Interaural time and intensity difference and the MLD.

Abstract

Masking-level differences (MLD) for a 600-cps low-pass transient were explored as a function of (1) interaural time difference (Δt; (2) interaural intensity difference (ΔI); and (3) combinations of Δt and ΔI. Masking-level difference here is the difference between two levels of coherent noise (N0), one required to mask a given condition of click, the other to mask a binaural in-phase click (S0). (1) MLD increases with signal Δt in a manner similar to that for interaural phase differences of the tonal frequency within the filtered transient. Furthermore, for larger values of Δt, where the transients no longer overlap in time, the MLD decreases in a manner suggesting temporal integration of two brief signals. (2) As signal ΔI increases, MLD approaches limiting value of about 7 dB, for signal monaural (Sm) condition. An interaural intensity difference of 24 dB yields an MLD of 6 dB, still a decibel or so short of the monaural value. (3) When ΔI is combined with Δt greater than 0.4 msec, the MLD decreases ΔI increases, no matter whether the louder signal is leading or lagging in time.