Acoustic reflex measures at high probe frequency: a phasor diagram approach

Acoustic reflex measures at high probe frequencies (above 660 Hz) have not been extensively reported in the published literature. Studies of the acoustic reflex at low probe frequencies conflict as to the effect of the reflex on resistance, although all researchers agree that the reflex increases the amount of negative reactance (stiffness). These differences may reflect methodological differences across studies. Lutman and his associates (Lutman and Martin 1979; Lutman et al., 1984) have used phasor diagrams to provide evidence for the effect of the reflex being on reactance, with constant resistance for low probe frequencies (220 and 660 Hz). The present study incorporated the use of this method in order to investigate the effect of the reflex at a 1000 Hz probe frequency in 30 normal ears. Phasor diagrams of probe tip susceptance and conductance values obtained for three stimuli at a 1000 Hz probe frequency were analysed qualitatively. Eighty-two out of a total of 90 phasor diagrams obtained were matched to the constant-resistance stiffness-change model, suggesting that similar effects of the reflex are seen at low and high probe frequencies in most cases. This was noted to be the case for ears that were either stiffness-dominated or at their natural frequency at the 1000 Hz probe. However, the effect of the reflex on mass-dominated systems was less clear and needs further clarification.