MEASUREMENTS OF THE BINAURAL TEMPORAL WINDOW USING A DETECTION TASK

Two experiments investigated the shape of the binaural temporal window using a detection task. In experiment 1, a 10-ms tone burst was prese nted binaurally out-of-phase during a burst of white noise, which chan ged from being interaurally uncorrelated, to correlated, and back to u ncorrelated. The tone occurred during the correlated portion of the no ise in one interval of each 2I-FC trial. Detection thresholds were rec orded using a 2-down/1-up adaptive procedure. Thresholds were measured for different durations of correlated noise (0-960 ms), frequencies o f tone burst (125, 250, 500, and 1000 Hz) and levels of noise [20, 30, 40, and 50 dB(SPL)/Hz]. Window shapes based on nine candidate functio ns were fitted to the data using the assumption that the binaural mask ing release was related to the overall interaural correlation of noise admitted by the window. Fitted windows included both a forward and a backward lobe. Gaussian functions tended to give closer fits than expo nential and rounded-exponential functions, and simple functions gave m on parsimonious fits that those which included dynamic-range-limiting terms. Using simple Gaussian fits, the shape of the window was largely independent of frequency and level, and the windows for individual li steners had equivalent rectangular durations ranging from 55 to 188 ms . The asymmetry was variable, although forward lobes were generally sh orter than backward lobes. Experiment 2 ruled out the possibility that the forward lobe might be an artefact caused by distraction of the li stener, when the interaural phase change in the noise closely followed the signal. In this experiment, the out-of-phase tone was presented d uring a burst of partially correlated noise which changed, after a var iable interval, to a fully correlated noise. Thresholds for detecting the tone rose (i.e., performance worsened) as the interval was increas ed. Distraction would have produced the opposite effect. (C) 1998 Acou stical Society of America.