This issue of The Caltech Effect features scientists and engineers whose research helps us better understand how we sense and make sense of the world.
Illustrated Story
How to Build a Space Telescope
The year was 2012. A small NASA telescope named NuSTAR launched on a rocket. When it reached space, its tightly folded mast stretched out to 33 feet, and two very new eyes started to record the light that reached them.
Caltech’s Zhongwen Zhan has a vision for the next generation of earthquake-monitoring networks: the use of lasers to assemble the most detailed picture yet of how the earth vibrates.
Multisensory perceptual illusions are surprising and fun, and they also provide insight into neural processing in the brain. The AV Rabbit, Caltech’s most-viewed video of 2018, reveals that an auditory stimulus can retroactively affect your visual perception.
Noelle Stiles (PhD ’15), then a visitor in biology and biological engineering, led the design of this illusion, with contributions from Shinsuke Shimojo, the Gertrude Baltimore Professor of Experimental Psychology and an affiliated faculty member of the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech, along with former Caltech postdoc Yukiyasu Kamitani (PhD ’01), Carmel Levitan of Occidental College, Monica Li (BS ’16), Ishani Ganguly (class of 2020), and Armand Tanguay (BS ’71) of USC.
Read the storythat accompanied the video’s original release in 2018.
About the Rabbit
This video features the Illusory Rabbit, an auditory-visual illusion named in homage to the Cutaneous Rabbit effect, a tactile phenomenon discovered in 1972. With the Cutaneous Rabbit, a series of rapid taps in two different spots on the forearm creates the illusion that tapping is also occurring in between, as if a rabbit were hopping along the skin.
“What you experience is that sound creates a visual ‘ghost’ of something you actually didn’t see,” explains Shimojo. Weirder still, stimuli that occur later in time influence the location of the ghost image. According to Shimojo, this is the first demonstration of “postdiction” (as opposed to prediction) in multisensory processing.
The research team recently showed that the illusion persists for much longer delays than originally thought: Yet another surprise!
.
Gallery
Sensors and Sensibilities
Like any scientist, Noelle Davis has an eye for detail. But this rising senior from Fort Worth, Texas, brings unusual focus to the visual world.
“The goal in all photography,” Davis says, “is to highlight the beauty in an interaction, person, or situation.” Credit: Mike Wong (PhD ’18)
1/11
“I take my best shots while cheering my lungs out,” Davis says.
2/11
During her first year at Caltech, Davis practiced and played with the men’s soccer team. Credit: Caltech Athletics
3/11
“Lovely blue swimming pools, but the water’s 175° and pH 1,” Davis says about Hot Creek Geological Site.
4/11
Davis asks: “Why does the cafeteria provide such an extraordinary array of fruit? Is this just a California thing? I don’t know, but I love it.”
5/11
Davis captured this image of cobalt oxide crystals in APh 109, Introduction to the Micro/Nanofabrication Laboratory.
6/11
“The nightmarish part of homework is supposed to be what’s in the problem set, not what’s literally on it,” Davis says.
7/11
On her first visit to Caltech, Davis fell in love with the plants on campus.
8/11
Annelise Thompson was among the performers Davis photographed at the Caltech Dance Show in April 2019.
9/11
Davis originally programmed this simulation for ACM 95b, Introductory Methods of Applied Mathematics.
10/11
Davis built this light sensor for EE/ME 7, Introduction to Mechatronics.
11/11
Photographic Memory
Noelle Davis uses a variety of lenses to document her Caltech experience. Through microscopes and telescopes, she contemplates the invisible worlds of nanoparticles and Jupiter’s moons. Through her camera’s viewfinder, she glimpses everyday scenes at Caltech.
While Davis takes all kinds of photographs, sports action is her forté.
Women’s basketball is her favorite Athletics Department assignment. With camera in burst mode, she clicks and shouts as she watches 5-foot-2-inch guard Grace Peng, who happens to be her roommate, “streak down the court, dart through defenders all a head taller than she is, and fling the ball up into the net.”
Goal-Driven Scholar-Athlete
Davis is herself a varsity athlete. Next season will be her fourth in Caltech’s soccer program, which is remarkable because the women’s team has only been in existence three years.
The Beavers had already hired a women’s soccer coach when Davis arrived in 2016, but it took another year to field a team. In the meantime, Davis and teammate Gabriella Chan played on the men’s team. The two also worked closely with the new coach to recruit women players. Davis, who plays midfield, was captain of the 2018–19 Caltech women’s soccer team.
Blogging Shutterbug
Davis blogs for Undergraduate Admissions under the handle Snapshots, where she recommends favorite classes, such as Geology 1. She posted this bird’s-eye view of Hot Creek Geological Site near Mammoth Lakes, which she captured during a three-day field trip for the class. Freshmen have been known to switch majors after taking Geology 1, Davis notes.
Her posts, which are sprinkled generously with her photographs, celebrate all things Caltech, from fresh raspberries at Chandler Café to cobalt oxide crystals at 1000x magnification.
“Every day, the kitchen is stocked with a colorful assortment,” she writes in her blog. “Trays brim with raspberries, strawberries, and sometimes even blueberries. Apples—usually the sweet and tangy Fuji, but occasionally the crisp, lightly floral-flavored Pink Lady—are piled in a wire basket. Citrus is next, including navel oranges and clementines or tangelos, depending on the season. Bunches of bananas and bowls of dried apricots, cranberries, and raisins round off the ensemble.”
Extra Sensor Perception
Above all, Davis is a scientist in the making.
Since 2017, she has been a member of Axel Scherer’s Nanofabrication Group, where she has contributed to the design of an implantable glucose-monitoring sensor for patients with diabetes.
Last summer, she interned at a San Jose-based sensor company that makes LIDAR (light detection and ranging) scanners used in self-driving cars. The summer before, she interned in a University of Texas analytical chemistry lab. Currently, she has a Summer Undergraduate Research Fellowship (SURF) at JPL, where she is evaluating telecommunication configurations of the Europa Clipper’s eight antennae.
Problem Sets and the Sense of Fear
In one of her blog entries, Davis ponders the subject of scary problem sets.
“I was working at my desk on a horribly long problem set for EE 44, Circuits and Systems, when I flipped the page, and there, standing innocently among the first-order circuit diagrams and p-operator algebra, was a big black spider,” she writes.
“This spider was big and furry like a tarantula, with red on its back like a black widow, as if it were some kind of hybrid between the two worst bugs of children’s fiction. After I finished panicking, I realized that it was actually a pretty cool spider. I sent a picture to my family group chat. According to my dad, who has a thing for bugs, it’s not a black-widow-tarantula hybrid mutant after all, just a jumping spider.”
Subbasement Dweller
Davis’s favorite campus sight is the walkway outside Moore Laboratory, decked out in spring flowers.
“My classmates and I spend a lot of time, day and night, in the Moore subbasement,” she explains. “There have been many times when I stayed overnight, such as when I wrote my assembly code for an EE/10b microcontroller project, and emerged, tired and groggy after staring at a computer screen for hours, to be greeted by these purple Jacaranda trees.”
In Her Spare Time
Wordsmith, graphic designer, and publications manager are some of the other hats Davis wears around campus. As co-editor-in-chief of the Big T yearbook, she chronicles memorable moments, such as the annual Caltech Dance Show.
Davis is also passionate about community service. Through the Caltech Y, where she is an executive committee member, she helped organize a river cleanup and a food drive. Farther afield, as co-president of the Caltech chapter of Engineers Without Borders, she is helping bring clean water to a village in the Himalayan foothills.
During her junior year, Davis received Caltech’s 2019 Donald S. Clark Memorial Prize, an honor bestowed for academic excellence and service to the campus community.
An Artist’s Eye
Everywhere she looks, Davis finds beauty. She created this Mandelbrot simulation, named for Benoit Mandelbrot (BS ’49), the Caltech mathematician known as “the father of fractal geometry,” to represent a fractal in mathematics based on a property of complex numbers. It began as a homework assignment, but she continued to tinker, enhanced the color and dynamic range, and entered the finished product in Caltech’s Art of Science competition.
A Sense of Connection
During a campus tour with her family, before Davis had decided to attend Caltech, she was captivated by members of a class (EE/ME 7) who had gathered around a small pool to demonstrate their mechanical and electrical engineering aptitudes with sensor-guided motorized boats. She was hooked. In her blog a year later, Davis deemed EE/ME 7 her favorite freshman-year course.
The boundless energy, creativity, empathy, and ambition of this multi-talented woman has been buoyed in no small part by philanthropy. Thanks to Caltech’s Chloe Curtis Endowed Scholarship Fund, The Ahmanson Foundation Collegiate Scholarship program, additional scholarship support from Student Affairs, and help from her parents, Davis is grateful that she will graduate debt-free next year. She plans to take a gap year before working toward a doctorate in electrical engineering.
Points of View
Five Researchers on Sensing
We asked members of the Caltech community to explain how sensing and sensors inspire their research.
The Sensory Passageway for Nicotine Addiction
In Dennis Dougherty’s lab, we study receptors in the brain that are drug targets for treating a variety of health conditions and disorders. A receptor functions as a means for two neurons to communicate when it is activated by specific chemicals that nature designed it to detect. I create amino acids that are not found in nature and use them to subtly change the nicotinic receptor nAChr, and I also make tiny changes to a chemical that it detects. My objective is to learn how cytisine, a smoking cessation drug, activates this receptor. To use an analogy, I make precise alterations to a key (cytisine) and a lock (nAChr), all to better understand nicotine addiction.
— Annet Blom (PhD ’19), former llene and Howard Marshall Fellow
The Sensitivity of Pectin
My adviser, Chiara Daraio, was combining plant cells with carbon nanotubes to create synthetic wood when she noticed the new material was responsive to temperature changes. Her curiosity led her to discover that pectin, an organic polymer found in wood and other plant cell walls, when dehydrated, outperforms the best thermal sensors on the market. Today, we continue to improve the stability and sensitivity of pectin. We aim to create inexpensive, flexible, temperature-sensing films that could be used, for example, in health-monitoring devices, car batteries, and electronics. Also, from our many experiments, I am developing computational and theoretical models to systematically explain pectin’s electrical properties.
— Linghui Wang, graduate student in applied physics
How a Drone "Sees"
As a SURF student in Soon-Jo Chung’s aerospace robotics lab, I helped test a sensor that could be used on an autonomous flying ambulance drone. The sensor, an IMU (inertial measurement unit), measures linear acceleration and angular velocity. Now, on a team led by Joel Burdick, I am building on what I learned to help design a tunnel-traversing drone for the DARPA Subterranean Challenge. The drone computes its position and plans its path using IMUs in combination with other instruments, including LIDAR (light detection and ranging), which measures the distance between the drone and obstacles, and a visualization system with high-definition cameras that feed into a flight controller. Sensors plus robust algorithms: Together, these are how we enable a drone to navigate and “see.”
— Anuj Chadha, Robert J. Kieckhefer, Jr. Memorial Scholarship recipient
Making Sense of Survival
We simulate naturalistic conditions for mice and observe responses necessary for survival. For example, predator avoidance: A dark expanding disk shown on an overhead monitor elicits fleeing or freezing because mice sense an approaching aerial predator. Or prey capture: Despite differences in the time each mouse requires to learn how to capture an insect, it always takes just one successful hunt for a mouse to become an efficient hunter. With two faculty advisers, Markus Meister and David Anderson (both from the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech), I study these behaviors and the involvement of evolutionarily conserved, relatively ancient subcortical structures of the brain. We want to understand these instinctive reactions and where that information is transformed into a successful motor output.
— Zeynep Turan, graduate student in neurobiology
What Creates Our Moral Sense?
Philosophers have long suspected that humans possess a unique faculty of perception dubbed “the moral sense,” which you can think of as an evolved capacity to perceive and react to morally significant events. In the Caltech Brain Imaging Center (part of the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech), my laboratory studies how this sense arises by peering inside the brains of people making difficult moral decisions, such as how to distribute scarce food resources among orphans. We find that how fairly people distribute these resources depends on how emotionally averse they are to inequity, and this is reflected in differences in brain activity. Our sense of fairness, viewed by philosophers as humans’ most complex capacity, is deeply rooted in the brain’s machinery.
— Steven Quartz, Professor of Philosophy
How to Build a Space Telescope
The year was 2012. A small NASA telescope named NuSTAR launched on a rocket. When it reached space, its tightly folded mast stretched out to 33 feet, and two very new eyes started to record the light that reached them.
Target
For NuSTAR’s initial target, Professor Fiona Harrison and her students chose a black hole that shines brightly in X-rays. They wondered: Was the telescope correctly aligned to see it? Would this novel telescope be able to capture an image?
See
“There were questions in my mind about whether we were going to succeed, and how long it was going to take,” Harrison says. “So when we saw the pictures of the black hole, we were all very relieved. It was just a point source, a very bright dot, but we could tell from its constituent colors that it was the right source.”
Invent
NuSTAR maps black holes, collapsed stars, and the remnants of exploded stars. It images them in high-energy X-rays, which no other telescope has been able to focus before. It can do this because Harrison’s research group worked for two decades to develop new detectors, electronics, and optics, and special coatings for the optics.
Diversify
“You have to pull from a lot of different sources when you’re trying to do something new,” Harrison says. A Danish collaborator on a country drive saw barns with curved glass windows that inspired an affordable method to shape the 266 glass cones in NuSTAR’s optics. Then, Harrison, her students, and a collaborator took a road trip to see how U.S. national labs and manufacturers produce certain coatings. “We stayed in a lot of Motel 6s,” she says. Upon their return, the researchers invented atom-thick layers that make NuSTAR’s optics more reflective than mirrors.
Detect
On NuSTAR, two sets of four crystal-shielded semiconductors detect when, where, and how hard each X-ray hits them. Chips bonded to these detectors record and transmit the information. For the electronics, Harrison’s group customized techniques developed by Caltech microelectronics innovator Carver Mead (BS ’56, MS ’57, PhD ’60).
Correct
As its data pours in, NuSTAR is helping astronomers learn how stellar explosions created and spread the elements that Earth is made of, what energy sources power extremely active galaxies, and which objects are which in the cosmos.
“I think my favorite discovery,” Harrison says, “is when we found completely unexpected pulses coming from one of these very, very bright sources that people had long assumed were massive black holes.” Turns out they were neutron stars.
Support
Each breakthrough validates efforts by generations of young scholars in Harrison’s research group, who worked without a guarantee of NuSTAR’s success.
“These fellowships help launch future generations of researchers,” Harrison says, adding that fellowships help students and their mentors try unproven, divergent approaches.
Explore
Now that they have flung open the high-energy X-ray window, Harrison’s research group is starting to explore ultraviolet wavelengths. She and her students have plans for a new space mission that will scan the sky and follow up on gravitational wave detections, bringing home another new view of the cosmos.
Caltech’s Zhongwen Zhan has a vision for the next generation of earthquake-monitoring networks: the use of lasers to assemble the most detailed picture yet of how the earth vibrates.
Zhan (PhD ’13), an assistant professor of geophysics, has repurposed a tool from industry to send a laser through an underground fiber optic cable and detect vibrations using the light that reflects back.
In partnership with the City of Pasadena, Zhan and his team are taking unused strands of optical fiber in the city’s telecommunication cables and turning those strands into the equivalent of 5,000 sensors. With so many data points grouped so closely together, scientists can watch a quake propagate in a way that is impossible with current networks, where sensors are kilometers apart. The map above shows the full extent of the Pasadena Array planned for October 2019. With success, Zhan hopes to set up similar networks in other cities.
“We can provide better earthquake hazard assessment for the future at no cost to the city,” he says. “This is an important public service because it could save lives, and it’s good for fundamental research, too.”
This image includes a snapshot of data captured by the nascent Pasadena Array on the morning of May 8, 2018. Zhan and his colleagues detected shaking from a 4.5-magnitude quake centered in Cabazon, California, about 90 miles away. (The “P” marks the primary wave, which is faster but weaker; the “S” is the secondary wave that is slower but causes most of the damage from a quake.)
The new seismic network also picked up shaking from a heavy vehicle as it traveled on the streets above. The researchers are able to tell the difference between natural and human-made vibrations because of the network’s high resolution. With more detectors, it is easier to distinguish a faraway quake from a big rig rumbling down the road.
On the roof of Caltech’s Millikan Library, there is a vibration generator that simulates quakes. The instrument was built during the 1970s to help scientists study how the building responds to shaking. Now, Zhan and his team use the shaker to reveal the geological characteristics of land in Pasadena. On occasion, late in the night, the researchers create miniature, artificial quakes—approximately 1.3 in magnitude—and detect the results with the Pasadena Array. Their findings ultimately could help the city identify the neighborhoods most at risk and prioritize which buildings to retrofit to protect against quakes.
Discretionary funds donated by Caltech trustee Li Lu will support Zhan’s fiber-optic cable seismology research and provide a much-needed upgrade to the Millikan shaker. Across the Institute, philanthropy gives Caltech a competitive edge in projects such as this one. “It’s great to have the flexibility to try exciting new things quickly,” Zhan says. “This is only possible because of our donors.”