Chandrakasan honored

March 18, 2009  PAGE 5

MIT Tech Talk

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 RESEARCH & INNOVATION

Climate change may widen gap  

between rich and poor, study finds 

A rising tide is said to lift all boats. Rising global 

temperatures, however, may lead to increased disparities 

between rich and poor countries, according to a recent 

MIT economic analysis of the impact of climate change 

on growth. 

After examining worldwide climate and economic data 

from 1950 to 2003, Benjamin A. Olken, associate profes-

sor in the Department of Economics, concludes that a 1 

degree Celsius rise in temperature in a given year reduces 

economic growth by an average of 1.1 percentage points 

in the world’s poor countries but has no measurable effect 

in rich countries. 

Olken says his research suggests higher temperatures 

will be disproportionately bad for the economic growth of 

poor countries compared to rich countries. 

The precise reasons why higher temperatures lower 

economic output are likely to be complex, but Olken’s 

results suggest the importance of temperature’s impact on 

agricultural output. His data also provide evidence for a 

relationship between temperature and industrial output, 

investment, research productivity and political stability.

“The potential impacts of an increase in temperature 

on poor countries are much larger than existing esti-

mates have suggested,” Olken says. “Although historical 

estimates don’t necessarily predict the future, our results 

suggest that one should be particularly attentive to the 

potential impact of climate change on poorer countries.”

Olken’s analysis is contained in “Climate Shocks and 

Economic Growth: Evidence from the Last Half Centu-

ry,” a paper co-authored by MIT economics graduate 

student Melissa Dell and Benjamin F. Jones, associate 

management professor at Northwestern University. The 

paper is currently under review for publication. Olken, 

who has been researching issues of growth and tempera-

ture for about two years, presented some of the find-

ings at a recent conference of the American Economic 

Association.

Growing hot-cold divide

It has long been observed that hotter countries, such as 

those in sub-Saharan Africa and parts of Latin America, 

tend to be poorer than cooler countries in North America 

and Europe; the main exceptions are hot, rich Middle East 

countries with oil reserves and cold, poor Communist or 

former Communist states like North Korea and Mongo-

lia. What contemporary scholars have debated, however, 

is whether climate has a significant effect on a country’s 

economy today or whether it is institutions and policies 

that now solely drive prosperity. 

To conduct their research, Olken and his co-authors 

used existing data sets of economic growth and productiv-

ity — everything from gross domestic product to the rate 

of publication of scientific papers — and combined them 

with country-by-country temperature and precipitation 

data from 1950 to 2003. 

Olken and his co-authors conclude that rising tempera-

tures do substantially reduce economic output and growth 

rates in both agricultural and industrial sectors, but only in 

countries that are already poor. Higher temperatures also 

reduce investment and innovation but, again, only in poor 

nations. 

Rising temperatures may also have political conse-

quences, the authors found. A one-degree rise in tempera-

ture in poor countries raises the likelihood of a so-called 

irregular leader transition (i.e., a coup) by 3.9 percentage 

points. 

Olken acknowledges that the long-term impact of 

temperature change might be different from the short-

term effect since countries may adapt to a particular 

climate over time. But his research found no such adapta-

tion over a 10-year time horizon. 

Should the future effects mirror recent history, world 

policy makers should be prepared for a widening gap 

between rich and poor countries as the globe continues to 

warm, he says. 

As planet warms, poor nations face economic chill

Stephanie Schorow

News Office

PHOTO / DONNA COVENEY

Associate Professor of Economics Benjamin Olken

Humans excel at recognizing faces, but how we do 

this has been an abiding mystery in neuroscience and 

psychology. In an effort to explain our success in this 

area, researchers are taking a closer look at how and why 

we fail. 

A new study from MIT looks at a particularly strik-

ing instance of failure: our impaired ability to recog-

nize faces in photographic negatives. The study, which 

appeared in the Proceedings of the National Academy 

of Sciences last week, suggests that a large part of the 

answer might lie in the brain’s reliance on a certain kind 

of image feature.

The work could potentially lead to computer vision 

systems, for settings as diverse as industrial qual-

ity control or object and face detection. On a differ-

ent front, the results and methodologies could help 

researchers probe face-perception skills in children with 

autism, who are often reported to experience difficulties 

analyzing facial information.

Anyone who remembers the days before digital 

photography has probably noticed that it’s much harder 

to identify people in photographic negatives than in 

normal photographs. “You have not taken away any 

information, but somehow these faces are much harder 

to recognize,” says Pawan Sinha, an associate professor 

of brain and cognitive sciences and senior author of the 

PNAS study.

Sinha has previously studied light and dark relation-

ships between different parts of the face, and found that 

in nearly every normal lighting condition, a person’s eyes 

appear darker than the forehead and cheeks. He theo-

rized that photo negatives are hard to recognize because 

they disrupt these very strong regularities around the 

eyes.

To test this idea, Sinha and his colleagues asked 

subjects to identify photographs of famous people in 

not only positive and negative images, but also in a third 

type of image in which the celebrities’ eyes were restored 

to their original levels of luminance, while the rest of the 

photo remained in negative.

Subjects had a much easier time recognizing these 

“contrast chimera” images. According to Sinha, that’s 

because the light/dark relationships between the eyes 

and surrounding areas are the same as they would be in a 

normal image.

Similar contrast relationships can be found in other 

parts of the face, primarily the mouth, but those rela-

tionships are not as consistent. 

“The relationships around the eyes seem to be 

particularly significant,” says Sinha.

Other studies have shown that people with autism 

tend to focus on the mouths of people they are looking 

at, rather than the eyes, so the new findings could help 

explain why autistic people have such difficulty recogniz-

ing faces, says Sinha.

The findings also suggest that neuronal responses in 

the brain may be based on these relationships between 

different parts of the face. The team found that when 

they scanned the brains of people performing the recog-

nition task, regions associated with facial processing (the 

fusiform face areas) were far more active when look-

ing at the contrast chimeras than when looking at pure 

negatives.

Other authors of the paper are Sharon Gilad of the 

Weizmann Institute of Science in Israel and MIT post-

doctoral associate Ming Meng, both of whom contrib-

uted equally to the work.

The research was funded by the Alfred P. Sloan Foun-

dation and the Jim and Marilyn Simons Foundation.

A human failure...      

...seen at face value

Anne Trafton

News Office

Can you tell who this person is? No? You are not alone. Research from MIT shows why it is harder to 

recognize people in photo negatives. Still wondering who it is? See page 6 for the answer.

Research probes why we have difficulty recognizing faces in photo negatives

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