Improving your cognitive toolkit - VI

Continuation of my abstracting of a few of the answers to the annual question at edge.org, "What scientific concept would improve everybody's cognitive toolkit?":

Clay Shirky - The Pareto Principle - "unfairness" is a law.

You see the pattern everywhere: the top 1% of the population control 35% of the wealth. On Twitter, the top 2% of users send 60% of the messages. In the health care system, the treatment for the most expensive fifth of patients create four-fifths of the overall cost...The Italian economist Vilfredo Pareto undertook a study of market economies a century ago, and discovered that no matter what the country, the richest quintile of the population controlled most of the wealth. The effects of this Pareto Distribution go by many names — the 80/20 Rule, Zipfs Law, the Power Law distribution, Winner-Take-All — but the basic shape of the underlying distribution is always the same: the richest or busiest or most connected participants in a system will account for much much more wealth, or activity, or connectedness than average...this pattern is recursive. Within the top 20% of a system that exhibits a Pareto distribution, the top 20% of that slice will also account for disproportionately more of whatever is being measured, and so on.
...The Pareto distribution shows up in a remarkably wide array of complex systems. Together, "the" and "of" account for 10% of all words used in English. The most volatile day in the history of a stock market will typically be twice that of the second-most volatile, and ten times the tenth-most. Tag frequency on Flickr photos obeys a Pareto distribution, as does the magnitude of earthquakes, the popularity of books, the size of asteroids, and the social connectedness of your friends.

And yet, despite a century of scientific familiarity, samples drawn from Pareto distributions are routinely presented to the public as anomalies, which prevents us from thinking clearly about the world. We should stop thinking that average family income and the income of the median family have anything to do with one another, or that enthusiastic and normal users of communications tools are doing similar things, or that extroverts should be only moderately more connected than normal people.

This doesn't mean that such distributions are beyond our ability to affect them. A Pareto curve's decline from head to tail can be more or less dramatic, and in some cases, political or social intervention can affect that slope — tax policy can raise or lower the share of income of the top 1% of a population, just as there are ways to constrain the overall volatility of markets, or to reduce the band in which health care costs can fluctuate.

However, until we assume such systems are Pareto distributions, and will remain so even after any such intervention, we haven't even started thinking about them in the right way; in all likelihood, we're trying to put a Pareto peg in a Gaussian hole.

Daniel Goleman - Anthropocene thinking

Our planet has left the Holocene Age and entered what geologists call the Anthropocene Age, in which human systems erode the natural systems that support life...of all the global life-support systems, the carbon cycle is closest to no-return. While such "inconvenient truths" about the carbon cycle have been the poster child for our species' slow motion suicide, that's just part of a much larger picture, with all the eight global life-support systems under attack by our daily habits.

We approach the Anthropocene threat with brains shaped in evolution to survive the previous geological epoch, the Holocene, when dangers were signaled by growls and rustles in the bushes, and it served one well to reflexively abhor spiders and snakes. Our neural alarm systems still attune to this largely antiquated range of danger.

Add to that misattunement to threats our built-in perceptual blindspot: we have no direct neural register for the dangers of the Anthropocene age, which are too macro or micro for our sensory apparatus. We are oblivious to, say, our body burden, the lifetime build-up of damaging industrial chemicals in our tissues.

The fields that hold keys to solutions include economics, neuroscience, social psychology and cognitive science — and their various hybrids. With a focus on Anthropocene theory and practice they might well contribute species-saving insights. But first they have to engage this challenge, which for the most part has remained off their agenda.

When, for example, will neuroeconomics tackle the brain's perplexing indifference to the news about planetary meltdown, let alone how that neural blindspot might be patched? Might cognitive neuroscience one day offer some insight that might change our collective decision-making away from a lemmings' march to oblivion? Could any of the computer, behavioral or brain sciences come up with an information prosthetic that might reverse our course?

Cats with thumbs...

I had to pass this on (my daughter found it).

The beginning and middle of human history

Nicholas Wade has done a fascinating article on Franis Fukayama and his new book "The Origins of Political Order." (Which I've pre-ordered for my Amazon Kindle - Publishing date of April 12). The book takes off where E.O. Wilson's "Sociobiology" left off, emphasizing cultural traits built around evolved behaviors like favoring relatives, reciprocal altruism, creating and following rules, and a propensity for warfare. Starting with the transition from tribes to states (which occurred in China 1000 years earlier than in Europe, ~200 BC versus 800 AD, he describes the natural selection that occurred as European countries tried different formulas for distributing power, with only England and Denmark (almost by accident) developing the essential institutions of a strong state, the rule of law, and mechanisms to hold the ruler accountable. This successful formula then became adopted by other European states, through a kind of natural selection that favored the most successful variation. The book stops with the French revolution, and a subsequent book will continue to the present. Fukayama still thinks the modern liberal state is the "end of history" (The title of his most famous book).

In a parallel universe with no feudalism, European rulers might have been absolute, just like those of China. But through the accident of democracy, England and then the United States created a powerful system that many others wish to emulate. The question for China, in Dr. Fukuyama’s view, is whether a modern society can continue to be run through a top-down bureaucratic system with no solution to the bad emperor problem. “If I had to bet on these two systems, I’d bet on ours,” he said.

The New Humanism

Just after I look at my morning email, in which a blog reader points me to this NPR piece on David Brooks new book "The Social Animal", I open the New York Times and find Brooks' column on this subject.  Even though I don't agree with many of his conservative views, I have enormous respect for Brooks' efforts to bring the insights of modern research on how humans really work into the political policy arena. His Op-Ed piece this morning is an exceptionally well done summary of how public policy, guided by the fantasy of the rational citizen, ignores the emotional brain that is really running the show.  Below I offer some (slightly rearranged) clips. His view of many policy failures (as in public education) is that they rely

...on an overly simplistic view of human nature. We have a prevailing view in our society — not only in the policy world, but in many spheres — that we are divided creatures. Reason, which is trustworthy, is separate from the emotions, which are suspect. Society progresses to the extent that reason can suppress the passions...the unconscious parts of the mind are most of the mind, where many of the most impressive feats of thinking take place. Second, emotion is not opposed to reason; our emotions assign value to things and are the basis of reason. Finally, we are not individuals who form relationships. We are social animals, deeply interpenetrated with one another, who emerge out of relationships.

This body of research suggests the French enlightenment view of human nature, which emphasized individualism and reason, was wrong. The British enlightenment, which emphasized social sentiments, was more accurate about who we are. It suggests we are not divided creatures. We don’t only progress as reason dominates the passions. We also thrive as we educate our emotions.

Now hundreds of thousands of researchers are coming up with a more accurate view of who we are.  When you synthesize this research, you get different perspectives on everything from business to family to politics. You pay less attention to how people analyze the world but more to how they perceive and organize it in their minds. You pay a bit less attention to individual traits and more to the quality of relationships between people. The research illuminates a range of deeper talents, which span reason and emotion and make a hash of both categories:

Attunement: the ability to enter other minds and learn what they have to offer.
Equipoise: the ability to serenely monitor the movements of one’s own mind and correct for biases and shortcomings.
Metis: the ability to see patterns in the world and derive a gist from complex situations.
Sympathy: the ability to fall into a rhythm with those around you and thrive in groups.
Limerence: This isn’t a talent as much as a motivation. The conscious mind hungers for money and success, but the unconscious mind hungers for those moments of transcendence when the skull line falls away and we are lost in love for another, the challenge of a task or the love of God. Some people seem to experience this drive more powerfully than others.

Science starts early.

Frank Kell reviews experiments that show that young children are often quite adept at uncovering statistical and causal patterns, and that many foundations of scientific thought are built impressively early in our lives. Infants make causal interpretations by integrating information in ways that closely mirror adults...certain sequences of events automatically elicit thoughts of causation at all ages. In addition to figuring out the causal relations underlying novel devices, children are also sensitive to highly abstract causal patterns associated with specific “domains” that correspond roughly to...biology, physical mechanics, and psychology.

...an infant learning language, upon hearing streams of syllables, not only has to notice how often certain syllables occur but also needs to infer higher-order patterns arising from those syllables. One study showed that 5-month-old infants can handle this challenge by rapidly tracking not only the sounds of the syllables but also visual patterns associated with each syllable. In the experiment, infants looking at a computer screen were repeatedly presented with abstract patterns of syllables and shapes. An “ABB” pattern, for instance, could be represented by certain shapes corresponding to the syllables “di ga ga.” When presented with a new pattern (ABA) with new syllables—such as “le ko le”—the infants looked longer at the shapes on the screen than if the new syllables were in the old ABB pattern. This suggests that they recognized it as a new, unfamiliar correlation...6-month-olds can take the next step and infer causation from certain kinds of correlations. In these experiments, researchers measured how long infants looked at animations showing “collisions” of shapes. In some animations, one object “launched” a second one, causing it to move, as when two billiard balls collide. When shown animations in which the balls reversed roles, infants looked longer at the new pattern than at the original one.

in thinking about biological phenomena such as disease or inheritance, children may make different inferences from patterns of covariation than they do for physical phenomena such as collisions or rotating gears. Another top-down expectation that children bring to living things, but not to artifacts, is an “essentialist bias”: the idea that something you can't see (e.g., “microstructural stuff ”) causes what you can see (“surface phenomena” such as feathers or fur) and is the essence of the thing being observed. This is a guiding principle in much of formal science, even as it can also lead to false inferences, such as that species are defined by fixed essences.

A map of well-being

For the last three years, Gallup has called 1,000 randomly selected American adults each day and asked them about their emotional status, work satisfaction, eating habits, illnesses, stress levels and other indicators of their quality of life. Here is an interactive graphic summary of the results, sorted by congressional districts, and a related article.

The significance of self control.

We can't have our cake and eat it too, and every major religious tradition advocates forsaking pleasure in the moment to realize greater, deferred rewards. A recent study by Moffitt et al. statistically controls for the potential confounds of intelligence and family background in examining life outcomes in a large, nationally representative sample of New Zealanders. From their abstract:

...is self-control important for the health, wealth, and public safety of the population? Following a cohort of 1,000 children from birth to the age of 32 y, we show that childhood self-control predicts physical health, substance dependence, personal finances, and criminal offending outcomes, following a gradient of self-control. Effects of children's self-control could be disentangled from their intelligence and social class as well as from mistakes they made as adolescents. In another cohort of 500 sibling-pairs, the sibling with lower self-control had poorer outcomes, despite shared family background. Interventions addressing self-control might reduce a panoply of societal costs, save taxpayers money, and promote prosperity.

The Threatening Scent of Fertile Women

I've finally had time to check out the abundant links to background articles in John Tierney's Feb. 21 article in the NYTimes. I had not realized that there was such firm evidence that men can unconsciously detect, via changes in womens' cues and behavior and perhaps via pheromones, when women are at the ovulation stage of their menstrual cycle.

...recent studies have found large changes in cues and behavior when a woman is at this stage of peak fertility. Lap dancers get much higher tips (unless they’re taking birth-control pills that suppress ovulation, in which case their tips remain lower). The pitch of a woman’s voice rises. Men rate her body odor as more attractive and respond with higher levels of testosterone.

I would recommend reading the whole article, which describes experiments supporting rather elaborate evolutionary psychology theories about maintaining breeding relationships while also enhancing genetic diversity, such as:

...the “good genes” evolutionary explanation for adultery: a quick fling with a good-looking guy can produce a child with better genes, who will therefore have a better chance of passing along the mother’s genes. But this sort of infidelity is risky if the woman’s unsexy long-term partner finds out and leaves her alone to raise the child. So it makes sense for her to limit her risks by being unfaithful only at those times she’s fertile....By that same evolutionary logic, it makes sense for her partner to be most worried when she’s fertile.

Hugs follow a 3-second rule.

A fascinating bit from ScienceNow points to work by Emese Nagy:

How long does a hug lasts? The quick answer is about 3 seconds, according to Nagy's study of the post-competition embraces of Olympic athletes. The long answer is more profound. A hug lasts about as much time as many other human actions and neurological processes, which supports a hypothesis that we go through life perceiving the present in a series of 3-second windows...Crosscultural studies dating back to 1911 have shown that people tend to operate in 3-second bursts. Goodbye waves, musical phrases, and infants' bouts of babbling and gesturing all last about 3 seconds. Many basic physiological events, such as relaxed breathing and certain nervous system functions do, too. And several other species of mammals and birds follow the general rule in their body-movement patterns. A 1994 study of giraffes, okapis, roe deer, raccoons, pandas, and kangaroos living in zoos, for example, found that although the duration of the animals' every move, from chewing to defecating, varied considerably, the average was...3 seconds...The results reinforce an idea current among some psychologists that intervals of about 3 seconds are basic temporal units of life that define our perception of the present moment...the "feeling of nowness" tends to last 3 seconds.

Hope over experience - the persistence of optimism

Many studies have shown that people are excessively optimistic about marriage, work, sports, health, and life expectancy. Maasey et al. have asked: does such optimism persists as people acquire feedback from real-world experiences? And, second, is optimism actually caused by desire or hope? These are important question, for many of life’s most consequential decisions (e.g., about health, investments, or relationships) feature both strong preferences and the chance to revise beliefs in light of new information (e.g., medical exams, balance statements, or a second date). They asked National Football League (NFL) fans to predict game outcomes before each week of the 17-week NFL season. Studying football predictions offered four important benefits:

First, the 17-week season provided participants with quick, frequent, and unambiguous feedback over a significant (and nonarbitrary) duration of time, and thus it provided an ideal context for evaluating the effect of experience on optimism. Second, NFL fans’ preferences for their favorite teams are strong and often held with a degree of intensity unlikely to be generated by incentives offered in the laboratory. Third, a number of alternative explanations for the effects of desirability, such as those implicating team strength and familiarity, can be controlled methodologically and statistically. Finally, unlike predictions in other emotionally important domains, football predictions offer the benefit of objective benchmarks—both ex ante and ex post—against which the accuracy of predictions can be evaluated.

Their results:

We found that people are optimistic in their predictions—they judge preferred outcomes to be more likely than nonpreferred outcomes. We extended this observation in two important ways. First, we showed that optimism persists despite extensive experience—football fans are as optimistic after 4 months of feedback as they are after 4 weeks of feedback. Second, we found that desirability fueled this optimistic bias. Using four distinct tests, and a wide variety of control variables, we found that optimistic predictions were robust and uniquely related to the desirability of the outcome.

Happy people live longer.

It's a common assumption that happier people live longer, but the convincing data on this has not been easy to come by. Studies have offered widely different and competing findings - some finding no causation or reverse causation, others suggesting that unidentified, unobserved factors influence both happiness and longevity and health. Frey points to work by Diener and Chan showing that many kinds of studies, using different methods, conclude that happiness has a positive causal effect on longevity and physiological health. One of the studies noted by their survey is a meta-analysis based on 24 studies that estimates that happy people live 14% longer than persons who report that they are unhappy. In a survey of people living in industrial countries, happier people enjoy an increased longevity of between 7.5 and 10 years. Happier people are also less likely to commit suicide, and they are less often the victims of accidents...In longitudinal studies individuals are followed over many years, to identify whether the happier ones live longer. In the famous "nun study" researchers asked young women about their subjective happiness level before they entered a monastery. Those who perceived themselves to be happier died at a median age of 93.5 years. Those who considered themselves to be less happy died at a median age of 86.6 years.

Conscious attention influences unconscious cognition.

This work by Martens et al. demonstrates that our conscious attention to one task area (such as noting geometric shapes) can sensitize unconscious processes in that area such as subliminal priming (facilitatory effects elicited by masked stimuli that are not consciously perceived.) This shows that unconscious processing is crucially dependent on top-down attention, and contrasts with the classical view that unconscious cognition is characterized by the lack of top-down influences.

Are unconscious processes susceptible to attentional influences? In two subliminal priming experiments, we investigated whether task sets differentially modulate the sensitivity of unconscious processing pathways. We developed a novel procedure for masked semantic priming of words (Experiment 1) and masked visuomotor priming of geometrical shapes (Experiment 2). Before presentation of the masked prime, participants performed an induction task in which they attended to either semantic or perceptual object features designed to activate a semantic or perceptual task set, respectively. Behavioral and electrophysiological effects showed that the induction tasks differentially modulated subliminal priming: Semantic priming, which involves access to conceptual meaning, was found after the semantic induction task but not after the perceptual induction task. Visuomotor priming was observed after the perceptual induction task but not after the semantic induction task. These results demonstrate that unconscious cognition is influenced by attentional control. Unconscious processes in perceptual and semantic processing streams are coordinated congruently with higher-level action goals.

Go easy on yourself...

Being a self critical person who rarely gets off his own case,  I was considerably softened by a Sarah Parker-Pope article in this morning's Science section of the NYTimes on:

...a burgeoning new area of psychological research called self-compassion — how kindly people view themselves...The research suggests that giving ourselves a break and accepting our imperfections may be the first step toward better health. People who score high on tests of self-compassion have less depression and anxiety, and tend to be happier and more optimistic. Preliminary data suggest that self-compassion can even influence how much we eat and may help some people lose weight.

The article contains links to several original research papers.

Sharing the spoils develops early in humans.

From Tomasello and collaborators:

Egalitarian behavior is considered to be a species-typical component of human cooperation. Human adults tend to share resources equally, even if they have the opportunity to keep a larger portion for themselves. Recent experiments have suggested that this tendency emerges fairly late in human ontogeny, not before 6 or 7 years of age. Here we show that 3-year-old children share mostly equally with a peer after they have worked together actively to obtain rewards in a collaboration task, even when those rewards could easily be monopolized. These findings contrast with previous findings from a similar experiment with chimpanzees, who tended to monopolize resources whenever they could. The potentially species-unique tendency of humans to share equally emerges early in ontogeny, perhaps originating in collaborative interactions among peers.

Politics in Madison, WI

I spend the spring, summer, and fall months in Madison, WI., writing this blog from my university office there, and so have been closely following the theatrical union busting efforts of the new Republican majority.  With all the agonizing over long term debt incurred by the states, I thought this graphic from yesterday's NY Times Magazine, from an article on New Jersey governor Christie, was revealing (click on figure to enlarge): 

Improving your cognitive toolkit - V

Continuation of my abstracting of a few of the answers to the annual question at edge.org, "What scientific concept would improve everybody's cognitive toolkit?":

Daniel Dennett - Look for the Cycles

A good rule of thumb...when confronting the apparent magic of the world of life and mind is: look for the cycles that are doing all the hard work....it turns out that all the "magic" of cognition depends, just as life itself does, on cycles within cycles of recurrent, re-entrant, reflexive information-transformation processes from the biochemical scale within the neuron to the whole brain sleep cycle, waves of cerebral activity and recovery revealed by EEGs. Computer programmers have been exploring the space of possible computations for less than a century, but their harvest of invention and discovery so far includes millions of loops within loops within loops. The secret ingredient of improvement is always the same: practice, practice, practice.

Andy Clark - We are engines of prediction

The basic idea is simple, the brain is basically an engine of prediction. To perceive the world is to successfully predict our own sensory states. The brain uses stored knowledge about the structure of the world and the probabilities of one state or event following another to generate a prediction of what the current state is likely to be, given the previous one and this body of knowledge. Mismatches between the prediction and the received signal generate error signals that nuance the prediction or (in more extreme cases) drive learning and plasticity.

Some Implications:

First, the notion of good ('veridical') sensory contact with the world becomes a matter of applying the right expectations to the incoming signal...Second, the time course of perception becomes critical. Predictive coding models suggest that what emerges first is the general gist (including the general affective feel) of the scene, with the details becoming progressively filled in as the brain uses that larger context — time and task allowing — to generate finer and finer predictions of detail...Third, the line between perception and cognition becomes blurred. What we perceive (or think we perceive) is heavily determined by what we know, and what we know (or think we know) is constantly conditioned on what we perceive (or think we perceive)...Fourth, if we now consider that prediction errors can be suppressed not just by changing predictions but by changing the things predicted, we have a simple and powerful explanation for behavior and the way we manipulate and sample our environment. In this view, action is there to make predictions come true.

A potpuorri of almost-posts

As I scan journals' tables of contents and abstracts of articles looking for potential MindBlog posts, I accumulate a list of post candidates. Most never make it into a post, yet are very interesting chunks. My list now is 30 pages long, and I though I would begin to dispel that list by selecting a few to pass as a list of links, hoping that a few readers might find an item useful to them.

Writing about testing worries boosts exam performance.

Memory formation without the hippocampus.

Temporary suppression of fear memories during adolescence.

Solving the cocktail party problem.

Your Brain on Improv....to be creative, you have to have this weird dissociation in your frontal lobe. One area turns on, and a big area shuts off, so that you're not inhibited, so that you're willing to make mistakes, so that you're not constantly shutting down all of these new generative impulses.

Control your spotlight.

Retracted Autism Study.

Past adversity strengthens.

Courage.

Your brain on technology.

Krugman - The New Voodo.

Oliver Sachs - Change your brain.

How stress damages or enhances different aspects of our vision

Richie Davidson, Alex Schackman and colleagues report a fascinating study that demonstrates that stress (painful, but not harmful, random electric shocks delivered to informed consent study participants) makes us more sensitive to our external surroundings as a way of learning where or what a threat may be, but interferes with our ability to do more complex thinking:

Stress can fundamentally alter neural responses to incoming information. Recent research suggests that stress and anxiety shift the balance of attention away from a task-directed mode, governed by prefrontal cortex, to a sensory-vigilance mode, governed by the amygdala and other threat-sensitive regions. A key untested prediction of this framework is that stress exerts dissociable effects on different stages of information processing. This study exploited the temporal resolution afforded by event-related potentials to disentangle the impact of stress on vigilance, indexed by early perceptual activity, from its impact on task-directed cognition, indexed by later postperceptual activity in humans. Results indicated that threat of shock amplified stress, measured using retrospective ratings and concurrent facial electromyography. Stress also double-dissociated early sensory-specific processing from later task-directed processing of emotionally neutral stimuli: stress amplified N1 (184–236 ms) and attenuated P3 (316–488 ms) activity. This demonstrates that stress can have strikingly different consequences at different processing stages. Consistent with recent suggestions, stress amplified earlier extrastriate activity in a manner consistent with vigilance for threat (N1), but disrupted later activity associated with the evaluation of task-relevant information (P3). These results provide a novel basis for understanding how stress can modulate information processing in everyday life and stress-sensitive disorders.

Uncertainty increases romantic attraction

Another interesting bit of work from Daniel Gilbert and collaborators:

This research qualifies a social psychological truism: that people like others who like them (the reciprocity principle). College women viewed the Facebook profiles of four male students who had previously seen their profiles. They were told that the men (a) liked them a lot, (b) liked them only an average amount, or (c) liked them either a lot or an average amount (uncertain condition). Comparison of the first two conditions yielded results consistent with the reciprocity principle. Participants were more attracted to men who liked them a lot than to men who liked them an average amount. Results for the uncertain condition, however, were consistent with research on the pleasures of uncertainty. Participants in the uncertain condition were most attracted to the men—even more attracted than were participants who were told that the men liked them a lot. Uncertain participants reported thinking about the men the most, and this increased their attraction toward the men.

Strategies for remembering.

Two recent articles offer different perspectives on retaining information. The interesting NYTimes magazine article by world class memory athlete Joshua Foer describes an ancient memory training tradition that flourished in ancient Greece before the invention of printing.  Brain imaging of  memory athletes who have engaged this training (who are of ordinary intelligence in virtually all other respects) shows more activation of brain areas known to be involved in spatial memory during memory tasks. The training derives from discoveries of Simonides of Ceos in the fifth century B.C.,

...who reasoned that just about anything could be imprinted upon our memories, and kept in good order, simply by constructing a building in the imagination and filling it with imagery of what needed to be recalled. This imagined edifice could then be walked through at any time in the future. Such a building would later come to be called a memory palace...a short Latin rhetoric textbook called “Rhetorica ad Herennium,” written sometime between 86 and 82 B.C. It is the only comprehensive discussion of the memory techniques attributed to Simonides to have survived into the Middle Ages. The techniques described in this book were widely practiced in the ancient and medieval worlds. Memory training was considered a centerpiece of classical education in the language arts, on par with grammar, logic and rhetoric...What distinguishes a great mnemonist...is the ability to create lavish images on the fly, to paint in the mind a scene so unlike any other it cannot be forgotten. And to do it quickly. Many competitive mnemonists argue that their skills are less a feat of memory than of creativity.

Both ancient and more recent memory enhancement techniques focus on the processing that occurs when we encode knowledge. A recent fairly simple experiment by Karpicke and Blunt suggests the effectiveness of another strategy that emphasizes practice.  From their introduction:

It is beyond question that activities that promote effective encoding, known as elaborative study tasks, are important for learning. However, research in cognitive science has challenged the assumption that retrieval is neutral and uninfluential in the learning process. Not only does retrieval produce learning, but a retrieval event may actually represent a more powerful learning activity than an encoding event. This research suggests a conceptualization of mind and learning that is different from one in which encoding places knowledge in memory and retrieval simply accesses that stored knowledge. Because each act of retrieval changes memory, the act of reconstructing knowledge must be considered essential to the process of learning.

Their abstract:

Educators rely heavily on learning activities that encourage elaborative studying, whereas activities that require students to practice retrieving and reconstructing knowledge are used less frequently. Here, we show that practicing retrieval produces greater gains in meaningful learning than elaborative studying with concept mapping. The advantage of retrieval practice generalized across texts identical to those commonly found in science education. The advantage of retrieval practice was observed with test questions that assessed comprehension and required students to make inferences. The advantage of retrieval practice occurred even when the criterial test involved creating concept maps. Our findings support the theory that retrieval practice enhances learning by retrieval-specific mechanisms rather than by elaborative study processes. Retrieval practice is an effective tool to promote conceptual learning about science.