degrees to fixate on the unusual objects. But in 1999, a team led by John Henderson found the opposite -- people spotted a microscope in a bar scene no sooner than a cocktail glass in the same location, and only moved an average of 3 degrees from where they had been looking previously.
Why the discrepancy? It's hard to know: Maybe, for example, Henderson's team's drawings were just too complicated for viewers to spot differences easily. Or perhaps a microscope in a bar is less unusual than an octopus on a farm. How can we ever measure what's "more unusual" in a given context?
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Posted by Dave Munger at 2:12 PM • Comments (10)
February 5, 2008
Category: Attention • Language • Memory • Research
A particular source of dread for politicians is how to respond to negative campaigning or other information impugning their character. By responding, they might only bring attention to an issue that voters hadn't even recognized: "Contrary to my opponent's claims, I have stopped beating my wife, and I haven't consumed more than a fifth of hard liquor in a single sitting."
Worse, many studies have found that even unequivocal denials fail to register in memory. In one study, participants read a report about the possible cause of a fire: a room full of oil paint and pressurized gas cylinders. Later in the report an addendum indicated the room was actually empty, but when questioned, most respondents still believed that the flammable materials in the room had caused the fire.
Clearly there is considerable power in being the first to assert the "truth." But surely people are capable of revising their opinions based on factual evidence. Some of the greatest works of literature in history hinge on readers recognizing that an early impression of a character turned out to be false, from Oedipus learning that he has married his mother to Elizabeth Bennet realizing that Mr. Darcy isn't actually a rat and a scoundrel. If we go on thinking Darcy is proud and prejudiced, we miss the whole point of the novel.
So why is it that sometimes we go on thinking Senator so-and-so is a wife-beater despite his denials but other times we re-evaluate our position based on the evidence? Are we just paying more (or less) attention? David Rapp and Panayiota Kendeou had student volunteers read 24 different "stories" involving a character who demonstrates a trait like sloppiness or laziness, which then may be immediately contradicted in the story. The stories were all just 13 sentences long, and each sentence was displayed one at a time on a computer screen. Here's the beginning of a sample story:
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Posted by Dave Munger at 4:07 PM • Comments (10)
December 31, 2007
Category: Attention • Memory • Perception • Research
[Originally posted on November 7, 2005]
What does it mean to have a gut feeling that you remember something? You see someone you recognize in a coffee shop. Do you remember her from high school? Or maybe you saw her on television. Could she be the manager of your local bank? Perhaps you don't know her at all ... but you've still got a feeling you do. What's that all about?
One theory of memory proposes that what we remember depends on our expectations. We're less likely to remember our old classmate at the coffee shop than at the high school reunion. At the bank, we might greet the manager by name, but we only get a vague sense of recollection when we see her in the checkout line at the grocery store. So what cues that sense of expectation? If the grocery store pipes in the same music they play at the bank, will we remember her then? What if it turns out she's not the bank manager, but another woman about the same height who happens to own the same blazer? Does the music help us notice the difference, or just make us more likely to ask a complete stranger about the status of our mortgage application?
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Posted by Dave Munger at 9:56 AM • Comments (2)
December 13, 2007
Category: Attention • Memory • Research
The human perceptual system is able to enforce a large array of illusions on our conscious experience. Most importantly, we hold the illusion of a complete and vivid picture of our surroundings, while in fact we selectively ignore nearly everything we see.
There's a good reason for this, of course: focusing on the task at hand generally consumes nearly all of the processing power our brains have to offer. If we need to shift our focus to another aspect of our surroundings, we can do it nearly instantaneously. But how do we decide which items to pay attention to? There are a couple possibilities. We might pay attention to the kind of things we've seen or heard about recently (priming). But the process might be more conscious: we pay attention to the kind of things we intend to do something about. For example, if I'm driving a car, I might notice red things more often than other colors, since I'm on the lookout for red traffic signals indicating that I need to stop.
So how do you find out if priming or intention is a more important factor in what we pay attention to? The first thing is to create a task that maxes out your multi-tasking ability. Take a look at this video (QuickTime required). You'll see one word flash while you hear another word. Your job is to ignore the audio words, snap your left hand if the printed word is pleasant, snap your right hand if the printed word is unpleasant, and knock on the table if the printed word is an animal. The audio words are just there to make the task more difficult; focus on the printed words:
A team led by Richard Marsh asked 103 college students to complete a similar task, but it went on for much longer: there were 100 trials, with just four animals over the course of the entire task. Pleasantness was rated on the using a scale on the computer, and the student volunteers had to press the slash key whenever an animal name appeared.
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Posted by Dave Munger at 2:32 PM • Comments (2)
December 6, 2007
Category: Attention • Face perception • Language • Movement and exercise • Research
When we are trying to understand what someone is saying, we rely a lot on the movement of their face. We pay attention to how their faces move, and that informs our understanding of what is said. The classic example of this is the McGurk effect, where the same sound accompanied by different facial movements gets interpreted differently.
Take a look at this short video clip (QuickTime required) of me talking, with my voice muffled by what sounds like cocktail party conversation:
Can you understand what I'm saying? What about after I stop moving? Can you understand me in the second part of that clip? Go ahead and replay the video to see if you can hear it the second time through.
That's right, I said two three-word phrases, not just one. If you're like me, you only heard background noise during the second part of the clip. In fact, I'm curious as to whether anyone can understand me at all. Let's make this one a poll:
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Posted by Dave Munger at 2:08 PM • Comments (27)
October 31, 2007
Category: Attention • Perception • Research
Does this ever happen to you? You're preparing green beans to be cooked, putting the stems in the trash and the beans in a bowl. Suddenly you realize you've started putting the stems in the bowl. The dinner guests will be arriving soon, and now you have to search through the beans to pull out the stems, in order to avoid an embarrassing incident later that evening.
Okay, maybe it's just me. But what's the best way to find the stems? Is it faster to pore over the bowl, methodically scanning for each remnant? Or is it better to step back and take a holistic view of the bowl, letting the stems "pop" out of a sea of green?
People who study visual search have found anecdotally that just "relaxing" and looking for objects based on "gut instinct" can often be more effective than actively directing attention to a search. Jeremy Wolfe calls this "relax" strategy "using the force." You can try it out. You'll be looking at a figure with two types of shapes:
Most shapes look like the one on the left: a circle with two gaps. Your job is to look for a circle with just one gap, and say whether the gap is on the left or the right. Now try it using the relax strategy on the image below:
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Posted by Dave Munger at 12:32 PM • Comments (37)
September 4, 2007
Category: Attention • Perception • Research
Countless change blindness studies have showed that we're extremely bad at noticing when a scene has changed. We fail to notice objects moving, disappearing, or changing color, seemingly right before our eyes. But sometimes we do notice the change. What sorts of changes are we more likely to notice? I've created a simple demo that may (or may not) help answer that question.
Take a look at this movie (
QuickTime required). It will show a scene for six seconds. Then it will briefly flash white, and the same scene will be shown for another six seconds. Can you spot what has changed?
I've put up a poll at the end of the post so we can see if this demo works (I'm not at all sure it will!). [Update: It looks like I've made the task too difficult. If you don't spot the change the first time you watch, play the movie again. You can repeat until you spot the change or you get bored with the task.]
There are certain types of changes that people are more likely to spot than others. Drug users will notice changes related to their substance of choice more reliably than non-users. In 2004, a team led by Melissa Beck found that that viewers are better at spotting probable changes (a flag starting to flap in the breeze) than improbable ones (a window changing size). Now, with a new team, Beck has started to uncover how this process occurs.
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Posted by Dave Munger at 11:11 AM • Comments (37)
August 28, 2007
Category: Attention • Movement and exercise • Perception • Research
We can recognize the faces of our friends very quickly from just a snapshot. Within 150 milliseconds of being flashed a photo, brain signals respond differently to photos containing animals than photos with no animals. We can categorize scenes as "beach," "forest," or "city" when they are flashed for even shorter periods.
But we also get a great deal of information from the
motion of people and animals. We can identify our friends and family members just from a
point-light display of them walking. We can also detect the emotions of point-light faces, and even the species of point-light animals.
Fascinating as point-light displays are, however, we rarely see them in real life. Point-light displays
suggest that motion gives us a great deal of information about the object we're looking at, but we can't be sure that real-world perception works the same way. A team led by Quoc Vuong has conducted a study to see if what we know about point-light displays transfers to real-world objects and scenes.
They constructed a set of composite movies like this one (
QuickTime required):
In every clip, a machine was superimposed with either a walking human figure (like in this clip) or another machine. To make the task even more difficult, viewers were shown two movies simultaneously, for just two thirds of a second. Viewers had to determine if
one of the two movies included a human. The relative visibility of the human figure was also varied.
Even more critically, half of the images they saw were animated, and half were still photos. Here are the results:
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Posted by Dave Munger at 3:23 PM • Comments (7)
August 23, 2007
Category: Attention • Memory • Perception • Research
Memory is a curious thing, and visual memory is even more curious. In some ways, we don't remember much about the scene that's right in front of us. As countless
change blindness studies have shown, we often don't notice even obvious changes taking place in a scene. Other studies have concluded that visual short term memory has a capacity of just three or four objects.
Yet I have vivid visual memories of scenes I have only glimpsed for a few seconds: A deer below the rim of the Grand Canyon; Michael Jordan draining a three-pointer to win the NBA championships; the standing ovation our daughter received at the school play. If I could only retain three or four of the items in those scenes in short-term memory, why are my long-term memories so vivid? How could they have ever
become long-term memories if my short-term memory couldn't even contain them?
Some researchers have suggested that any additional details in those memories are filled in by verbal descriptions -- the "gist" of the scenes, instead of the actual visual imagery. But this explanation doesn't match up with the rich visual memories I have of some places. Could some other process be responsible for the richness of visual memories?
There is some evidence that visual memory for scenes increases with longer viewing time. But can we remember more than the four items supposedly retainable in short-term visual memory?
David Melcher showed photos of scenes to volunteers for periods ranging from 5 to 20 seconds. But he also added a twist:
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Posted by Dave Munger at 1:59 PM • Comments (10)
July 12, 2007
Category: Attention • Learning and testing • Research
This is a guest post by Daniel Griffin, one of Greta's top student writers from Spring of 2007.
Does anything seem stick out about this sentence? I'm sure that if I told you to keep looking for yellow highlighted words, you would not have much trouble finding them in these first few sentences. You could even make it simpler for yourself and just look for any highlighted word. The only highlighted portions are yellow, so what is the difference? Let's say that by now you are used to searching for these highlighted words by just looking for a different color background than just the usual white. Does it take any longer to find the yellow word in this sentence? For most of us the answer to this question would be not especially, but I bet you glanced twice at "find." If I were to write the rest of this post in this fashion you would have to change your visual searching strategy to not just look for highlighted words, but yellow words in particular.
This kind of visual searching strategy is called an "attentional set". More specifically, an attentional set is an innate part of our information processing that prioritizes certain stimuli, such as yellow highlighted words, for selection. So why would we create this set when look for things? Well, using a certain set prevents things other than what we are looking for from distracting us. The problem with creating and using a set is that we do not always use the set that is best for what we are doing. With this in mind, Andrew Leber and Howard Egeth studied our visual searching strategies and the effects of past experience.
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Posted by Aaron Couch at 9:53 AM • Comments (5)
May 23, 2007
Category: Attention • Perception • Research
The visual system is very good at noticing a new object coming into view. However, the system isn't perfect. If a second object appears near the first one, it takes a little longer to spot it. This phenomenon, known as inhibition of return, has been well-documented. We discussed it in a 2005 post:
If an object appears in one part of our field of view, it temporarily delays our ability to detect another object appearing near it. The effect begins about a third of a second after the first object appears and lasts about a second. If the second object appears sooner than that, we actually notice it quicker. Subsequent research revealed that the effect became progressively smaller at greater and greater distances from the spot where the first object appeared--surprisingly, we're quicker to spot other objects appearing farther away from the original object.
Recently some researchers have suggested that inhibition of return might make us better food foragers. If we've already looked for, say, a grub, in a particular spot, then it's more efficient for us to focus our attention on a new spot. The problem with this explanation is that foraging is typically much slower than the observed effect. When you think about it, the typical inhibition of return experiment, with letters or other symbols rapidly flashing at viewers, isn't really much like foraging at all.
To do a realistic foraging experiment, you'd need something like a holodeck -- the computer-controlled room in Star Trek which allows simulation of nearly any sort of environment.
At the Beckman Institute of the University of Illinois they've actually got a piece of equipment that comes close: a room with translucent walls, floor and ceiling. Each wall can have an image projected on it to simulate a complete immersion in a three-dimensional world. Here's a schematic of the room, called a Virtual Reality Cube:
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Posted by Dave Munger at 2:53 PM • Comments (4)
May 9, 2007
Category: Attention • Color perception • Research
"I just didn't see him" is a claim that's repeated over and over in accident reports. Drivers earnestly claim that they simply didn't notice the bicycle/pedestrian/motorcycle they crashed into. The claim is made so frequently that certainly there must be a grain of truth to it. Yet it certainly isn't the case that car drivers can't see such obstacles -- after all, they can see traffic signals that are much smaller than a bike or a motorcycle.
What they mean to say is that their attention was otherwise engaged -- perhaps by a phone conversation, perhaps by other traffic, or perhaps because they were trying to find something -- a street sign, a restaurant, a gas station. Human attention is a fickle thing, and in many cases we don't notice very obvious details changing right before our eyes.
Consider the following movie (QuickTime required): One image will be displayed for a number of seconds, followed by a white screen, and then a second picture -- the same image with one very obvious detail changed. Can you spot the change (don't cheat--just watch it once!)?
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Posted by Dave Munger at 3:48 PM • Comments (42)
May 3, 2007
Category: Attention • Development / Aging • Perception • Research • Video Games / Technology
How many moving objects can you keep track of at once? Clicking on the image below will take you to Lana M. Trick's web site, where she has a nifty demo of a multi-object tracking task. You're asked to keep track one to four of the smiley-faces as they move randomly around the screen. Then when the faces stop moving, you click on the ones you were supposed to follow. Go ahead, give it a try!
You'll notice there are four levels of difficulty. Most adults can, with a little practice, track four out of ten randomly moving objects for ten seconds -- they fall apart when there are more than four objects to track or more than ten total objects (the "most difficult" trial features four objects to track and twelve total). But when do kids develop the ability to track multiple objects? Very young infants can track a single object moving by itself quite easily, but what about several objects moving among others?
Trick's research team developed a task that could be followed by kids as young as five. Previous studies of multiple-object tracking used colored shapes, which were uninteresting to young kids, who became distracted during the task. Trick's team told kids they'd be looking for sinister "spies" among normal, happy people (just like the demo you just tried). They found that five-year-olds understood the task, and reliably completed it when the faces weren't moving. Then they performed the same test on kids ranging in age from 5 to 19. The results are below.
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Posted by Dave Munger at 4:45 PM • Comments (10)
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