Amid a neuroscience debate about how animals and people focus on distinct objects within cluttered scenes, some of the newest and best evidence comes from the way bats see with their ears.

Bats demonstrate remarkable skill in tracking targets such as bugs through the trees in the dark of night. Brown University neuroscience Professor James Simmons, the review paper's author, has long sought to explain how they do that.
It turns out that experiments in Simmons' lab point to the "temporal binding hypothesis" as an explanation. The hypothesis proposes that people and animals focus on objects versus the background when a set of neurons in the brain attuned to object features all respond in synchrony, as if shouting in unison "yes, look at that!" When the neurons don't respond together to an object, the hypothesis predicts, an object is relegated to the perceptual background.
Because bats have an especially acute need to track prey through crowded scenes, albeit with echolocation rather than vision, they have evolved to become an ideal testbed for the hypothesis.
"Sometimes the most critical questions about systems in biology that relate to humans are best approached by using an animal species whose lifestyle requires that the system in question be exaggerated in some functional sense so its qualities are more obvious," said Simmons, who plans to discuss the research at the 2014 Cold Spring Harbor Asia Conference the week of September 15 in Suzhou, China.
A Focus of Frequencies
Advertisement
Of course it's more complicated than just that. Many things could reflect the same frequency pairs back at the same time. The real question is how a target object would stand out. The answer, Simmons writes, comes from the physics of the echolocation sound waves and how bat brains have evolved to process their signal. Those factors conspire to ensure that whatever the bat keeps front-and-center in its echolocation cone will stand out from surrounding interference.
Advertisement
With support from sources including the U.S. Navy, Simmons's research group has experimentally verified this. In key experiments (some dating back 40 years) they've sat big brown bats at the base of a Y-shaped platform with a pair of objects – one a target with a food reward and the other a distractor – on the tines of the Y. When the objects are at different distances, the bat can tell them apart and accurately crawl to the target. When the objects are equidistant, the bat becomes confused. Crucially, when the experimenters artificially weaken the high-pitched harmonic from the distracting object, even when it remains equidistant, the bat's acumen to find the target is restored.
In further experiments in 2010 and 2011, Simmons' team showed that if they shifted the distractor object's weakened high frequency signal by the right amount of time (remember: 15 microseconds per decibel) they could restore the distractor's ability to interfere with the target object by restoring the synchrony of the distractor's harmonics. In other words, they used the specific predictions of the hypothesis and their understanding of how it works in bats to jam the bat's echolocation ability.
If targeting and jamming sound like words associated with radar and sonar, that's no coincidence. Simmons works with the U.S. Navy on applications of bat echolocation to navigation technology. He recently began a new research grant from the Office of Naval Research that involves bat sonar work in collaboration with researcher Jason Gaudette at the Naval Undersea Warfare Center in Newport, R.I.
Simmons said he believes the evidence he's gathered about the neuroscience of bats not only supports the temporal binding hypothesis, but also can inspire new technology.
"This is a better way to design a radar or sonar system if you need it to perform well in real-time for a small vehicle in complicated tasks," he said.
Source-Eurekalert