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

The masking level difference (MLD) is a psychoacoustic phenomenon deri ved 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 (si gnals and noise in phase at the two ears). The purpose of this study w as to determine if the MLD derived from the late components (P1, N1, P 2, N2) of the auditory evoked potentials was a physiological correlate of the behavioral MLD. Subjects were 15 young adults with normal hear ing. Comparisons were made between behavioral and late potential thres holds 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 beh avioral or late-potential thresholds to So and S-pi conditions. The S- pi-No threshold was significantly lower than the SoNo threshold, yield ing an MLD for both the behavioral and physiological responses. The ma gnitudes of both the behavioral and late-potential MLD were larger wit h the narrow band noise than with the wide band noise. Evidence, there fore, is provided that the late-potential MLD reflects similar process es as are responsible for the behavioral MLD.