Daniel Simons's Blog

How experts recall chess positions

In 2011, a computer (Watson) outplayed two human Jeopardy champions.  In 1997, chess computer Deep Blue defeated chess champion Garry Kasparov. In both cases, the computer "solved" the game—found the right questions or good moves—differently than humans do.  Defeating humans in these domains took years of research and programming by teams of engineers, but only with huge advantages in speed, efficiency, memory, and precision could computers compete with much more limited humans.

What allows human experts to match wits with custom-designed computers equipped with tremendous processing power?  Chess players have a limited ability to evaluate all of the possible moves, the responses to those moves, the responses to the responses, etc. Even if they could evaluate all of the possible alternatives several moves deep, they still would need to remember which moves they had evaluated, which ones led to the best outcomes, and so on.  Computers expend no effort remembering possibilities that they had already rejected or revisiting options that proved unfruitful.

This question, how do chess experts evaluate positions to find the best move, has been studied for decades, dating back to the groundbreaking work of Adriaan de Groot and later to work by William Chase and Herbert Simon.  de Groot interviewed several chess players as they evaluated positions, and he argued that experts and weaker players tended to "look" about the same number of moves ahead and to evaluate similar numbers of moves with roughly similar speed.  The relatively small differences between experts and novices suggested that their advantages came not from brute force calculation ability but from something else: knowledge.  According to De Groot, the core of chess expertise is the ability to recognize huge number of chess positions (or parts of positions) and to derive moves from them.  In short, their greater efficiency came not from evaluating more outcomes, but from considering only the better options. [Note: Some of the details of de Groot's claims, which he made before the appropriate statistical tests were in widespread use, did not hold up to later scrutiny—experts do consider somewhat more options, look a bit deeper, and process positions faster than less expert players (Holding, 1992). But de Groot was right about the limited nature of expert search and the importance of knowledge and pattern recognition in expert performance.]

In de Groot's most famous demonstration, he showed several players images of chess positions for a few seconds and asked the players to reconstruct the positions from memory.  The experts made relatively few mistakes even though they had seen the position only briefly.  Years later, Chase and Simon replicated de Groot's finding with another expert (a master-level player) as well as an amateur and a novice.  They also added a critical control: The players viewed both real chess positions and scrambled chess positions (that included pieces in implausible and even impossible locations). The expert excelled with the real positions, but performed no better than the amateur and novice for the scrambled positions (later studies showed that experts can perform slightly better than novices for random positions too if given enough time; Gobet & Simon, 1996).  The expert advantage apparently comes from familiarity with real chess positions, something that allows more efficient encoding or retrieval of the positions.

Chase and Simon recorded their expert performing the chess reconstruction task, and found that he placed the pieces on the board in spatially contiguous chunks, with pauses of a couple seconds after he reproduced each chunk.  This finding has become part of the canon of cognitive psychology: People can increase their working memory capacity by grouping together otherwise discrete pieces of items to form a larger unit in memory.  In that way, we can encode more information into the same limited number of memory slots.

They In 1998, Chris Chabris and I invited two-time US Champion and International Grandmaster Patrick Wolff (a friend of Chris's) to the lab and asked him to do the chess position reconstruction task. Wolff viewed each position (on a printed index card) for five seconds and then immediately reconstructed it on a chess board.  After he was satisfied with his work, we gave him the next card.  After he finished five real positions and five scrambled positions, we asked him to describe how he did the task.

The video below shows his performance and his explanations (Chris is the one handing him the cards and holding the stopwatch—I was behind the camera). Like other experts who have been tested, Wolff rarely made mistakes in reconstructing positions, and when he did, the errors were trivial—they did not alter the fundamental meaning or structure of the position. Watch for the interesting comments at the end when Wolff describes why he was focused on some aspects of a position but not others.

HT to Chris Chabris for comments on a draft of this post

Comments: Please make your comments on the Google+ notice of this post. That will permit more interaction:

Sources cited:

For an extended discussion of chess expertise and the nature of expert memory, see Christopher Chabris's dissertation:  Chabris, C. F. (1999).  Cognitive and neuropsychological mechanisms of expertise: Studies with chess masters.  Doctoral Dissertation, Harvard University. http://en.scientificcommons.org/43254650

Chase, W. G., & Simon, H. A. (1973).  Perception in chess.  Cognitive Psychology, 4, 55-81.

de Groot, A.D. (1946). Het denken van de schaker. [The thought of the chess player.] Amsterdam: North-Holland. (Updated translation published as Thought and choice in chess, Mouton, The Hague, 1965; corrected second edition published in 1978.)

Holding, D.H. (1992). Theories of chess skill. Psychological Research, 54(1), 10–16.

Gobet, F., & Simon, H.A. (1996a). Recall of rapidly presented random chess positions is a function of skill. Psychonomic Bulletin & Review, 3(2), 159–163.

New guide to writing and revising

Over the past 20 years of teaching, writing, and editing, I have compiled a set of tips, tricks, and pet peeves that I share with students and colleagues. I've decided to make this writing guide more widely available in case others will find it useful. The emphasis is on scientific writing, but the same principles apply to most non-fiction (including journalism). The most recent version of the file is available from my personal website at http://goo.gl/Z66gq.

The first part of the guide gives some broad principles of effective writing. The next section provides suggestions for editing and revising a manuscript. After that comes a list of common writing mistakes and my pet peeves. The last section provides a revision worksheet. The worksheet is perhaps the most useful part of the writing guide. It is a systematic way to edit papers, progressing from high-level organization to the word level, with a box to check after you complete each step. By following the steps in the revision worksheet, your writing will be more concise, more precise, and easier to read.

If you use this guide or the worksheet for one of your own revisions, I'd be curious to hear whether it helped you. If you have suggestions for future versions of this file, I'd love to see those too. Rather than posting comments here, please post them to the following page on Google+: http://goo.gl/gKjWj

Feel free to share the file itself with your students or fellow writers.

Ghost busters, parapsychology, and the first study of inattentional blindness

Originally posted last year our now-inactive Psychology Today blog:

Until last week, I thought I knew the full history of research on inattentional blindness. Inattentional blindness is the failure to notice a fully-visible but unexpected object or event when you are focusing attention on something else. I've been conducting research on the topic since the late 1990s, and I thought I was familiar with all of the work that came before mine. I knew all about Ulric Neisser's work in the 1970s on selective looking, including many of his unpublished studies from that era. I knew about the dichotic listening studies that partially motivated his research. I knew about Arien Mack and Irv Rock's groundbreaking studies during the 1990s on inattentional blindness in simplified computer displays (their book gave the phenomenon its scientific name). I knew about studies of tunnel vision in pilots as well as the literature on focused attention and distraction that provides a mechanistic explanation for what we see and what we miss.

Yet, none of those literatures cite what might well be the first experimental documentation of inattentional blindness. In fact, it's likely that none of those researchers knew about these studies. None of us can really be faulted for missing them- they appeared in an unexpected place that fell well outside the focus of our research. The source is unlikely, but seasonally appropriate…

Last week I got an email from a colleague in our department about Mary Roach's book "Spook: Science Tackles the Afterlife." I haven't read the book (although I've been meaning to-a couple of her other books are on my reading list now). In it, Roach cites a couple of studies (on pages 251-252) that addressed a somewhat bizarre question given modern scientific sensibilities: Is it possible to induce a "genuine" paranormal experience? Specifically, is it possible to make people believe they've seen a ghost?

More than 50 years ago, Tony Cornell, a parapsychology researcher, decided to test how people would react upon seeing him dressed as a ghost. Would they experience him as a "real" ghost or as something more mundane? He published a series of studies in two papers in the Journal of the Society for Psychical Research, the first of which was titled "An experiment in apparitional observation and findings." He stated his goal:

An experiment in apparitional observation has been undertaken in Cambridge to determine how many people would claim to have experienced the seeing of an apparition or ghost.

Each night, Cornell or his assistants dressed in a white sheet and strolled down a path, making various hand gestures before shedding the sheet 4.5 minutes later. Other assistants observed how many people were "in a position to observe the apparition." His finding: "although it was estimated that some 70-80 persons were in a position to observe the apparition, not one was seen to give it a second glance or to react in any way." That's true even though a number of cows apparently followed the ghost around.

Although Cornell's finding is consistent with later studies of inattentional blindness, his conclusion isn't. He finds it unlikely that nobody saw the ghost because:

a white-clad figure in the middle of a damp grass field, followed by a number of cows, is hardly to be ignored at the best of times…. If no one saw it consciously, one can only surmise that they did not want to see it. Cornell attributes the failure to notice the ghost to "the absence of a more subtle psi factor which is always present in genuine apparitional experience.

Cornell's second paper, "Further Experiments in Apparitional Observation," is even more prescient. He dressed as a ghost at a local movie theater. During a trailer film, he walked across the stage and back again, remaining visible for a total of 50 seconds. After the trailer, he polled the audience, and of those who responded, 68% claimed to have seen something and 32% claimed to have seen nothing peculiar, with many people not responding. Only about 50% saw anything during the ghost's first pass across the stage, and many failed to describe it accurately.

Although you can feel Cornell's disappointment that his "apparition" was not mistaken for a "real" ghost, his studies are remarkable both because they anticipated contemporary studies of inattentional blindness and because they actually tested inattentional blindness in the real world rather than in video or on a computer display. Only one other study has done that in the 50 years since (Ira Hyman and colleagues' unicycling clown study from earlier this year). Perhaps more importantly, Cornell's studies were the first to show how easily we can miss the fake paranormal events around us!

Hat tip to Carol Nickerson for spotting these citations in Roach's book.

Sources Cited:

Cornell, A. D. (1959). An experiment in apparitional observation and findings Journal of the Society for Psychical Research, 40 (701), 120-124

Cornell, A. D. (1959). Further experiments in apparitional observation Journal of the Society for Psychical Research, 40 (706), 409-418

Hyman, I., Boss, S., Wise, B., McKenzie, K., & Caggiano, J. (2009). Did you see the unicycling clown? Inattentional blindness while walking and talking on a cell phone Applied Cognitive Psychology, 24 (5), 597-607 DOI: 10.1002/acp.1638

Think video games make you smarter? Not so fast…

Updated on 9/13/11 at 4:50pm: Minor tone/wording update to the conclusion and a little more detail on alternative explanations for correlational results after the break.

Try to spot the flaw in this study. A scientist recruits a group of subjects to test the effectiveness of a new drug that purportedly improves attention. After giving subjects a pre-test to measure their attention, the experimenter tells the subjects all about the exciting new pill, and after they take the pill, the experimenter re-tests their attention. The subjects show significantly better performance the second time they're tested.

This study would never pass muster in the peer review process—the flaws are too glaring. First, the subjects are not blind to the hypothesis—the experimenter told them about the exiting new drug—so they could be motivated to try harder the second time they take the test. The experimenter isn't blind to the hypothesis either, so they might influence subject performance as well. There's also no placebo control condition to account for the typical improvement people make when performing a task for the second time. In fact, this study lacks all of the gold-standard controls needed in a clinical intervention.

Walter Boot, Daniel Blakely and I have a new paper that just appeared in Frontiers in Psychology this week (link) that argues for similarly serious flaws in many of the studies underlying the popular notion that playing action video games enhances cognitive abilities. The flaws are sometimes more subtle, but they're remarkably common: None of the existing studies include all the gold-standard controls necessary to draw a firm conclusion about the benefits of gaming on cognition. When coupled with publication biases that exclude failures to replicate from the published literature, these flaws raise doubts about the mere existence of a benefit.

The evidence in favor of a benefit from video games on cognition takes two forms: (a) expert/novice differences and (b) training studies.

The majority of studies compare the performance of experienced gamers to non-gamers, and many (although not all) show that gamers outperform non-gamers on measures of attention, processing speed, etc (e.g., Bailystock, 2006; Chisholm et al., 2010, Clark, Fleck, & Mitroff, 2011; Colzato et al., 2010; Donohue, Woldorff, & Mitroff, 2010; Karle, Watter, & Shedden, 2009; West et al., 2008). Such expert/novice comparisons are useful and informative, but they do not permit any causal claim about the effects of video games on cognition. In essence, they are correlational studies rather than causal ones. Perhaps the experienced gamers took up gaming because they were better at those basic cognitive tasks. That is, gamers might just be better at those cognitive tasks in general, and their superior cognitive skills are what made them successful gamers. Or, some third factor such as intelligence or reaction times might contribute to interest in gaming and performance on the cognitive tasks.

Fortunately, few researchers make the mistake of drawing causal conclusions from a comparison of experts and novices (although media headlines do occasionally make that mistake). We argue, though, that it's not even clear that there are real differences between gamers and non-gamers on these basic cognitive measures. The reason is that most studies suffer from the same problem as the attention-drug thought experiment I described at the start of this post. Experts in these studies are recruited because they are gamers (novices are often recruited because they are non-gamers), meaning that the subjects have a reason to suspect that their game experience is relevant to their performance in the experiment. Many gamers are familiar with claims in the media and in the scientific literature that gamers outperform non-gamers on cognition and perception tasks. Consequently, they are highly motivated to perform well. They are akin to a drug treatment group that has been told how wonderful the drug is. In other words, they are not blind to their condition. When the tasks are at least somewhat similar to the games they've played, they might well figure out the hypothesis of the study. The only way around this motivation effect is to recruit subjects with no mention of gaming and only ask them about their gaming experience after they have completed the primary cognitive tasks, but only a handful of studies have done that. And, even when they have done so, gamers might still be more motivated to perform well than novices because they are asked to perform a game-like task on a computer. In other words, any expert-novice differences might reflect different motivation and not different cognitive abilities.

Even if we accept the claim that gamers outperform non-gamers on cognitive tasks, such differences do not permit the conclusion that gaming affects cognition. The only way to do that is to use a training intervention, much like a clinical trial, in which non-gamers receive game experience and the experimenter measures improvements in cognitive abilities following training (e.g., Green & Bavelier, 2003; 2006a; 2006b, 2007). Training studies are far more expensive and time-consuming to conduct, and only a handful of labs have even attempted them. And, at least one large-scale training study has failed to replicate a benefit from action game training (Boot et al., 2008; see also Irons, Remington, & McClean, 2011 and Murphy & Spencer, 2009 for cross-sectional failures to replicate). In our Frontiers paper, we discuss a number of concerns about these training studies, which, taken together, raise serious concerns about the validity of the claim that games benefit cognition:

The studies are not double-blind. The experimenters know the hypotheses and could subtly influence the experiment outcome. Such experimenter bias effects are likely to be small, though.
The subjects themselves might not be entirely blind to the hypothesis. In a drug study, a placebo condition is considered to be inadequate if subjects can figure out whether they are in the experimental or the control condition. For example, if the drug has nasty side effects but a placebo does not, the subjects can guess that they are receiving the drug (as can the experimenter), foiling the purpose of having the placebo baseline condition. In video game training studies, subjects might well see a connection between their training condition and the cognitive tasks. If so, motivation effects could creep back into the results.
Those training studies that find a benefit of game training often show an unusual pattern in which the control group shows no improvement at all from pre-test to post-test. One of the most consistent findings in the literature on learning and practice is that people do better with practice. The control group should show improvement from the pre-test to the post-test. And, if game training affects cognition, the improvement should be bigger in the experimental condition. When the control condition shows no improvement the second time they do a task, we should be worried that the control group is somehow inadequate. Almost all of the published training studies showing a benefit of video game training relative to a control group show no test-retest effect in the control group. The studies failing to replicate a training benefit typically show the expected test-retest improvement in both groups, but no selective benefit for video game training. That raises the concern that the "action" in these studies comes not from a benefit of action game training but from some unusual cost in the control condition.
It is not entirely clear how many independent replications of training benefits actually exist in the literature. There are now a number of papers showing that 10, 30, or even 50 hours of training produces benefits on one or two reported outcome measures. When conducting a large-scale training study, it's typical to test a large battery of outcome measures because it would be prohibitively expensive to do all of that training with just one chance to find a benefit. Yet, many of the papers touting the benefits of training for cognition only discuss the results of one or two outcome measures, leaving open the possibility that the same subjects actually were tested on many unreported outcome measures. Moreover, based on the game scores noted in some of these papers, it appears that data from different outcome measures with some of the same trained subjects were reported in separate papers. That is, the groups of subjects tested in separate papers might have overlapped. If so, then the papers do not constitute independent tests of the benefits of gaming. Unfortunately, these details are underreported in the manuscripts, so there might be far fewer independent replications of the benefits of gaming. Together with the known failures to replicate training benefits and possible file drawer issues, it is unclear whether the accumulated evidence supports a benefit of training at all.

Given that expert/novice studies tell us nothing about a causal benefit of video games for cognition and that the evidence for training benefits is mixed and uncertain, we argue that the enthusiasm for video game training as a cognitive elixir needs to be reigned in. In some ways, the case that video games can enhance the mind is the complement to recent fear mongering that the internet is making us stupid. In both cases, the claim is that technology is altering our abilities. And, in both cases, the claims seem to go well beyond the evidence. The cognitive training literature shows that we can enhance cognition, but the effects of practice tend to be narrowly limited to the tasks we practice (see Ball et al., 2002; Hertzog, Kramer, Wilson, & Lindenberger, 2009; Owens et al., 2010; Singley & Anderson, 1989; for examples and discussion). Practicing crossword puzzles will make you better at crossword puzzles, but it won't help you recall your friend's name when you meet him on the street. None of the gaming studies provide evidence that the benefits, to the extent that they exist at all, actually transfer to anything other than simple computer-based laboratory tasks.

If you enjoy playing video games, by all means do so. Just don't view them as an all-purpose mind builder. There's no reason to think that gaming will help your real world cognition any more than would just going for a walk. If  you want to generalize your gaming prowess to real-world skills, you could always try your hand at paintball. Or, if you like Mario, you could spend some time as a plumber and turtle-stomper.

Citation for our Frontiers in Psychology article:

Boot WR, Blakely DP and Simons DJ (2011) Do action video games improve perception and cognition? Front. Psychology 2:226. doi: 10.3389/fpsyg.2011.00226.  Link to Full Text

Other Sources Cited:

Ball, K., Berch, D. B., Helmers, K. F., Jobe, J. B., Leveck, M. D., Marsiske, M., et al. (2002). Effects of cognitive training interventions with older adults: A randomized controlled trial. JAMA: Journal of the American Medical Association, 288(18), 2271-2281.
Bialystok, E. (2006).  Effect of bilingualisim and computer video game experience on the simon task.   Candadian Journal of Experimental Psychology, 60, 68-79.
Chisholm, J.D., Hickey, C., Theeuwes, J. & Kingston, A. (2010) Reduced attentional capture in video game players.  Attention, Perception, & Psychophysics, 72, 667-671.
Clark, K., Fleck, M. S., & Mitroff, S. R. (2011). Enhanced change detection performance reveals improved strategy use in avid action video game players. Acta Psychologica, 136, 67-72.
Colzato, L. S., van Leeuwen, P. J. A., van den Wildenberg, W. P. M., & Hommel, B. (2010). DOOM'd to switch: superior cognitive flexibility in players of first person shooter games. Frontiers in Psychology, 1, 1-5.
Donohue, S. E., Woldorff, M. G., & Mitroff, S. R. (2010). Video game players show more precise multisensory temporal processing abilities. Attention, Perception, & Psychophysics, 72, 1120-1129.
Green, C. S. & Bavelier, D. (2003). Action video game modifies visual selective attention. Nature, 423, 534-537.
Green, C.S. & Bavelier, D. (2006a). Effect of action video games on the spatial distribution of visuospatial attention. Journal of Experimental Psychology: Human Perception and Performance, 1465-1468.
Green, C. S. & Bavelier, D. (2006b). Enumeration versus multiple object tracking: the case of action video game players. Cognition, 101, 217-245.
Green, C.S. & Bavelier, D. (2007). Action video game experience alters the spatial resolution of attention. Psychological Science, 18, 88-94.
Hertzog, C., Kramer, A. F., Wilson, R. S., & Lindenberger, U. (2009). Enrichment effects on adult cognitive development. Psychological Science in the Public Interest, 9, 1–65.
Irons, J. L., Remington, R. W. and McLean, J. P. (2011), Not so fast: Rethinking the effects of action video games on attentional capacity. Australian Journal of Psychology, 63: no. doi: 10.1111/j.1742-9536.2011.00001.x
Karle, J.W., Watter, S., & Shedden, J.M. (2010).  Task switching in video game players:  Benefits of selective attention but not resistance to proactive interference.  Acta Psychologica, 134, 70-78.
Murphy, K. & Spencer, A. (2009). Playing video games does not make for better visual attention skills. Journal of Articles in Support of the Null Hypothesis, 6, 1-20.
Owen, A.M., Hampshire, A., Grahn, J.A., Stenton, R., Dajani, S., Burns, A.S., Howard, R.J., & Ballard, C.G. (2010).  Putting brain training to the test.  Nature, 465, 775-779.
Singley, M. K., & Anderson, J. R.  (1989). The transfer of cognitive skill.  Cambridge, MA.: Harvard University Press.
West, G. L., Stevens, S. S., Pun, C., & Pratt, J. (2008). Visuospatial experience modulates attentional capture: Evidence from action video game players. Journal of Vision, 8, 1-9.

Harry Potter and the Illusion of Potential

A variant of this post first appeared on my Psychology Today blog on November 16, 2010.

Why is the story of Harry Potter so appealing? The success of the series depends on engaging characters and compelling storytelling-it's a classic tale of good vs. evil and a coming of age story. That's true, but many stories have those qualities. I think there's a deeper magic at work here, one that capitalizes on a pervasive cognitive illusion. It's a cognitive illusion that underlies almost all fantasy (and much science fiction) writing and that contributes to the success of countless movies and television shows. It involves a sort of wish fulfillment.

As a child, I fantasized about how my life would change if I suddenly discovered my "Spiderman" powers and could scale buildings. Or, I envisioned how radically my life would change if I could figure out how to teleport myself instantly from one location to another (most of that fantasizing emerged when I was trudging home from school). Perhaps you have had similar fantasies, or maybe yours were more mundane: imagining discovering you had tremendous athletic prowess at a sport you had never tried or that you would be a virtuoso musician if you just found the right instrument.

We all, at times, fall prey to the illusion of potential-the belief that we can acquire skills or abilities with minimal effort or practice. The illusion of potential relies on the corollary belief that we have vast pools of untapped brain power just waiting to be released. The myth that we only use 10% of our brain is a direct statement of this idea. Hucksters use the belief in untapped potential to sell everything from miracle exercise regimens (great results with minimal effort) to ultra-fast speed reading. Self-claimed psychics argue that they discovered their abilities. Mentalists and magicians know that their audiences are likely to find appeals to untapped potential compelling and use them liberally in their patter.

Not surprisingly, popular culture gives people what they want. The idea of untapped potential is a staple of fantasy books and movies. In fact, it might well be the defining feature of classic fantasy writing; the central character discovers a hidden ability they didn't know they had. One of the common features of science fiction writing involves changing one element of how the universe works and then playing out the consequences. In many cases, that defining characteristic involves untapped potential (e.g., Verner Vinge's brilliantly conceived idea of "Focus" in his award-winning novels A Fire Upon The Deep and A Deepness In The Sky).

The theme of untapped potential pervades television dramas. The subtitle of NBC's hit series Heroes actually restates the definition of untapped potential: "ordinary people discovering extraordinary abilities." The success of Heroes inspired a slew of shows with the same theme: CBS's The Mentalist features a detective with "unusual powers of observation," ABC's Section 8 was about "especially brainy individuals," and Fox's Lie to Me centers on "a man who uses his preternatural skill at reading body language to help solve mysteries." (Note that Lie to Me is based loosely on Paul Ekman, a prominent psychologist and expert on face perception. If Ekman has exceptional skill in reading faces, it's because he spent decades studying and training, not because he had some secret talent.) The "untapped potential" plotline is one of the oldest forms of narrative, the rags-to-riches story in which a character finds themselves suddenly transformed, revealing the princess hidden in the lowly servant.

The illusion of potential and the fantasy of discovering hidden powers helps explain the exceptional popularity of Harry Potter. In the books, some people have magical abilities waiting to be revealed and other people are "muggles." Yes, they hone those skills, but the abilities are there waiting to be discovered and released. That one element-the discovery of a previously unknown ability that reveals itself with little effort or work-is central to the story's success. It taps our fantasies and cognitive illusions. The Harry Potter stories allow us to vicariously experience the ability to teleport ourselves home from school. It's cognitive illusion wish fulfillment at its best.

Gorilla suit winner

Last month, in celebration of the release of the paperback edition of The Invisible Gorilla, we teamed up with HalloweenCostumes.com to raffle away a deluxe gorilla suit to one lucky buyer of our book. I have just been informed that the lucky winner is Professor Bennett Schwartz, a cognitive psychology professor at Florida International University. Even better, he plans to use the gorilla suit in his cognitive psychology class! (Just a heads up, Bennett — once you've worn a gorilla suit in class, there's no going back…)

Congrats Bennett, and thanks to a href="http://www.halloweencostumes.com"... and to everyone who participated in the promotion for making the launch of our paperback edition a success. The book is now officially a New York Times Bestseller!

The consequences of being ignored (for colored shapes, at least)

I have just returned from the annual Vision Sciences Society meeting and saw some really fascinating presentations. Over the next couple weeks, I'll feature a few of them. The first one addresses the consequences of being ignored (if you are a colored shape, that is).

One of this year's more intriguing presentations, at least for me, came on the first night's poster session. My former graduate student and now superstar prof. at the University of Delaware, Steve Most, showed that what you ignore at one time can affect what you notice later. He combined two traditionally distinct tasks, negative priming and inattentional blindness. In a typical negative priming study, people might view two overlapping shapes of different colors, but focus on just one of them to make some judgment about it. When you selectively focus on just one of the shapes, you actively inhibit or ignore the other shape, and doing so has consequences. For example, if the shape you ignored later becomes a target shape that requires a response, you will be a little slower to respond. Typically, your response to the previously ignored shape would be slowed by 10-20 milliseconds relative to your speed if you had not ignored it. It's a small effect that emerges when you average across many trials.

In contrast, Inattentional Blindness studies typically use a single critical trial in which an object appears unexpectedly while people are focusing on something else. The central finding is that people often fail to notice dramatic and obvious stimuli (e.g., chest-thumping gorillas) when their attention is focused on some other aspect of the display and they don't know it's coming. (See The Invisible Gorilla for a lot more discussion.)

Most and his colleagues combined these two tasks in an original way to ask an intriguing question: If people ignore a shape or color repeatedly, will they be less likely to notice it when it appears unexpectedly in a different task? That is, does ignoring a color have a lasting effect on what we see, affecting not just how fast we process it later, but whether we see it at all?

Each trial in the study had a sequence of tasks. First, subjects viewed a cross and had to judge whether the horizontal or vertical line was longer. Then, they saw one green digit and one red digit and immediately afterward they were shown a color and had to report the corresponding digit. Only after doing this sequence of tasks 48 times did the experience the critical trial. This time, when the cross appeared, either a green or red shape unexpectedly appeared along with it. The question is whether the color they had been asked to report on the immediately prior trial influenced noticing of the unexpected shape. For example, on trial 48 they might have been asked to report the red digit. Then, on trial 49, a green shape appeared alongside the cross. The question would be whether having focused on red and ignored green on the preceding trial would make people less likely to notice an unexpected green shape.

The core finding: when people had just been asked to report the green digit and the shape was green, 72% noticed the shape. But, when asked to report the red digit and the shape was green, only 44% noticed. In other words, ignoring the green digit led people to miss the green unexpected shape. Setting your attention to ignore green things inhibits noticing of other green things, even those you don't know are there.

What is most remarkable about this result is that the inhibition from a negative priming task had such a large effect on noticing of something unexpected. Negative priming effects tend to be small delays in how long it takes to process something, not large effects on whether or not you see it. what is unclear is whether you actually need 48 trials of practice to produce this sort of effect. If not, then be careful what you choose to ignore — it might keep you from noticing something important later.

update: corrected the description of the colors of the digits and shapes.

Reference Cited:

Most, S. B., Kuvaldina, M., Dobson, K., & Kennedy, B. L. (2011, May). Prior perceptual decisions drive subsequent perceptual experience: Negative priming increases inattentional blindness. Poster presented at the annual meeting of the Vision Sciences Society. Naples, FL. http://www.visionsciences.org/abstract_detail.php?id=16.522

The Best Illusions of the Year

On Monday evening I attended the Best Illusion of the Year Contest in Naples Florida. (I live tweeted it as well — that was far more of a challenge than I had expected. See @profsimons if you're interested). The winning illusions always receive a lot of visibility online, so I thought I would draw your attention to two illusions that were not among the winners, but that were fantastic nonetheless. First, a little background.



The contest coincides with the annual Vision Sciences Society meeting, and it highlights 10 new visual illusions selected by a panel of expert vision scientists from a huge number of submissions (this year, more than 170 distinct entries). Each contestant has 5 minutes to try to wow the crowd of nearly 1000 spectators with the originality and spectacularity of their illusion. At the end of the presentations, audience members vote for their choice of the best illusion, and the top 3 vote-getters win cool sculptures (as in the past 2 years, skeptic and magician James Randi gave a mentalism demonstration while the votes were counted).

This year, there were at least 5 illusions that might have placed among the winners in previous years — it was a remarkably strong year, and most of the presentations were terrific. The winning illusion was a beautiful example of change blindness presented by Jordan Suchow, a graduate student at Harvard (co-created with George Alvarez, a Harvard Psychology Professor). He had presented the effect at last year's Vision Sciences meeting, and I blogged about it then as well. The effect received a huge round of applause from the audience, including an incredulous shout of "no way" from the back of the room. Here's the winning demo:

Now for a couple of illusions that didn't win this year but could have. Peter Tse, one of the greatest living illusion-creators and a regular participant in the contest, presented an important illusion, one with a strong theoretical motivation. His illusion isn't as dramatic or flashy as some of the other contestants, but it is elegant and theoretically important. His illusion was a novel variant of one created years ago by Stuart Anstis (another well-known vision scientist and illusion creator, who's own presentation of his earlier illusion immediately followed Tse's presentation at the contest. Anstis showed many effects in his presentation, and you can see his official contribution to the contest here.). Anstis originally showed that people mislocalize a flashed stimulus when it is presented against a rotating background. Anstis's effect is driven by the way our visual system detects and processes moving and stationary stimuli.

Tse's innovation was to show that you could induce the same sort of mislocalization using only your mind. He presented white dots rotating in one direction and black dots rotating in the opposite direction in the same display and flashed dots at 12 and 6 o'clock. Critically, if you focus attention on the black dots, you see the red dots slanted to the left (at 11 and 5 o'clock), and if you focus attention on the white dots, the displacement goes in the other direction. The finding shows that the way you focus attention affects where you perceive the dots to appear, even though the display itself is unchanging. In other words, the mislocalization effect shown by Anstis is not purely visual — it depends not just on your eyes, but on your mind. You can view Tse's illusion here.

A second wonderful presentation came from Arthur Shapiro, another great illusion-maker and a multiple-year winner of the Best Illusion of the Year contest. He presented a dramatic enhancement of a classic demonstration, first documented by Albert Michotte. If you view two shapes, one moving left-to-right and the other moving right-to-left so that their paths cross, the motion is ambiguous. They either appear to pass over each other or to bounce off each other. Shapiro presented a version in which the shapes appeared to bounce when they stood out from the background (high contrast) but to pass through each other when they didn't (low contrast). He then showed that you could get the bouncing effect even when it meant that the features had to swap locations. Finally, he showed that you perceive the items as passing through each other when viewed in the periphery but as bouncing when viewed at the center of your gaze. It was one of the most compelling examples of the illusion I've seen. You can view it here.

You can view all 10 of this year's illusions at neuralcorrelate.com. You can also view all of the finalists from previous contests, including my entry from last year, The Monkey Business Illusion:

If you're interested, you can see my presentation of the illusion (I wore a gorilla suit and showed some other cool stuff). I'd also encourage you to check out Art Shapiro's website: He has developed some fantastic interactive illusions and his site allows you to try out a wide range of variations of his effects. Peter Tse's site also has a lot of great illusions he has created over the past decade.

If you enjoy great illusions like these, please consider helping to support next year's illusion contest by participating in our charity promotion! Just select the Neural Correlate Society as the charity you would like us to support.

Another early study of Inattentional Blindness

Back in October on our Psychology Today blog, I posted about my re-discovery of what I then thought was the earliest systematic study of inattentional blindness. Turns out I was wrong.

Inattentional blindness is the failure to notice a fully-visible but unexpected object when you are focusing attention on something else. It is the phenomenon illustrated by our invisible gorilla studies. That study was conducted in the 1950s by a Tony Cornell, a parapsychology researcher — he found that people often didn't notice him while he pranced around campus dressed as a ghost! (check out the post — it is one of my favorites. I'll eventually repost it here).

As it turns out, there was at least one earlier experiment. Fifty years earlier, in fact. Just this week, my colleague Ira Hyman (he of unicycling clown fame) pointed me to a section of a chapter from a book by Hugo Munsterberg, written in 1908!

Hugo Munsterberg's book on eyewitness psychology. Source: http://goo.gl/qL4ol

In it, he describes the following experimental result:

I stood on a platform behind a low desk and begged the men to watch and to describe everything which I was going to do from one given signal to another. As soon as the signal was given, I lifted with my right hand a little revolving wheel with a colour-disk and made it run and change its color, and all the time, while I kept the little instrument at the height of my head, I turned my eyes eagerly toward it. While this was going on, up to the closing signal, I took with my left hand, at first, a pencil from my vest-pocket and wrote something at the desk; then I took my watch out and laid it on the table; then I took a silver cigarette-box from my pocket, opened it, took a cigarette out of it, closed it with a loud click, and returned it to my pocket; and then came the ending signal. The results showed that eighteen of the hundred had not noticed anything of all that I was doing with my left hand. Pencil and watch and cigarettes had simply not existed for them.

That's a pretty clear example of inattentional blindness, with at least some failure to notice objects and events happening outside the focus of attention. It has the flavor of a magician's misdirection, with social cues directed to the other hand (see Kuhn, 2009 for an example).

My favorite part of Munsterberg's report, though, was his description of his own mistaken intuitions. He too suffered from an illusion of attention, the belief that people typically notice salient and distinctive events.

I had made my movements of the left are so ostentatiously, and I had beforehand so earnestly insisted that they ought to watch every single movement, that I hardly expected to make any one overlook the larger part of my actions.

Just as we had expected people to notice when a person in a gorilla suit walked through a scene and thumped her chest at the camera, Munsterberg also had the wrong intuition about what people would and wouldn't notice.

I might try to replicate his method in my own lab — it's one of the few real-world studies of inattentional blindness and provides a nice intermediary to magical misdirection and laboratory studies of focused attention and inattention.

Sources Cited:

Munsterberg, Hugo (1908). On the Witness Stand: Essays on Psychology and Crime. Clark Boardman Co., NY, New York.

Munsterberg's book is available online here.

Kuhn, G., Tatler, B., & Cole, G. (2009). You look where I look! Effect of gaze cues on overt and covert attention in misdirection Visual Cognition, 17 (6), 925-944 DOI: 10.1080/13506280902826775

Hyman, I., Boss, S., Wise, B., McKenzie, K., & Caggiano, J. (2009). Did you see the unicycling clown? Inattentional blindness while walking and talking on a cell phone Applied Cognitive Psychology, 24 (5), 597-607 DOI: 10.1002/acp.1638

Cornell, A. D. (1959). An experiment in apparitional observation and findings. Journal of the Society for Psychical Research, 40(701), 120-124.

invisible gorillas and motorcycle safety

One of the most common sorts of motorcycle accidents involves a failure of attention: The driver of a car turns left in front of an oncoming motorcycle, failing to yield the right of way. In many cases, both the rider and driver report that the driver looked right at the motorcycle before turning—they looked without seeing. Such accidents could well be an example of the illusion of attention, our tendency to assume that we will notice anything important that happens right in front of our eyes.

For the launch of our paperback edition, we are conducting a charity promotion, and one of the participating charities is the BMW MOA Foundation, a rider group that actively promotes safety education through their magazine and Rider Performance University. I recently penned a short essay for the magazine and website on how everyday illusions and mistaken intuitions increase the danger for motorcyclists. You can read it here.

If you're a rider (or a bicyclist) and have experienced a looked-but-failed-to-see accident, please share your experiences with readers in the comments. (And, if you pre-order our paperback, you can target our donation to the BMW MOA Foundation or to any of a number of other great charities).