Simultaneous and non-simultaneous masking tasks are often introduced to listeners in terms of the veridical relative positions of the signal and masker. Here we report that the actual
perceived temporal positions of the signal and masker do not always match those descriptions. We asked normal-hearing adults about the
perceived presentation time of a brief "signal" that was presented either before, during, or after a longer "masker." The task was either to mark the
perceived presentation time of the signal on a schematic diagram of the masker, or simply to judge whether the signal occurred inside or outside of the masker. Listeners tended to
perceive the signals as having occurred later than they actually had. This
temporal distortion was most marked for signals that were presented near the end of the masker. Signals that were presented 25-100 ms before the end of the masker were
perceived as occurring outside of the masker 50% of the time. Similar results were obtained with different masker durations (150, 300, and 450 ms), and various combinations of signal and masker spectra. This phenomenon may provide a measure of the time it takes to switch attention from a foreground to a background stimulus. [Work supported by NIH.].
