Temporal gap detection measured with multiple sinusoidal markers: effects of marker number, frequency, and temporal position.

Detection thresholds were measured for silent temporal gaps within combinations of two, three, or four sinusoidal markers (i.e., combinations of one or two pre-gap markers with one or two post-gap markers). The markers were selected from the frequency range 2000-3100 Hz. Sinusoidal frequencies F1 and F4 were used as pre-gap markers, while F2 and F3 served as post-gap markers. Temporal gap detection (TGD) thresholds were measured from sets of three normal-hearing adults who tracked 70.7% correct detection thresholds adaptively across blocks of 50 two-interval, two-alternative, forced-choice trials. For symmetric marker conditions, where pre- and post-gap markers were equivalent in frequency (e.g., F1 = F2 or F1 = F2 and F3 = F4), TGD thresholds were < 10 ms. However, for asymmetric marker frequency alignments across the silent gap, including stimulus configurations where only three markers were presented on a trial (e.g., F1 = F2, F2 not equal to F3, no F4), performance was highly variable and was dramatically disrupted by the presentation of a second post-gap marker. The multiple-marker results reveal that TGD depends greatly on the number of markers presented, both in terms of the marker temporal position before and after the silent gap signal and the marker frequency alignment (symmetry) across the gap. These results, which cannot be predicted from models of the auditory periphery, may reflect perceptual mechanisms that are important in grouping and organizing auditory images.