Alternate Author Name(s)

Dr. Joseph S. Puleo Jr., PhD '77

Document Type

Dissertation

Date of Award

1977

Keywords

Psychophysiology, Psychoacoustics, Backward masking

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

First Advisor

Richard E. Pastore

Second Advisor

Richard G. Burright

Third Advisor

Jane A. Connor

Abstract

A series of related experiments was designed to investigate the effectiveness of contralateral cueing information in reducing monotic backward masking in the presence of a second, continuous masking noise. It was hypothesized that any facilitatory effects of the cue on detection performance would depend on the degree to which the specific types of cueing information were associated with the nature of the deficits produced by the backward masking stimulus.

In the first three experiments, the cue and (with a 0.5 probability) the signal were presented simultaneously during the single observation interval and were identical (except for phase) in their average long-term frequency spectrum. While significant reductions in backward masking occurred in all cue conditions, these effects were not affected differentially by the particular interaural correlation of cue and signal beyond the very small differences obtained for simultaneous masking (i.e., with no backward masking stimulus). In Experiment III, which parametrically manipulated the phase relationship between the cue and signal, it was found that the greatest improvements occurred when the cue lagged the signal in phase by 30 to 90°. However, the pattern of this improvement was neither gaussian [as would befit a perfect cross-correlator (SKE) detection mechanism], nor sharply peaked near zero phase [as would be the case if the detection mechanism was sensitive primarily to interaural timing cues]. These differential phase effects were attributed largely to the release from simultaneous masking, with an additional large reduction in backward masking which was not differentially sensitive to the phase manipulations.

In the final two experiments, the signal was a sinusoid and the cue was either a burst of band-limited noise centered at the signal frequency, or a gap in an otherwise continuous broadband noise. The noise burst cue was manipulated in terms of its frequency bandwidth (and thus spectral complexity), while the gap cue was manipulated with regard to its temporal properties (i.e., onset and offset) relative to the observation interval. None of these cues were very effective in reducing simultaneous masking. The data resulting from manipulations of the noise burst cue showed that, relative to the noncued condition, significant reductions in backward masking occurred regardless of the type of cue employed. Although the narrower-band cues were somewhat more effective than the wider-band cues in improving detection performance, these differences were not behaviorally significant. With the gap cues, the only significant reductions in backward masking occurred when the cue was simultaneous with and extended in time 1 msec. before the observation interval. The pattern of results obtained in this study indicated that it may have been the temporal, rather than spectral properties, of the cue which accounted for the significant reductions in backward masking. Since the temporal cues generally were not effective in reducing simultaneous masking, these results imply that temporal uncertainty may be a major factor involved in backward masking.

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