Backward and forward masking with reproducible noise bursts

This study investigated the effects of two "frozen" narrow-band waveforms with different waveform envelopes 50 msec in duration and centered at 250 Hz, on temporal masking at short masking intervals and, further, assessed the effects of phase shifts on backward and forward masking. Four normal-hearing experienced Ss detected a monaurally presented 250-Hz tone burst, 12 msec in duration, that either preceded, occurred simultaneously with, or followed a burst of the narrow-band noise. A 2IFC technique was used with a transformed up-down procedure for threshold estimation. The masking intervals from onset of masker to onset of tonal pulse ranged from -30 to +70 msec. The 3 phasic conditions for the signal were in-phase, 90 degrees out-of-phase, and 180 degrees out-of-phase. Results of this experiment substantiated the data of other researchers who have shown greater backward than forward masking at short masking intervals and greater masking was found for all simultaneous conditions than for any of the backward or forward masking conditions. In addition, differences between the two noise waveforms, as well as the phase shifts, had a significant effect on the thresholds obtained for the backward and forward masking conditions, as well as for the simultaneous masking conditions. Criterion change and waveform storage are discussed as possibly having an effect up these variables.