Dichotic temporal interactions: Fusion and temporal order

Several phenomena are associated with a monotonic increase in interaural temporal asymmetry (Δt) of equally intense auditory stimuli: lateralization of a fused stimulus in the direction of the lead ear, when Δt is in the microsecond range, the subsequent breakup of the fused stimulus with Δt in the millisecond range, followed by temporal order judgments at Δts longer than 20 msec. Two of these binaural phenomena are investigated, using the same experimental paradigm: the breakup of the fused sound into two separately perceived stimuli and the judgment of temporal order. A V-shaped function describes the relationship of discrimination to interaural temporal asymmetry. The left segment of this function, decreasing as Δt increases from 2 to 8 msec, crosses the 75% discrimination level at a dichotic temporal separation of 6 msec and reflects the breakup of the fused stimulus. The right segment of this function, increasing from 12 to 128 msec, crosses the 75% discrimination level at a dichotic temporal separation of 18 msec, reflecting temporal order discrimination. The data are discussed in terms of the literature on temporal order judgments, and considered in terms of an overall framework which assumes that all of the phenomena which occur as a function of increased Δt result from different processing operations on the temporal continuum separating the dichotic stimuli (Sternberg & Knoll, 1973).