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How do you test the hearing of a toad?

When humans receive a hearing test it is usually in a trailer when you are young and in middle school or it when you are older and in a doctor's office. You wear some large headphones and raise a hand when you hear a sound. During that test tones of varying frequency are played into the headphones and usually the tester wants to see if you can hear the really high and really low tones. As you get older, you can't hear the really high tones anymore. 
Toads are not as cooperative as middle schoolers (at least in some ways) and refuse to raise their little hands when I play them tones. Instead we test their hearing like we would a newborn baby. Newborn babies sometimes have their hearing tested by having a few patches placed on their head to record electrical signals from their hearing nerve and from the hearing centers of the brain. If the baby has a signal - he/she can hear the tone. 
I do the same thing with toads except instead a patch on the skin, I use a small electrode just beneath the skin since toad skin is sensitive to chemicals and sometimes slippery. Also, instead of a trailer, I perform these experiments in field stations, hostals, apartments and at Centro Jambatu in Ecuador and Peru. I also give them a little bit of paralytic that keeps them still throughout the test (~50 min per test). Then put them in a large trunk, lined with acoustic foam and play tones at varying frequencies. I increase the sound level at each frequency until I see the hearing nerve fire and viola! We know what the frog ear is sensing (or not sensing).
An ABR set up at a field site in Peru.
After the test the toad is kept nice and moist and recovers in 30 min - 2 hours, depending on the species. I've seen test subjects immediately try to eat and mate the night after testing, so they don't seem too upset about the whole ordeal.
The software used in my experiments was developed in Denmark in the lab of Dr. Jakob Christensen-Dalsgaard at SDU. He and I have spent many great and frustrating hours in the field together and my hearing data would not exist without him. 
Dr. Jakob Christensen-Dalsgaard
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