Perception of spasmodic dysphonia speech in background noise

The purpose of this investigation was to judge whether the Lombard effect, a characteristic change in the acoustical properties of speech produced in noise, existed in adductor spasmodic dysphonia speech, and if so, whether the effect added to or detracted from speaker intelligibility. Intelligibility, as described by Duffy, is the extent to which the acoustic signal produced by a speaker is understood by a listener based on the auditory signal alone. Four speakers with adductor spasmodic dysphonia provided speech samples consisting of low probability sentences from the Speech Perception in Noise test to use as stimuli. The speakers were first tape-recorded as they read the sentences in a quiet speaking condition and were later tape-recorded as they read the same sentences while exposed to background noise. The listeners used as subjects in this study were 50 undergraduate university students. The results of the statistical analysis indicated a significant difference between the intelligibility of the speech recorded in the quiet versus noise conditions (F(1,49) = 57.80, p < or = .001). It was concluded that a deleterious Lombard effect existed for the adductor spasmodic dysphonia speaker group, with the premise that the activation of a Lombard effect in such patients may detract from their overall speech intelligibility.     

Use of speech-modulated noise adds strong “bottom-up” cues for phonemic restoration

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.     

The effect of a flashing visual stimulus on the auditory continuity illusion

The effect of a visual stimulus on the auditory continuity illusion was examined. Observers judged whether a tone that was repeatedly alternated with a band-pass noise was continuous or discontinuous. In most observers, a transient visual stimulus that was synchronized with the onset of the noise increased the limit of illusory continuity in terms of maximum noise duration and maximum tone level. The smaller the asynchrony between the noise onset and the visual stimulus onset, the larger the visual effect on this illusion. On the other hand, detection of a tone added to the noise was not enhanced by the visual stimulus. These results cannot be fully explained by the conventional theory that illusory continuity is created by the decomposition of peripheral excitation produced by the occluding sound.     

Backward masking and asymmetry of processing for vowels differing in acoustical similarity

Several investigations have reported problems in demonstrating for vowels the phenomena of backward masking and right ear advantage so easily demonstrated for consonants. An experiment is reported on the dichotic backward masking (BM) of acoustically similar and dissimilar sets of vowels in consonant-vowel syllables. The results suggest that increasing perceptual difficulty by varying the acoustic similarity of the stimulus set augments BM. A second experiment showed that the right ear advantage (REA) was augmented by manipulating the acoustic similarity of the stimulus set and by decreasing intelligibility through the addition of noise. This and other evidence was employed to ascribe variations in both REA and BM to the interaction of perceptual processing time with information decay in precategorical acoustical storage. It is argued that this process interaction underlies statistical interactions in dichotic data which show that variations in difficulty (discriminability, noise addition, brain deterioration) affect most adversely the least favoured items (those presented earlier, those on the unattended ear, those on the left ear).     

Blocking the development of stimulus control when stimuli indicate periods of nonreinforcement

To learn whether prior discrimination training based on one stimulus would block learning about a subsequently added stimulus, rats were first trained to press a bar on a variable-interval schedule of food reinforcement. Occasional stimuli were presented during which no reinforcement was available. Responding became suppressed in the presence of these stimuli. Stimuli could be noise, light, or a compound of noise plus light. A group trained with noise in Phase 1, then trained with the compound in Phase 2, showed less suppression to light in a subsequent test than a group that had the same compound training in Phase 2 but only variable-interval training in Phase 1. This showed that prior training with noise blocked the development of control by light during compound training. Two further groups showed that noise training following compound training did not have the same effect on control by light.     

Discrepant visual speech facilitates covert selective listening in "cocktail party" conditions

The presence of congruent visual speech information facilitates the identification of auditory speech, while the addition of incongruent visual speech information often impairs accuracy. This latter arrangement occurs naturally when one is being directly addressed in conversation but listens to a different speaker. Under these conditions, performance may diminish since: (a) one is bereft of the facilitative effects of the corresponding lip motion and (b) one becomes subject to visual distortion by incongruent visual speech; by contrast, speech intelligibility may be improved due to (c) bimodal localization of the central unattended stimulus. Participants were exposed to centrally presented visual and auditory speech while attending to a peripheral speech stream. In some trials, the lip movements of the central visual stimulus matched the unattended speech stream; in others, the lip movements matched the attended peripheral speech. Accuracy for the peripheral stimulus was nearly one standard deviation greater with incongruent visual information, compared to the congruent condition which provided bimodal pattern recognition cues. Likely, the bimodal localization of the central stimulus further differentiated the stimuli and thus facilitated intelligibility. Results are discussed with regard to similar findings in an investigation of the ventriloquist effect, and the relative strength of localization and speech cues in covert listening.     

Test of Spanish sentences to measure speech intelligibility in noise conditions

This article describes the development of a test for measuring the intelligibility of speech in noise for the Spanish language, similar to the test developed by Kalikow, Stevens, and Elliot (Journal of the Acoustical Society of America, 5, 1337–1360, 1977) for the English language. The test consists of six forms, each comprising 25 high-predictability (HP) sentences and 25 low-predictability (LP) sentences. The sentences were used in a perceptual task to assess their intelligibility in babble noise across three different signal-to-noise ratio (SNR) conditions in a sample of 474 normal-hearing listeners. The results showed that the listeners obtained higher scores of intelligibility for HP sentences than for LP sentences, and the scores were lower for the higher SNRs, as was expected. The final six forms were equivalent in intelligibility and phonetic content.     

The role of small changes in the acoustic environment in modifying the startle reflex.

When either the intensity or frequency spectrum of an approximately 70-db. SPL narrow-band noise was abruptly changed by a small amount, the rat's response to a startle stimulus presented 64 msec later was inhibited. When similar small frequency changes preceded the startle stimulus by ony 5 msec, the latency of the startle response was reduced, but even relatively large changes in intensity of the antecedent stimulus had no effect on response latency. These findings provide added support for the generalization that the neural processes associated with startle are engaged by small changes in the auditory environment. They also point to a measure of separation between the processes responsible for inhibition and those responsible for latency shift.     

Suppression During Binocular Rivalry Broadens Orientation Tuning

ABSTRACT— During binocular-rivalry suppression, an ordinarily visible stimulus is erased from awareness, but how is the sensory representation of that stimulus affected? Although it is established that rivalry suppression attenuates signal strength, the influence of suppression on signal fidelity remains unknown. Here, we show that noise plays a hitherto undiscovered role in the degradation of the percept under suppression. In Experiment 1, we measured psychometric functions for a stimulus presented under dominance and suppression, and found that the slope of these functions was shallower under suppression—a result suggesting that the signal representation was rendered noisier. Experiment 2 then revealed the source of this noise: An examination of the influence of suppression on the orientation bandwidth of noise masking showed that tuning bandwidth is significantly broadened under suppression. Thus, the discriminability of a suppressed stimulus is weakened not only by a general decrease in signal strength, but also by broader orientation tuning that introduces more noise in the neural representation of the suppressed stimulus.     

Information integration and the identification of stimulus noise and criterial noise in absolute judgment

Two main classes of theories have been proposed regarding range effects in unidimensional absolute-identification tasks. One class posits that as range is increased, criterial noise increases but stimulus noise remains constant. Another class posits increasing stimulus noise but constant criterial noise. In this study, an effort is made to help decide this issue. Multiple observations are used in several absolute-identification tasks of varying range. A stimulus integration model is proposed in which averaging takes place over stimulus internal representations, thereby reducing stimulus variance; on the other hand, it is assumed that criterial variance is unaffected by the number of observations. The model allows one to identify the relative amounts of stimulus noise and criterial noise inherent in observers' recognition judgments. The model yields good fits to data in several experiments, and it is concluded that both stimulus noise and criterial noise increase as range in the absolute-identification task is increased.     

Hearing speech in noise: seeing a loud talker is better

Seeing the talker improves the intelligibility of speech degraded by noise (a visual speech benefit). Given that talkers exaggerate spoken articulation in noise, this set of two experiments examined whether the visual speech benefit was greater for speech produced in noise than in quiet. We first examined the extent to which spoken articulation was exaggerated in noise by measuring the motion of face markers as four people uttered 10 sentences either in quiet or in babble-speech noise (these renditions were also filmed). The tracking results showed that articulated motion in speech produced in noise was greater than that produced in quiet and was more highly correlated with speech acoustics. Speech intelligibility was tested in a second experiment using a speech-perception-in-noise task under auditory-visual and auditory-only conditions. The results showed that the visual speech benefit was greater for speech recorded in noise than for speech recorded in quiet. Furthermore, the amount of articulatory movement was related to performance on the perception task, indicating that the enhanced gestures made when speaking in noise function to make speech more intelligible.     

Speech Intelligibility and Recall of Spoken Material Heard at Different Signal‐to‐noise Ratios and the Role Played by Working Memory Capacity

We studied speech intelligibility and memory performance for speech material heard under different signal‐to‐noise (S/N) ratios. Pre‐experimental measures of working memory capacity (WMC) were taken to explore individual susceptibility to the disruptive effects of noise. Thirty‐five participants first completed a WMC‐operation span task in quiet and later listened to spoken word lists containing 11 one‐syllable phonetically balanced words presented at four different S/N ratios (+12, +9, +6, and +3). Participants repeated each word aloud immediately after its presentation, to establish speech intelligibility and later on performed a free recall task for those words. The speech intelligibility function decreased linearly with increasing S/N levels for both the high‐WMC and low‐WMC groups. However, only the low‐WMC group had decreasing memory performance with increasing S/N levels. The memory of the high‐WMC individuals was not affected by increased S/N levels. Our results suggest that individual differences in WMC counteract some of the negative effects of speech noise. Copyright © 2012 John Wiley & Sons, Ltd.     

Free-operant escape-avoidance of noise by rats

A series of experiments was conducted to establish free-operant escape-avoidance responding in rats using noise as the stimulus. Naive rats did not acquire a bar-press response on an escape-avoidance of noise schedule. Similarly, free-operant responding established using escape-avoidance of shock was not maintained when noise was substituted for shock. Noise stimuli of 110 dB did maintain responding, but at a lower level than during training, when the noise stimuli had first been paired with shock. Noise stimuli of 97 dB and 87 dB were not effective under those same conditions. Additional rats were trained on a free-operant escape-avoidance schedule of shock and then exposed to a delayed conditioning procedure in which noise was the conditioned stimulus and shock was the unconditioned stimulus. When these subjects were then tested with noise alone, two of the three subjects conditioned and tested with 105-dB noise displayed escape-avoidance of noise, but none of the rats conditioned and tested at 97 dB displayed escape-avoidance of noise. The results suggest that free-operant escape-avoidance of noise can be demonstrated; however, only higher intensity noise stimuli that have been paired with shock are effective.     

The roles of stimulus control and reinforcement frequency in modulating the behavioral effects of d-amphetamine in the rat.

The behavioral effects of d-amphetamine have been shown to be modulated by stimulus control, with less impairment of performance occurring when control is great. When the fixed-consecutive-number schedule is used (on which at least a specified consecutive number of responses must be made on one operandum before a single response on another will produce a reinforcer), response rate tends to be invariant but reinforcement frequency is not. This study asks whether the differences in reinforcement frequency that usually accompany changes in stimulus control could themselves be responsible for the performance differences. Two versions of the fixed-consecutive-number schedule of reinforcement were combined into a multiple schedule within which stimulus control was varied but differences in reinforcement frequency were minimized by omitting some reinforcer deliveries during the component that usually had the higher reinforcement frequency. In one component, a compound discriminative stimulus was added with the eighth consecutive response on the first lever; a single response on the second lever was then reinforced. In the other component, no such stimulus was presented. With no added stimulus, large decreases occurred in the number of runs satisfying the minimum requirement for reinforcement at doses of drug that produced only minimal changes when an added stimulus controlled behavior. Thus, increased stimulus control diminishes the behavioral changes produced by d-amphetamine even when the possible contribution by baseline reinforcement rate is minimized.     

Spectral restoration of speech: Intelligibility is increased by inserting noise in spectral gaps

In order to function effectively as a means of communication, speech must be intelligible under the noisy conditions encountered in everyday life. Two types of perceptual synthesis have been reported that can reduce or cancel the effects of masking by extraneous sounds: Phonemic restoration can enhance intelligibility when segments are replaced or masked by noise, and contralateral induction can prevent mislateralization by effectively restoring speech masked at one ear when it is heard in the other. The present study reports a third type of perceptual synthesis induced by noise: enhancement of intelligibility produced by adding noise to spectral gaps. In most of the experiments, the speech stimuli consisted of two widely separated narrow bands of speech (center frequencies of 370 and 6000 Hz, each band having high-pass and low-pass slopes of 115 dB/octave meeting at the center frequency). These very narrow bands effectively reduced the available information to frequency-limited patterns of amplitude fluctuation lacking information concerning formant structure and frequency transitions. When stochastic noise was introduced into the gap separating the two speech bands, intelligibility increased for “everyday” sentences, for sentences that varied in the transitional probability of keywords, and for monosyllabic word lists. Effects produced by systematically varying noise amplitude and noise bandwidth are reported, and the implications of some of the novel effects observed are discussed.     

Intelligibility of interrupted meaningful and nonsense speech with and without intervening noise

The insertion of noise in the silent intervals of interrupted speech has a very striking perceptual effect if a certain signal-to-noise ratio is used. Conflicting reports have been published as to whether the inserted noise improves speech intelligibility or not. The major difference between studies was the level of redundancy in the speech material. We show in the present paper that the noise leads to a better intelligibility of interrupted speech. The redundancy level determines the possible amount of improvement. The consequences of our findings are discussed. in relation to such phenomena as continuity perception and pulsation threshold measurement. A hypothesis is formulated for the processing of interrupted stimuli with and without intervening noise: for stimuli presented with intervening noise, the presence in the auditory system of an automatic interpolation mechanism is assumed. The mechanism operates only if the noise makes it impossible to perceive the interruption.     

Referential coding and attention-shifting accounts of the Simon effect

Summary Stoffer (1991) and Umiltá and Nicoletti (1992) have proposed an attention-shifting account of the Simon effect. However, Hommel (1993) has presented evidence suggesting that the effect can be explained in terms of referential coding, without invoking attentional shifts. Five experiments are reported here, whose primary purpose is to test implications of the referential-coding account. All of the experiments compared conditions in which a noise stimulus was presented in the position opposite the target stimulus with conditions in which it was not. Contrary to the referential-coding account, (a) the basic Simon effect was larger without a fixation point to serve as a referent than with one; (b) the noise stimulus increased the magnitude of the Simon effect when a fixation point was used, but not when there was no fixation point; and (c) the magnitude of the Simon effect obtained in the presence of a noise stimulus was reduced substantially when the noise and the target (and, if present, the fixation point) were in different colors. The results, although counter to predictions of the referential-coding account, can be accommodated by the attention-shifting account if it is assumed that a fixation point provides an anchor that minimizes attention shifts.     

Word recognition in loud noise

Loud noise has been shown to bias environmental stimulus selection to high-priority or ‘dominant’ task and stimulus features while causing relative neglect of less dominant aspects. The present concern was whether a similar influence of noise would occur when selecting, or rather, retrieving information from memory. Separate groups performed a semantic recognition task in 95 dB(A) ‘noise’ or 70 dB(A) ‘quiet’ conditions. Recognition of semantically ‘high-dominance’ words was reliably faster in noise but ‘low-dominance’ recognition was not impaired relative to performance in quiet conditions. On this basis, the results only partially support a possible common principle governing selection of environmental and memorial information in noise. However, they confirm Eysenck's (1975) contention that arousal may affect retrieval processes (in addition to initial learning) and that failure to account for the former influence may obscure inferences drawn from previous research.     

Variations in intensity and frequency moderate the facilitative effects of a complex rhythm stimulus on long-term memory consolidation in the day-old chick (Callus gallus)

The authors have previously shown that exposure to 1 min of a complex, but not an isochronous, rhythm stimulus facilitates long-term memory consolidation in chicks (Gallus gallus) trained on a passive-avoidance task (S. R. Toukhsati & N. S. Rickard, 2001). The acoustic parameters of this stimulus were explored further in the current study. Retention was found to be best facilitated when the complex rhythm stimulus was presented at intensities between 5 and 15 dBA above background laboratory noise levels and at a frequency of 1 kHz. Removal of an accent from the stimulus did not moderate the effect. These findings provide confirmation that memory in an avian species can be facilitated by exposure to a complex rhythm stimulus and suggest that pattern repetition may be an important feature of this effect.     

Seeing to hear better: evidence for early audio-visual interactions in speech identification

Lip reading is the ability to partially understand speech by looking at the speaker's lips. It improves the intelligibility of speech in noise when audio-visual perception is compared with audio-only perception. A recent set of experiments showed that seeing the speaker's lips also enhances sensitivity to acoustic information, decreasing the auditory detection threshold of speech embedded in noise [J. Acoust. Soc. Am. 109 (2001) 2272; J. Acoust. Soc. Am. 108 (2000) 1197]. However, detection is different from comprehension, and it remains to be seen whether improved sensitivity also results in an intelligibility gain in audio-visual speech perception. In this work, we use an original paradigm to show that seeing the speaker's lips enables the listener to hear better and hence to understand better. The audio-visual stimuli used here could not be differentiated by lip reading per se since they contained exactly the same lip gesture matched with different compatible speech sounds. Nevertheless, the noise-masked stimuli were more intelligible in the audio-visual condition than in the audio-only condition due to the contribution of visual information to the extraction of acoustic cues. Replacing the lip gesture by a non-speech visual input with exactly the same time course, providing the same temporal cues for extraction, removed the intelligibility benefit. This early contribution to audio-visual speech identification is discussed in relationships with recent neurophysiological data on audio-visual perception.