Calling someone “birdbrained” is not exactly a compliment. But a recent study demonstrates that our avian friends have a lot more smarts than we generally give them credit for—especially pigeons.
In lab tests, common pigeons were taught to read some of the same subtle cues in x-rays and microscope slides that medical professionals look for to distinguish between healthy and cancerous tissue. After just over two weeks of training, the pigeons could make the correct diagnosis 85 percent of the time, an astonishing level of accuracy that rivals the performance of human pathologists.
While you won't be booking an appointment with a pigeon doctor anytime soon, the results suggest that the birds could play a role in evaluating new medical imaging techniques and creating better display technologies.
“Pigeons may not be able to write poetry, but they’ve had millions of years to develop the abilities that they need to navigate a very complicated and dangerous world,” quips study leader Richard Levenson, a professor in the department of pathology and laboratory medicine at the University of California, Davis. “So it doesn’t surprise me that they can do pathology!”
Evolutionarily speaking, birds evolved tiny brains to facilitate flight: “Heavy heads don’t lift off,” says co-author Edward Wasserman, a professor of psychology and brain science at the University of Iowa.
The pigeon brain would fit on the tip of an index finger, but Wasserman calls it “a marvel of miniaturization” packed with a prodigious amount of visual intelligence that is in some respects superior to our own. Pigeons, for example, have four to five color receptors in the eye, whereas we only have three. They also appear to have better peripheral vision than humans, says Wasserman.
Moreover, the birds spend endless hours scanning the ground for small seeds and insects, so they have one of nature’s most finely honed abilities to analyze complex visual patterns and detect anomalies.
These traits inspired Levenson and his team to examine how well pigeons perform when evaluating medical imagery. They trained 16 birds using digitized images taken from mammograms and biopsy slides. The images were displayed on a touch screen flanked by blue and yellow “choice buttons.” In one trial, the yellow button signified “benign” and the blue button “malignant.” When the pigeon pecked the button corresponding to the correct answer, it was rewarded with pellets delivered to a dish.
Some of the tests involved finding micro-calcifications—calcium deposits that, in certain configurations, may indicate breast cancer—in the mammogram slides. The challenge of detecting these patterned white specks against a complex background is similar to what pigeons already routinely do in their visually cluttered environments.
The birds learned through trial and error without any verbal or other cues, says Wasserman. In the beginning, they were choosing the right button 50 percent of the time, which is what one would expect by pure chance. By day 15, however, the avian study subjects were 85 percent correct in determining whether tissue samples were normal or cancerous. After 25 days of training, the pigeons achieved a nearly 90 percent success rate, the team reports this week in PLOS ONE.
Pigeons can accomplish this diagnostic feat in part because they possess impressive long-term visual memories, being able to recall more than 1,800 images. But memory alone is not enough—for diagnostic tests, viewers also need to be able to generalize based on what they have seen in the past when confronted with completely novel images. Humans, for instance, can be shown photographs of different types of trees, and despite their varying shapes, colors and sizes, we can still label them all as “trees.”
Pigeons are also capable of generalizing. An earlier study by Wasserman showed that they can be taught to sort photographs into distinct categories like baby, bottle, shoe and tree. And in a 2009 study, psychologist Shigeru Watanabe from Keio University in Japan trained pigeons to differentiate paintings by Monet from those by Picasso.
"People often believe that the evolution of intelligence and higher cognitive ability occurred along a single line of evolution, namely mammals—in particular primates, great apes and finally humans," says Watanabe. But recent studies of comparative cognition have revealed that intelligence has evolved along many different branches of the tree of life, he says, and a good example is this highly developed visual cognition in birds.
“What really struck me about this current study is that despite their complexity, the pigeons learned to discriminate the medical imagery even faster than other stimuli, like faces and physical objects,” says Brett Gibson, an associate professor of psychology at the University of New Hampshire who specializes in animal cognition.
Gibson foresees a time when pigeons may be used with security scanners at airports to help spot suspicious items, or even to identify the faces of known terrorists. “There are lots of ways that their acute visual system can be used to help humans,” he adds.
Levenson agrees, but he says that pigeons are not about to replace pathologists and radiologists. For one thing, the birds didn’t hit a home run with certain types of breast masses in mammograms that have visually complex lesions and are extremely hard to read even for human radiologists.
And even for the lower-level tasks where the birds matched human abilities, there would be huge regulatory and legal hurdles to actually using them in diagnosis.
“What would the FDA think about pigeons?” muses Levenson. “I shudder to think.” Instead, the study team thinks the birds can replace trained medical technologists in some of the tedious grunt work of evaluating the products of new imaging systems, which are constantly being developed to improve the accuracy of cancer diagnosis.
In the meantime, though, an essential mystery remains: How do they do it? “Pigeons have the visual and intellectual wherewithal to master this task,” says Wasserman. “But that is not to say that how they do it is the same as how people do it.”
Pigeons may be tracking entirely different visual cues, so knowing what exactly they are seeing and how they are evaluating that information might help humans or even computers master better ways of analyzing medical images. Wasserman would next like to test the birds with advanced cameras that can track their eyes movements, and look at their performance examining the latest tool in diagnostic technology, 3D radiographs.
“We’ve got some extremely exciting opportunities ahead,” the pigeon expert effuses.