Hurricane Melissa turned sharply to devastate Jamaica − how forecasters knew where it was headed

Source: The Conversation – USA (2) – By Ethan Murray, Postdoctoral Researcher, NOAA Hurricane Research Division, University of Colorado Boulder

High-level steering winds sent Hurricane Melissa on a sharp turn directly into Jamaica on Oct. 28, 2025. Cooperative Institute for Meteorological Satellite Studies/University of Wisconsin-Madison

Hurricane Melissa grew into one of the most powerful Atlantic tropical cyclones in recorded history on Oct. 28, 2025, hitting western Jamaica with 185 mph sustained winds. The Category 5 hurricane blew roofs off buildings and knocked down power lines, its torrential rainfall generated mudslides and flash flooding, and its storm surge inundated coastal areas.

Melissa had been wobbling south of the island for days, quickly gaining strength over the hot Caribbean Sea, before taking a sharp turn to the northeast that morning.

An animation of the hurricane between central America and Jamaica.
Hurricane Melissa, shown on Oct. 27, 2025, grew into an extremely powerful 185-mph hurricane just south of Jamaica before turning sharply northeastward and crashing into the island.
NOAA

As a hurricane researcher, I work with colleagues at NOAA’s Atlantic Oceanographic and Meteorological Laboratory to improve predictions of hurricanes’ tracks and strengths. Accurate forecasts of Melissa’s turn to the northeast gave many people across Jamaica, Cuba and the eastern Bahamas extra time to evacuate to safer areas before the hurricane headed their way.

Throughout 2025, most hurricanes similarly veered off toward the open Atlantic, sparing the U.S. mainland. To understand the forces that shaped these storms and their paths, let’s take a closer look at Melissa and the 2025 hurricane season.

The origins of Atlantic tropical cyclones

Before they evolve into powerful hurricanes, storm systems start out as jumbled clusters of clouds over the open ocean.

Many of 2025’s Atlantic tropical cyclones began life far from the U.S. coastline in the warm waters west of Africa, near the Cape Verde islands. These Cape Verde hurricanes are consistently blown toward the United States, especially during peak hurricane season.

A map shows 13 storms, most starting far from the U.S. and curving off into the open Atlantic.
Storm tracks for the 2025 Atlantic tropical cyclone season, through Oct. 26. Hurricane Melissa’s meandering track is seen far to the south, just off the coast of Jamaica.
Sandy14156/Wikimedia Commons, using NOAA data

The driving force steering these storms is a hot, semi-permanent high-pressure air mass often found spinning above the Atlantic Ocean known as the Bermuda high or Azores high.

When this high-pressure system, or subtropical ridge, is positioned farther east, closer to the Azores islands, its strong, clockwise-rotating winds typically curve tropical cyclones briskly out to sea toward their demise in the cold North Atlantic. When the high-pressure ridge is closer to the U.S. and centered over Bermuda, it can send storms crashing into the U.S. coast.

How the Bermuda high-pressure system can steer tropical cyclones. Many of 2025’s storms were steered out to sea by the high-pressure system being positioned further to the East.

Because that high-pressure system was positioned further east in summer and fall 2025, many of the season’s strongest storms, such as hurricanes Erin, Gabrielle and Humberto, swung east of the U.S. mainland. Combined with an active jet stream above the Southeast U.S., most tropical cyclones were steered away from the Atlantic coast.

The clouds that eventually became Hurricane Melissa traveled farther to the south, avoiding the Bermuda high and making their way into the Caribbean Sea.

Tropical cyclones’ high-stakes balancing act

After a tropical cyclone forms, its path is guided by the movement of air surrounding it, known as atmospheric steering currents. These steering currents direct the forward movement of storms in the Atlantic at speeds ranging from a sluggish 1 mph to a blistering 70 mph or more.

Hurricane Melissa’s meandering track was determined by these steering currents. At first, the system was caught between winds from high-pressure systems to its northwest and southeast. This setup trapped the storm over the warm Caribbean Sea for days, just to the south of Jamaica.

An animation shows the direction of steering winds over four days
Charts of high-level steering currents over five days, Oct. 23-27, 2025, show the influences that kept Hurricane Melissa (red symbol) in place for several days. The strong curving winds in red are the jet stream, which would help steer Melissa northeastward toward the open Atlantic.
Cooperative Institute for Meteorological Satellite Studies/University of Wisconsin-Madison, CC BY-ND

As a tropical cyclone is steered by outside forces, its internal makeup also constantly evolves, changing how the storm interacts with its steering currents.

When Hurricane Melissa was a weak, lopsided system, it didn’t receive much of a push from its upper-level environment. But as the hurricane gained strength from the very warm ocean below, it grew taller. Like a skyscraper reaching high into the air, major hurricanes like Melissa have towering thunderstorms and feel more of a push from upper-level winds than weaker storms do.

Melissa’s center also became aligned vertically, allowing the tropical cyclone to rapidly intensify from 70 mph to a staggering 140 mph sustained winds in 24 hours.

A map shows warm water temperatures south of Jamaica, where Hurricane Melissa passed through.
Hurricanes need ocean temperatures above about 80 degrees Fahrenheit (27 degrees Celsius) for a storm to gain enough energy to strengthen. The water south of Jamaica was much warmer than that while Hurricane Melissa meandered there, quickly gaining strength on Oct. 26, 2025.
NOAA Coral Reef Watch

Eventually, the precarious atmospheric balancing act holding Melissa in place collapsed. A ripple in the jet stream known as an atmospheric trough steered the hurricane to the northeast and into the Jamaican coast.

Melissa’s snail’s pace of about 2 mph was rare but not unheard of. Slow storms like Melissa are more common in October, as steering currents are often very weak or pushing in opposite directions, which can trap a tropical cyclone in place. Similar steering currents affected Hurricane Matthew in 2016.

Tragically, stalled tropical cyclones often bring prolonged rainfall, winds, flash flooding and storm surge with them. The wind and downpours can be extreme for mountain communities, as their high topography enhances local rainfall that can trigger mudslides and flooding, as Jamaica saw from Melissa.

Improving storm track forecasting

Meteorologists generally understand how atmospheric steering currents guide tropical cyclones, yet forecasting these wind patterns remains a challenge. Depending on the atmospheric setup, certain hurricanes can be harder to forecast than others, as changes to steering currents can be subtle.

New approaches to hurricane track forecasting include using machine learning models, such as Google DeepMind, which outperformed many traditional models in forecasting storm tracks this hurricane season. Rather than solving a complex set of equations to make a forecast, DeepMind looks at statistics of previous hurricane tracks to infer the path of a current storm.

NOAA Hurricane Hunter reconnaissance data can also accelerate progress in predicting tropical cyclone paths. Recent tests show how accounting for specific measurements from within a hurricane can improve forecasts. Certain flight patterns that Hurricane Hunters and drones fly through strong hurricanes can also improve predictions of a storm’s path.

Scientists and engineers aim to further improve hurricane track and intensity forecasts through research into storm behavior and improving hurricane models to better inform the public when danger is on the way.

The Conversation

Ethan Murray receives funding from the Office of Naval Research and National Science Foundation. He works for The University of Miami and NOAA Atlantic Oceanographic and Meteorological Laboratory.

ref. Hurricane Melissa turned sharply to devastate Jamaica − how forecasters knew where it was headed – https://theconversation.com/hurricane-melissa-turned-sharply-to-devastate-jamaica-how-forecasters-knew-where-it-was-headed-268183

Agricultural drones are taking off globally, saving farmers time and money

Source: The Conversation – USA (2) – By Ben Belton, Professor of International Development, Michigan State University

A farmer in China operates a drone to spray fertilizer on fields. Wang Huabin/VCG via Getty Images

Drones have become integrated into everyday life over the past decade – in sectors as diverse as entertainment, health care and construction. They have also begun to transform the way people grow food.

In a new study published in the journal Science, we show that use of agricultural drones has spread extremely rapidly around the world. In our research as social scientists studying agriculture and rural development, we set out to document where agricultural drones have taken off around the world, what they are doing, and why they have traveled so far so fast. We also explored what these changes mean for farmers, the environment, the public and governments.

From toys to farm tools

Just a few years ago, agricultural drones were expensive, small and difficult to use, limiting their appeal to farmers. In contrast, today’s models can be flown immediately after purchase and carry loads weighing up to 220 pounds (100 kg) – the weight of two sacks of fertilizer.

Their prices vary from country to country due to taxes, tariffs and shipping costs. In the U.S., a drone owner can expect to spend US$20,000 to $30,000 for the same equipment that a farmer in China could buy for less than $10,000. However, most farmers hire service providers, small businesses that supply drones and pilots for a fee, making them easy and relatively affordable to use.

A promotional video for the DJI Agras T100 agricultural drone, which can carry a maximum load of 220 pounds (100 kg).

Agricultural drones are now akin to flying tractors – multifunctional machines that can perform numerous tasks using different hardware attachments. Common uses for drones on farms include spraying crops, spreading fertilizer, sowing seeds, transporting produce, dispensing fish feeds, painting greenhouses, monitoring livestock locations and well-being, mapping field topography and drainage, and measuring crop health. This versatility makes drones valuable for growing numerous crops, on farms of all sizes.

Technological leapfrogging

We estimated the number of agricultural drones operating in some of the world’s leading agricultural countries by scouring online news and trade publications in many different languages. This effort revealed where agricultural drones have already taken off around the world.

Historically, most agricultural technology – tractors, for example – has spread from high-income countries to middle- and then lower-income ones over the course of many decades. Drones partially reversed and dramatically accelerated this pattern, diffusing first from East Asia to Southeast Asia, then to Latin America, and finally to North America and Europe. Their use in higher-income regions is more limited but is accelerating rapidly in the U.S.

China leads the world in agricultural drone manufacturing and adoption. In 2016, a Chinese company introduced the first agriculture-specific quadcopter model. There are now more than 250,000 agricultural drones reported to be in use there. Other middle-income countries have also been enthusiastic adopters. For instance, drones were used on 30% of Thailand’s farmland in 2023, up from almost none in 2019, mainly by spraying pesticides and spreading fertilizers.

In the U.S., the number of agricultural drones registered with the Federal Aviation Administration leaped from about 1,000 in January 2024 to around 5,500 in mid-2025. Industry reports suggest those numbers substantially underreport U.S. drone use because some owners seek to avoid the complex registration process. Agricultural drones in the U.S. are used mainly for spraying crops such as corn and soy, especially in areas that are difficult to reach with tractors or crop-dusting aircraft.

Safer, but not risk-free

In countries such as China, Thailand and Vietnam, millions of smallholder farmers have upgraded from the dangerous and tiring job of applying agrochemicals by hand with backpack sprayers to using some of the most cutting-edge technology in the world, often using the same models that are popular in the U.S.

Shifting from applying chemicals with backpack sprayers to drones substantially reduces the risk of direct exposure to toxins for farmers and farmworkers.

However, because drones usually spray from a height of at least 6 feet (2 meters), if used improperly, they can spread droplets containing pesticides or herbicides to neighboring farms, waterways or bystanders. That can damage crops and endanger people and nature.

Saving labor or displacing it?

Drones save farmers time and money. They reduce the need for smallholders – people who farm less than 5 acres (2 hectares), which account for 85% of farms globally – to do dangerous and tiring manual spraying and spreading work on their own farms. They also remove the need to hire workers to do the same.

By eliminating some of the last remaining physically demanding work in farming, drones may also help make agriculture more attractive to rural youth, who are often disillusioned with the drudgery of traditional farming. In addition, drones create new skilled employment opportunities in rural areas for pilots, many of whom are young people.

On the downside, using drones could displace workers who currently earn a living from crop spraying. For instance, according to one estimate from China, drones can cover between 10 and 25 acres (4 to 10 hectares) of farmland per hour when spraying pesticides. That is equivalent to the effort of between 30 and 100 workers spraying manually. Governments may need to find ways to help displaced workers find new jobs.

A person pours liquid into a tank attached to a drone, while standing near a large field.
An agricultural worker fills a drone tank with pesticide spray at a farm in Brazil.
Mateus Bonomi/Anadolu Agency via Getty Images

Sky’s the limit

Drones spray and spread fertilizers and seeds evenly and efficiently, so that less is wasted. They may also reduce damage to crops in the field and consume less energy than large farm machines such as tractors.

In combination, these factors may increase the amount of food that can be produced on each acre of land, while reducing the amount of resources needed to do so. This outcome is a holy grail for agricultural scientists, who refer to it as “sustainable intensification.”

However, much of the evidence so far on yield gains from drone-assisted farming is anecdotal, or based on small studies or industry reports.

The drone revolution is reshaping farming faster than almost any technology before it. In just five years, millions of farmers around the world have embraced drones. Early signs point to big benefits: greater efficiency, safer working conditions and improved rural livelihoods. But the full picture isn’t clear yet.

The Conversation

The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.

ref. Agricultural drones are taking off globally, saving farmers time and money – https://theconversation.com/agricultural-drones-are-taking-off-globally-saving-farmers-time-and-money-265154

SNAP benefit freeze will leave millions nationwide struggling to pay for food – including 472,711 people in Philadelphia

Source: The Conversation – USA (2) – By Félice Lê-Scherban, Associate Professor of Epidemiology, Drexel University

Currently, SNAP benefits average just over $6 per person per day. Catherine McQueen/Moment Collection via Getty Images

The Supplemental Nutrition Assistance Program, or SNAP, is the largest, most effective tool the U.S. has to reduce food insecurity. As of late 2025, it helps more than 42 million people – including 2 million Pennsylvanians and nearly half a million Philadelphians – buy groceries.

But starting Nov. 1, 2025, Pennsylvania will stop distributing SNAP benefits due to the federal government shutdown, which began Oct. 1.

Félice Lê-Scherban, a public health researcher and associate professor of epidemiology at Drexel University, studies food insecurity among low-income young children and their families in Philadelphia. The Conversation U.S. asked her about the program and what impact its suspension would have – especially in Philadelphia.

What is SNAP?

SNAP benefits – sometimes called food stamps – are provided through a federally funded program administered by the states. The amount of help received depends on a family’s income and the number and ages of the people in the household. Currently, benefits average just over US$6 per person per day. In Pennsylvania, the monthly benefits are loaded onto participants’ electronic benefits transfer cards, or EBT cards, during the first 10 business days of each month.

Researchers have found that SNAP benefits reduce poverty and food insecurity – a term for when people don’t have consistent access to enough food for all household members to lead active, healthy lives. It also contributes to healthy growth and development in childhood, and lower risks for obesity, diabetes, hypertension and poor mental health later in life.

Studies have also found that when eligible families lose access to SNAP benefits, even temporarily, they are more likely to get sick, and their children are at a greater risk of developmental delays.

Additionally, losing SNAP and similar benefits can strain household finances, forcing low-income people to choose between skipping meals or forgoing other basic needs like rent, utilities and prescription drugs.

How is the government shutdown affecting SNAP benefits in Pennsylvania?

The Department of Agriculture notified SNAP state agency directors in October that it would stop funding the program should the shutdown continue past Nov. 1. The federal agency directed all states to withhold November benefits until further notice.

The USDA is taking this step even though it has more than $5 billion in its coffers, which could fund approximately two-thirds of what the nation spends each month on SNAP benefits.

In the more than 60-year history of SNAP and the programs that preceded it, the USDA has never before refused to spend contingency funds to disburse monthly benefits. During previous shutdowns, including the 35 days in 2018-2019, the federal government used the department’s contingency funds to ensure SNAP wasn’t interrupted.

On Oct. 17, the Pennsylvania Department of Human Services issued a statement to the more than 2 million Pennsylvanians participating in SNAP. It warned them that they won’t receive their November benefits or any benefits thereafter until the USDA releases funds again.

Pennsylvania is also among 17 states that have suspended approving new SNAP applications until the government reopens, leaving hundreds, if not thousands, of food-insecure families in a prolonged state of hardship.

This disruption is likely to rattle the broader economy. About 12% of U.S. grocery sales are made with SNAP benefits, and over 9,800 supermarkets and other Pennsylvania retailers accept them.

What does this mean for people in Philadelphia?

There are over 470,000 SNAP recipients in Philadelphia – 3 in 10 Philadelphians – who will not receive these benefits until the government shutdown ends.

In the meantime, state agencies are urging people who get SNAP benefits to visit food banks, food pantries and soup kitchens, which are run by nonprofits and not the government. Unfortunately, it seems unlikely that those organizations will be able to keep up. For every meal nonprofits provide, SNAP provides nine.

Additionally, the Pennsylvania state budget impasse – the Commonwealth has been without a budget for nearly four months – has already affected other state-run programs that food banks in Philadelphia rely on.

This is particularly troubling because even when receiving their full benefit, most people who are enrolled in SNAP across the country say that they frequently struggle to afford a healthy diet.

Low-income parents and guardians in Philadelphia, according to research I’ve conducted and studies by my colleagues, say they strain to stretch their dollars to feed their children amid rising food prices, and sometimes skip meals or delay paying bills when the benefit runs out before the end of the month.

A robust body of evidence has demonstrated the serious mental and physical harm that food insecurity – even for short periods – causes across the lifespan. It can lead to billions of dollars of avoidable costs due to health care and educational needs, and lost productivity.

How this disruption of SNAP and other nutrition programs increases food insecurity will be hard to measure. The Trump administration has canceled the USDA’s long-standing annual report on food security.

What can state and federal leaders do to fund the program?

The federal government and Pennsylvania lawmakers have options to at least restore some SNAP benefits in the state while the shutdown continues.

The USDA can reverse its earlier ruling and disburse its more than $5 billion in emergency funds and issue guidance that states should continue to accept and process new SNAP applications. This would help states provide at least partial benefits to their residents enrolled in SNAP and ensure that new applicants get all the benefits they’re eligible for.

The federal government can allocate discretionary and reserve funds to SNAP for the duration of the shutdown so benefits are not interrupted. The government did this with Supplemental Nutrition for Women, Infants, and Children, or WIC benefits, as well as farm aid earlier this month.

The government of Pennsylvania and other state governments can pick up the costs of the program for November with their own state budget stabilization funds, also known as “rainy day funds.” Pennsylvania’s rainy day fund holds more than $7 billion – well above what’s needed to cover its SNAP benefits for November. Some states have already committed to doing this.

Read more of our stories about Philadelphia and Pennsylvania.

The Conversation

Félice Lê-Scherban is the Philadelphia site principal investigator of Children’s HealthWatch. She receives funding from the National Institutes of Health. The content is solely the responsibility of the authors and does not represent the official views of the National Institutes of Health.

ref. SNAP benefit freeze will leave millions nationwide struggling to pay for food – including 472,711 people in Philadelphia – https://theconversation.com/snap-benefit-freeze-will-leave-millions-nationwide-struggling-to-pay-for-food-including-472-711-people-in-philadelphia-268337

How Hershey’s chocolate survived an attack from Mars − and adopted a business strategy alien to its founder

Source: The Conversation – USA (2) – By John Haddad, Professor of American Studies, Penn State

Hershey’s chocolates are made in Hershey, Pa., a town once considered an industrial utopia.
Gary Burke/Moment Collection via Getty Images

Walk into any grocery store to stock up for Halloween and you will discover that, for chocolate treats, you have two basic choices:

Will it be Mars or Hershey?

I often buy both, but that is beside the point. The point is that the two giants compete for market share, but both enjoy robust sales. In other words, a relatively stable duopoly defines the U.S. chocolate candy market.

But it wasn’t always like this.

Before the 1960s, the Hershey Chocolate Corp. reigned supreme as the undisputed chocolate king. It was in that decade that Mars went for Hershey’s jugular. Hershey Chocolate’s response brought lasting change – to its candy business, the local community and Hershey Park, its chocolate-themed amusement park.

As a professor of American studies at Penn State Harrisburg who has recently published a book on Hershey Park, I am astounded by how these changes continue to reverberate today.

Milton Hershey’s paternalistic capitalism

Before the 1960s, change was not a word one associated with either the town of Hershey, Pennsylvania, or its famous chocolate company. Better words would be “stability” and “productivity” – and this was by the founder’s design.

Black and white portrait of man with mustache wearing three-piece suit
Milton Hershey founded Hershey Chocolate and built up the town of Hershey, Pa., for his employees.
Bettman/Bettman Collection via Getty Images

When Milton Hershey entered the confection industry in the 1880s, violent clashes between corporations and labor roiled American society. Hershey imagined a better way: paternalistic capitalism.

In the early 1900s, he built a chocolate factory and planned community out in the farms and pastures of central Pennsylvania. Instead of offering men and women wage-earning jobs and nothing else, he took care of his workers. They owned nice homes and benefited from a generous array of free or subsidized services and amenities: snow removal, garbage collection, trolley lines, good schools, a junior college, zoo, museum, sports arena, library, community center and theater.

They even had their own amusement park.

But this was a reciprocal relationship. In return, employees were expected to work hard, exhibit loyalty, practice clean living and refrain from labor agitation. With the exception of a strike during the Great Depression, the company and town lived in harmony. Milton Hershey called the place an “industrial utopia,” and residents largely agreed.

“Moving to Hershey,” one recalled, “was like moving to paradise.”

Harmony also defined Hershey’s relations with Mars. At the time, Hershey produced only solid chocolate – think of Hershey bars and Kisses. In contrast, Frank Mars’ company specialized in chocolate-covered snacks, suches Snickers or Milky Way, in which milk chocolate is poured over nuts, caramel or nougat.

Where did that chocolate coating come from?

Hershey, of course.

In those days, Mars was a client, not a rival. Without competition, Hershey enjoyed the luxury of not having to worry about market share. Amazingly, the company did not advertise under Milton Hershey and continued this policy after his death in 1945.

Hershey in crisis

Everything changed in 1964. The catalyst for change was Forrest Mars, the founder’s hard-charging son who was a true disrupter.

After seizing control of his father’s company, Forrest Mars set his sights on dethroning Hershey. As reporter and author Joël Glenn Brenner explains, the younger Mars boldly terminated the partnership with Hershey while ordering his engineers to learn how to make Hershey-caliber chocolate in six months. He also modernized the factory and ordered a surge in advertising, all to wrestle market share away from Hershey, the “sleeping giant.”

Sepia-toned photograph of woman working large machine in a factory
The production line at the Hershey chocolate factory in 1969.
Peter Simins/Pix/Michael Ochs Archives via Getty Images

The strategy worked. By the decade’s end, Mars had caught Hershey in terms of market share and pushed the chocolate colossus into crisis.

The good news for Hershey was that it had at the helm two forward-looking leaders, Harold Mohler and Bill Dearden. Though standard practice had always been to hire locally and from within, Mohler and Dearden recruited outsiders with MBAs from Harvard and Wharton to initiate sweeping reforms aimed at modernizing its archaic business practices.

The company opened a public relations office, conducted market research, installed IBM mainframe computers to crunch numbers, retrained its sales force and created a marketing department. Many employees, a new executive joked, were so behind the times that they had thought marketing was “what their wives did … with a shopping cart.”

This effort culminated with the release of the company’s first TV commercials starting in 1969. The sleeping giant had awoken.

An iconic TV commercial for Reese’s, which was purchased by Hershey in the early 1960s.

The company’s next move altered the town forever. As a cost-cutting measure, it terminated the free services and amenities at the core of Milton Hershey’s vision. The era of paternalism was over.

As the company liquidated assets, residents howled in protest.

“It was a very traumatic time for the community,” one executive recalled.

For residents, the only consolation was that at least the amusement park would stay the same.

Or would it?

By the late 1960s, Hershey Park had degenerated into what one executive called “an iron park with a bunch of clanging rides.” Leadership faced a pivotal decision: renovate the park or close it forever.

The park had such a “rich heritage,” one executive recalled, that to shutter it would “put a stamp of negative feeling within the community.”

The company elected to renovate.

Hersheypark’s transformation

But how to renovate was another matter.

In the 1960s and 1970s, owners of traditional amusement parks had to think twice before investing in their properties. That was because Disneyland, the nation’s first theme park, had caused a sensation when it debuted in 1955. Its incredible popularity, and the opening of the more spectacular Disney World in 1971, placed pressure on old-fashioned amusement parks everywhere.

After commissioning a feasibility study, Hershey officials decided to gamble: Instead of fixing up the old amusement park, they would convert it into a Disney-style theme park. To pay for the massive overhaul, they redirected capital earned from the dismantling of Milton Hershey’s paternalism. Reborn as “Hersheypark” in 1973, the ever-growing complex has become a mecca for chocolate lovers and thrill-ride seekers from across the Northeast.

Pharmacy shelves lined with Halloween candy
Hershey and Mars products are ubiquitous in trick-or-treat hauls.
Lindsey Nicholson/UCG/Universal Images Group via Getty Images

Every year, Halloween reminds me of this remarkable transformation. The stores become stocked with Hershey brands, and the theme park comes alive with its spooky “Dark Nights” entertainment.

In the past, workers at the Hershey plant would joke that they had “chocolate syrup in their veins.” These days, they clearly have innovation too, and that creative spirit is largely due to Forrest Mars. By giving Hershey the jolt it needed, he shook up the status quo and changed the chocolate company, town and park forever.

Read more of our stories about Philadelphia and Pennsylvania.

The Conversation

John Haddad does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

ref. How Hershey’s chocolate survived an attack from Mars − and adopted a business strategy alien to its founder – https://theconversation.com/how-hersheys-chocolate-survived-an-attack-from-mars-and-adopted-a-business-strategy-alien-to-its-founder-267722

CDC’s ability to prevent injuries like drowning, traumatic brain injury and falls is severely compromised by Trump cuts

Source: The Conversation – USA (3) – By Greta Massetti, Professor of Population Health Sciences, Georgia State University

Motor vehicle crashes kill more than 40,000 people in the U.S. every year. Cavan Images/Getty Images

Much has been written about the unprecedented impact that the second Trump administration has had on the Centers for Disease Control and Prevention, from massive job cuts and entire programs being wiped out to leadership shake-ups and the undermining of science. But behind every headline, countless stories have gone untold about the real-world impacts that these changes will have on everyday people.

I’m a public health expert who spent 18 years as a scientist at the CDC. I see the systematic dismantling of the agency as a significant risk to the country’s ability to keep Americans safe and give medical professionals the data needed to keep them that way.

Most of my time at the CDC was spent in the National Center for Injury Prevention and Control, one of the hardest hit of the agency’s programs. The center has lost more than half of its staff through layoffs alone and as many as two-thirds when other reductions are accounted for.

Injuries affect people of all ages

More Americans die from injuries and violence in the first half of life than from any other cause, including cancer, HIV or the flu. These include suicide, overdose, homicide and unintentional injuries.

The mass layoffs that the Trump administration has carried out in 2025 struck at the core of the injury center’s programs on violence prevention and eliminated the work being done to prevent unintentional injuries like drowning, traumatic brain injuries, falls in older adults and motor vehicle crashes.

As of late October, only the CDC programs focused on overdose prevention, suicide and the National Violent Deaths Reporting System remain in the injury center.

Unintentional injuries cost the U.S. $4.5 trillion annually and directly affect workforce and community stability. This includes $323 billion in medical care as well as costs from lost work productivity.

Every unintentional injury represents a preventable tragedy — a fall, a crash, a drowning — that alters the course of a life. Like me, many Americans are eager for information about keeping their loved ones safe.

Making youth sports safer

One critical injury center program that was cut from CDC in April is its HEADS UP program, which is aimed at preventing and reducing head trauma. The program includes online courses for youth coaches, health care providers, schools, athletic trainers and others that provide information about how to protect kids from concussions and other serious brain injuries.

Traumatic brain injury affects more than 230,000 people in the U.S. A traumatic brain injury is a disruption in the normal function of the brain that can be caused by a bump, blow or jolt to the head, or a penetrating head injury.

People of all ages are at risk of experiencing a traumatic brain injury. For young people, concussions from contact sports account for 45% of all emergency department visits for a traumatic brain injury each year.

Older female doctor in a lab coat examines a young boy who is holding an ice pack to his head.
Concussions in youth contact sports are the cause of nearly half of all traumatic brain injury emergency room visits annually.
SDI Productions/E+ via Getty Images

HEADS UP specifically aims to create education and awareness around youth traumatic brain injuries. Currently, 45 states recommend or require HEADS UP materials or training to be used by sports programs and schools in their concussion prevention laws.

The elimination of the CDC’s injury prevention team will undoubtedly result in a loss of progress in preventing these avoidable injuries. It will also leave gaps in states whose coaches are unable to fulfill their training requirements.

Preventing drownings

Drowning is the No. 1 cause of death for children ages 1 to 4, and fatal and nonfatal drownings cost the U.S. $56 billion each year. Drowning deaths have been increasing steadily among young children since 2019.

When CDC’s drowning prevention team was eliminated, the injury center was the only federal public health department focused on preventing drowning.

It did so on a shoestring: With only $2 million annually appropriated by Congress, the team stretched every penny to maximize its impact on public health by strengthening data systems and supporting communities in getting access to lifesaving swimming and water safety skills.

Every drowning death of a young child is a preventable, costly tragedy.

The critical work of the CDC’s drowning prevention team brought critical lifesaving work to communities across America by providing water safety skills and training to more than 22,000 children in 2024 alone. At a cost of just $110 per child, teaching a child to swim reduces their risk of drowning by up to 88%.

Illustration of a hand reaching out of the water for help, with a 'no swimming' sign in the background.
Drowning deaths have been rising in young children.
fadfebrian/iStock via Getty Images Plus

Keeping older adults safe from falls

Injuries also affect older adults in significant ways.

Falls are the leading cause of injury and death among adults age 65 and over, and 1 of 4 older adults falls each year. Falls result in hospitalizations, hip fractures and traumatic brain injuries, which can be debilitating and deadly for older adults.

A CDC program known as STEADI – short for Stopping Early Accidents, Deaths and Injuries – provides educational materials to make preventing falls a routine part of clinical care that doctors provide. Staff cuts resulted in the elimination of STEADI.

In the U.S. $2 out of every $3 of the $80 billion spent in medical costs on falls are paid by Medicare, representing 9% of the total Medicare spending on older adults.

Strategies aimed at reducing falls in older adults are key to lowering Medicare spending, showing how the critical work of the CDC is essential to reducing health care costs to individuals and taxpayers.

A caregiver helps support an elderly woman as she braces herself against two walls.
About 9% of Medicare spending in older adults stems from falls.
sasirin pamai/iStock via Getty Images Plus

Safer roads for drivers and pedestrians

In the U.S., motor vehicle crashes are a leading cause of death, killing more than 100 people every day and over 40,000 people each year. In 2023, deaths from road crashes resulted in an estimated $457 billion in medical costs and expenses.

Experts at CDC’s injury center developed tools for helping to better track and monitor motor vehicle crash injuries. This work made it possible for states to look at trends in transportation-related injuries within hours instead of waiting for the previous two- to three-year lag in data.

Before this program was eliminated by the Trump administration, CDC’s experts created resources for parents of teen drivers like me to keep their teens safe on the road. They also shared information to improve the safety of child passengers and older adult drivers.

Turning complex data into usable information

When health care providers and others face questions about keeping children and adults safe, they have long turned to the CDC to translate complex information into practical, actionable advice.

For instance, CDC’s clinical guidance helped improve diagnosis of mild traumatic brain injuries in children and teens and has guided doctors in emergency rooms and clinics to provide consistent, high-quality care to their patients. CDC experts also provided data on emergency department visits due to drowning injuries and practical resources for doctors and pharmacists to identify patients at risk of falls.

As a public health expert, I see the deep cuts to CDC’s injury prevention programs as serious threats to public health broadly. As a mother, sister, daughter and neighbor, I worry that my loved ones and their doctors will not have the information and resources they need to stay healthy and injury-free.

The Conversation

Greta Massetti does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

ref. CDC’s ability to prevent injuries like drowning, traumatic brain injury and falls is severely compromised by Trump cuts – https://theconversation.com/cdcs-ability-to-prevent-injuries-like-drowning-traumatic-brain-injury-and-falls-is-severely-compromised-by-trump-cuts-267531

Washington state settles controversy over child abuse law that tested the limits of ‘priest-penitent’ privilege

Source: The Conversation – USA (3) – By Ann M Murphy, Professor of Law, Gonzaga University

Under church law, Catholic priests are forbidden from breaking the ‘seal of confession.’ Miguel Sotomayor/Moment via Getty Images

For months, a Washington state bill generated controversy over two critical interests: protecting children from abuse and protecting the freedom of religion.

Signed by the governor in May 2025, SB 5375 designated clergy as mandatory reporters, requiring them to report child sexual abuse, physical abuse and neglect – even if they learned of the abuse during a confidential sacred rite.

Some faiths, including the Catholic Church and Eastern Orthodox churches, prohibit clergy from revealing information learned through a confession or sacrament. In the Catholic Church, there are no exceptions – and the penalty for disclosure is excommunication.

In mid-October, however, Washington state announced it would not enforce the mandatory reporting requirement for information learned during confidential rites. On Oct. 14, 2025, a federal court approved the state’s agreements with groups of Catholic and Orthodox clergy who had sued to block that part of the law, arguing it violated their religious freedom. The U.S. Department of Justice had also intervened, claiming the law discriminates against Catholics.

Reporting laws can be complicated by what is known as “legal privilege”: the rights granted to certain people, such as spouses or lawyers of suspects, to keep confidentiality by refusing to cooperate with an investigation. As a law professor, I have written often about clergy privilege, as well as other legal privileges. The attorney-client privilege is the oldest, dating to the 16th century, but the “priest-penitent privilege” has a long history as well.

US landscape

It was not until the 1960s that U.S. states began using mandatory reporting laws to protect children from abuse. Some laws apply to any person who learns of abuse. Others specifically mention categories of people, such as nurses and teachers.

A teacher in a striped sweater crouches as she speaks with a girl, seated on a bench, who wears a red sweater and black skirt.
People designated as mandatory reporters must share information about suspected abuse with authorities.
10’000 Hours/Digital Vision via Getty Images

Today, a majority of states require religious personnel to report suspected child abuse to law enforcement. However, most have an exemption for clergy who learn about abuse during a rite or prayer.

Several states do not have such an exemption. However, the text of their laws do not specifically mention religious leaders, which may be why they did not provoke as much controversy as Washington’s bill. For example, North Carolina requires “any person” who suspects abuse to report it.

Before SB 5375, Washington excluded clergy entirely from mandatory reporting requirements that apply to many other professionals, such as medical professionals, therapists and school personnel.

Now, under the October agreements filed in court, clergy are included in the list of mandatory reporters, but they are not required to report anything they learn about during a confession or sacred rite. The Vatican also instructs bishops to report abuse by priests, deacons and prelates to civil authorities.

2 key issues

There are two issues at play in clergy reporting laws.

One is whether clergy must take the initiative to report abuse that they learn about through their professional duties.

The other is whether clergy members have an evidentiary privilege – that is, the right to refuse to testify in court, or to answer questions during investigations, in order to protect their parishioners’ privacy.

Although mandatory reporting and clergy privilege are separate issues, both may apply in particular cases.

In 2021, for example, three children sued officials in the Church of Jesus Christ of Latter-day Saints for its failure to report their father’s abuse to authorities. The children ultimately lost their negligence case against the church because, although Arizona had a mandatory reporting statute, it also has an exception for information learned through confession or other confidential communication.

Washington state recognizes a “priest-penitent privilege.” Therefore, a priest who hears about abuse during confession may refuse to divulge what he’s heard if called into a legal proceeding. Originally, however, Washington’s new law would have required clergy to make an initial report to law enforcement, breaking the “seal of confession” – but they could have refused to cooperate with the resulting investigation.

Now, under the stipulations, clergy do not need to make an initial report if they learn of abuse through a confidential rite such as confession. In contrast, other individuals who have a legal privilege under Washington state law – for example, a spousal privilege or a physician privilege – must still report in the event of child abuse.

An older man in a suit holds his head in his hand as he sits at a table with a younger man taking notes.
Attorney-client privilege is intended to protect someone’s right to accurate legal advice.
Nitat Termmee/Moment via Getty Images

History of privilege

Under English law, the origin of most early American law, the “minister’s privilege,” as it was called, was not recognized after the Protestant Reformation of the 16th century.

In the U.S., a clergy privilege was first recognized in 1813. In People v. Philips, a Catholic priest in New York was summoned to testify about the return of some stolen jewelry – which apparently he required a parishioner to do, after hearing about the theft during confession. The court reasoned that requiring the priest to testify about what the parishioner revealed would violate his religious liberty.

Four years later, in another New York case, People v. Smith, the court found that a minister did not have grounds for a privilege because, as a Protestant, he was not bound by the same “seal of confession” rules as Catholic priests. In 1828, the New York Legislature passed a statute broadening the privilege to include all ministers and priests.

The general theory of all testimonial privileges is that it protects confidential communications that society wishes to foster. Attorney-client privilege, for example, exists so that the client may receive the best advice. The benefit of a privilege – the right to legal representation or the right to the free exercise of religion – is considered more important than society’s quest for truth.

There is a legal maxim that “the public has a right to every man’s evidence.” Privileges are an exception to this rule and thus are narrowly applied by courts.

In the United States, 1 in 4 children experience child abuse or neglect. If society believes that information about child abuse, even if disclosed during a religious rite, is more important than shielding that information, then the clergy privilege should be eliminated or weakened in such cases.

Religious freedom is a core constitutional guarantee. The question is how society should balance these two important interests.

The Conversation

Ann M Murphy does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

ref. Washington state settles controversy over child abuse law that tested the limits of ‘priest-penitent’ privilege – https://theconversation.com/washington-state-settles-controversy-over-child-abuse-law-that-tested-the-limits-of-priest-penitent-privilege-264002

Rediscovery of African American burial grounds provides long-overdue opportunities for collective healing

Source: The Conversation – USA (3) – By Joanna Gilmore, Adjunct Professor in Museum Studies and Bioarchaeology, College of Charleston

In the course of construction work in 2013, the remains of 36 individuals of African descent were uncovered in the heart of downtown Charleston, South Carolina. They had lain hidden for some 200 years in an unmarked 18th-century burial ground.

For more than two centuries, such burial grounds, especially those in the former American slave states, have often been erased or obscured – paved over by parking lots, built upon by highways or private development, or simply left unknown and untended. In recent years, descendant communities in places such as Bethesda, Maryland, Richmond, Virginia, St. Petersburg, Florida, and Sugarland, Texas, have called for greater recognition and respect for these long-neglected sites.

As a public archaeologist and educator who has spent over a decade working in Charleston, South Carolina, I co-direct the Anson Street African Burial Ground project – the community-led effort to honor and respectfully lay to rest the 36 African ancestors whose remains were uncovered in 2013.

This Charleston project reflects a growing recognition of African American burial grounds as important historical memory sites and unique sources of genealogical information. Yet there is still limited public understanding about how engaging with these places of sacred rest can promote collective healing, reconciliation and cross-cultural understanding.

An old, faded tombstone.
A tombstone bearing the name of Caezer Smith and dated 1839 is displayed on the site of a recently rediscovered African burial ground in Kingston, N.Y., in August 2024.
AP Photo/Seth Wenig

Cemeteries obscured by history

Since the British colonial period, racist laws and customs across America prevented enslaved and free people of African descent from using white burial grounds to bury their dead. On plantations, enslavers controlled where and how the enslaved were buried and whether burials could be marked or visited. In cities from Charleston to New York, segregated burial grounds, many now forgotten, were established by local authorities for indigent Black and white people.

Pushed to the margins, people of African descent maintained burial traditions and used impermanent or specific grave markers such as shells, bottles, clocks or ceramics – items that were culturally meaningful but often invisible or unimportant to white observers. As a result, many of these sites were neither recorded in historical documents nor officially recognized as burial grounds.

From the 1770s, African American churches, benevolent societies and funeral homes sought to establish cemeteries where Black communities could honor the dead with dignity. What began regionally – especially in Charleston and Philadelphia – quickly spread nationally during the 19th century across the American South and North.

In the decades after Reconstruction, and especially during the Jim Crow era, nearly 6 million African Americans moved north and west to escape racial violence and seek better opportunities – an event known as the Great Migration. This movement often severed ties between families and ancestral burial grounds in the South. As churches and burial societies lost members, many cemeteries fell into disrepair and were officially labeled “abandoned” by local authorities or developers.

In both rural and urban areas, Black burial grounds were often located on less valuable lands, sites that today are increasingly threatened by gentrification, development and the effects of climate change.

The Gullah Geechee, who descend from enslaved Africans from West Africa and still preserve unique cultural traditions in the southeastern U.S., argue these burial sites were never abandoned and that ancestors are still present. This perspective views the dead as actively connected to the living. For them, lacking formally designated cemetery space doesn’t make the sites any less sacred.

A tradition of sacred spaces

For many African Americans, especially in the South, death during slavery was seen as not merely an ending but a spiritual return — a “homegoing.”

Rooted in West African spiritual worldviews and carried through other traditions in America, the act of burial was often viewed as a release from bondage, a return to the ancestors and a step toward wholeness.

The Gullah Geechee traditions of coastal South Carolina emphasize ancestral presence, spiritual continuity and the sanctity of the land. In that worldview, with a porous boundary between the living and the dead, proper burial and remembrance are not only cultural imperatives but necessary for community well-being.

It was not until the early 1990s that recognition of rights over ancestral remains and sacred burial grounds began to find a wider audience.

Inspired by the 1990 Native American Graves Protection and Repatriation Act that recognized Indigenous rights over ancestral remains, African American communities increasingly asserted their own rights to ethical research, respectful handling and meaningful memorialization, especially during the 1991 New York African Burial Ground project, which reshaped public memory and archaeological ethics.

Discovered during construction in lower Manhattan, the 18th-century burial ground contained the remains of more than 400 enslaved and free Africans. Community advocacy led to the site’s protection, descendant-led research, ceremonial reburial and the establishment of a national memorial in 2006.

A monument plaque.
The Outdoor Memorial of the African Burial Ground National Monument in lower Manhattan is an important archaeological find of the 20th century and one of the most preeminent memorials to the struggle of Africans and African descendants.
Keith Getter/Getty Images

Since this time, across the U.S. and the Atlantic world, descendant-led ceremonies from Portsmouth, New Hampshire, to Key West, Florida, have restored dignity to ancestral remains.

Meanwhile, efforts to preserve African American burial grounds, including by national scholar organizations and federal lawmakers, continue amid political debates over how history should be remembered and taught.

What made the Anson Street project unique

In Charleston, the Anson Street African Burial Ground project stands out for the way Gullah Geechee traditions and descendant collaboration shaped every stage of the process — from scientific study to reinterment.

Launched as a community-led initiative in 2017, the team began by listening. Through regular gatherings, they invited questions about the ancestors’ lives and identities, and about their hopes for the reburial, centering Black community voices at every stage. The team combined scientific investigations of ancestry and health while also creating space for spiritual guidance, ceremony and descendant leadership. In doing so, the project became more than a study of the past; it became a communal act of repair and remembrance, reconnecting Charleston’s present communities with the ancestors whose stories had long been buried.

Over the next two years, the team wove this commitment into every aspect of its work: youth art programs, a college course on memorial design, public exhibitions, and school partnerships. One of the most moving moments came from conversations with schoolchildren, who decided that the ancestors should be given names before they were reburied.

That naming ceremony took place in April 2019. The names were conferred by Natalie Washington-Weik, a Yorùbá-Orisa Ọ̀ṣun priestess, a spiritual leader in a West African tradition and an African historian. She described the ritual as an “important step forward in reclaiming the humanity of the deceased people who were most likely forced to travel across the Atlantic Ocean under the terror of other humans – who saw them merely as animals.”

The ancestors were finally reinterred in a powerful public ceremony that reflected their ancestries and West-Central African spiritual traditions.

When pain is acknowledged, healing can occur

The 2019 naming and reinterment ceremonies were not simply commemorations; they were rituals of remembrance and healing.

Construction for a permanent memorial at the Anson Street site, designed by artist Stephen L. Hayes Jr., has now begun. At its center is a basin fabricated with sacred soil collected from 36 African-descended burial grounds across the Charleston region. From the basin, 36 bronze hands will rise – cast from living community members whose profiles reflect those of the ancestors. Raised in gestures of prayer, resistance and reverence, these hands link past to present.

Throughout the memorialization process, community members reflected on what it meant to participate in such a project. Many spoke of feeling pride, reverence, joy, sadness and peace. “This conversation makes me feel complete,” one participant said.

As Charleston demonstrates, these projects are not only about preserving the past – they are acts of recognition, respect and reconciliation, helping communities nationwide confront and honor the histories long denied to African-descended peoples.

The Conversation

Joanna Gilmore has received funding from the City of Charleston, the National Geographic Society, and the College of Charleston. She previously worked for the Gullah Society, Inc. a not-for-profit organization.

ref. Rediscovery of African American burial grounds provides long-overdue opportunities for collective healing – https://theconversation.com/rediscovery-of-african-american-burial-grounds-provides-long-overdue-opportunities-for-collective-healing-260394

Combien de temps un moustique peut-il survivre sans piquer un humain ?

Source: The Conversation – in French – By Claudio Lazzari, Professeur des Universités, Département de biologie animale et de génétique, Université de Tours

La capacité d’un moustique à survivre sans piquer un humain dépend de plusieurs facteurs : son état de développement, son sexe, son espèce, son environnement et ses besoins physiologiques. Contrairement à ce que l’on pourrait penser, tous les moustiques ne se nourrissent pas de sang et même ceux qui le font n’en ont pas besoin en permanence pour survivre.


À leur naissance, tous les moustiques mènent une vie aquatique et se nourrissent de matière organique et de petits organismes. Cette période dure entre une et deux semaines, selon l’espèce, la température et la disponibilité en nourriture. Ils traversent quatre stades larvaires consacrés à l’alimentation et à la croissance, puis un stade de nymphe mobile au cours duquel une transformation corporelle profonde en moustique adulte a lieu, et durant lequel ils ne se nourrissent pas.

Au cours de leur vie, les moustiques occupent ainsi deux habitats complètement différents : l’eau et le milieu aérien, et utilisent des ressources différentes. À la différence d’autres insectes piqueurs, comme les punaises de lit ou les poux, qui se nourrissent de sang durant toute leur vie, les moustiques ne le font qu’à l’état adulte.

Moustiques mâles vs moustiques femelles

Il existe plus de 3 500 espèces de moustiques différentes, dont seule une petite fraction pique les humains, soit environ 200 espèces, dont 65 sont présentes en France hexagonale.

Les mâles ne piquent jamais. Ils se nourrissent exclusivement de nectar de fleurs et de jus de plantes, riches en sucres, qui leur fournissent toute l’énergie nécessaire à leur survie. Leur espérance de vie est généralement courte, de quelques jours à quelques semaines dans des conditions idéales.

Les femelles, en revanche, ont une double alimentation. Elles se nourrissent également de nectar pour vivre au quotidien. Cependant, lorsqu’elles doivent produire leurs œufs, elles ont besoin d’un apport en protéines que seul le sang peut leur fournir. Elles peuvent piquer des humains, mais aussi d’autres animaux, selon leurs préférences. Certaines espèces sont assez éclectiques en ce qui concerne leurs hôtes, piquant tout ce qui se présente à elles, tandis que d’autres montrent une préférence marquée pour le sang humain.

La plupart des moustiques se nourrissent du sang d’animaux à sang chaud, comme les oiseaux et les mammifères, y compris les êtres humains, mais certaines espèces peuvent aussi piquer des animaux à sang-froid, comme des grenouilles ou des chenilles de papillons.

Combien de temps une femelle peut survivre sans piquer ?

Une femelle moustique peut survivre plusieurs jours, voire quelques semaines sans piquer, pourvu qu’elle ait accès à une source de sucre, comme du nectar. Ce sont donc ses besoins reproductifs, et non sa survie immédiate, qui la poussent à piquer. Sans repas de sang, elle ne pourra pas pondre, mais elle ne mourra pas pour autant rapidement.

La femelle du moustique tigre Aedes albopictus, vecteur des virus de la dengue, du Zika ou du chikungunya, peut par exemple vivre environ un mois en tant qu’adulte dans des conditions optimales. Pendant cette période, elle peut survivre sans piquer, à condition de trouver une autre source de nourriture énergétique. Il en va de même pour Culex pipiens, le moustique le plus commun en France hexagonale, qui est également capable de transmettre certains virus responsables de maladies telles que la fièvre du Nil occidental ou l’encéphalite japonaise.

Influence de l’environnement

La température, l’humidité et la disponibilité en nourriture influencent fortement leur longévité. Un milieu chaud et humide, avec de l’eau stagnante, des hôtes et du nectar à proximité, favorise une reproduction rapide et des repas fréquents. En revanche, une température relativement basse ralentit le métabolisme des insectes et leur permet d’espacer les repas.

Il est également à noter que certains moustiques entrent en diapause, une sorte d’hibernation, pendant les saisons froides et peuvent survivre plusieurs mois sans se nourrir activement. Selon l’espèce, les œufs, les larves, les nymphes ou les adultes peuvent subir cette sorte de « stand-by physiologique » durant l’hiver. Si on ne les voit pas, ce n’est pas parce qu’ils sont partis, mais parce qu’ils sont cachés et plongés dans un profond sommeil.

The Conversation

Claudio Lazzari a reçu des financements de INEE-CNRS, projet IRP “REPEL”.

ref. Combien de temps un moustique peut-il survivre sans piquer un humain ? – https://theconversation.com/combien-de-temps-un-moustique-peut-il-survivre-sans-piquer-un-humain-267882

Neurotechnologies : vivrons-nous tous dans la matrice ? Conversation avec Hervé Chneiweiss

Source: The Conversation – in French – By Hervé Chneiweiss, Président du Comité d’éthique de l’Inserm, Inserm; Centre national de la recherche scientifique (CNRS); Sorbonne Université

Hervé Chneiweiss Inserm, Fourni par l’auteur

Les neurotechnologies progressent à grands pas, d’abord motivées par des applications médicales, par exemple pour améliorer le quotidien de personnes paralysées ou souffrant de maladies dégénératives. Elles sont suivies de près par le développement d’applications récréatives qui vont de la relaxation au jeu vidéo. Des recherches récentes montrent notamment qu’il est possible de détecter des mots pensés par les participants.

Hervé Chneiweiss est neurologue et neuroscientifique, président du comité d’éthique de l’Institut national de la santé et de la recherche médicale. Il a coprésidé le comité d’experts qui a rédigé une recommandation sur les neurotechnologies qui doit être adoptée le 7 novembre, lors de la 43e session de la Conférence générale de l’Unesco qui se tiendra à Samarcande (Ouzbékistan). Le chercheur a reçu Elsa Couderc, cheffe de rubrique Science et Technologie à « The Conversation France », pour parler des risques d’addiction, de la détection de nos émotions et de nos pensées, de la vie privée mentale… et de comment la protéger.


The Conversation : Jouer à un jeu vidéo sans manette, voilà qui va séduire plein de monde ! Mais on pourrait y voir des risques aussi, j’imagine ?

Hervé Chneiweiss : Oui, on peut envisager des risques en termes d’addiction ou d’utilisation de vos pensées les plus intimes, par exemple.

Pour comprendre les discussions autour de l’addiction et des neurotechnologies, je vous propose de remonter un peu dans le temps. Il y a trente ans déjà, alors que je travaillais en tant que neurologue sur la maladie de Parkinson, on a posé des implants cérébraux chez certains malades parkinsoniens jeunes et très rigides pour faire de la stimulation cérébrale profonde à haute fréquence, qui permet de débloquer leurs mouvements. C’est à ce moment que la communauté scientifique a constaté certains cas d’effets secondaires de cette stimulation sous forme de troubles compulsifs de comportement soit dans le domaine de la sexualité (hypersexualité) soit dans celui des compulsions d’achat.

En effet, en stimulant le cerveau de ces patients, on libérait manifestement trop de dopamine. Or, la dopamine est le principal neurotransmetteur d’un circuit qu’on appelle le « circuit de la récompense », ou reward en anglais – ce dernier est plus approprié que le terme français, car il traduit l’idée d’« obtenir ce que j’avais prévu d’obtenir ». Ainsi, avec nos électrodes, nous provoquions une libération de la dopamine en excès à un certain endroit du cerveau, ce qui perturbait les processus de décision et orientait les patients vers des comportements compulsifs.

Ces effets secondaires sont assez fréquents – environ un malade sur cinq les expérimente au début de la pose de l’implant, puis ils régressent et disparaissent en général au bout d’un mois ou deux. Il a été jugé que la potentielle survenue de ces effets indésirables était acceptable compte tenu du bénéfice attendu de la thérapeutique.

Depuis, les technologies ont beaucoup progressé : il existe tout un panel de techniques qui permettent de détecter les signaux du cerveau, ou bien de stimuler son activité. Ces techniques utilisent des dispositifs invasifs – comme les électrodes implantées dans le cerveau de patients parkinsoniens, dans les années 1990 – ou bien non invasifs – par exemple, des casques munis de petites électrodes que l’on pose sur la tête.

Le neurogaming utilise pour l’instant des casques posés sur le crâne, et non des électrodes implantées profondément dans le cerveau, comme pour le traitement de la maladie de Parkinson il y a quelques années. Y a-t-il, là aussi, un risque de surstimulation du circuit de la dopamine, et donc de compulsion ?

H. C. : Effectivement, il faut bien faire la différence entre deux types de dispositifs : d’un côté, ceux qui permettent la collecte d’informations sur l’activité cérébrale ; de l’autre, des systèmes qui vont moduler ou stimuler l’activité cérébrale – l’influencer, en somme.

En 2018 déjà, Rodrigo Hübner Mendes a réussi à conduire une Formule 1 simplement avec un casque posé sur la tête. Le signal d’électro-encéphalogramme était suffisamment bien décodé pour lui permettre de piloter cette voiture alors qu’il était tétraplégique et ne pouvait pas toucher le volant. Il l’a conduite simplement avec un casque qui détectait son activité cérébrale et donc, selon sa volonté, son intention d’accélérer ou de tourner à droite ou à gauche que l’interface cerveau-machine transmettait au système de pilotage de la Formule 1. C’est de la pure détection.

Et c’est exactement la même chose avec les systèmes « brain to speech », c’est-à-dire la capacité de décoder l’activité cérébrale responsable du langage avec une interface cerveau-machine, qui traduit cette activité en paroles en un dixième de seconde. Il s’agit de dispositifs qui pourraient venir en aide à des gens qui ont fait un accident vasculaire cérébral, qui ont des troubles du langage, ou par exemple dans la maladie de Charcot. C’est un des domaines des neurotechnologies qui avance le plus vite aujourd’hui. On sait désormais le faire avec des électrodes à la surface du cerveau, et non plus avec des électrodes profondes. D’ici cinq ans, on arrivera probablement à faire la même chose avec des électrodes à la surface du scalp, sur l’extérieur du crâne. Il s’agit là encore de détection.

C’est complètement différent des systèmes de stimulation ou de modulation, dans lesquels la machine envoie un signal au cerveau pour modifier l’activité cérébrale. Dans le premier cas, on ne modifie pas l’activité cérébrale, on se contente de la détecter. Dans le deuxième cas, on modifie l’activité cérébrale.

Est-ce que l’on sait aujourd’hui faire de la stimulation avec des implants non invasifs ?

H. C. : Oui, c’est ce qui se passe aujourd’hui dans le domaine médical avec la stimulation magnétique transcrânienne, qui est très utilisée pour la rééducation des accidents vasculaires cérébraux. On va inhiber l’activité d’une région du cerveau pour permettre la récupération d’une autre région du cerveau. Des résultats prometteurs ont été rapportés pour soigner certaines formes de dépression nerveuse grâce à des petits boîtiers de stimulation électrique, que l’on appelle DCS, qui sont des systèmes de stimulation continue.

Ces dispositifs sont aussi vendus en prétendant que ça peut permettre la relaxation, mais là, il n’y a aucune preuve scientifique que ça fonctionne.

D’autres types de stimulation non invasive peuvent être envisagés, par exemple avec des ultrasons pour essayer de lutter contre des tumeurs et contre des plaques amyloïdes dans la maladie d’Alzheimer.

Il va de soi que ces dispositifs capables de stimuler l’activité cérébrale intéressent beaucoup les gens qui aimeraient bien manipuler d’autres gens. Ces possibilités sont ouvertes par les grands progrès faits en neuroscience depuis trente ans, notamment en découvrant que d’autres régions du cerveau, moins profondes que celles impliquées dans la maladie de Parkinson, sont impliquées dans ces processus de décision : dans le cortex préfrontal, qui est au-dessus du nez, ou dans le cortex temporal. Ces zones sont en surface, relativement accessibles aujourd’hui.

L’objectif des gens qui développent ces technologies à des fins récréatives est d’essayer d’optimiser l’addiction, en stimulant directement les centres de la récompense ou de l’appétit, en corrélation évidemment avec un acte d’achat – ou avec ce qu’on cherche à faire aux gens pour tenter d’orienter les choses dans les jeux vidéo.

Ce qui est fait actuellement, c’est d’essayer de détecter (et non de stimuler – du moins, pas encore) avec ces casques l’état émotionnel de la personne et de modifier le degré de difficulté ou les épreuves du jeu vidéo en fonction de cet état émotionnel.

Est-il facile de détecter les émotions et les pensées aujourd’hui ?

H. C. : La réponse est différente pour les émotions – pour lesquelles oui, c’est facile – et pour les pensées – pour lesquelles, c’est plus difficile, mais on y vient.

Les émotions et la fatigue mentale sont des choses qu’on décrypte d’une façon macroscopique. Par exemple, quand vous êtes fatiguée, votre « saccade oculaire » ralentit, c’est-à-dire que vos yeux balayent moins rapidement la scène devant vous – ce qu’ils font en permanence. Le rythme des saccades est très facile à détecter.

De plus, selon notre degré émotionnel, différentes régions de notre cerveau sont plus ou moins actives. Comme ces régions sont assez grosses, en volume, il est possible de détecter leur niveau d’activité avec différents dispositifs : un casque posé à la surface du crâne ; une imagerie par résonance magnétique (IRM) fonctionnelle – un appareil qui est gros, certes, mais non invasif : nous n’avons pas besoin d’électrodes implantées dans le cerveau pour détecter ces signaux ; des plugs (bouchons) qu’on met dans les oreilles ainsi que de petits systèmes qui fonctionnent dans le proche infrarouge et qui mesurent des changements de vascularisation à la surface du cerveau. Ces dispositifs permettent de mesurer un certain nombre de changements d’activité de certaines régions du cerveau.

Par exemple, avec un casque posé sur la tête, donc non invasif, on peut réaliser des électro-encéphalogrammes (EEG). Quand vous commencez à être fatiguée, on voit des ondes de plus grande amplitude apparaître, puis des pointes d’une forme bien particulière si vous êtes vraiment en train de vous endormir. Ces signaux sont faciles à détecter avec un casque EEG.

Par contre, si vous pensez « J’ai faim » ou que vous vous préparez à prononcer un mot, là c’est plus dur. Des groupes de recherche académique californiens
– l’Université de Californie à San Diego et celle de Berkeley, mais aussi Caltech – ont fait des avancées récentes sur le sujet, avec les électrodes placées à la surface du cerveau et des systèmes d’intelligence artificielle entraînés à reconnaître certains motifs d’activité du cerveau du patient – c’est ce que l’on appelle le brain to speech, dont je parlais tout à l’heure. Ils ont découvert que les mêmes régions soutenaient le langage parlé intentionnel et le langage intérieur. Nous nous approchons donc là de la possibilité de détecter la base de la pensée. L’objectif est ici de venir en aide et de restaurer l’autonomie de personnes gravement cérébrolésées. Malheureusement, nous ne connaissons pas les intentions réelles de sociétés commerciales qui développent aussi ce type d’électrodes de surface.

En termes d’encadrement, est-ce que ces dispositifs, que ce soient des casques, des plugs dans les oreilles ou des implants, sont encadrés aujourd’hui, par exemple avec des autorisations de mise sur le marché comme pour les médicaments ?

H. C. : Si c’est un dispositif médical, il y a tout l’encadrement habituel. Si c’est un dispositif non médical, il n’y a rien : aucune garantie.

Dans la déclaration de l’Unesco, vous recommandez de classer « sensibles » certaines données biométriques, qui ne semblent pas susceptibles de donner accès aux émotions ou aux pensées au premier abord. Pourquoi ?

H. C. : On peut utiliser des données qui ne sont pas directement des données cérébrales ou neurales pour faire des déductions sur l’état émotionnel ou de santé : on a parlé des mouvements des yeux, mais il y a aussi le rythme cardiaque combiné à des données comportementales ou à la voix.

Par exemple, si vous enregistrez la voix d’une personne atteinte de la maladie de Parkinson, même débutante, vous allez voir qu’il y a des anomalies de fréquence qui sont caractéristiques de cette maladie. Il n’y a pas forcément besoin d’être capable d’enregistrer l’activité cérébrale pour déduire des choses très privées.

Donc, on a regroupé cet ensemble sous le terme de « données neurales indirectes et données non neurales » : ces données qui, combinées et interprétées par l’intelligence artificielle, permettent de faire des inférences sur nos états mentaux.

Vous recommandez donc de protéger toutes les données neurales – qu’elles soient directes ou indirectes –, car elles permettent d’en déduire des états mentaux, et ce, afin de protéger nos « vies privées mentales ». Pouvez-vous nous expliquer ce que vous entendez par là ?

H. C. : Parmi les droits fondamentaux, il y a le droit à la vie privée. C’est le droit d’empêcher qui que ce soit de connaître les éléments de votre vie privée que vous ne souhaitez pas qu’il ou elle connaisse.

Nos pensées, nos idées, nos désirs, tout ce qui se passe dans notre tête, sont ce que nous avons de plus intime et, donc, de plus privé. La vie mentale est au cœur même de la vie privée.

Souvent, quand on parle d’atteinte à la vie privée, on pense à la diffusion d’une photo qui serait prise à un endroit ou avec une personne, alors qu’on n’avait pas forcément envie que cela se sache. Mais vous imaginez si demain on pouvait avoir accès à vos pensées ? Ça serait absolument dramatique : la fin totale de toute forme de vie privée.

En pratique, imaginons que notre conversation en visioconférence soit enregistrée par un fournisseur de services Internet. Nos saccades oculaires, qui sont donc des données neurales indirectes, sont bien visibles. Est-il possible, aujourd’hui, d’en déduire quelque chose ?

H. C. : En principe, il pourrait y avoir un petit message qui s’affiche sur mon écran en disant : « Attention, la personne en face de vous est en train de s’endormir, il faudrait veiller à raconter quelque chose de plus intéressant. » (rires) Sauf que nous sommes en Europe, et que dans le règlement européen sur l’IA, l’AI act, l’utilisation de logiciels ayant pour objectif de détecter ou d’analyser le comportement des personnes, en dehors de la médecine ou de la recherche, est interdite.

Avec le règlement général sur la protection des données (RGPD) pour protéger nos données personnelles, puis avec l’AI Act, l’Union européenne a déjà pris des mesures de protection de la vie privée et de l’autonomie des individus… Parce qu’une fois que vous avez ces différentes données, vous pouvez essayer de manipuler les personnes, en biaisant leur jugement, ou en essayant de leur faire prendre des décisions qui ne sont plus prises en autonomie. Notre vie privée mentale est aussi la base de notre liberté d’expression et de notre liberté de penser.

Aujourd’hui, dans le cadre d’autres nouvelles technologies, on en vient à chercher à protéger les mineurs, notamment en leur interdisant l’accès à certains dispositifs. C’est le cas sur certains réseaux sociaux et c’est en discussion pour certaines IA génératives, comme ChatGPT. Est-ce une direction que vous recommandez pour les neurotechnologies ?

H. C. : Tout à fait ! Il ne faut jamais oublier que le cerveau d’un enfant n’est pas un petit cerveau adulte, mais un cerveau en développement. De la même façon, le cerveau d’un adolescent n’est pas un petit cerveau adulte, mais un cerveau en révolution – qui se reconfigure.

Aujourd’hui, l’impact de l’utilisation de ces procédés de neurotechnologies sur ces cerveaux en développement est totalement inconnu et, en particulier, la réversibilité de tels impacts potentiels.

Même pour des applications médicales, pourtant mieux encadrées, les choses ne sont pas si simples. Il y a, par exemple, des cas de patients ayant reçu des implants cérébraux pour soigner des pathologies, notamment des céphalées de Horton, avant que l’entreprise responsable de l’implant fasse faillite et ferme, laissant les patients avec des implants sans maintenance. À l’heure où les développements technologiques sont menés en grande partie par des entreprises privées, quels sont les espoirs et les mécanismes qui permettent de croire qu’on peut cadrer le développement des neurotechnologies pour protéger les citoyens du monde entier de potentiels abus ?

H. C. : On parle là de « développement responsable » des technologies. Ce sont des problématiques que nous avons abordées dans le cadre de l’Organisation de coopération et de développement économiques (OCDE), avec une recommandation (no 457), publiée en décembre 2019, qui énonçait neuf principes pour un développement responsable des neurotechnologies. C’est ensuite aux États membres de l’OCDE de la mettre en pratique. Dans ce cas, il n’y en a que 38, bien moins qu’à l’Unesco, avec 195 pays membres.

La nouvelle déclaration qui doit être signée à l’Unesco reflète une vision qui part des droits humains et qui protège les droits humains fondamentaux ; à l’OCDE, il s’agit d’une vision qui cherche le développement économique. Nous cherchions donc dans quelles conditions les entreprises pourront le mieux développer leurs produits : parmi ces conditions, la confiance que le consommateur peut avoir dans le produit et dans l’entreprise.

Malheureusement, dans ce contexte-là, pour l’instant, on n’a pas encore de réponse claire à votre question, sur ce que l’on appelle en anglais « abandonment », que l’on appellerait en français l’« abandon neural ». Des propositions sont en cours d’élaboration, par exemple au niveau du comité Science & société du programme européen EBRAINS.

Néanmoins, au niveau français, avec différents ministères, en collaboration avec les entreprises, avec le secteur associatif et aussi avec le secteur académique, on a élaboré une charte française de développement responsable des neurotechnologies, qui a l’intérêt de vraiment avoir été une coconstruction entre les différents partenaires, une codécision qui porte sur la protection du consommateur, sur son information et sur la prévention des mésusages des neurotechnologies. Elle a été publiée en novembre 2022. La signer est une démarche volontaire, mais qui marche aujourd’hui plutôt bien puisqu’on en est, à ce jour, à une cinquantaine de partenaires : beaucoup d’entreprises, d’associations, d’académies et des agences de régulation.

Ce qui est intéressant aussi, c’est que nous avons ensuite porté cette proposition au niveau européen. La charte européenne des neurotechnologies est très inspirée de la charte française. Elle a été publiée en mai 2025 et a déjà recueilli près de 200 signataires. Le but est d’apporter aux différentes sociétés qui y adhèrent une sorte de « label » pour dire aux consommateurs, « On a fait le choix de respecter mieux vos droits et donc de s’engager dans cette charte des neurotechnologies ».

Cette démarche est plus que nécessaire. Une étude américaine, réalisée en 2024 par la Neurorights Foundation sur 30 entreprises, majoritairement américaines, qui commercialisent des casques EEG et d’autres produits de neurotechnologie, montre que 29 de ces 30 entreprises ne respectaient absolument pas les recommandations de l’OCDE. Par exemple, certaines collectaient et/ou revendaient les données sans l’accord des personnes.

La philosophie, en portant cette discussion auprès de la Conférence générale de l’Unesco, c’est d’avoir une plateforme mondiale, d’ouvrir la discussion dans des pays où elle n’a pas déjà lieu ?

H. C. : Oui, les recommandations de l’Unesco servent en général de base aux différentes juridictions des États membres pour mettre en place des lois afin de protéger les citoyens de l’État.

Avec les neurotechnologies, on est vraiment à un niveau constitutionnel parce qu’il s’agit de droits fondamentaux : le droit à la vie privée, le droit à l’autonomie, le droit à la liberté de pensée, le droit à la liberté d’agir, mais aussi le droit à l’accès aux technologies si elles sont utiles – que les gens qui en ont besoin puissent y avoir accès.

Le Chili est le premier pays à avoir explicité ces droits dans sa Constitution. Le Colorado et la Californie aux États-Unis ont déjà légiféré pour encadrer les neurotechnologies. En France, c’est dans la loi bioéthique, telle qu’elle a été révisée en 2021, que l’on trouve des éléments pour essayer de protéger contre des abus. Au niveau européen, c’est la déclaration de Léon (2023).

Ainsi, même si les déclarations de l’Unesco ne sont pas contraignantes, elles inspirent en général les juristes des pays correspondants.

Y a-t-il des risques que la déclaration de l’Unesco ne soit pas signée en novembre lors de la Conférence générale ?

H. C. : Maintenant que les États-Unis se sont retirés, je ne crois pas… La conférence intergouvernementale que j’ai présidée au mois de mai a adopté la recommandation, il y avait 120 États. Les choses ne sont pas faites, bien sûr, mais on espère que le passage à l’Assemblée générale, avec les 195 pays présents, sera plutôt une formalité.

Les instances internationales sont très formelles. Elles fonctionnent comme ça ; et c’est peut-être une limite du fonctionnement onusien, qui s’appuie sur l’idée un peu irénique de René Cassin et d’Éléonore Roosevelt, après ce qui s’était passé d’effroyable pendant la Deuxième Guerre mondiale, que les États sont de bonne volonté.

On n’est plus tout à fait dans ce cadre-là.

H. C. : Oui, vous avez remarqué, vous aussi ? Mais, si ça marche, on sera surtout heureux d’y avoir contribué en temps et heure. Parce que là, et c’est une chose qui est assez remarquable, c’est qu’on prend les mesures au bon moment. Pour une fois, les réflexions éthiques et de gouvernance ne sont pas en retard sur la technique.

On espère donc que ce sera vraiment utile, et que les neurotechnologies continueront à se développer à bon escient, parce qu’on en a absolument besoin, mais que, grâce à cette prise de conscience précoce, on évitera les abus, les utilisations détournées ou malveillantes de ces technologies.

Et donc : vivrons-nous tous dans la matrice (je fais référence au film Matrix) ?

H. C. : Peut-être qu’il peut y avoir de bons côtés à la matrice et de mauvais côtés. Si ces différents procédés pouvaient rendre leur autonomie, par exemple, à des personnes âgées qui souffrent d’une perte d’autonomie, à des malades qui sont en perte d’autonomie, ou aider des enfants qui ont des difficultés à apprendre à mieux apprendre, là on aura vraiment gagné. Par contre, si c’est pour soumettre les individus à des volontés d’entreprises monopolistiques, là on aura tout perdu. Mais l’avenir n’est pas écrit. C’est à nous de l’écrire.

The Conversation

Toutes les fonctions listées ci-après l’ont été à titre bénévole:
Expert pour les neurotechnologies auprès de l’OCDE de 2015 à ce jour.
Ancien président du Comité international de bioéthique de l’UNESCO (2019-2021) et co-auteur du rapport sur les enjeux éthiques des neruotechnologies (2021).
Co-président du groupe d’experts ad hoc sur la recommandation UNESCO sur les neurotechnologies (2024-2025).
Président du Comité intergouvernemental sur la recommandation sur les neurotechnologie (12-16 mai 2025).
Membre du Comité de la Charte française des neurotechnologies
Co-auteur de la charte européenne des neurotechnologies

ref. Neurotechnologies : vivrons-nous tous dans la matrice ? Conversation avec Hervé Chneiweiss – https://theconversation.com/neurotechnologies-vivrons-nous-tous-dans-la-matrice-conversation-avec-herve-chneiweiss-268421

Maths au quotidien : Full HD, 4K, 8K… ou pourquoi il n’est pas toujours utile d’augmenter la résolution de sa télévision

Source: The Conversation – in French – By Saad Benjelloun, Responsable du département de mathématiques, Pôle Léonard de Vinci

Pourquoi acheter une télévision 8K plutôt qu’une 4K ou Full HD ? La question revient souvent, tant l’offre technologique semble avancer plus vite que nos besoins. Plus de pixels, plus de netteté… mais jusqu’à quel point notre œil est-il capable de percevoir la différence ? Derrière cette interrogation se cache un outil mathématique puissant utilisé en traitement du signal et en optique : l’analyse de Fourier.


Une télévision 4K affiche environ 8 millions de pixels, contre 33 millions pour la 8K. Sur le papier, c’est une avalanche de détails supplémentaires.

Mais l’œil humain n’est pas un capteur parfait : sa capacité à distinguer des détails dépend de la distance de visionnage et de l’acuité visuelle. Autrement dit, si vous êtes trop loin de l’écran, les pixels supplémentaires deviennent invisibles. Un écran 8K de 55 pouces vu à trois mètres sera perçu… presque comme un écran 4K.

Les limites de notre perception visuelle

Il existe des méthodes qui permettent de décomposer un signal (par exemple une image ou un son) en ses fréquences spatiales ou temporelles. Pour une image, comme celles affichées par les télévisions dont nous parlons, les basses fréquences correspondent aux grandes zones uniformes (un ciel bleu, un mur lisse) tandis que les hautes fréquences traduisent les détails fins (les brins d’herbe, le grain de peau).




À lire aussi :
Des caméras 3D dans nos smartphones : comment numériser notre environnement ?


Nos yeux, comme un appareil photo, n’ont qu’une capacité limitée à percevoir ces hautes fréquences. Cette capacité dépend encore plus de l’acuité visuelle de chacun. Ainsi l’œil humain a une résolution maximale proche de 120 pixels par degré angulaire. Cette acuité correspond à pouvoir distinguer un objet de quinze centimètres à une distance d’un kilomètre, ou un grain de poussière à trois mètres : il est clair que la majorité des personnes ont une acuité visuelle moindre !




À lire aussi :
Aveugles, malvoyants : que voient-ils ?


Sur une image, cette limite s’appelle la fréquence de coupure : au-delà, les détails sont trop fins pour être distingués, quelle que soit la richesse de l’image.

Si l’on applique cette logique, la 8K ne devient vraiment utile que si :

  • l’écran est très grand,

  • ou que l’on s’assoit très près,

  • ou encore si l’on zoome dans l’image (par exemple en retouche professionnelle).

Sinon, la fréquence maximale que peut capter notre œil est déjà atteinte avec la 4K. En d’autres termes, la 8K « code » des détails… que notre système visuel ne peut pas lire.

Un outil mathématique puissant, la « transformée de Fourier », inventée par Joseph Fourier en 1817, permet de quantifier cet effet.

Une transformée de Fourier révèle le « contenu fréquentiel » d’un signal — autrement dit sa répartition entre les différentes bandes de fréquence. Reposons donc notre question, mais mathématiquement cette fois : « est-ce que ces pixels additionnels correspondent encore à des fréquences spatiales perceptibles ? »

Ce que dit la transformée de Fourier

Illustrons cela avec un exemple visuel d’une image et son spectre de Fourier. Si pour un son ou un signal radio, la transformée de Fourier est elle-même un signal unidimensionnel, pour une image en deux dimensions, le spectre de Fourier et lui-même en deux dimensions avec des fréquences dans chacune des directions de l’espace.

comparaison de résolution
Une image affichée avec deux résolutions différentes, et les transformées de Fourier correspondantes.
USC-SIPI Image Database pour la photo ; Saad Benjelloun pour les modifications, Fourni par l’auteur

Nous voyons dans l’exemple une image basse résolution (HD simulée) et son spectre de Fourier, ainsi qu’une version haute résolution (4K simulée) et son spectre. Le centre du carré correspond aux faibles fréquences (autour de la valeur (0,0)).

Dans la version haute résolution (4K simulée), le spectre contient plus de hautes fréquences (zones colorées vers les bords, contrairement aux zones noires pour le spectre de la version full HD), ce qui correspond aux détails supplémentaires visibles dans l’image.

Utiliser des filtres pour couper les hautes et basses fréquences

Regardons de plus près ce qui se passe en manipulant ce spectre — on parle alors de filtres.

On filtre l’image original en supprimant les hautes fréquences et en ne laissant passer que les basses fréquences (on parle de filtre passe-bas).
Saad Benjelloun, Fourni par l’auteur

Alors que l’image originale est nette et contient beaucoup de détails, on voit que l’image filtrée, avec les hautes fréquences supprimées, devient floue, les contours fins disparaissent. On le voit ainsi sur le nouveau spectre de Fourier après filtrage : seules les basses fréquences au centre ont été gardées, les hautes fréquences (détails) sont supprimées.

C’est exactement ce qui se passe quand on compresse trop une image ou quand on affiche une image HD sur un grand écran 4K : les hautes fréquences sont limitées. D’ailleurs, c’est pour cette raison que les téléviseurs 4K et 8K utilisent des techniques de « suréchantillonnage » (upscaling en anglais) et d’amélioration d’image pour tenter de reconstituer et renforcer ces hautes fréquences manquantes et offrir une meilleure qualité visuelle.

On filtre l’image originale en supprimant les basses fréquences et en ne laissant passer que les hautes fréquences (on parle de filtre passe-haut).
Saad Ben Jelloun, Fourni par l’auteur

Inversement, sur l’image filtrée avec les basses fréquences supprimées, il ne reste que les contours et détails fins, comme un détecteur de bords. Dans le spectre de Fourier, le centre (basses fréquences) est supprimé, seules les hautes fréquences autour des bords subsistent.

Alors, faut-il absolument acheter une 8K pour votre suivre votre prochaine compétition sportive préférée ? Pas forcément. À moins d’avoir un très grand salon !

The Conversation

Saad Benjelloun ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d’une organisation qui pourrait tirer profit de cet article, et n’a déclaré aucune autre affiliation que son organisme de recherche.

ref. Maths au quotidien : Full HD, 4K, 8K… ou pourquoi il n’est pas toujours utile d’augmenter la résolution de sa télévision – https://theconversation.com/maths-au-quotidien-full-hd-4k-8k-ou-pourquoi-il-nest-pas-toujours-utile-daugmenter-la-resolution-de-sa-television-266414