Dichotic interference effects in gap detection

Abstract

Thresholds for detecting a temporal gap in a 20-Hz-wide band of noise (the target) were measured for the target alone, and in the presence of multiple 20-Hz-wide flanking bands presented to the opposite ear. The flanking bands caused gap thresholds to increase, and this effect was greater at higher levels of the flanking bands. The impairment to gap detection was greater when the flanking bands were comodulated with the target (i.e., had the same envelope) than when they were not comodulated, except at very low and high levels of the flanking bands. A series of supplementary experiments was conducted to investigate why the difference between comodulated and noncomodulated bands was reduced at high levels. The results suggest that this was not due to inter-aural crosstalk. It may have been partly caused by: (1) a central masking effect that reduced the effective sensation level of the target band at high levels of the contralateral flanking bands; (2) reduced independence of the flanking bands owing to broadening of the auditory filters at high levels. The results are discussed in terms of perceptual grouping processes.

Gap detection in modulated noise: Across-frequency facilitation and interference

“…Previous experiments that have measured gap detection in a single band of noise accompanied by other bands of noise not carrying the gap have consistently shown an elevation in gap threshold due to the flanking bands and, moreover, have generally found this elevation to be more pronounced for comodulated flanking bands than for random flanking bands (Grose and Hall, 1993a;Moore et al, 1993). In contrast, the results of experiment 2 showed no consistent elevation of gap threshold in the presence of comodulated flanking bands and, overall, gap thresholds were more elevated for random flanking bands than for comodulated flanking bands.…”

“…If this cue is such that observers who do not get prior exposure to a continuous presentation mode are unlikely to learn it, then a different pattern of results may emerge from 'unexposed' observers. This might account for the different data patterns between the experiment 2 and other published studies (e.g., Grose and Hall, 1993a;Moore et al, 1993). To assess this possibility, three naive observers were recruited and tested in a subset of the gated conditions of experiment 2.…”

“…Existing studies that have examined the detection of gaps in single noise bands in the presence of other noise bands -either comodulated or random -have found no indication of a detection advantage (Grose and Hall, 1993a;Moore et al, 1993;Hall et al, 2007). All of these studies used gated presentation.…”

“…Relative to this baseline, gap detection performance typically improves if additional noise bands are added that also contain the synchronous gap (Grose and Hall, 1988;Grose, 1991;Hall et al, 1996;Grose and Hall, 1997). At the same time, gap detection performance typically declines if additional noise bands are added that do not contain the gap (Grose and Hall, 1993a;Moore et al, 1993).…”

“…Sensitivity to this decorrelation could signal the presence of the gap. This hypothesis was tested by Grose and Hall (1993a) using a single flanking band of noise, and by Moore et al (1993) using eight flanking bands of noise. Both studies found that the presence of additional bands of noise not carrying the gap -either comodulated or random -was detrimental to detection of a gap in a single target band of noise.…”