Acoustic Habituation In Cats As A Function Of Stimulus Rate And Role Of Temporal Conditioning Of Middle Ear Muscles

1. 1. Evoked auditory responses at the medial geniculate body (MG), inferior colliculus (IC) and cochlear nucleus (CN) were recorded for 1 h from chronically implanted electrodes in cats during the presentation of two types of repetitive click stimulation — regular and random. The regular click stimuli, with equal inter-stimulus intervals, were given at rates of 1/sec, 1 5 sec and 1 10 sec. The random click stimuli, with unequal inter-stimulus intervals, had mean rates of 1/sec and 1 10 sec and minimum inter-stimulus intervals of 250 msec and 2 sec respectively. 2. 2. Acoustic habituation was observed at all auditory nuclei studied, with least habituation occurring at the CN and the greatest habituation at the MG. 3. 3. The theory of “temporal conditioning” of middle ear muscles was not confirmed. Random stimulation elicited response changes similar to those observed during regular stimulation. 4. 4. Action of middle ear muscles in acoustic habituation appears negligible since cats with inactivated middle ear muscles yielded similar results to those observed in normal cats in regard to a 1/sec stimulus.