Masking level differences: auditory evoked responses with homophasic and antiphasic signal and noise.

Two studies were devised to determine if objective quantification of the masking level difference is possible using the auditory evoked response (AER). In the first study, click stimuli were presented under three conditions: both the stimulus and masker in phase (SoNo); stimulus in phase, masker antiphasic (SoN pi); and stimulus antiphasic with masker in phase (S pi No). In the second study 1000 Hz puretone stimuli were presented under SoNo and S pi No phasic conditions. AER's were obtained at various intensity levels for each condition. The AER demonstrated differences in N1-P2 amplitudes evoked by the homophasic and antiphasic conditions for threshold and suprathreshold levels.