EFFECTS OF NOISE BANDWIDTH ON THE LATE-POTENTIAL MASKING LEVEL DIFFERENCE

The masking level difference (MLD) is a psychoacoustic phenomenon derived from the subtraction of S-pi-No thresholds (signals pi-radians out of phase and noise in phase at the two ears) from SoNo thresholds (signals and noise in phase at the two ears). The purpose of this study was to determine if the MLD derived from the late components (P1, N1, P2, N2) of the auditory evoked potentials was a physiological correlate of the behavioral MLD. Subjects were 15 young adults with normal hearing. Comparisons were made between behavioral and late potential thresholds to 500 Hz stimuli in So and S-pi conditions in quiet, and to 500 Hz stimuli in SoNo and S-pi-No conditions in narrow band (50 Hz) and wide band (600 Hz) noise. No significant differences were seen for behavioral or late-potential thresholds to So and S-pi conditions. The S-pi-No threshold was significantly lower than the SoNo threshold, yielding an MLD for both the behavioral and physiological responses. The magnitudes of both the behavioral and late-potential MLD were larger with the narrow band noise than with the wide band noise. Evidence, therefore, is provided that the late-potential MLD reflects similar processes as are responsible for the behavioral MLD.