On the Locating Sound post, Gerd Riesselmann left this comment:
Female crickets locate male crickets by the sounds they make. However, the head of a cricket is too small to locate the sound by measuring the time difference between the incoming signals.
So how does the cricket locate sound?
It does it by “hardwiring” movement and sound recognition. Basically that is: If a sound reaches the right ear, a movement to the right is triggered. After that the system sleeps for sometime. Same for the left ear.
This makes the cricket move to the target in a zick-zack kind of way.
This exact behaviour has been implemented in a robot already: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.106.1665&rep=rep1&type=pdf
The robot cricket is pretty cool:
A bit larger then the average cricket though.
Another update from Gerd (via G+):
I found it in the book “Die Entdeckung der Intelligenz – Können Ameisen denken?” by Holk Cruse, Jeffrey Dean and Helge Ritter. Unfortunately there is no English edition, as far as I know. The book contains quite a lot of examples of robots simulating animal behavior (they are called Animaten in German). The special cricket robot itself was mentioned in another book, though, but it seems I gave it away. And unfortunately I can’t remember it’s title.
Rereading the according chapter I unfortunately have to correct myself: Crickets have a special organ that physically measures the difference of sound pressures directly. Basically by allowing the sound to reach both the eardrums from both outside and inside, which makes the ear one organ with two eardrums and four entrances. One entrance leads to the front of the right, another to the front of the left eardrum, like for us. But an additional entrance leads from the right between the two eardrums, and yet another does the same from the left . The principle is called “coupled eardrums”
However, for crickets this is limited to a very narrow range of frequencies (that of male crickets, of course). It’s a very special solution. But frogs apply the same mechanisms to a broader range of frequencies. There’s a small paragraph on this in the Wikipedia article on sound locating: “Ho showed that the coupled-eardrum system in frogs can produce increased interaural vibration disparities when only small arrival time and sound level differences were available to the animal’s head. Efforts to build directional microphones based on the coupled-eardrum structure are underway.” The article mentions flies as using this system, too, so it seems to scale very well 🙂
Now you know!