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Monday, May 23rd, 2016
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| 12:00a |
Why children confuse simple words Imagine, for a moment, you are a parent trying to limit how much dessert your sugar-craving young children can eat.
“You can have cake or ice cream,” you say, confident a clear parental guideline has been laid out.
But your children seem to ignore this firm ruling, and insist on having both cake and ice cream. Are they merely rebelling against a parental command? Perhaps. But they might be confusing “or” with “and,” as children do at times, something studies have shown since the 1970s. What seems like a restriction to the parent sounds like an invitation to the child: Have both!
But why does this happen? Now a study by MIT linguistics professors and a team from Carleton University, based on an experiment with children between the ages of 3 and 6, proposes a new explanation, with a twist: In examining this apparent flaw, the researchers conclude that children deploy a more sophisticated mode of logical analysis than many experts have previously realized.
Indeed, say the linguists, children use almost entirely the same approach as adults when it comes to evaluating potentially ambiguous sentences, by testing and “strengthening” them into sentences with more precise meanings, when disjunction and conjunction (“or” and “and”) are involved.
While using this common approach, however, children do not test how a sentence would change if “and” were directly substituted for “or.” This more modest procedural problem is what leads to the confusion about cake and ice cream.
“Children seem to interpret disjunction like conjunction,” observes Danny Fox, the Anshen-Chomsky Professor in Language and Thought at MIT and co-author of a paper detailing the study. However, Fox adds, although “it has been claimed children are very different from adults in the interpretation of logical words,” the study’s larger implication is almost the opposite — namely that “the child is [otherwise] identical to the adult, but there is a very small parameter that distinguishes them.”
Quirky as this finding seems, it confirms a specific prediction Fox and some other researchers had made, based on previous studies in formal semantics (the area of linguistics that investigates the logic of natural language use). As such, the study reinforces what we know about the procedures both children and adults deploy in “and/or” matters.
“There’s a certain kind of computation we can now say both children and adults do,” says Raj Singh PhD ’08, an associate professor of cognitive science at Carleton University and the lead author of the new report.
The paper, “Children interpret disjunction as conjunction: Consequences for theories of implicature and child development,” is being published in the journal Natural Language Semantics. The co-authors are Singh; Fox; Ken Wexler, emeritus professor of psychology and linguistics at MIT; Deepthi Kamawar, an associate professor of psychology at Carleton University; and Andrea Astle-Rahim, a recent PhD graduate from Carleton University.
What adults do: the two-step
To understand how children conflate “or” with “and,” first consider how adults normally clarify what sentences mean. Suppose you have a dozen cookies in a jar on your desk at work, and go to a meeting. When you come back, a colleague tells you, “Marty ate some of the cookies.”
Now suppose you find out that Marty actually ate all 12 cookies. The previous sentence — “Marty ate some of the cookies” — may still be true, but it would be more accurate to say, “Marty ate all of the cookies.”
To make this evaluation, adults compute “scalar implicatures,” a technical phrase for thinking about the implications of the logical relationship between a sentence and its alternatives. For “Marty ate some of the cookies,” there is a two-step computation. The first step is to think through some alternatives, such as what happens if you substitute “all” for “some” (leading to “Marty ate all of the cookies”). The second step is to realize that this alternative spells out a specific new meaning — that all 12 cookies have been eaten, not just a few of them.
We then realize the sentence “Marty ate some of the cookies” more accurately means: “Marty ate some, but not all, of the cookies.” And now we have a “strengthened” version of the first sentence.
The same process applies to the sentence, “Jane ate cake or ice cream.” The sentence is true if Jane ate one or the other, and still technically true if she ate both. But once we compute the scalar implicatures, we realize that “Jane ate cake or ice cream” is a “strengthened” way of saying she ate one or the other, but not both.
Fox has conducted extensive research over the last decade formalizing our computations of scalar implicatures and identifying areas where tiny differences in the logical “space of alternatives” can have far-reaching consequences. The current paper stems in part from work Singh pursued as a doctoral student collaborating with Fox at MIT.
Why “or” and “and” merge for children
The research team conducted the study’s experiment by testing 59 English-speaking children and 26 adults in the Ottawa area. The children ranged in age from 3 years, 9 months, to 6 years, 4 months. The linguists gave the subjects a series of statements along with pictures, and asked them to say whether the statements were true or false.
For instance: The children were shown a picture with three boys holding an apple or a banana, along with the statement, “Every boy is holding an apple or a banana,” and then asked to say if the statement was true or false. The children were asked to do this for a full range of scenarios — such as one boy holding one type of fruit and two boys holding the other — along with a varying set of “and/or” statements. The researchers repeated five sets of such trials, with the pictures changing each time.
The results suggest that children are computing scalar implicatures when they evaluate the statements — but they largely do not substitute disjunctions and conjunctions when testing out the possible meaning of sentences, as adults do.
That means when children hear “cake or ice cream,” they are generally not replacing “or” in the phrase with “and,” to test what would happen. Without that contrast, the children still “strengthen” the meaning of “or,” but they strengthen it to mean “and.” Thus “or” and “and” can blur together for children.
“They [children] don’t use ‘cake and ice cream’ as an alternative,” Fox says. “As a result, ‘cake or ice cream’ is expected, if we are right about the nature of the computation, to become ‘cake and ice cream’ for the children.”
And while we tend to think children are wrong to draw that conclusion, it is still the result of computing scalar implicatures — it just happens that, as Singh observes, those computations create divergent outcomes for children and adults.
A universal process
Other scholars say the study is a significant piece of research. Emmanuel Chemla, a scholar at CNRS in France, who has conducted previous research in this area, notes that the study’s “highly counterintuitive prediction” appears to be “entirely correct.” (Disclosure: Chemla has collaborated with some of the authors previously.)
Chemla also praises the study’s blend of formal semantic analysis with its experimental structure, stating that this kind of interdisciplinary approach is “often highly praised and called for, but rarely taken to such a high level.” And he adds that in the future, it will be “important to develop a full theory of how children arrive at this stage, and how they move from it to an adult-like competence.”
The researchers say they agree with the need to examine that transition to the adult pattern of strengthening. In the meantime, they hope colleagues will consider the additional evidence the study provides about the formal logic underlying our language use.
“The computational system of language is actually telling us how to do certain kinds of thinking,” Wexler suggests. “It isn’t us just trying to [understand] things pragmatically.”
Additionally, the scholars believe evidence from other languages besides English supports their conclusions. In both Walpiri, a language of indigenous Australians, and American Sign Language, there is a single connective word that functions as both “or” and “and” and appears subject to the strengthening process identified for children. And, Singh notes, linguists are now replicating the study’s findings in French and Japanese.
In general, Fox observes, across languages, and for children and adults alike, “The remarkable logical fact is that when you take ‘and’ out of the space of alternatives, ‘or,’ becomes ‘and.’ This, of course, relies on the nature of the computation that we’ve postulated, and, hence, the results of the study provide confirmation of a form that I find rather exciting.”
So, yes, your children may not understand what you mean about dessert. Or perhaps they are just being willful. But if they confuse “or” with “and,” then they are not being childish — at least not in the way you may think. | | 12:00a |
The price of regret Let’s say you’ve just found a nice jacket in a store and are deciding whether to buy it. It’s a little pricey, so should you wait and hope it goes on sale in the future? Perhaps. Then again, the jacket might go out of stock before that happens, and you might never acquire it at all. Is it worth paying more now to avoid that feeling of regret?
For many people, evidently, it is. And as a paper co-authored by an MIT scholar suggests, not only do consumers tend to buy goods partly to avoid that feeling of regret, but some retailers fail to notice this behavioral quirk and thus miss an opportunity to increase their revenues.
Indeed, some retailers could have profits 7 to 10 percent higher if they pursued different pricing strategies, the study finds. That is, generally higher prices with occasional sales mixed in will yield more revenue than consistently low prices, at least for fashionable goods.
“The high-value customers will still buy the product,” says Karen Zheng, an assistant professor of operations management at the MIT Sloan School of Management. “They want to [avoid] this feeling of regret, which would occur if they wait now and then cannot get it in the future.” For such items, the research finds, if retailers fail to recognize consumers’ emotions, they could stock insufficient amounts of merchandise and may forgo up to 14 percent of consumer demand.
The paper, “Markdown or Everyday Low Price? The Role of Behavioral Motives,” appeared recently in print in the journal Management Science. The co-authors are Zhang and Özalp Özer, the Ashbel Smith Professor of Management at the University of Texas at Dallas.
Different products, different strategies
In the paper, the scholars used existing empirical research from behavioral economics to build a new model of consumer decision making. They focused on two subjective factors that influence consumers: the feeling of regret that stems from either failing to cash in on a discount or missing out on a potential purchase, on the one hand, and the misperception of the products’ future availability, on the other. Consumers often believe products remain in stock for a shorter time than the goods actually do.
“Human beings are not good at dealing with uncertainty,” Zheng says.
To see how ignoring these factors while crafting retail strategies can yield suboptimal results for companies, consider two retailers that emphasize clothing: JCPenney and Macy’s. In 2012, as the scholars note in the paper, JCPenney switched to a strategy of everyday low prices in an effort to boost revenue. (It’s the same kind of strategy all-purpose retailers such as Costco and Sam’s Club use.) Macy’s, by contrast, tends to employ a strategy in which higher regular prices alternate with intermittent sales, at least for goods that are more expensive in the first place.
Which is a better approach? The JCPenney switch to consistently lower prices did not yield the revenue bump its management had anticipated. Indeed, the company fired the CEO who initiated this change within two years, and returned to using promoted sales.
The approach of using promoted sales works better for JCPenney because, as Zheng and Özer write in the paper, “branded fashion items tend to induce strong stockout regret but weak high-price regret.” If you buy that nice jacket, you will likely disregard how much you paid for it as time goes on, and be happy that you have it in the first place. The occasional discounts, meanwhile, attract more price-conscious customers. Switching to everyday low prices took away these factors.
The same thing does not hold for more mundane pieces of clothing, however, such as T-shirts. In such cases, consumers generally do not intensely regret missing out on certain T-shirts, because many suitable alternatives are available. Instead, consumers want to avoid paying too much for a T-shirt; here, the high-price regret is stronger, compared with the stockout regret.
What makes Macy’s pricing work, Zheng concludes, is that it uses different strategies for different categories of clothing: higher prices and occasional sales for the big-ticket clothes, mixed with everyday low prices for less-coveted items.
“It’s a smarter strategy to differentiate your pricing based on products,” Zheng says. “The behavioral factors are not independent of the products.”
Continuing research
For her part, Zheng is continuing to develop research related to consumer behavior and pricing strategies, while looking at the issue from slightly different angles. One of her ongoing studies, along with Georgia Perakis, the William F. Pounds Professor of Management at MIT Sloan, examines how much price markdowns affect the way consumers perceive the quality of products in the first place.
Overall, Zheng notes, it is hard for retailers to get pricing strategies right all the time, especially when they sell a diverse range of products. Thus, retailers should recognize which kinds of emotions and perceptions motivate consumers. In a world full of unknowns, consumers usually want to resolve their purchasing decisions fairly quickly. After all, who really want to be checking back to see if that nice jacket will be on sale, several weeks or months in the future? | | 11:00a |
Hot new solar cell A team of MIT researchers has for the first time demonstrated a device based on a method that enables solar cells to break through a theoretically predicted ceiling on how much sunlight they can convert into electricity.
Ever since 1961 it has been known that there is an absolute theoretical limit, called the Shockley-Queisser Limit, to how efficient traditional solar cells can be in their energy conversion. For a single-layer cell made of silicon — the type used for the vast majority of today’s solar panels — that upper limit is about 32 percent. But it has also been known that there are some possible avenues to increase that overall efficiency, such as by using multiple layers of cells, a method that is being widely studied, or by converting the sunlight first to heat before generating electrical power. It is the latter method, using devices known as solar thermophotovoltaics, or STPVs, that the team has now demonstrated.
The findings are reported this week in the journal Nature Energy, in a paper by MIT doctoral student David Bierman, professors Evelyn Wang and Marin Soljačić, and four others.
While all research in traditional photovoltaics faces the same underlying theoretical limitations, Bierman says, “with solar thermophotovoltaics you have the possibility to exceed that.” In fact, theory predicts that in principle this method, which involves pairing conventional solar cells with added layers of high-tech materials, could more than double the theoretical limit of efficiency, potentially making it possible to deliver twice as much power from a given area of panels.
“We believe that this new work is an exciting advancement in the field,” Wang says, “as we have demonstrated, for the first time, an STPV device that has a higher solar-to-electrical conversion efficiency compared to that of the underlying PV cell.” In the demonstration, the team used a relatively low-efficiency PV cell, so the overall efficiency of the system was only 6.8 percent, but it clearly showed, in direct comparisons, the improvement enabled by the STPV system.
The basic principle is simple: Instead of dissipating unusable solar energy as heat in the solar cell, all of the energy and heat is first absorbed by an intermediate component, to temperatures that would allow that component to emit thermal radiation. By tuning the materials and configuration of these added layers, it’s possible to emit that radiation in the form of just the right wavelengths of light for the solar cell to capture. This improves the efficiency and reduces the heat generated in the solar cell.
The key is using high-tech materials called nanophotonic crystals, which can be made to emit precisely determined wavelengths of light when heated. In this test, the nanophotonic crystals are integrated into a system with vertically aligned carbon nanotubes, and operate at a high temperature of 1,000 degrees Celsius. Once heated, the nanophotonic crystals continue to emit a narrow band of wavelengths of light that precisely matches the band that an adjacent photovoltaic cell can capture and convert to an electric current. “The carbon nanotubes are virtually a perfect absorber over the entire color spectrum,” Bierman says, allowing it to capture the full solar spectrum. “All of the energy of the photons gets converted to heat.” Then, that heat gets re-emitted as light but, thanks to the nanophotonic structure, is converted to just the colors that match the PV cell’s peak efficiency.
In operation, this approach would use a conventional solar-concentrating system, with lenses or mirrors that focus the sunlight, to maintain the high temperature. An additional component, an advanced optical filter, lets through all the desired wavelengths of light to the PV cell, while reflecting back any unwanted wavelengths, since even this advanced material is not perfect in limiting its emissions. The reflected wavelengths then get re-absorbed, helping to maintain the heat of the photonic crystal.
Bierman says that such a system could offer a number of advantages over conventional photovoltaics, whether based on silicon or other materials. For one thing, the fact that the photonic device is producing emissions based on heat rather than light means it would be unaffected by brief changes in the environment, such as clouds passing in front of the sun. In fact, if coupled with a thermal storage system, it could in principle provide a way to make use of solar power on an around-the-clock basis. “For me, the biggest advantage is the promise of continuous on-demand power,” he says.
In addition, because of the way the system harnesses energy that would otherwise be wasted as heat, it can reduce excessive heat generation that can damage some solar-concentrating systems.
To prove the method worked, the team ran tests using a photovoltaic cell with the STPV components, first under direct sunlight and then with the sun completely blocked so that only the secondary light emissions from the photonic crystal were illuminating the cell. The results showed that the actual performance matched the predicted improvements.
“A lot of the work thus far in this field has been proof-of-concept demonstrations,” Bierman says. “This is the first time we’ve actually put something between the sun and the PV cell to prove the efficiency” of the thermal system. Even with this relatively simple early-stage demonstration, Bierman says, “we showed that just with our own unoptimized geometry, we in fact could break the Shockley-Queisser limit.” In principle, such a system could reach efficiencies greater than that of an ideal solar cell.
The next steps include finding ways to make larger versions of the small, laboratory-scale experimental unit, and developing ways of manufacturing such systems economically.
This represents a “significant experimental advance,” says Peter Bermel, an assistant professor of electrical and computer engineering at Purdue University, who was not associated with this work. “To the best of my knowledge, this is a new record for solar TPV, using a solar simulator, selective absorber, selective filter, and photovoltaic receiver, that reasonably represents actual performance that might be achievable outdoors.” He adds, “It also shows that solar TPV can exceed PV output with a direct comparison of the same cells, for a sufficiently high input power density, lending this approach to applications using concentrated sunlight.”
The research team also included MIT alumnus Andrej Lenert PhD ’14, now a research fellow at the University of Michigan, MIT postdocs Walker Chan and Bikram Bhatia, and research scientist Ivan Celanovic. The work was supported by the Solid-State Solar Thermal Energy Conversion (S3TEC) Center, funded by the U.S. Department of Energy. |
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