Any reflex dependent on the auditory system can give information about the behavior of this system. Muscular, vasomotor, and secretomotor effects of acoustic stimulation have been used to study the auditory system. Some responses require an intact alert animal; others occur in anesthetized or decorticated preparations. Some are set off by weak acoustic stimuli (conditioned reflex); others are only effective with overthreshold sounds.
An example of the latter, the pinna reflex, has been used in guinea pigs where it is well developed. The response to brief sounds and transients is easily elicited in a normal-hearing alert animal. Relatively intense sounds are required, varying in frequency at about 80 db. above threshold. The animal may become adapted in a short time so that the twitch of the ear can, with repeated stimuli, no longer be elicited. The response is often used in guinea pigs to select animals with healthy ears for