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) concomitant time and intensity disparity. Masking-level difference is the difference between two levels of a noise (N0): one required to mask a given condition of click, the other to mask a binaural in-phase click (S0). Results show that: (1) The Δt function has two distinct segments: (a) for short-time separations, the MLD is governed by interaural phase relations, and has a maximum that approximates the Sπ condition; (b) for longer Δt, the MLD shows a systematic decrease and ultimately approaches the signal monaural (Sm) condition. (2) For increasing ΔI, the MLD increases monotonically and reaches a maximum of 6–7 dB at signal monaural. A ΔI of 24 dB yields an MLD that is still 1–2 dB below Sm. (3) When ΔI is added to a fixed Δt, the effect, in most cases, is a degradation of the MLD that would have resulted from time difference alone. In general, for the combination, MLD decreases as ΔI increases.