arf@gagme.chi.il.us (jack schmidling) (06/22/91)
Article 4646 (45 more) in sci.bio: From: troach@netcom.COM (Tom Roach) Subject: Bat's sonar revisited >There is no doubt that the bat can catch insects on the wing, and there is a fairly good presumption that it uses sound, and "chirped" sound at that, to dothis.... For a bat, or anything else, to be able to distinguish a 10 nanosecond differential in time of arrival of a sound wave is difficult for me to believe. ARF says: Two points of interest here. First of all, for what it is worth, the echo-location calls of bats are pulses of short duration and vary in frequency and rep-rate as a function of distance to the target. The "chirps" one (a human) hears are socializing calls. They are used to find and identify young/parents, for courting and during grooming and play time. Second point is that the vast majority of insect catches are made in the inter-femoral membrane. This is wing-like tissue streatching from hind leg to leg on bats that have them. It serves the purpose of a large net for the ones that get away. The bats pokes his head into the net to retreive the captured prey while in flight. The point being that if the resolution requirement was based on a direct hit by the much smaller mouth, it was based on a false assumption. >Anybody out there with more information, or better yet, an explanation to discount/explain anything I have said above? It is impossible to prove a negative but studies have been done in totally dark rooms with wires from floor to ceiling, on one foot centers. The bats rarely hit the wires and echo clicking is continuous while the bats are in flight. I do not recall the species of bat but my experiments with Eptesicus fuscus (Big Brown Bat) were not quite as dramatic. They would frequently run into random wires even with the lights on but never into larger objects. Whether they are doing something else, we will not know until we know. However, we didn't know they were clicking until someone had the bright idea to listen for sounds out of the human range. arf
davidh@uhunix1.uhcc.Hawaii.Edu (David A. Helweg) (06/23/91)
> > Article 4646 (45 more) in sci.bio: > From: troach@netcom.COM (Tom Roach) > Subject: Bat's sonar revisited > > fairly good presumption that it uses sound, and "chirped" sound at that, to > dothis.... For a bat, or anything else, to be able to distinguish a 10 > nanosecond differential in time of arrival of a sound wave is difficult > for me to believe. > >Anybody out there with more information, or better yet, an explanation > to discount/explain anything I have said above? The "10-nanosecond" paper that I referred to is written by J. Simmons et al., and appears in Journal of Acoustical Society of America in 1990. I don't have the exact reference at my fingertips and there is almost certainly more than one article by Simmons' lab for that year. I'll post the exact reference when I can find it. One important point to keep in mind here is that Simmons collects his data in the lab, using "acoustic jitter" methodology. This requires a bat lying on a platform to discriminate between an artificial echo that is generated after a *fixed* delay and an artificial echo that is returned after a stochastic delay with a mean delay equal to that of the fixed delay. Thus, the echoes are "jittered" in time-of-arrival. The bats Simmons used were capable of discrim- inating between stationary and jittering echoes with a jitter envelope of 10 nsecs. As you have guessed, this setup is anything but ecologically realistic. The bats crawl to the correct side (the jittered side) of the platform and get a mealworm reward. They are not even hearing true echoes, rather, they are presented with a delayed copy of their outgoing cry. But the important point is that the animals seem to be able to detect those incredibly miniscule portions of time. This is truly a puzzle, in terms of neural coding. Certainly individual neurons have a margin of error in their firing rates and neurotransmitter release of about a millisecond. But it is a far stretch of the imagination to think of even a population of neurons that cascade onto another layer (etc) that could achieve the kind of resolution Simmons reports. I'm certainly not saying that it isn't possible, but after working in the field of animal cognition for some time, I would first look to see if the electronics and behavioral paradigm weren't providing some kind of cue to the bats.... As for ecological validity, do humans need the neural system that allows us to invent email for survival? (I'm sure I'll get it for that statement ;-)) dah
pbrewer@urbana.mcd.mot.com (Philip Brewer) (06/26/91)
> Two points of interest here. First of all, for what it is worth, the > echo-location calls of bats are pulses of short duration and vary in > frequency and rep-rate as a function of distance to the target. Different species of bat echo-locate different ways. One well-studied species (I forget which one, but could find out if anybody is really interested) varies pulse frequency and rep-rate in a more complex fashion than just as a function of distance to the target. First, they use one sort of call to locate a possible prey object. Once they have one, they switch to a different call. This latter call is tuned so that the echo return will doppler back at a specific frequency. If the echo return is not at that frequency, it means that the bat's notion of the relative velocity was wrong. It will then change the tone of the call based on a new estimate of relative velocity. So, they extract more data from the pulse return than simply the range. They can estimate the range based on not only the time between call and pulse, but also (since they know the closing rate) based on the previous range minus the relative distance traveled. -- Philip Brewer pbrewer@urbana.mcd.mot.com Motorola Urbana Design Center ...!uiucuxc!udc!pbrewer Kie estas la fajro, mak?