Effects of envelope discontinuities on perceptual restoration of amplitude-compressed speech

An interrupted signal may be perceptually restored and, as a result, perceived as continuous, when the interruptions are filled with loud noise bursts. Additionally, when the signal is speech, an improvement in intelligibility may be observed. The perceived continuity of interrupted tones is reduced when the signal level is ramped down and up before and after the noise burst, respectively--an effect that has been attributed to envelope discontinuities at the tone-noise interface [Bregman, A. S., and Dannenbring, G. L. (1977). Can. J. Psychiatry 31, 151-159]. The hypothesis of the present study was that the perceptual restoration of speech would also be reduced with similar envelope discontinuities that may occur in real life due to the release time constants of hearing-aid compression. In an effort to make the conditions more relevant to hearing aids, speech was amplitude-compressed and normal-hearing listeners of varying ages were recruited. Envelope amplitude ramps were placed at the onsets/offsets of speech segments of interrupted sentences and the restoration effect was measured in two ways: objectively as the improvement in intelligibility when noise was added in the gaps and subjectively through the perceived continuity measured by subjects' own reporting. Both measures showed a reduction as the ramp duration increased--a trend observed for subjects of all ages and for all ramp configurations. These findings can be attributed to envelope discontinuities, with an additional contribution from reduced speech information due to ramping and temporal masking from loud noise bursts.