Effects of linear frequency modulated ramps on stapedius muscle reflex (SMR) in children

Abstract

Thirty 6-year-old children with normal hearing, speech discrimination, and SMRs to tones and noise were given FM stimulation. A 2000-Hz tone was presented at 15 dB + SMR threshold until SMR decayed. The frequency was either modulated upward (to 40000 Hz) or downward (to 1000 Hz) in 100 ms for a series of intensity steps until a full contralateral SM contraction was recorded. Decay of the tonal SMR preceded FM testing at each step. The reciprocal to the 2000-Hz rising ramp was also employed and presented re the 4000-Hz tonal SMR. Ramps were filtered to equate intensity. All FM ramps induced a reactivation of the SMR. When equated at the percent of full contraction the 2000-Hz rising ramp had a larger dynamic range than either the falling or reciprocal conditions. The SMR waveform morphology varied with sound intensity. At high levels the SMR onset and offset was fast and the amplitude high, but as the sound intensity decreased onset and offset times increased and amplitudes reduced resulting in a broadening of the waveform.