Troll darksense and bat sonar

From: Dag Stålhandske <>
Date: Sat, 8 Sep 2001 16:58:38 +0200

I am glad that so many people have replied to my little paper on troll darksense. This discussion group has so far appeared to be dominated by metaphysics, which I do not find very interesting. (Go on, those who are interested in that subject, however. This is the right forum for Gloranthan metaphysics too and those who are not very interested, like me, can easily sort it away as long as you have a subject line that clearly states your subject.) It seems like most people who have replied have put some thought into the matter. Here is my attempt to reply most of you.

ON BATS AND TROLLS I got my fact on bat sonar by using the google search engine with the words: bat sonar. The articles I have read were:

Astounding bat mobility Neuroethology echolocation in the bat Frequency of Bat Sonar

The basics of bat sonar are these:
"Bats that echolocate are of the suborder Microchiroptera within the mammalian order Chiroptera. Within the Microchiropteran suborder there are over 800 species of bats, and these bats produce all manner of sounds for echolocation, from bisonar pulses to clicks and other calls. Many of the Microchiropteran bats that echolocate do so for the purpose of catching prey, mainly insects. Therefore their echolocation abilities are a premier sensory modality in their nervous systems. Bats like the mustached bat pictured above have nervous systems highly dedicated to the task of echolocation, and are an excellent species to study from a neuroethological perspective."
(Direct quote from Neuroethology echolocation in the bat.) In layman's term that means that certainly not all bats use echolocation. Those that do use many different forms of echolocation. Those that do use echolocation however, are such that evolution has spent a great deal of effort in optimising their nervous system to make echolocation as effective as possible.

Based on this I believe that those who wish to discuss from a scientific point of view should not say: "bats are like this" or "bats do like this". There are a great many species of bats and all do not use echolocating. Those that do have many different forms of sonar and ways of using them. Therefore I believe we should state what type of bat we are referring to and give a reference to show from where we got our facts. Those that prefer to discuss the matter from a role-playing, rather than scientific, point of view, should of course feel free to do that. Personally I feel that the point "this makes play more interesting" is much more valid than "this is much more scientifically correct" in this situation. You could also discuss the matter from an exegetic point of view (exegesis is the "scinece" -yeah, sure- of carefully interpreting holy scriptures) and try to "read between the lines" from various RQ supplements.

Some of you have pointed out that bats can fly in dense formations appearently without colliding. If this could be achieved only by sonar, it would be strong evidence that bats can use their sonars effectively without being disturbed by all the other bats' sonars. However, avoiding collision with one another can be achieved through many other senses: touch (feel the draft when you come close to another bat), hearing or sight. According to the Swedish National Encyclopeida the oft-repeated statement that bats are blind is untrue, megachiroptera have good eyesight, microchiroptera have unimpressive sight but are not blind. Many birds, that certainly do not have sonar, can fly in dense flocks without colliding. However, if a sonar-using species of bat prefers to hunt in large flocks, that would be strong evidence that bats are not significantly disturbed by each others sonars.

On the matter whether individual trolls use different frequencies, it seems that the various forms of echolocating bats all use rather broad spectra of frequencies. The reader can find more information on this in Therefore it is reasonable to assume that trolls do hear one another's sonar signals and if they are not to be disoriented by them, their brain must be able to somehow differentiate between their own signals and those of others. Furthermore, the troll must be able to do so without much conscious effort. Many species, including humans, have an impressive ability to subconsciously intergrate and analyse information. Consider for instance the cocktailparty-effect. A human can follow a conversation between several people among a cacaphony of voices. Apparently neither the physical location of the speakers, their voices or the subject spoken of is critical to this ability, but if all change simultaneously, it is not longer p! ossible to follow. Similarly a human can easily listen to a single instrument in a symphony. When I studied perception psychology (in 1994), no artificial signal processing could perform a similar feat without human help, though the technology might have improved since. Similarly, according to the "Astounding bat mobility" a big brown bat (eptesicus fuscus) could detect an insect in a bush. A most impressive feat given all the echos that must be bouncing from the leaves.

Some of the questions we have raised are largely dependent on the physics of sonar. Such as is a troll can look around a corner by clever use of a bounce, if a troll has 360 degrees vision, to what extent headgear will hamper sonar, how you hide from sonar, how useful sonar is in medicine and prospecting. Regardless of how good ability to process sonar information a troll has, it will be of little use in prospecting if sonar cannot penetrate more than a few inches into rock. Other matters, however, are dependent on the exact physiology of and nature of the sonar used and on the trolls perceptive/neurological ability to process that information. Such questions are whether a troll can jam another troll, how much information a troll can get from listening to another trolls sonar, to what extent sonar can be used for long-range communication, to what extent a troll is disturbed by sonar echos from other trolls and whether a troll can move its head while using the sonar. If it can ! integrate the information on exactly how much it has turned its head with the information it has received from the sonar, the troll can bloody breakdance while using sonar if it pleases him. If a troll can "signature" his ultrasound and easily sort out other echos like some of you have suggested, trolls would not be very disturbed by other trolls use of ultrasound, jamming a troll would be very hard (the signal would have to be so strong it "blinded" the troll, the equivalent of a bang that blasts your eardrums or a light so harp you are blinded for a few moments) and communication by ultrasound would be much easier than I envisioned. My descripiton assumed that trolls had a fairly simple ultrasound generator and not a very effective signal processing ability. Problem is, science cannot tell us anything about troll neurology or the troll sonar generator, since trolls don't exist (I believe!). Similarly, we cannot use evolutionary logic since trolls were not created by evolutio! n. Therefore it all boils down to the fact that real world analogi

Therefore I encourage each Narrator to interpret sonar in a way he thinks will be as interesting for game purposes as possible. An active detector (i.e. something that send out singals as well as receives them), is always a tactical dilemma. If you use it, you make your presence very obvious to anyone with a similar detector or with a passive version of your detector. It can be interesting to have troll characters discuss exactly how much and in what way they will use darksense. In that case you can go all the way with sonar signatures, sonar communication etc. However, if only one player is a troll or only one player is very interested in these matters, I suggest you use some simple no-frills model for how a troll sonar works. By all means say that no troll is able to hear another troll's sonar at all for some reason, it may not make sense scientifically but who cares. If you feel sonar is somehow disruptive to the mythical, magical atmosphere of the game, just toss it out th! e entire sonar model as described in trollpak out the window. Darksense will let a troll see in the dark as good as a human can see normally, minus colour. If it's stupid but works, it ain't stupid.

HIDING FROM SONAR Maybe I should elaborate what I meant by hiding by leaning against a wall. I did not mean that this this would be a very effective way of hiding if the troll is heading towards you and you hide facing the troll. What I meant was that yo could make yourself harder to detect be pressing yourself against a so that the troll is now facing your left or right. By turning sideways, you make yourself a smaller target for the troll's sonar and by pressing yourself against the wall you reduce the contrast against the environment. Furthermore, since the average cave wall is very irregular, you are in partial sonar "shadow". Regardless of how skilled a troll is in interpreting the sonar information he receives, this should reduce the chance of the troll detecting the hiding person when compared to standing in the middle of the tunnel.

REGARDING THE MATTER OF 360 DEGREE VISION Snead said that sonar was fairly focused, Simon Hibbs pointed out that the emitter was in the snout according to trollpak. Unforutnately Simon did not give a page reference. What I found after a brief search was this: "However, this snout is modified for sound production and reception -not smelling." On page 24 sidebar under the heading "smell" in Book 1 Uz Lore. I does not specifically state that the snout is the source of ultrasound, but it seems a reasonable guess. If it should be possible to see 360 degrees the sound must travel in that direction too and the troll must be able to detect an echo coming from behind. The latter is obvious that it can do, you can certainly hear sounds coming fro behind, and there is no reason to say that a troll could not, especially since it according to trollpak uses the bones of the head and not just not the ears. So even if their ears are very directionally selective, and there is nothing under the heading "hearing" in trollpak that suggests that, a troll would be able to detect sonar from behind. The question is whether sufficient sound is travelling backwards from the face the troll is facing. Sonar may start as being focused, but it is still subject to Huygens principle and thus spreads in all directions, though certainly not equally much in all direction. (This is the reason you can hear around a corner, even if the wall were perfectly sound absorbing.) Therefore, I believe that a troll should have!  360 degrees vision with the vision straight ahead much better than from behind. However, that is only the scientific view.

The most valid conterpoint I have heard in this matter, in my view, was made by James Frusetta:

"Defintely not according to Gloranthan sources -- since the Zong cult
has the "secret" that allows them do so (which is actually just moving their head around in a traditional pattern). If uz could do it, no need for a secret! "

I accept that and say that trolls in our world will not have 360 degress vision but a vision roughly similar to a human.

TROLL HEADGEAR I stated that any headgear would more or less hamper a trolls sonar, since a troll uses his entire headbone to detect the sonar echo and anything between the head and the ultrasound could block or dampen it. A troll's headgear would of course leave the snout and ears free, but it could hardly leave the head free, or it would not be headgear at all! Exactly how much a helmet that leaves a trolls ears and snout free would disturb a troll's sonar is anybody's guess. I said that it would be enough for a troll sentry not to wear the helmet until danger approached, but not dampening enough to make the helmet useless. That seemed like a reasonable compromise. Once again, do what you believe fits the interests of a good game best.

HOW USEFUL SONAR IS FOR COMMUNICATION When I said that trolls did not use sonar for communication I did so because it would be the easiest option. Also I am not too fond of trolls having a "radio" with several kilometer range. (Complete with "radio talk", it would probably be necessary to say the troll equivalent of "over" when the transmission is over since their is a several seconds delay for the message to reach the recipient.) It spoils the mood if trolls can chit-chat as much as they like when sneaking up on humans. Assuming that the darksense had a rather simple transmitter, I made it not very useful for communication. However a closer look at troll pak book 1 page 28 the sidebar shows that trolls do use some ultrasonic sounds for communication. However, it does not seem to be a full language, rather a set of signals.

Dag Stålhandske

End of The Glorantha Digest V8 #524

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