There are new clues in the quest for a fully coherent theory of the perception and neural representation of size-variant human vowels in the Mongolian gerbil.

Previous investigations in the US (see: Science 2.0, Beachcombing in Academia, February 15th 2012) found that Mongolian gerbils can easily be trained to recognise vowel sounds in human speech.

Now, however, Uwe Firzlaff and colleagues from the Division of Neurobiology, Department Biologie II, Ludwig-Maximilians-Universität München, in Germany, have drawn attention to the fact that the larger the (human) speaker, the lower the formant frequencies of the spoken vowels tend to be.

Raising the question – what happens (electrophysiologically) in the auditory pathways of the Mongolian gerbil (previously trained to identify human vowels) if the human speakers are of different sizes?

"Gerbils trained to discriminate two standard vowels, correctly assigned vowels spoken from different-sized human speakers. Complementary electrophysiological recordings from neurons in the auditory brainstem, midbrain, and primary auditory cortex show that the auditory brainstem retains a truthful representation of the frequency content of the presented vowel sounds."

Spectral processing plots of the human vowel sounds and electrophysiological recordings of the superior olive and other hearing-related neurological structures in the gerbils showed that “…the auditory brainstem retains a truthful representation of the frequency content of the presented vowel sounds.”

Details are published in the journal Hearing Research Volume 261, Issues 1-2, March 2010, Pages 1-8