Bat echolocation

A data point with some relevance to bat echolocation, at least for one kind of bat.

“Echolocating bats rely on an innate speed-of-sound reference”

They extrapolate likelihood of confirming this phenomenon in other species.

Below, this earlier report (2017) is framed in terms of plans and execution, but does acknowledge
“a complex sensory sequence based on a sensorimotor feedback-loop”

“Bats pre-adapt sensory acquisition according to target distance prior to takeoff even in the presence of closer background objects”

Other work reported by Amichai:

and by Yovel:

Hi Bruce

The abstract to the article starts like this:

Animals must encode fundamental physical relationships in their brains.

This seems rather implausible. But the examples they give for saying this seems plausible:

A heron plunging its head underwater to skewer a fish must correct for light refraction, an archerfish shooting down an insect must “consider” gravity, and an echolocating bat that is attacking prey must account for the speed of sound in order to assess its distance.

In these examples, refraction, gravity and the speed of sound affect the feedback connection between action and controlled variable. Assuming that the heron is controlling the optical angle to the fish, this angle will change as soon as the heron’s eye enters the water. But it can still control the angle despite this sudden change to the feedback function. So I think you could model this without giving the model the laws of refraction. The archerfish probably also controls the optical angle to its target but the connection from output to input is ballistic and its trajectory is affected by gravity. Thus the angle and distance to the target will affect the course of the output to the target. My guess is that the archerfish always tries to release it’s “arrow” when the insect is at a particular angle and distance with respect to the archerfish.

The effect of changing speed of sound does present an interesting problem if one assumes that the timing of the echo return is used as an absolute measure of distance from the reflecting surface. Since the speed of sound changes fairly substantially with temperature (and to some extent with altitude) it seems that timing cannot be a very accurate measure of absolute distance unless bats come equipped with a table of sound speed as a function of temperature and altitude. But for some reason, the authors conclude that bats come equipped with an innate knowledge of the speed of sound (I presume at some standard temperature and altitude). I have no idea how they come to this conclusion. But here’s what they say:

We addressed this question by shifting the speed of sound and assessing the sensory behavior of a bat species that naturally experiences different speeds of sound. We found that both newborn pups and adults are unable to adjust to this shift, suggesting that the speed of sound is innately encoded in the bat brain.

I would like to know what they mean by assessing the the sensory behavior that results from a shift in the speed of sound? Since they say that the research was conducted on “a species of bat that naturally experiences different speeds of sound” it seems like variations in the speed of sound are not a problem for these bats in terms of navigating around in the dark. So I don’t know what they mean by the finding that " both newborn pups and adults are unable to adjust to [the speed of sound shift that they created]". Very puzzling.

It would be nice if someone could get a copy of this paper to see what they did and what they found that led them to conclude that “the speed of sound is innately encoded in the bat brain”.



According to the paper that I read at one of the links I posted, they trained bats to fly to a perch and then changed the atmosphere in the chamber substituting hydrogen instead of nitrogen. The bats came up short of the perch. This was unexpected. They then raised bat pups in that atmosphere and trained them, with the same results.

Hi Bruce

Very interesting! This sounds like what happened to Kohler after he had learned to ride a bike wearing inverted lens goggles. When the lenses went back to normal he could ride no better than when he first started with the inverted lenses. This suggests a couple things: 1) the bats are using the time echo delay to determine distance 2) the ability to perceive the time delay is innate 3) the ability to control this variable is learned and 4) they learn to control that variable in an acoustic environment where a particular time delay is an analog of a particular distance, just as we learn to ride a bicycle in an optical environment where a particular position in the visual field is an analog of a particular location in space. The next step would be to see if the bats who came up short in the hydrogen environment would eventually learn to make it to the perch after a few more trials, just as Kohler learned to ride a bike again after the inverted lenses were removed.

Apparently the changes in echo delay caused by variations in air temperature and pressure are not big enough to matter in terms of the bat maintaining a safe distance from reflective surfaces. According to my calculations, if there is as much as a 30 degree Fahrenheit difference in temperature in the environment in which the bat flies, that results in only a 3% difference in the speed of sound. So the accuracy of perception of absolute distance using just echo delay as the analog of distance would probably be good enough for avoiding collisions.

By the way, there is a 73% difference in the speed of sound between hydrogen and nitrogen; the speed in hydrogen is 1270 m/s and for nitrogen its 349 m/s, very close to the nominal value at 20 C, which is 340 m/s. So moving the bats from a nitrogen to a hydrogen atmosphere produced a very large change in the relationship between echo delay and actual distance, one that was nearly as great as the change in relationship between optical and actual spatial orientation produced by inverted lenses.

A basic tenet of PCT-based research ( which you can read about in The Study of Living Control Systems) is that you don’t produce disturbances (in this case, a disturbance to the feedback function) that might overwhelm the organism’s ability to control – that is, if you want to find out what variable they are controlling.