Outside ofthe laboratory, listening conditions are often less than ideal, and when attending to sounds from a particular source, portions are often obliterated by extraneous noises. However, listeners possess rather elegant reconstructive mechanisms. Restoration can be complete, so that missing segments are indistinguishable from those actually present and the listener is unaware that the signal is fragmented. This phenomenon, called temporal induction (TD, has been studied extensively with nonverbal signals and to a lesser extent with speech. Earlier studies have demonstrated that TI can produce illusory continuity spanning gaps of a few hundred milliseconds when portions ofa signal are replaced by a louder sound capable of masking the signal were it actually present. The present study employed various types of speech signals with periodic gaps and measured the effects upon intelligibility produced by filling these gaps with noises. Enhancement of intelligibility through multiple phonemic restoration occurred when the acoustic requirements for TI were met and when sufficient contextual information was available in the remaining speech fragments. It appears that phonemic restoration is a specialized form of TI that uses linguistic skills for the reconstruction of obliterated speech.In everyday life, portions of speech and other acoustic signals are often obliterated by extraneous transient noises such as coughs, slamming doors, and traffic sounds. However, we possess sophisticated mechanisms that can restore the segments of these signals that have been obliterated by noise. The rule governing restoration is simple, and its consequences manifold. Restoration can occur when an extraneous sound is capable of masking a signal and when there is sufficient contextual information to establish the identity of an obliterated fragment. This restoration, which has been called temporal induction (TI), is complete, so that when appropriate conditions are met, listeners cannot distinguish restored sounds from those actually present.A review of the literature has indicated that there are three basic types ofTI (Warren, 1984). The simplest form of restoration has been called homophonic continuity. If three levels of the same sound (e.g., 60-, 70-, and 80-dB levels of a noise each lasting 300 msec) are presented in succession and repeated without pauses, the 6O-dB level appears to be on continuously with the other levels heard as intermittent pulsed additions. Apparent continuity of the faintest sound occurs despite the fact that this level is actually present for less than half of the time. Homophonic continuity is a subtractive process. Thus, when Portions of this work were supported by grants from the National Institutes of Health (DC00208) and the Air Force Office of Scientific Research (88-0320). These experiments were outlined in a paper presented at the 119th meeting of the Acoustical Society of America, with a briefabstract appearing in the Ioumal of the Acoustical Society (VoL 87, Supp1. 1,1990, S71). The authors are w...

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Perspective theories for the Muller-Lyer illusions have considered them to reflect constancies normally permitting the viewer to compensate for distance in estimating the true size of three-dimensional objects. Our experiments suggest a rather different perspective theory involving object recognition.A novel experimental procedure was used. Each of the separate groups of thirty subjects viewed only one of nineteen experimental drawings based on the Muller-Lyer figures. They judged the overall length of the shaft and divided it into subjectively equal quarters. The major findings were that the effect of each component angle was generally independent of other angles and independent of any overall perspective appearance of the figure. The shortening effect produced by an acute angle was limited to the contiguous quarter, while the lengthening effect of an obtuse angle extended undiminished from the contiguous quarter to the next quarter.Perspective photographs are shown, demonstrating that these angle-induced changes in apparent length can compensate selectively for the different perspective distortions occurring for the component parts of a single three-dimensional object. Such expansions and contractions provide no direct help in estimating overall size or distance of the object. But they do make possible recognition of the actual shape of the object and its orientation to the viewer, as well as producing errors when judging the length of Muller-Lyer figures.

When deleted segments of speech are replaced by extraneous sounds rather than silence, the missing speech fragments may be perceptually restored and intelligibility improved. This phonemic restoration (PhR) effect has been used to measure various aspects of speech processing, with deleted portions of speech typically being replaced by stochastic noise. However, several recent studies of PhR have used speech-modulated noise, which may provide amplitude-envelope cues concerning the replaced speech. The present study compared the effects upon intelligibility of replacing regularly spaced portions of speech with stochastic (white) noise versus speech-modulated noise. In Experiment 1, filling periodic gaps in sentences with noise modulated by the amplitude envelope of the deleted speech fragments produced twice the intelligibility increase obtained with interpolated stochastic noise. Moreover, when lists of isolated monosyllables were interrupted in Experiment 2, interpolation of speech-modulated noise increased intelligibility whereas stochastic noise reduced intelligibility. The augmentation of PhR produced by modulated noise appeared without practice, suggesting that speech processing normally involves not only a narrowband analysis of spectral information but also a wideband integration of amplitude levels across critical bands. This is of considerable theoretical interest, but it also suggests that since PhRs produced by speech-modulated noise utilize potent bottom-up cues provided by the noise, they differ from the PhRs produced by extraneous sounds, such as coughs and stochastic noise.

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