The effect of temporal placement on gap detectability

The detectability of a masked sinusoid increases as its onset approaches th e temporal center of a masker. This study was designed to determine whether a similar:change in detectability would occur for a silent gap as it was p arametrically displaced from the onset of a noise burst. Gap thresholds wer e obtained for 13 subjects who completed five replications of each conditio n in 3 to 13 days. Six subjects were inexperienced listeners who ranged in age from Is to 25 years; seven subjects were highly experienced and ranged in age from 20 to 78 years. The gaps were placed in 150-ms, 6-kHz, low-pass ed noise bursts presented at an overall level of 75 dB SPL; the bursts were digitally shaped at onset and offset with IO-Ins cosine-squared rise-fan e nvelopes. The gated noise bursts were presented in a continuous, unfiltered , white noise floor attenuated to an overall level of 45 dB SPL. Cap;onsets were parametrically delayed from the onset of the noise burst (defined as the first nonzero point on the waveform envelope) by 10, 11, 13, 15, 20, 40 , 60, 110, 120, and 130 ms. Results of ANOVAs indicated that the mean gap t hresholds were longer when the gaps were proximal to signal onset or offset and shorter when the gaps approached the temporal center of the noise burs t. Also, the thresholds of the younger, highly:experienced subjects were si gnificantly shorter than those of the younger, inexperienced subjects, espe cially at placements close to signal onset or offset. The effect of replica tion (short-term practice) was not significant nor was the interaction betw een gap placement and replication. Post hoc comparisons indicated that the effect of gap placement resulted from significant decreases in gap-detectab ility when the gap was placed close to stimulus onset and offset. (C) 1999 Acoustical Society of America. [S0001-4966(99)06312-2].