Perception
May 12, 2008
Category: Memory • Perception • Research
We're pretty good at remembering objects in a complex scene. We can even remember those objects when we move to a different location. However, the research so far has found that memory for the original view is a little better than memory when we've moved to a different location. Much of that research, however, has focused on relatively complex movements: Viewers are asked to remember an array of objects viewed from one side of a room, then are transported to a different part of the room and asked to decide whether the objects are arranged in the same pattern (actually, they're sitting at a computer watching static images, but the camera has moved).
This sort of motion actually encompasses two separate motions: translation and rotation. For example, in this crude figure representing a room, a viewer moving from the bottom to the right-hand side of the room would have to not only walk to a different part of the room, but also rotate his body (or at least his head) to see the objects in the room.
So what about simpler forms of motion? Do translating and rotating alone affect memory for the arrangement of objects in a scene? Rotating is difficult to assess independently, since if you rotate your body too much, you're no longer viewing the scene. But David Waller was able to consider two different types of translation in scenes: backwards and forwards, and side-to-side.
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Posted by Dave Munger at 2:09 PM • Comments (6)
March 31, 2008
Category: Movement and exercise • Perception • Research
Researchers have known for some time that people are surprisingly accurate at visually judging distances to objects as far as 25 meters away. If you're allowed to briefly look at an object up to that distance away, then blindfolded, you'll walk right up to it with great precision. If you walk halfway, you can throw a ball the remaining distance, again, quite accurately.
But in 2000 Marla Bigel and Colin Ellard attempted a simple replication of the study: instead of viewing the object, volunteers were led blindfolded to the object and back, and asked to walk back to the object again. Now, instead of accurately walking the distance, they systematically overestimated the distance to the object. Could our feet deceive us more than our eyes, even when we're simply asked to retrace a path we've just taken?
There's another possible explanation: maybe being led is what causes the deception. In a new study, Ellard and Sarah Shaughnessy asked 30 volunteers to walk blindfolded along a roped-off 10-meter pathway. They could use the ropes to guide themselves, but were never led by researchers. As before, they walked the distance to the object, then returned to the starting point, and finally attempted to walk the same distance again. Another group of volunteers simply looked at the object and then tried to walk to it blindfolded. Here are the results.
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Posted by Dave Munger at 2:28 PM • Comments (13)
March 25, 2008
Category: Face perception • Perception • Research
Do you recognize the faces in this picture?
Sure you do -- you could recognize the authors of this blog anywhere, even upside-down. It might take you just a bit longer to realize that something isn't quite right with the picture. I'll show you what the problem is at the end of this post.
We've known for decades that the human perceptual system is especially good at recognizing faces, but that ability breaks down in predictable ways when the faces are upside-down. While it takes us a bit longer to recognize objects when they are inverted, faces take even longer compared to other things.
For example, you might be able to tell whether two faces are identical or slightly different when they are upside down, but you'll be quicker to note a similar difference in, say, two houses. When people try to recognize inverted faces, different brain regions are activated compared to recognizing upright faces, but nonface objects activate the same regions whether upside-down or right side up.
But maybe faces aren't the only objects that are special in this way. A team led by Catherine Reed showed observers pairs of pictures of human figures like the one below.
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Posted by Dave Munger at 8:13 AM • Comments (10)
March 20, 2008
Category: Music • Perception • Research
Point-light displays are an amazing demonstration of how the visual system creates order out of what initially seems to be a random pattern. Take a look at this short movie (QuickTime required). Just looking at the first frame, it might be difficult to tell what's being displayed, but after watching for just a second, it all becomes quite clear:
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Posted by Dave Munger at 3:10 PM • Comments (11)
February 19, 2008
Category: Color perception • Perception • Research
Take a look at this amazing illusion created by Arthur Shapiro (you'll need the latest version of Flash Player to see it):
You're looking at two donut-shaped figures whose "holes" are gradually changing color from black to white and back again. It appears that the holes are changing in an opposite pattern -- when one is light, the other is dark, and so on. But if you click to remove the surrounding donuts, you'll see that the two holes are actually changing together.
If you're still not convinced, get a friend to help. One of you looks at the light donut and the other looks at the dark donut. Then each of you says "light" when your donut hole turns light. You'll soon be saying "light" simultaneously!
Shapiro calls this the Contrast Asynchrony illusion, and he argues that it can tell us a lot about how the visual system works. Below is an interactive version of the illusion. You can manipulate all sorts of variables to change the way the illusion appears. There's even more than one way to eliminate the appearance of the illusion entirely. Can you figure out what you need to do to make the illusion disappear?
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Posted by Dave Munger at 2:22 PM • Comments (45)
February 13, 2008
Category: Memory • Movement and exercise • Perception • Reasoning • Research
Which of these two pictures is more memorable?
The shot on the left is interesting primarily because Nora's in it -- if it was just a picture of a muddy trail, it wouldn't be notable at all to most people. The shot on the right is a dramatic mountain scene that you might remember even though (or perhaps because) there's not a human in sight.
But a seasoned hiker might be more interested in the photo of the muddy trail, which gives more information about the difficulty of the hike than a panoramic shot. Just as expert chess players are good at remembering the position of chess pieces on the board, maybe expert hikers are better at remembering details about trails than novice hikers.
The classic study of expert and novice chess players was conducted in 1973 by William Chase and Herbert Simon, and found that chess experts could remember configuration of chess boards better than novices -- as long as the chess pieces were arranged in a plausible game configuration, and not just randomly arrayed.
Since then, dozens of studies have found that experts in a variety of fields have better memory for things related to their area of expertise, from football formations to chest X-rays. But according to a research team led by Satoru Kawamura, all of these results can be explained by perceptual chunking: Experts are better than novices at lumping information into manageable groups. Hiking scenes, they argue, aren't easily chunked in the same way. Do expert hikers still have better memory for scenes relevant to hiking?
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Posted by Dave Munger at 11:06 AM • Comments (17)
January 31, 2008
Category: Memory • Perception • Research
When we watch a movie, we're usually not conscious of the cuts made by the editor. The camera angle may change dozens of times during a scene, and we follow along as if the flashing from one viewpoint to another wasn't at all unusual. You might think this is just because we've been accustomed to watching TV and movies, but researchers have found that even people who've never seen a motion picture have no difficulty following along with the cuts and different camera angles in a video.
But little research has actually been done on the impact of changing camera angles in a movie on our perception and memory of a scene. While cutting abruptly between camera angles seems unnatural, moving a camera from place to place while filming can be quite realistic: after all, people walk around all the time; their own viewpoint is constantly changing. One study did find that people have better memories for a static scene filmed with a moving camera, compared to two still shots taken from the beginning and end- points of the camera's motion.
But what about dynamic scenes? If the people in a scene are themselves moving, will an abrupt cut to a new camera angle disorient the viewer? Filmmakers have found anecdotally that a 180-degree shift in a cut can be extremely disorienting -- that's why when watching a football or basketball game we usually see the action from just one side of the field or court. But do smaller cuts have a similar impact?
A team led by Bärbel Garsoffky showed computer-generated ten-second movies of a half-court basketball game to 12 volunteers. In some of the movies, the camera maintained a steady position either at the side of the court or midcourt, looking straight at the hoop, like this:
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Posted by Dave Munger at 1:53 PM • Comments (28)
January 17, 2008
Category: Development / Aging • Perception • Research
Take a look at this slideshow (QuickTime required). You'll first see a photo in perfect focus. Then 12 more pictures will flash by, each of them blurred using Photoshop. Finally, the original photo will appear again. Is it the same as before, or slightly blurrier or sharper?
I'll give the answer after a few readers have had a chance to make a guess in the comments. Most people with normal vision will gradually adapt to blurry photos (though it might take a little longer than I've allowed in this movie). Then when they see a photo that's in focus, it seems too sharp -- as if it's been artificially sharpened like this picture:
Photos that are slightly out of focus (though not as blurry as the set of blurry photos they adapted to) will seem just right. But what about older individuals, whose eyes are less sensitive to contrast and brightness, and whose visual systems in the brain may also have degraded?
A team led by Sarah Elliott showed sequences similar to the movie above to 10 young adults (average age 25) and 10 older adults (average age 74). Their sequences were much longer (about 2 minutes), and several tests were administered, with blurred, neutral, and sharpened images. At the end of the sequence, the viewers were asked if the properly focused image seemed too blurry or too sharp.
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Posted by Dave Munger at 12:06 PM • Comments (21)
January 2, 2008
Category: Movement and exercise • Perception • Research
You might think humans are equally good at estimating distances no matter which direction they're looking. After all, we use the same visual tools to make those estimates -- binocular disparity (the different views we see from each eye), occlusion (whether one object is in front of or behind another), and so on. But consider the situation depicted to the right. Nora is inching her way down a steep rock column, with near-vertical drops on either side of her. If she underestimates the distance to flat ground below, she might decide she doesn't need to worry about falling. Overestimating the vertical distance isn't as big a problem: if she descends too slowly and carefully, she'll still live to tell the story.
On flat ground, overestimating distances could spell trouble: you might pack too much food for a hike, unnecessarily burdening yourself and perhaps not even making it to your destination. In fact, people do make systematic errors in estimating distance based on how much weight they're carrying; it's possible that they might make the same sort of errors estimating vertical distance. Since it takes more effort to climb up a mountain than climbing down, maybe we misjudge up distances as longer than down distances.
Russell Jackson and Lawrence Cormack took college students to the base of a 40-foot-tall wall and asked them to estimate the distance to the top by telling a research assistant to back away from the wall until their distance from the wall was equal to its height. Then they took them to the top of the wall and asked them to estimate the distance down using the same system (actually, half the students estimated the distance down first). This graph shows the results:
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Posted by Dave Munger at 9:05 AM • Comments (22)
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 26, 2007
Category: Development / Aging • Perception • Research
[Originally posted on February 20, 2006]
Here's a picture of our daughter Nora at about 3 months of age. She looks like she's fairly aware of the events going on around her (arguably more aware than she sometimes appears now, at age 12). However, as our knowledge of how infants begin to perceive the world around them has increased, we've learned that the world of a three-month-old literally looks different to them than the world we perceive as adults. That's because vision, which seems so obvious and instinctive, is actually an active process. When we perceive the world visually, we're not just passively "seeing" what's there, we're constantly determining where one object ends and the next one begins. We're applying logical rules to help break objects into groups and understand how the two-dimensional image on the inside of our eye corresponds to a three-dimensional physical world.
In the picture of Nora, for example, how do we know that the bonnet isn't part of her body? Because it's a different color, white? But the white buckle is part of the baby carrier. Clearly the set of rules we've learned are not simple. But when do we learn them? And in what order?
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Posted by Dave Munger at 9:57 AM • Comments (10)
November 1, 2007
Category: Emotion • Perception • Research • Taste
This article was originally posted on May 10, 2006
Recent research suggests that one of the reasons that as many as 97 percent of women and 68 percent of men experience food cravings is because of visual representations of food. When we picture food in our minds, our desire for the food increases. So why not just distract the visual system? One research team attempted just that, tempting volunteers with pictures of chocolate, and then distracting them with either a randomly changing visual image or an auditory task. The participants who watched the visual image experienced fewer food cravings.
I've attempted to reproduce the type of display these researchers suggest may distract you from your cravings (click on the image to start the animation).
The original research, however, didn't take into account whether participants were hungry. Perhaps if you're already hungry, the visual distraction won't help.
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Posted by Dave Munger at 2:24 PM • Comments (8)
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)
October 10, 2007
Category: Music • Perception • Research
There are lots of people who, with training, can identify musical notes when they know the starting point -- when they hear a song starting with "C," they can name the rest of the notes in the song. But much rarer is the ability to identify musical notes without
any context. This is what people are talking about when they talk about "perfect pitch" or "absolute pitch."
Let's do a quick test to get a rough sense of how many CogDaily readers have absolute pitch. Listen to this note:
Now, what note is it?
Obviously these results won't be perfect, but they should give us a general idea. I'll give the answer below so you can see how many people got it right.
But what is the nature of absolute pitch? Do people with "absolute pitch" ever make mistakes? Does the ability change as we age? A team led by E. Alexandra Athos recently published the results of the largest-ever study of absolute pitch. They collected data from over 2,000 individuals, 981 of whom were defined as having absolute pitch. They're
still collecting data online, and you can participate -- even if you don't have perfect pitch. So what did they find?
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Posted by Dave Munger at 2:32 PM • Comments (30)
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)
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