Binaural forward and backward masking: Evidence for sluggishness in binaural detection

The threshold of a short interaurally phase‐inverted probe tone (20 ms, 500 Hz, S_π ) was obtained in the presence of a 750‐ms noise masker that was switched after 375 ms from interaurally phase‐inverted (N_π ) to interaurally in‐phase (N_o ). As the delay between probe‐tone off set and noise‐phase transition is increased, the threshold decays from the N_π S_π threshold (masking level difference=0 dB) to the N_o S_π threshold (masking level difference=15 dB). The decay in this ‘‘binaural’’ situation is substantially slower than in a comparable ‘‘monaural’’ situation, where the interaural phase of the masker is held constant (N_π ), but the level of the masker is reduced by 15 dB. The prolonged decay provides evidence for additional binaural sluggishness associated with ‘‘binaural forward masking.’’ In a second experiment,‘‘binaural backward masking’’ is studied by time reversing the maskers described above. Again, the situation where the phase is switched from N_o to N_π exhibits a slower transition than the situation with constant interaural phase (N_π ) and a 15‐dB increase in the level of the masker. The data for the binaural situations are compatible with the results of a related experiment, previously reported by Grantham and Wightman [J. Acoust. Soc. Am. 65, 1509–1517 (1979)] and are well fit by a model that incorporates a double‐sided exponential temporal integration window.