|
Author
|
Topic: The New Huntmastersbbs!2: Question about coyotes ability
|
Rich Higgins
unknown comic
|
posted December 11, 2004 09:41 AM
to pinpoint source of sound.
Bill Martz and Steve Craig stated that coyotes cannot distinguish between volume and proximity. That is to say that they perceive loud sounds as being close and muted as being distant. I believe that a coyote can pinpoint the source regardless of volume. Agree? Disagree?
Robb Krause stated recently that coyotes hear on a horizontal plane. They cannot differentiate between sounds on a vertical plane. That is they cannot tell if a sound originates from the base of a tree or ladder or from the top. Agree? Disagree?
[ June 08, 2006, 11:22 PM: Message edited by: Leonard ]
IP: Logged
|
|
albert
Knows what it's all about
Member # 98
|
posted December 11, 2004 10:29 AM
I believe that Bill and Steve are right. I believe this because I feel that louder volumes call more coyotes. Why because it thinks what ever is making the noise is close. I don't think that a coyote is smart enough to whether it has covered 1/2 mile or a mile. it just thinks that because of the volume that it is just over the next"hill". I have seen many coyotes walking past looking for the source of the sound. I feel that this happens quite often when howling.
I also feel that a coyote can reconize sound on it's vertical scale. I am quite certain that i have seen coyotes loking up in the sky looking for the source of the sound. geese fly crows cawing etc. The reason it may appear that it doesn't is that expierence tells a coyote that a rabbit making a distress sound is on the ground not up in the sky. So the coyotes limited logic tells it to look on the ground for a critter in distresss not in the sky.
--------------------
for what it's worth, eh!
Posts: 195 | From: Parkland, saskatchewan, canada | Registered: Feb 2003
| IP: Logged
|
|
varmit hunter
Knows what it's all about
Member # 37
|
posted December 11, 2004 10:40 AM
This is going to be like stepping into a Bear trap.
Rich, As you well know I open 98% of my stands with a wide open blast. Many times I have had one coming in wide open before I finished the first series. I am of the believe that you don't blow them out of the country.
I totally agree that they can" pinpoint" the location of the sound.
As far as the vertical goes. I have had many of them look up at me when calling from a tripod are tree stand.
Ronnie
--------------------
Make them pay for the wind.
Posts: 932 | From: Orange,TX | Registered: Jan 2003
| IP: Logged
|
|
Leonard
HMFIC
Member # 2
|
posted December 11, 2004 10:41 AM
Hmmm? I disagree with the theory that coyotes rely on volume to judge distance. Seen that so many times, I don't know where to start? I believe they have a good fix on distance, when within reasonable proximity, regardless of sound volume. I don't think it applies from distances between ½ to a mile distant, but inside that, roughly, they know how far away is the sound, regardless of how loud it is.
Also disagree with Krause; no surprise there, right? In fact, I prove it to my own satisfaction when calling at night. If the sound is coming from a speaker mounted under my rear bumper, and I switch it to a speaker mounted above the cab, I can see the eye reflection much better, the closer I am to the light source and the sound source. In other words, they look down, eighteen inches off the ground, in one case, and the eye shine is indistinct. But, they look up, to the source of the sound, above the cab, and light up very brightly. They are looking up, and they are looking down, and don't have a bit of trouble telling the difference.
WHAT DO YOU THINK?
Good hunting. LB
[ December 11, 2004, 10:44 AM: Message edited by: Leonard ]
--------------------
EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32367 | From: Upland, CA | Registered: Jan 2003
| IP: Logged
|
|
Tim Behle
Administrator MacNeal Sector
Member # 209
|
posted December 11, 2004 01:06 PM
A few years ago, I set up in a small valley. I put the caller at the base of a tree and the speaker about 8' up in the branches, then sat on the side of the hill watching.
A couple of minutes after the coyote puppy tape started, I had a wet bitch sitting on her butt at the base of the tree looking up.
She had to have known there was no way a puppy could get up a tree, but she ran right in and sat down to look for it.
I don't think most animals make it a habit to look up. But if that is where the sound is, they don't have any problem looking right at the source.
--------------------
Personally, I carry a gun because I'm too young to die and too old to take
an ass kickin'.
Posts: 3160 | From: Five Miles East of Vic, AZ | Registered: Jun 2003
| IP: Logged
|
|
Greenside
seems to know what he is talking about
Member # 10
|
posted December 11, 2004 01:25 PM
Here's my theory:
Unlike humans coyotes can cock their ears independent of their head. This gives them the ability the pinpoint the exact direction of the sound in the snap of a finger. I would make a guess that it would be closer than a degree from a mile away. If you take a partner out howling to locate coyotes and after one responds, if on the count of three you both pointed to where you heard the howl, I think you would be lucky to be within 5 degrees of each other.
For the volume of the sound to determine location, I'm not quite sure.
I'm not a sound engineer but to a certain extent this is what I think happens. Sound attenuates(I think that's the word) or fads the farther it gets from the source. I'm not sure if you could straight line graph it, but this might be close if I give an example.
You start out on a stand calling loud, say 100 decibels and a coyote hears you from a mile away. At the mile distance he might be hearing only 10 decibels of sound as he starts coming to the call. You continue calling but gradually decrease the volume. When the coyote gets to the one half mile mark you are calling at 50 decibels and the coyote is still hearing the same volume in decibels as he started out with at the one mile mark. When he's at 250 yds you are only calling at 25 decibels and he's still hearing the same as when he started out.
I think that's one of the reasons we get hard chargers. The coyote thinks that because he's not hearing the sound volume increasing that he's not getting closer so he keeps charging till he runs right over the top of you.
The opposite of that would be if you kept calling at the same volume as what you started with the volume would be incresing as the coyote got closer to your your location. I think this is one of the reason coyotes start coming slower to the call. They know their getting closer and they start using their eyes and nose to locate your position.
If you are in a tree stand, the first kiss will get a coyote to look your direction, on the second kiss he'll look right up at you.
Dennis
Posts: 719 | From: IA | Registered: Jan 2003
| IP: Logged
|
|
Leonard
HMFIC
Member # 2
|
posted December 11, 2004 07:02 PM
To offer another point to ponder. I can drive while playing distress sounds, and a coyote coming from either side will change direction, and wind up coming in behind the vehicle.
In other words, I am quite sure that a coyote can hear a sound, at a certain fixed volume, while at a fast trot. I believe it is quite reasonable that the coyote can be assuming that the distressed rabbit is running away from him, or something is dragging it away. Of course, they cannot reason, but I don't think they scratch their little head and say: "hey, that sound should be getting louder" or "that sound is way too loud." With the variation of wind currents, I believe that they aren't necessarily spooked by loud sound.
Good hunting. LB
--------------------
EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32367 | From: Upland, CA | Registered: Jan 2003
| IP: Logged
|
|
Byron South
Knows what it's all about
Member # 213
|
posted December 12, 2004 03:30 PM
I absolutely believe that a coyote can pinpoint with pretty good accuracy where the call is originating from, even from a great distance. I have many times witnessed coyotes called from way out yonder with just one series blown from a call. Most of the time they come in a pretty direct route, unless there are terrain features that inhibit his forward progress. I don't think the volume has much to do with it other than it has to be loud enough for them to hear it. I don't vary the volume of my calling very much from beginning to end of my stands, with the exception of toning it down sometimes when I have one checking up fairly close. When I'm calling with a hand call I believe that emotion and desperation gets their goat more, than too much or too little volume. I'm not one of those that believes coyotes are spooked with to much volume, but I have seen coyotes spooked when they get very close to a speaker that is playing very loud. It's usually to late for him at that point though. I have gotten in the habit of muteing the call when I get one close. This sometimes makes them stop or at least slow down. Coyotes hearing is considerably more acute than humans. The coyotes ability to rotate their ears and the larger size enables them to detect and pinpoint sounds of reasonable volume from great distances whether the sound is up in a tree or on the ground. I don't use extra loud distress sounds unless it is windy, and I try not to hunt unless I have a client on windy days.
Answer:
1.I agree that a coyote can pinpoint the source regardless of volume.
2. I disagree that a coyote is limited by horizontal hearing.
Coyote are in FACT spooked by unpracticed shooters making loud BANG, BANG, BANG, noises at them.
Byron ![[Big Grin]](biggrin.gif)
[ December 12, 2004, 03:35 PM: Message edited by: Byron South ]
--------------------
"Coming to the Call" predator hunting videos. Volumes I, II, III and IV. Order two or more and pay no S&H www.comingtothecall.com
Posts: 313 | From: Texas | Registered: Jun 2003
| IP: Logged
|
|
Leonard
HMFIC
Member # 2
|
posted December 12, 2004 04:23 PM
Talk about looking up. I was making a tape, one time, in a local quarry, no hunting allowed.
For me, it was close and private, I didn't think about the possibility of calling a coyote in the middle of the day.
Well, I did, which was okay, just to work him and see his reaction, and vary the presentation, etc.
All was going nicely, until an airplane went overhead, and my only thought was that it messed up my recording. A quick look over at the coyote, and he was following that Cessna as intently as I was.
Good hunting. LB
--------------------
EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32367 | From: Upland, CA | Registered: Jan 2003
| IP: Logged
|
|
Greenside
seems to know what he is talking about
Member # 10
|
posted December 13, 2004 08:12 AM
How many of you have had a turkey in a pasture or one that's hung up in a timber 40 yards in front of you? He's facing you, in full strut, and he throws his head straight out at you and gobbles. He sounds very loud and close. The next thing he does is spin 180 degress and gobbles again. His location and the volume of the gobble is the same as the first time, but this time he sounds like he's 100 yds away. If you couldn't see him you would probably assume he had moved away from you.
That's from a human perpective, but I think it might be very similiar to a coyotes.
IMHO, coyotes can be fooled if you keep that in mind. Howl directly at them with a megaphoned howler, then remove the megaphone and howl away from them. I think coyotes will hear that as two coyotes in two different locations even though the sound originated from the exact same place. Ones close and the other one is far off based solely on volume.
Shoot me down!
Dennis
Posts: 719 | From: IA | Registered: Jan 2003
| IP: Logged
|
|
Leonard
HMFIC
Member # 2
|
posted December 13, 2004 09:07 AM
Not me. As a matter of fact, I use that method in my bag of tricks, when I have an animal hang up, mostly at night. I will turn and call normally, but 180º from the coyote's direction. I don't know the exact theory, but sometimes they decide to come closer. For some reason, I think it works slightly different than muting the volume. Just don't expect me to prove that it works. I have had that demanded of me before; it makes me cranky. ![[Smile]](smile.gif)
Good hunting. LB
--------------------
EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32367 | From: Upland, CA | Registered: Jan 2003
| IP: Logged
|
|
R.Shaw
Peanut Butter Man, da da da da DAH!
Member # 73
|
posted December 13, 2004 09:29 AM
I agree with Dennis.
I believe from a long distance, the coyote gets a line to the sound. He travels that line until arriving at the source. The exact location is obtained when the coyote is much closer. Say 100 yards or less.
Gun fire scaring coyotes. If you have ever been shot at, there is a lot more associated with it than just a loud bang.
Randy
Posts: 567 | From: Nebraska | Registered: Jan 2003
| IP: Logged
|
|
Steve Craig
Lacks Opposable Thumbs/what's up with that?
Member # 12
|
posted December 13, 2004 09:55 AM
"coyotes can not distingusih between volume and proximity".
Not what I said. I stated that Volume, EQUALS proximity! And this goes for lions as much or more than the other predators. You want to call more lions, increase your volume. Bears too! I have been from the old school that has always taught to start out quiet and then build and then back down again. I have since changed my thoughts on this reasoning, and have proven(to myself) beyond a shadow of a doubt that the louder I play my caller, the closer my target animals come in, and the higher success rates I have. A very good example is I have played the mouse vocalizations on my WT at full volume and the coyotes and fox still pour in on top of the caller. Yet I do not know of any 100 pound mice, but it sure sounds like one. Played at that level, it sure doesnt sound like any mouse I have ever heard. But it works and works well. Randy Shaw was just here for a hunt, and you can ask him what he thinks of this volume thing. I put 20 coyotes,6 fox and 2 bobcats in front of him and the only volume level I used was #5 and 6 on the WT. The two highest volume settings. I had both bobcats less than 30 yards from the speakers. Coyotes and fox ran up to the speakers and one jumped on it. I dont care what you use. If it works for you,Great! Keep doing it your way. This is what works for me and my success rates have gone up because of it.
As far as Mr.Krause's statement about them hearing or not hearing on a vertical plane.
His ignorance or inexperience is showing. Nothing wrong with being ignorant, it just means one doesnt know enough about a particular subject AT THIS TIME! I feel he needs a few more miles and critters under his belt before making such a blanket statement. What in the wide,wide, world of sports am I supposed to do with all those coyotes,bobcats, lions and foxes that come in and put their noses(or at least try too) in that speaker that I have hung 3 to 6 feet HIGH off the ground? (at full volume too! hehe) I guess Randy Shaw was not supposed to shoot that coyote that came in to my caller and stood on a shear cliff 75 feet high and looked DOWN at the speaker! You want to have some fun in the hills, and cliffs, use 2 WT callers and put one high and the other low and watch what a coyote will do. He will spot both speakers. Or maybe I was not supposed to shoot all those Indiana coyotes that came to my deer stands and looked UP at me in that tree 12 to 20 feet OFF the ground while blowing that hand call. Hundreds of them over the last 40 years. Or what about the hundred or so coyotes that died from looking DOWN at me over the river or creek bank there too! Coyotes,bobcats,fox and lions all will look up and will look down to locate the sound. This fact does come from years of experience and has the numbers and miles behind it to prove it. You guys are sure learning a few more tidbits about how to call more lions!
FWIW
Steve
[ December 13, 2004, 10:05 AM: Message edited by: Steve Craig ]
--------------------
Yes, we did produce a near-perfect republic. But will they keep it? Or will they, in the enjoyment of plenty, lose the memory of freedom? Material abundance without character is the path of destruction. - Thomas Jefferson
Posts: 442 | From: Cottonwood,Az, USA | Registered: Jan 2003
| IP: Logged
|
|
Bryan J
Cap and Trade Weenie
Member # 106
|
posted December 13, 2004 09:57 AM
Great topic Rich, I love these topics that make me think about what I do and why. They raise questions in my mind as to how the coyote interprets my presentation.
Higher pitched sounds seem to work better for me. I believe this is the case because my set up almost requires a coyote to run me over. Higher pitched sounds are more directional than lower pitched sounds and I believe that the higher pitched sounds make it easier for the coyote to pinpoint exactly where the sound is coming from. I like to throw my distress sounds around like Greenside mentioned with the howls. I always thought that I was mimicking a flopping animal in distress. The changes that I make in volume I have always considered to be changing the level of strength and distress in the animal that I am mimicking. All in all, the only thing I know for sure is if a coyote doesn’t hear it they will not respond.
Posts: 599 | From: Utah | Registered: Feb 2003
| IP: Logged
|
|
albert
Knows what it's all about
Member # 98
|
posted December 13, 2004 12:06 PM
I agree great topic, good answers.
--------------------
for what it's worth, eh!
Posts: 195 | From: Parkland, saskatchewan, canada | Registered: Feb 2003
| IP: Logged
|
|
Jay Nistetter
Legalize Weed, Free the Dixie Chicks
Member # 140
|
posted December 13, 2004 02:35 PM
How do you explain why a good retriever looks up to scan the sky when he hears ducks or geese? Hmmm. More than once I've seen coyotes look up at ravens and crows when I'm sure they couldn't have glimpsed any movement. Where does the "vertical plane" begin and end? Is is one inch below the ground to 18 inches above? Three feet? 50 yards? And yes, I have had coyotes with their nose to the ground never once looking up at me, but have been busted by those that did.
I just cannot fathom that a coyote doesn't perceive loudness of source to proximity. Makes me wonder about what I see when a coyote is mousing. He hears a noise and abrupty turns and pounces on the precise spot where the mouse is (or darn close). If the sound were exaggerated, I'd bet money that the coyote would overshoot the potential meal.
--------------------
Understanding the coyote is not as important as knowing where they are.
I usually let the fur prime up before I leave 'em lay.
Posts: 1006 | From: Arizona | Registered: Feb 2003
| IP: Logged
|
|
keekee
Knows what it's all about
Member # 465
|
posted December 13, 2004 03:15 PM
Great topic!
I think predators do judge distance by sound. If the louder the sound the closer they are to the sound. I always tone my volumme down to work a predator, even grey foxes do the same thing. Good example....I can have a predator hung up say 60 yards away, I can tone down my calling and bring them on in sometimes, LB said this as well, I will turn around and call away from the predator, this to me, makes them think they prey is further away or another predator is leaving with its dinner. Same with howling. I have done this turkey hunting for a long time.
I also think predators can tell pretty close as to were the sound is coming from. I have been calling from tree stands, rocks, that give me good view points and had coyotes come in and look right up were I was right at me. So I also think they can point out the sound very well. I was seting in a deer stand a few years ago and seen a coyote cross a old growed up field, I always carry a call so I got the call out and started calling. The next thing I new I had another coyote seting 20 yards behind me looking right up the tree I was seting in. Im sure he was trying to figure how that rabit got hung in that tree! Till he seen me move and left, the first coyote came out of the brush on a run and when I lip sqeaked to stop him for the shot he looked right at me as I released the shot.
Brent
--------------------
Kee's Custom Calls
http://www.keescalls.com
Posts: 295 | From: Southern Ohio | Registered: Dec 2004
| IP: Logged
|
|
Byron South
Knows what it's all about
Member # 213
|
posted December 13, 2004 04:42 PM
R.Shaw,
I'm very familiar with what gunfire sounds like on the recieving end. I'm also aware that it will make a coyote turn wrong side out trying to make an escape. That line about the BANG, BANG, BANG, was an attempt at humor on my part .
I also agree somewhat with what has been said about a coyote getting a line on where the sound is eminating from, from a great distance. The closer they get to the sound the closer they are able to determine the excact position of the source, regardless of volume. Common sence is all that is needed to know that louder distress cries will reach more animals. You simply call a larger area with louder sounds. I don't however always find it nesasary to call a coyote from 2-3 miles a way. Don't like sitting there that long, and I absolutely hate late comers . If I was calling Lions as Steve, in big country, I would most certainly want to call loud because of the area needed to cover to get the attention of the more widely spaced Lions. For coyotes though, I believe any resonably loud call will be detected by coyotes as far away as I intend to call them from. In most of the area that I call. Coyotes in most of the areas I hunt have natural barriers that inhibit, and to a certain extent, prevent them from approaching from further than 3/4 to 1 mile away. In many of my spots the coyotes are inhibited from responding to my attempts from less than 1/2 mile. This is typical in the East (I live in East Texas). In most of the places that I call I'm within pretty close proximity to the target animal. If I were to play the distress call loud enough for them to hear it in the next county, they would hear it but not respond because they would have to be exposed to too many obsticles such as houses, county roads, open pasture. These coyotes are wired tight and are very hesitant about moving away from cover in the daylight. So in short it serves no useful purpose to try and call them from the next zip code. They won't come. Example: I recently obtained a new place to hunt here in East Texas. Its approximately 500 acres. I could easily get on one end and call my head off where every animal on the 500 acres and the surrounding properties would here me. Will this work to my advantage? Probably not. This place is mostly open hay meadow with brushy swampy patches of brush and trees interspursed all through it. Experince has taught me that I'm better off slipping into close proximity to these brushy portions and calling into them. Not real loud so as not to alert the coyotes at my next set 1/2 mile away and make my approach to it difficult. Did I mention they are very reluctant to cross the open hay meadow during broad daylight?
Summary: While I don't believe that loud calling will spook coyotes, I also don't believe that it is a great idea to crank the call to its loudest setting at every stand. Common sence, experience, and woodmanship skills have to play a role in detemining many of the things that seperate the "so so" callers from the consistantly successful callers.
Byron
--------------------
"Coming to the Call" predator hunting videos. Volumes I, II, III and IV. Order two or more and pay no S&H www.comingtothecall.com
Posts: 313 | From: Texas | Registered: Jun 2003
| IP: Logged
|
|
Steve Craig
Lacks Opposable Thumbs/what's up with that?
Member # 12
|
posted December 13, 2004 05:08 PM
Byron,
I used to think just like you do! hehehe
I now believe that the 15 coyotes I used to call using my old methods have increased to 20 using the new! The lion has been one of the best teachers for me in this regard. Bill had been telling me this for quite a while, but old habits are hard to break, and sometimes we simply do not want to change, even when a change is for the better. Quite frankly, this principle applies to all aspects of our lives. Funny how we get into a rut and dont even know it untill someone or something or some situation wakes us up. I am enlightened! New situations and new techniques has opened a whole nuther realm for me to explore. Truely liberating! HeHe
FWIW
Steve
--------------------
Yes, we did produce a near-perfect republic. But will they keep it? Or will they, in the enjoyment of plenty, lose the memory of freedom? Material abundance without character is the path of destruction. - Thomas Jefferson
Posts: 442 | From: Cottonwood,Az, USA | Registered: Jan 2003
| IP: Logged
|
|
Leonard
HMFIC
Member # 2
|
posted December 13, 2004 05:22 PM
Well, to answer the question of the moment, I fall on the side that high volume almost never is a negative. Where I hunt, I tend to crank it up whenever it pleases me. Lowering the volume, once your animal is relatively close can be a problem, especially if it is abrupt.
I just do not believe that a coyote is usually detered by too loud a volume. If they are, they usually let you know it, and I oblige. But, I have seen a lot of coyotes check up, for no other reason than I lowered the volume. Of course, at a certain point, they might check up anyway, but I try to be ready for that situation.
A lot of these habits of ours are probably due to the fact that we all hunt different looking terrain.
Good hunting. LB
--------------------
EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32367 | From: Upland, CA | Registered: Jan 2003
| IP: Logged
|
|
Byron South
Knows what it's all about
Member # 213
|
posted December 13, 2004 06:08 PM
Steve,
Begging your pardon, I have always been open to trying new ideas, but have pretty much been self taught through trial and error . Hard knocks you might say. I have also learned quite a bit though from listening to those that have "been their done that". Steve, I respect you and your opinion very much because you fall into the catagory of "been there done that". I have never had the problem of limiting my learning ability by having a closed mind. If you could, please point to the part where you don't agree with what I said and liberate me. I am your clay .
As far as what bill smartz has to say, I could care less . I wouldn't take lessons on calling coyotes from him, and I sure as hell ain't taking any life lessons from him.
Your friend
Byron
--------------------
"Coming to the Call" predator hunting videos. Volumes I, II, III and IV. Order two or more and pay no S&H www.comingtothecall.com
Posts: 313 | From: Texas | Registered: Jun 2003
| IP: Logged
|
|
Rich Higgins
unknown comic
|
posted December 13, 2004 06:20 PM
Steve, let me burden you with my ignorance as well. Your statement "volume EQUALS proximity" to a lion or coyote still implies that a coyote cannot distiguish between loud and near or far and muted. If this is incorrect please edify me.
IP: Logged
|
|
Rich Higgins
unknown comic
|
posted December 13, 2004 07:33 PM
"I appreciate irony. I hope you do too, Steve. Robb's statement was based upon education, not ignorance. Since you are obviously unaware of his background please permit me to edify you. Robb has a degree in wildlife management and it is the scholar that submits these statements for our consideration and debate based upon such publications as follows. From Robb.
----------------------------------------------------------------------------
Robb sent me an email saying this:
""I didnt just pull that idea out of my rectal database of limited and biased observation(s). : )
Talk to your local/favorite "audiologist" on how your ears (and coyotes arent that much different) and hearing process and localization of sound sources works."""
---------------------------------------------------------------------------
In a nutshell, vertical location is more affected by experience and Tone of the sound, than by actual physical location. You can be fooled on the Vertical plane. BY COMPARISON Horizontal location is much more developed than what little vertical location abilities are and are used thusly, and if you read what a lot of these guys have written, it makes sense there too. Coyote comes in from wayyyyyy out there, and then after coming in, then, it looks up at the final closing distance. Which is interesting as well, since we are only talking about hearing ability, and in the some of the cases brought before us, (LBs airplane) would the coyote still "look up" if it was blindfolded and if so would it be looking directly at the plane ? In the case of the Jays Retriever dog, would he look up, even if the sound was coming from ground ?
The coyote's (Canis latrans) preference for use of three senses in hunting was: vision, audition, and olfaction, in order of decreasing importance (Wells and Lehner 1978).
heres a dry read, haha http://www.ie.ncsu.edu/kay/msf/sound.htm
and .........
This extract is lengthy but is a good breakdown of hearing process in general. Including overhead noises and interpretation there of. Other than the L shaped Canal, and ears that can move for more left - right configuration, canine hearing isnt much different than human hearing. (had that link and quote yesterday)
Physical Acoustic Perspective
When an acoustic event occurs in the natural environment, sound waves from that event propagate in all directions. The waves encounter objects in the environment with which they interact by reflection and diffraction. The constructive and destructive interference of all the resulting waves creates a rich acoustic admixture that is further enriched when there are multiple sound sources.
One of the potential objects encountered in the environment is a listener. At the listener's position, sound waves are arriving at different times and from different directions. As shown in Figure 1, there is typically one straight-line path along which the initial waves of each event first reach the listener. This initial direct sound provides the least compromised information about the direction of the sound event. Later, sound waves are reflected back from objects in the environment which arrive from many directions with many different time delays. This indirect sound provides information about the environment and the relative position of the sound event within the environment, especially its distance from the listener. For as long as the sound event persists, direct sound and indirect sound are simultaneously present and virtually indistinguishable.
Figure 1. Depiction of sound events in an environment. There is one direct sound path (thick line) between the event and the listener and many indirect sound paths (thin lines)
When a sound wave encounters the listener, there are two acoustic results depending on the frequency: 1) high-frequency energy is specularly reflected away, and 2) low-frequency energy diffracts and bends around the listener. In between, there is a transition band which is centered around 1500 Hz, the frequency whose wavelength is approximately equal to the diameter of the head. This acoustic phenomenon can be thought of as analogous to ocean waves hitting the piling of a pier: small waves bounce off of it while large waves bend around and go past it.
The sound waves that reach the listener's two eardrums are affected by the interaction of the original sound wave with the listener's torso, head, pinnae (outer ears), and ear canals. The composite of these properties can be measured and captured as a "head-related transfer function," HRTF. The complexity of the interaction of the sound wave with the acoustics of the listener's body makes the HRTF at each ear strongly dependent on the direction of the sound.
When a sound event is equidistant from the two ears, the sound arrives at each ear from the same direction and the HRTFs are very similar (but not identical due to slight asymmetries of the head). The region in which sound sources are equidistant from the two ears is called the median plane. (The similarity of acoustic information is often given as the reason why localization accuracy is poor on the median plane.) There are two other names by which researchers refer to planes in 3-D space. One is the horizontal plane which is level with the listener's ears. The other is the frontal plane (or lateral plane) which divides the listener's head vertically between the front and the back. These planes are illustrated in Figure 2.
Figure 2. Relationship of the median, horizontal, and frontal (lateral) planes to the listener's head.
When the source is not equidistant from the ears, the signal arrives at each ear from a different direction and the HRTFs are far from identical. The ear nearest the sound source is called the ipsilateral ear and the ear farthest from the sound source is called the contralateral ear. The position of a sound source relative to the center of the listener's head is most conveniently captured as a vector expressed in terms of two angles, azimuth and elevation, and one scalar, distance (see Figure 3). Azimuth is measured as the angle between a projection of the vector onto the horizontal plane and a vector extending directly in front of the listener. A progressive movement from 0 to 360-degrees would take the source completely around the listener's head. (There is no general agreement as to whether 90-degrees azimuth represents the listener's left or right.) Elevation is measured as the angle formed between the vector and the horizontal plane rising to 90-degrees overhead or descending to minus 90-degrees below.
Figure 3. Specifying the position of a sound event relative to the head in terms of azimuth, elevation, and distance.
Return to Article Table of Content
As shown in Figure 4, the signals arriving at the ear drums can be examined from two perspectives: the time domain and the frequency domain. If we imagine that the sound event is a simple impulse, we can easily identify the features that are dependent just on the acoustics of the listener. From the standpoint of the time domain, the signals that reach the two ears are no longer impulsive. The energy has been spread over 1-3 msec by the acoustic interaction with the listener's body. Comparing the two ears, the sound arriving at the ipsilateral ear is generally more intense and arrives earlier than that at the contralateral ear. These differences between the two ears are called the interaural intensity difference (IID) and the interaural time difference (ITD) respectively. When a sound source is completely to the side near 90-degrees azimuth on the horizontal plane, the ITD reaches a maximum near .7 to .8 msec.
Figure 4. Time domain and frequency domain representations of HRTFs for the ipsilateral and contralateral ears (adapted from Kendall et al 1990)
A comparison of impulse responses measured for different locations will reveal few significant patterns. But, if those impulse responses are converted to energy-time curves (similar to those of Hiranaka and Yamasaki 1983), more significant trends emerge. These energy-time curves, also called envelope functions, capture the dispersion of the impulse's energy across time (while omitting the waveform's positive and negative excursions).
Figure 5 shows energy-time curves measured at the eardrum position of the Kemar mannequin for 36 azimuth angles on the horizontal plane. Most significantly, one can see the variation in the delay of the initial sound that accompanies change of azimuth. Around 270-degrees (the far contralateral side), the symmetry of sound circling the head in both directions disrupts the pattern of the peaks. There are also clear patterns in the delayed energy after the initial peak. (The delayed sound reduces gain between 150-and 270-degrees, probably reflecting a reduction in sound from the pinna.)
In the frequency domain, Figure 4 reveals that HRTF magnitude profiles vary tremendously across frequency. Comparing the two ears, we see that the magnitude profiles are more similar for low frequencies than for high frequencies. The differences become increasingly noticable above1,500 Hz (the wavelength of the head diameter), because the head is increasingly effective at blocking waves at these higher frequencies.
Figure 5. Energy-time curves measured at the eardrum position of the Kemar mannequin for 36 azimuth angles on the horizontal plane. The curve at the bottom of the graph was measured at 0 degrees azimuth (front) and subsequent curves proceed by 10-degree increments completely around the head to 350 degrees (from Kendall et al 1990).
Plots of the HRTF phase are typically difficult to interpret. The phase function "wraps" repeatedly from - to +, because the time delays exceed the wavelengths of most frequencies. Much more significant information is revealed when phase is reinterpreted in terms of time delay, expressed either as phase delay or group delay. Phase delay captures the time delay of each frequency and group delay captures the time delay of the amplitude envelope of each frequency (see Smith 1985 for a more complete description). Figure 4 represents HRTF phase as phase delay. The delays are greatest for the lowest frequencies, because the diffraction of waves around the head causes the low-frequency waves to move more slowly than the high-frequency waves. Between 500 and 2,500 Hz there is a region in which delay makes a transition from a low-frequency region to a high-frequency plateau. The approximate center of this region lies at 1,500 Hz, clearly an important region for both magnitude and phase.
There are numerous acoustic factors which add complexity and richness to HRTFs. For example, there is a clear magnitude peak in the region around 3,000 Hz that is caused by the resonance of the ear canal. There are also notches and other fine details in the magnitude response caused by the constructive and destructive interference of the direct wave with sound reflected off the body. Reflected sound below 2,000 Hz is mainly from the torso and above 4,000 Hz it is mainly from the pinnae; in between there is a region of overlapping influence (Kuhn 1987).
Return to Article Table of Content
A comparison of HRTFs measured for adjacent directions will reveal many significant patterns. Figure 6a illustrates the patterns that can be observed in the magnitude response of the ipsilateral ear on the horizontal plane between 0- and 180-degrees azimuth. For example, the bandwidth of the spectral peak near 3,000 Hz widens as the sound source moves from front to back. A deep notch in the 8,000 Hz region migrates upward in frequency as the source moves toward the back and then virtually disappears. The 4,000 Hz region shows a deep notch between 100- and 130-degrees in azimuth. Figure 6b reveals related trends in group delay.
Figure 6a
Figure 6b
Figure 6. Ipsilateral HRTFs measured at the eardrum position of the Kemar mannequin for 19 azimuth angles on the horizontal plane: (a) magnitude response (from Kendall et al 1990), and (b) phase response expressed in group delay. The curve at the bottom of each graph was measured at 0 degrees azimuth (front) and the curve at top of each graph was measured at 180 degrees azimuth (rear).
These frequency domain profiles can also be viewed from the perspective of the differences between the two ears. Interaural intensity differences and interaural time differences vary in quite complex ways across frequency. Figure 7 shows the frequency-dependent interaural magnitude difference and the interaural time difference (expressed as group delay) for a single direction.
Figure 7. Frequency-dependent interaural magnitude difference and the interaural group-delay difference for a sound source at 90 degrees in the horizontal plane. (Original data was measured with the Kemar mannequin and then smoothed.)
HRTFs change very little when the distance of the originating sound event changes provided that the event is more than two meters away from the head. Beyond two meters, the sound wave from the acoustic event is approximately planar. (This means that HRTFs recorded at least two meters from the head can be utilized to simulate sound sources farther away, provided that environmental cues to distance are also present.) Less than two meters from the head, the sound waves from the acoustic event are more spherical, the effective angle between the sound event and the individual ears changes, and the HRTFs diverge significantly from those recorded farther away. Figure 8 shows a series of HRTFs recorded at varying distances directly in front of the head. The perception of distance close to the head appears to depend on these alternative HRTFs.
Figure 8. Magnitude response of sources located at 0 degrees azimuth, 0 degrees elevation, at distances of 90 inches (solid line), 24 inches (dashed line), and 4.5 inches (dotted line).
A comparison of HRTFs from different individuals will reveal that spectral features do not entirely match. The magnitude of individual HRTFs will vary in gross shape and as well as in details. Figure 9 compares the ipsilateral HRTFs of two individuals on the frontal plane. And although there are considerable differences in shape and detail, it can be seen that the overall trends are quite similar. For example, both individuals show the same trend in the upward migration of notch frequencies as elevation rises. This suggests that while individuals possess heads of different sizes and pinnea of different shapes, the acoustic processes that forge the individual HRTFs are the same. Nonetheless, interaural phase differences will be especially affected by head size because of the difference in the separation of the ears. The magnitude of interaural phase cues for children must be quite different from those for adults.
Return to Article Table of Content
Figure 9. HRTFs on the frontal plane for two subjects. The sound increases in elevation (solid-line: 0 degrees; long dashes: 10 degrees; short dashes: 20 degrees; and dotted line: 30 degrees) (from Kendall and Martens 1984).
HRTF Measurement Techniques
HRTFs are generally measured by recording test signals in one of three ways: 1) at the blocked entrance of the ear canal with a miniature microphone capsule, 2) within the ear canal with a probe tube, or 3) at the ear drum position with a dummy head. In all three cases, the head must be kept perfectly still during the measurement and environmental sound must be eliminated. The measurements made at each position have a stable, fixed relationship to measurements made at another position (Moller 1992). For example, measurements made with a probe tube placed at least 15 mm into the ear canal are closely related to those at the ear drum position. There is a fixed ratio between the magnitude spectra of the two up to around 7,000 Hz. Above 7,000 Hz (and sometimes below) notches in the two measurements are offset from each other and create push-pull spectral differences. (There is typically a poor signal-to-noise ratio in the notches which may cause inaccuracies when one transforms one type of measurement into another.)
Measurements made at the ears must be processed in order to isolate the part that represents the actual HRTFs. The acoustic signals measured at the ears can be represented as the products of the transfer functions of the source, S(w), and the recording equipment, T(w), with the ipsilateral ear, Hi(w), or the contralateral ear, Hc(w):
S(w) T(w) Hi(w) or S(w) T(w) Hc(w).
A reference measurement without a human subject is the product of the source and recording equipment alone, S(w) and T(w). Therefore, the HRTFs can be isolated by dividing the reference from the measurements in the ears:
S(w) T(w) Hi(w) = Hi(w) and S(w) T(w) Hc(w) = Hc(w)
S(w) T(w) S(w) T(w)
This computation is typically performed by first transforming the time-domain measurements to the frequency domain via the FFT where the complex-valued division can be performed directly. Alternatively, the complex valued frequency data can be converted to magnitude and phase, after which, the complex division is achieved by subtracting the gain in dB and the phase of the reference measurement from the ear measurement data. The impulse response for HRTF is then computed by transforming the frequency-domain HRTF to the time domain via the inverse FFT.
Psychoacoustic Perspective
A listener's judgment of the direction of an acoustic event is dominated by the sound that reaches the listener along the shortest, most direct path (otherwise the judgment of the direction of the event would be ambiguated by the indirect sound). This preference given to the initial sound is called the "precedence effect" (Wallach et al. 1949) or the "law of the first wavefront" (Blauert 1971). Even these initial sound waves are radically transformed in comparison to those of the original event. The sound arriving at each ear is spectrally modified by the HRTF, each ear has a different transformation, and the transformation changes as the head and/or the source moves. The auditory system performs the phenomenal task of integrating the information arriving at the two ears into a single, fused perceptual image of the acoustic event in space: the auditory system extracts out the directional information and reconstructs an estimate of the original source spectrum. This is accomplished in spite of the fact that there is no direct, structural representation of spatial information in the peripheral auditory system as there is in the peripheral visual system when light is focused onto the retina. (No wonder that research into three-dimensional sound has lagged behind research into three-dimensional vision!)
Classical psychoacoustics focused on the separation of the two ears and proposed the duplex theory of sound localization (Rayleigh 1907). Experimenters attempted to construct a theory of localization by compositing results from many experiments conducted with the ultimate acoustic building blocks, sine waves. These experiments demonstrated that interaural differences, that is, differences in the acoustic signals simultaneously presented to the left and right ears, strongly affect spatial perception. Interaural intensity difference (IID) and interaural time difference (ITD) each make a significant impact on perceptual judgments in a separate frequency range. Above 1500 Hz there is acoustic shadowing by the head and localization judgments are dominated by the intensity difference between the ears (IID). Below 1500 Hz the head is not a significant acoustic obstacle, there is a less significant intensity difference, and localization judgments are dominated by the time difference between the ears (ITD). (Consider too that above 1500 Hz ongoing phase differences would often exceed 360 degrees, making it impossible to judge time delay on the basis of these phase differences.) The differentiation in perceptual processing appears to be coupled to the acoustic properties of the head.
These observations do not, however, provide sufficient explanation for human localization. In fact, IID and ITD only affect the extent of the lateralization of the sound source, that is, its perceived position along the interaural axis, a left/right axis between the ears. With only ITD and IID, a person cannot judge whether an acoustic event is in front, above, behind, or below. This ambiguity of location at a given degree of lateralization has been called the "cone of confusion" (Woodworth 1954) depicted in Figure 10. It is now commonly accepted that the seeming uncertainty of spatial location on the cone of confusion is disambiguated by the complex acoustic profiles of the HRTFs. The classic psychoacoustic experiments supporting the duplex theory of localization did not utilized the frequency-dependent interaural magnitude difference and interaural phase difference typical of HRTFs. Then too, the duplex theory ignored the influence of alternative temporal cues above 1500 Hz such as interaural onset differences (see Blauert 1974 for a comprehensive review). Acoustic events in natural environments also exhibit ongoing perturbations that provide additional opportunities for grasping onto interaural temporal cues. The classical psychoacoustic stimuli were impoverished, and the results are only partially useful in understanding localization in everyday listening situations.
Figure 10. The cone of confusion (based on Woodworth 1954; adapted from Kendall et al 1990).
Modern psychoacoustic research has turned its attention to binaural hearing and the role of HRTFs in localization. In the broadest context, binaural means combining information from the two ears (as opposed to monaural which means using information from one ear or from each ear independently). Use of the word "binaural" also implies the kind of frequency-dependent interaural cues typical of HRTFs. This change in the focus of research is also accompanied by a shift toward the use of broadband stimuli, rather than sine waves.
Even though HRTFs are very rich in acoustic detail, perceptual research suggests that the auditory system is selective in the acoustic information that it utilizes in making judgments of sound direction. Evidence reveals that monaural phase information is irrelevant to spatial perception and that interaural phase information is extremely important. Wightman and Kistler (1992) have demonstrated that low-frequency interaural time difference is the dominant localization cue for sounds that contain energy below 2.5 kHz. For sounds that lack this low-frequency energy, interaural intensity difference provides the most likely basis for localization. It is still unclear though how much influence high-frequency time differences might have, since experiments have shown the time difference between the temporal envelops of high-frequency sounds are quite detectable (Henning 1974). Although the majority of research focuses on binaural cues, there is research into monaural spectral cues that suggests they are important for sound sources at the sides (Musicant and Butler 1985). There is also evidence that elevation in particular is influenced by the spectral content of the sound source itself (which is received at both ears), such that high-pitched/bright sounds are typically localized higher than low-pitched/dark sounds (Butler 1973).
There are important differences between the vertical and horizontal dimensions in the resolution with which people can resolve the spatial location of a sound source, an effect that Blauert terms "localization blur" (Blauert 1974). The highest resolution is evident in the horizontal dimension, especially in front of the listener where the minimum audible angle is 2-degrees or less depending upon the exact nature of the experimental task. That angle increases to near 10-degrees at the sides and narrows to near 6-degrees in the rear. By comparison, the resolution in the vertical dimension is quite low. The vertical minimum audible angle in front is near 9-degrees and steadily increases until overhead when it reaches 22-degrees. (See Blauert 1974 for a summary of research in this area.) Spatial acuity is apparently not as important for auditory perception as it is for the visual system.
While front/back discrimination is possible on the basis of the full acoustic information in HRTFs, it is also clear that head movement plays a dominant role in resolving front/back confusions (Wallach, 1940). This is particularly important for sound sources located near the median plane where other acoustic information provides few interaural differences. Figure 11 illustrates how the location of sound sources in front and in back of the listener, is disambiguated by a turn of the head toward the right. For the sound source in front of the listener, turning the head toward the right causes the left ear to receive sound earlier and with greater intensity. For a sound source behind the listener, it is the right ear that receives the earlier and more intense sound. Wallach's classic experiments also clearly demonstrated that dynamic interaural cues would override HRTFs when the two were placed into conflict.
Return to Article Table of Content
Figure 11. A dynamic head turn to the right disambiguates whether a sound source is in front or in back of the listener (adapted from Kendall et al 1990).
Individual Differences
There is debate at present concerning the impact of individual differences and the extent to which people can localize with HRTFs other than their own. HRTFs vary tremendously among individuals and interaural differences are strongly affected by differences in head size and in the size and orientation of pinnae. It appears that some individual's HRTFs improve other individual's localization accuracy (Butler & Belendiuk, 1977; Wightman & Kistler, 1989), but that large differences in head size can undermine localization (Morimoto & Ando, 1983). Wenzel et al. (1993) report that elevation judgments and front-back differentiation are more like to degrade with non-individualized HRTFs. At the same time, it appears that effective localization can occur in many cases in which the ears receive directional transfer functions (DTFs) whose details differ significantly from measured HRTFs. Kendall and Rodgers (1982) used low-order filters to create cartoon-like approximations of natural HRTFs while Martens (1987) and Kendall et al. (1988) describe the use of principal components analysis to create artificial DTFs. Comparison of results suggests the following:
1. individuals generally localize better with their own HRTFs than with those of others.
2. Some individuals have HRTFs that are superior and these HRTFs can sometimes improve the others' localization.
3. In order for one individual's HRTFs to work for another, the head sizes must be approximately the same.
4. Localization can be achieved with synthetic DTFs whose details differ from measured HRTFs.
Neurophysiological Perspective
Although neurophysiology is not part of the educational background of many computer music and audio professionals, it is an area from which many of the most important new ideas and discoveries about hearing continue to come. This is especially true for directional hearing. (For comprehensive reviews see Phillips and Brugge 1985; Casseday and Covey 1987; Kuwada and Yin 1987). Its terminology and perspective are quite distinct from physical acoustics and psychoacoustics. The purpose of this section is to familiarize the reader with this important context for understanding directional hearing and, in particular, to point out the special adaptations in the auditory system for sound localization. Although terminology is introduced somewhat gently, it is undoubtedly helpful if the reader has some basic familiarity with the field, especially the physiology of the auditory system.
Peripheral System
While the pinna is clearly adapted to auditory localization, the peripheral neurological system has little or no specialization for directional hearing. The peripheral neurological system transforms the acoustic ear signals into neural activity and seems most clearly designed to capture the spectral/temporal decomposition of incoming acoustic waves. The primary function of the signal decomposition would appear to be the identification of the sound source, i.e., the sounding object and its excitation. This strongly conditions the structure of the neural mechanisms that underlie human localization, since, at the level of the peripheral neurological system, source information commingles with spatial information.
The acoustic signal at the outer ear is converted to mechanical energy by the linkage of the ear drum to the middle ear (see Figure 12). This mechanical energy is converted to fluid pressure by the linkage of the stapes to the flexible oval window at the base of the cochlea. Stapes motion at the oval window initiates a traveling wave of displacement down the basilar membrane. As this wave travels, it is increasingly damped by the changing mass and shape of the basilar membrane. From base to apex, the wavelength lengthens and the velocity decreases. The extent of membrane displacement is related to the spectral content of the wave such that maximal displacement occurs near the base for high frequency components and near the apex for low frequency components. There are sensory receptor cells located along the basilar membrane called inner and outer hair cells which respond maximally at a characteristic frequency. These frequencies run from high to low along the membrane from base to apex and are arranged nearly logarithmically. Thus, distance along the basilar membrane is approximately proportional to the log of the characteristic frequency. In this way spectral information is spatially mapped onto a neurological representation. There is no spatial representation of location as there is in the peripheral visual system.
The motion of the basilar membrane causes displacement of the cilia of the hair cells and changes to the cell potential. The resulting potential can be viewed as containing an AC and a DC part. The AC part captures the temporal changes of the waveform itself. The DC part can be viewed as the average value of the potential over a period. At high frequencies, the DC part is the only response. For example, above 5 KHz the temporal structure of a sine waveform is not individually resolved (no AC part) and the inner hair cells respond only to the temporal envelope (captured by the DC part). Thus, the neurological representation of temporal information shifts gradually from the waveform itself at low frequencies to the signal envelope at high frequencies. (Thus, it appears that the most appropriate representation for time delay at low frequencies is phase delay and at high frequencies is group delay.)
Figure 12. Peripheral auditory system: (a) physical structure showing pinna, eardrum, middle ear, oval window, and cochlea; (b) conceptual representation of the uncoiled cochlea which is divided down the middle by the basilar membrane.
Neural Pathways
The basilar membrane creates a neural representation of the acoustic activity taking place in the physical world and this information is initially transformed and retained in the action potential firing patterns of fibers innervating (furnishing neural connections to) the basilar membrane from the cochlear nucleas (CN). These auditory nerve fibers bifurcate up to the anteroventral cochlear nucleus (AVCN) and down to the dorsal cochlear nucleus (DCN). (Follow Figures 13a and 13b for a diagramatic representation.) The goal of the central neurological system and subsequent neurological processing will be to construct a representation of information about the physical world that is useful for survival, information such as the identity of a sound source and its location.
Figure 13. Representation of the primary auditory neural pathways important for directional hearing: (a) projections to and from the superior olives (SO) constitute the heart of the binaural system; (b) monaural pathways and the integration of binaural information in the DNLL. Abbreviations are explained in the text.
At the beginning of the neural processing, the source information and the directional information are confounded. The most direct strategy for segregating the directional information from source information is to extract directional information from the differences between the ears, i.e., binaural information. The auditory neurological system forms symmetric left and right neural pathways for this binaural information. To simplify the discussion of these binaural pathways, we will trace the evolution of one path; same-side connections will be refered to as ipsilateral and opposite-side connections as contralateral.
The origin of the binaural pathways is the AVCN which is the source of projections to both the ipsilateral and contralateral superior olive (SO) (Stotler 1953). Projections in and out of the superior olive are represented in Figure 13a. The medial superior olive (MSO) is innervated by both the ipsilateral and contralateral cochlear nuclei. Its input is dominated by low-frequency fibers that retain the fine temporal structure from the basilar membrane. There is strong evidence suggesting that the MSO is a coincidence detector for interaural time differences (Goldberg and Brown 1968). The lateral superior olive (LSO) is directly innervated only by the ipsilateral cochlear nucleus. It is connected to the contralateral coclear nuclei through an intermediate connection in the contralateral medial nucleus of the trapezoid body (MNTB). The MNTB appears to provide an inhibitory input to the LSO. Both inputs are dominated by high frequency fibres. Evidence suggests that the LSO detects interaural intensity differences (Boudreau and Tsuchitani 1968).
The LSO and MSO project to and converge on two targets, the inferior colliculus central nucleus (ICC) and the dorsal nuclei of the lateral lemniscus (DNLL). This gives rise to the possibility that IID and ITD information is conjoined. Moreover, both ipsilateral and contralateral LSO project to the ICC, suggesting that information from both binaural pathways are combined, though only the ipsilateral projection includes LSO low-frequencies. The ICC is also the target of projections from the contralateral AVCN and the DCN. (See Figure 13b.) These projections contain monaural, rather than binaural information. In the ICC, the targets of the MSO and LSO lie within that of the AVCN and overlap with each other, giving rise to the possibility that monaural source information is recombined with binaural information. The ipsilateral DNLL projects to the contralateral DNLL (Figure 13b) providing a clear opportunity for integrating information from both binaural pathways which can then be passed on through projections to the ipsilateral and contralateral ICC. The DNLL is also connected to the greater superior colliculus (not shown in Figure 13) providing binaural auditory information with a path to motor centers.
The inferior colliculus has been the site of much work on IID and ITD. Research with low-frequency tones reveals neurons which respond to a "characteristic delay" (Rose et al. 1966). Similar results have been found with amplitude modulated high-frequency tones (Yin et al. 1984). The "phase locking" that occurs with the envelope of the high frequency tone is just like that of the low-frequency tones. Thus, there appears to be a single system of ITD detection that extends from the phase of low-frequency tones and to the envelope of high-frequency tones.
Although less clear in mammals, research with barn owls has shown that a spatial referent map of auditory space exists in the equivalent to the inferior colliculus (Knudsen and Konishi 1978). Individual neurons respond to acoustic stimulation from a narrow spatial region and neighboring cells respond to sources in adjacent spatial regions. Not only that, but azimuth is associated with ITDs and elevation with IIDs (Moiseff and Konishi 1981).
After the convergence of binaural and monaural information in the IC, pathways ascend to the medial geniculate body (MGB) and then the auditory cortex (shown in both Figures 13a and 13b). One might expect that a spatial referent map would be found in the auditory cortex of mammals. Instead, spatial information appears to be coded in the temporal firing pattern of a group of neurons (Middlebrooks et al. 1994). This allows spatial information to be projected on top of other neural maps
IP: Logged
|
|
GUTPILE
Knows what it's all about
Member # 448
|
posted December 13, 2004 08:44 PM
If I read all of this, can I get a Diploma ? Crap, I don't have a clue !!!!
--------------------
Guns have two enemies: RUST & POLITICIANS.
TOO FEW PEOPLE MAKE TOO MANY DECISIONS FOR TOO MANY PEOPLE
Posts: 132 | From: Curlew Wa | Registered: Nov 2004
| IP: Logged
|
|
Leonard
HMFIC
Member # 2
|
posted December 13, 2004 08:45 PM
Rich, that does nothing for me, even if you had not started out by suggesting that his opinion has more value because of his degree. At least, that's the way I took it.
What I will allow, is that calling from a ladder, with a coyote coming from a height of two feet off the ground, they most likely don't have that much of a clue, and make assumptions. Two feet high ground level or six feet off the ground amount to much the same thing, from a couple hundred yards distance.
Other than that, if the purpose of all those paragraphs was to convince me (or anybody else)that black is white; I know all I need to know about the subject, as a practical matter.
Good hunting. LB
edit: of course, I'm sure we all can agree with at least this much, since it is abundantly obviously:
"The LSO and MSO project to and converge on two targets, the inferior colliculus central nucleus (ICC) and the dorsal nuclei of the lateral lemniscus (DNLL). This gives rise to the possibility that IID and ITD information is conjoined. Moreover, both ipsilateral and contralateral LSO project to the ICC, suggesting that information from both binaural pathways are combined, though only the ipsilateral projection includes LSO low-frequencies. The ICC is also the target of projections from the contralateral AVCN and the DCN. (See Figure 13b.) These projections contain monaural, rather than binaural information. In the ICC, the targets of the MSO and LSO lie within that of the AVCN and overlap with each other, giving rise to the possibility that monaural source information is recombined with binaural information. The ipsilateral DNLL projects to the contralateral DNLL (Figure 13b) providing a clear opportunity for integrating information from both binaural pathways which can then be passed on through projections to the ipsilateral and contralateral ICC. The DNLL is also connected to the greater superior colliculus (not shown in Figure 13) providing binaural auditory information with a path to motor centers."
[ December 13, 2004, 08:50 PM: Message edited by: Leonard ]
--------------------
EL BEE Knows It All and Done It All.
Don't piss me off!
Posts: 32367 | From: Upland, CA | Registered: Jan 2003
| IP: Logged
|
|
|
UBBFriend: Email this page to someone!
Printer-friendly view of this topic
