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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Very high intelligibility was found for a number of narrow-band filtering conditions. Four hundred listeners (20 groups of 20 subjects) were presented with bandpass filtered CTD sentences (‘‘everyday speech’’) and monosyllabic words. Separate groups received center frequencies of 370, 530, 750, 1100, 1500, 2100, 3000, 4200, or 6000 Hz at 70 dBA SPL. In experiment 1, intelligibility of single 1/3-octave bands with steep filter slopes (96 dB/oct) averaged more than 95% for sentences centered at 1100, 1500, and 2100 Hz, and more than 50% for monosyllabic words centered at 1500 and 2100 Hz. Experiment 2 used the same center frequencies with extremely narrow bands (slopes of 115 dB/oct intersecting at the center frequency)−intelligibility remained relatively high for most bands, with greatest intelligibility at 1500 Hz (77% for sentences, 18% for words). In experiment 3, 1/3-octave bands (96 dB/oct) centered at 370 and 6000 Hz were presented simultaneously either diotically or dichotically (when presented separately in experiment 1, intelligibility of these bands did not differ significantly, and averaged 23% for sentences and 3% for monosyllabic words). When the bands were combined, diotic and dichotic presentations were equivalent. Intelligibility rose to an average of 77% for sentences and 34% for words. [Work supported by NIH Grant No. DC00208.]

Two types of perceptual synthesis (or auditory induction) have been reported that can minimize or cancel the effects of masking upon speech: Phonemic restoration can enhance intelligibility of speech when segments are replaced or masked by noise, and contralateral induction can prevent mislateralization of speech masked at one ear [see R. M. Warren, Psychol. Bull. 96, 371–383 (1984)]. A third type of auditory induction, ‘‘spectral restoration,’’ is reported, which can enhance intelligibility when deleted regions of the speech spectrum are replaced by noise. Separate groups of listeners heard lists of sentences consisting of two widely separated bands having low intelligibility. When an appropriate noise was added to the spectral gap separating the bands, a significant improvement in intelligibility was observed. It is suggested that spectral restoration represents a mechanism capable of enhancing comprehension of speech when portions of its spectrum are masked.