Bats calculate where their prey is headed-by building on the fly predictive models of target motion from echoes, Johns Hopkins University researchers find. The models are so robust, bats can continuously track prey even when it temporarily vanishes behind echo-blocking obstacles like trees.
Although predicting object motion-paths through vision has been extensively studied, these findings, published recently in the journal PNAS, are primary to look at the comparable process in hearing. The work enhances the understanding of auditory guided behaviours in animals & humans including sight impaired people who listen sounds to trace objects in their surroundings.
“Just the way, a tennis sportsman must need to determine when & where they’re going to hit the ball, a bat must anticipate when & where it’ll make contact with the insect it’s hunting” said senior author Cynthia F. Moss, a neuroscientist & professor of Psychological & Brain Sciences. “The insect is flying. The bat is additionally flying. During this very rapidly changing environment, if the bat were to only believe the knowledge it got from the foremost recent echo, it might miss the insect.”
The bat uses the time delay between each echolocation call & the resulting echoes to work out how distant prey is. They tilt their heads to catch the changing intensity of echoes to work out where the prey is in the horizontal plane. Bats must put together echo information about object distance & direction to successfully track an erratic moving insect.
But because bats are such a good-hunters, the research team thought that the bats must even be somehow using this information to predict where they prey is headed. To check this in the lab, they designed an experiment that closely mirrored things of a bat hunting in the wild.
They trained bats to stay on a perch & track the insects. The team recorded the bat’s echolocation calls & head movements as they changed where the insects moved & how quickly. They also added obstacles that interrupted the echoes.
“We devised mathematical models to check the data and we came up with different hypothesis of what the bats might be doing” said co-first author Clarice Anna Diebold, a doctoral candidate in Psychological & Brain Sciences.
If bat wasn’t predicting where the insect would be, its head movements would always lag behind the target. But that wasn’t the case. If the bat kept his head during a fixed position, which sometimes reflected where the insect ended-up, that might eliminate the prediction theory. But that wasn’t happening either. And if the bat was only using information from the echoes to estimate velocity, that wouldn’t be enough to elucidate the extent of the bat’s precision.
“We hypothesized that bats use both the speed-information from the timing of the echoes and further adjust their head aim” said co-first author Angeles Salles, a postdoctoral fellow. “When we tested this model with our data, we saw it fit alright.”
The findings upend the previous accepted notion that bats don’t predict an insect’s future position, a conclusion largely drawn from a 1980s study done before high-speed video was widely available.
“The question of prediction is vital because an animal must plan ahead to make a decision what it’s getting to do next” said Salles. “A visual animal or a human’s features a stream of information coming-in, except for bats it’s remarkable because they’re doing this with only brief acoustic snapshots.”
Although bats are studied here, the findings apply to any animals that track moving sounds & even to people just like the blind, who use clicks & cane taps to assist them navigate while avoiding obstacles.