Signal-correlated Noise Research Articles

Sound Level Changes the Auditory Cortical Activation Detected with Functional Near-Infrared Spectroscopy.

Functional near-infrared spectroscopy (fNIRS) is a viable non-invasive technique for functional neuroimaging in the cochlear implant (CI) population; however, the effects of acoustic stimulus features on the fNIRS signal have not been thoroughly examined. This study examined the effect of stimulus level on fNIRS responses in adults with normal hearing or bilateral CIs. We hypothesized that fNIRS responses would correlate with both stimulus level and subjective loudness ratings, but that the correlation would be weaker with CIs due to the compression of acoustic input to electric output. Thirteen adults with bilateral CIs and 16 with normal hearing (NH) completed the study. Signal-correlated noise, a speech-shaped noise modulated by the temporal envelope of speech stimuli, was used to determine the effect of stimulus level in an unintelligible speech-like stimulus between the range of soft to loud speech. Cortical activity in the left hemisphere was recorded. Results indicated a positive correlation of cortical activation in the left superior temporal gyrus with stimulus level in both NH and CI listeners with an additional correlation between cortical activity and perceived loudness for the CI group. The results are consistent with the literature and our hypothesis. These results support the potential of fNIRS to examine auditory stimulus level effects at a group level and the importance of controlling for stimulus level and loudness in speech recognition studies. Further research is needed to better understand cortical activation patterns for speech recognition as a function of both stimulus presentation level and perceived loudness.

Spatial Release From Informational and Energetic Masking in Bimodal and Bilateral Cochlear Implant Users.

Purpose Spatially separating speech and background noise improves speech understanding in normal-hearing listeners, an effect referred to as spatial release from masking (SRM). In cochlear implant (CI) users, SRM has often been demonstrated using asymmetric noise configurations, which maximize benefit from head shadow and the potential availability of binaural cues. In contrast, SRM in symmetrical configurations has been minimal to absent in CI users. We examined the interaction between two types of maskers (informational and energetic) and SRM in bimodal and bilateral CI users. We hypothesized that SRM would be absent or "negative" using symmetrically separated noise maskers. Second, we hypothesized that bimodal listeners would exhibit greater release from informational masking due to access to acoustic information in the non-CI ear. Method Participants included 10 bimodal and 10 bilateral CI users. Speech understanding in noise was tested in 24 conditions: 3 spatial configurations (S0N0, S0N45&315, S0N90&270) × 2 masker types (speech, signal-correlated noise) × 2 listening configurations (best-aided, CI-alone) × 2 talker gender conditions (different-gender, same-gender). Results In support of our first hypothesis, both groups exhibited negative SRM with increasing spatial separation. In opposition to our second hypothesis, both groups exhibited similar magnitudes of release from informational masking. The magnitude of release was greater for bimodal listeners, though this difference failed to reach statistical significance. Conclusions Both bimodal and bilateral CI recipients exhibited negative SRM. This finding is consistent with CI signal processing limitations, the audiologic factors associated with SRM, and known effects of behind-the-ear microphone technology. Though release from informational masking was not significantly different across groups, the magnitude of release was greater for bimodal listeners. This suggests that bimodal listeners may be at least marginally more susceptible to informational masking than bilateral CI users, though further research is warranted.

Speech spoken by familiar people is more resistant to interference by linguistically similar speech.

Understanding speech in adverse conditions is affected by experience-a familiar voice is substantially more intelligible than an unfamiliar voice when competing speech is present, even if the content of the speech (the words) are controlled. This familiar-voice benefit is observed consistently, but its underpinnings are unclear: Do familiar voices simply attract more attention, are they inherently more intelligible because they have predictable acoustic characteristics, or are they more intelligible in a mixture because they are more resistant to interference from other sounds? We recruited pairs of native English-speaking participants who were friends or romantic couples. Participants reported words from closed-set English sentences (i.e., Oldenburg Matrix Test; Zokoll et al., 2013) spoken by a familiar talker (the participant's partner) or an unfamiliar talker. We compared 3 masker conditions that are acoustically similar but differ in their demands: (1) English Oldenburg sentences; (2) Oldenburg sentences in a language incomprehensible to the listener (Russian or Spanish); and (3) unintelligible signal-correlated noise. We adaptively varied the target-to-masker ratio to obtain 50% speech reception thresholds. We observed a large (∼5 dB) familiar-voice benefit when the target and masker were both English sentences. This benefit was attenuated (to ∼2 dB) when the masker was in an incomprehensible language and disappeared when it was signal-correlated noise. These results suggest that familiar voices did not benefit intelligibility because they were more predictable or because they attracted greater attention, rather familiarity with a target voice reduced interference from maskers that are linguistically similar to the target. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Evaluating time-reversed speech and signal-correlated noise as auditory baselines for isolating speech-specific processing using fNIRS.

Evidence using well-established imaging techniques, such as functional magnetic resonance imaging and electrocorticography, suggest that speech-specific cortical responses can be functionally localised by contrasting speech responses with an auditory baseline stimulus, such as time-reversed (TR) speech or signal-correlated noise (SCN). Furthermore, these studies suggest that SCN is a more effective baseline than TR speech. Functional near-infrared spectroscopy (fNIRS) is a relatively novel, optically-based imaging technique with features that make it ideal for investigating speech and language function in paediatric populations. However, it is not known which baseline is best at isolating speech activation when imaging using fNIRS. We presented normal speech, TR speech and SCN in an event-related format to 25 normally-hearing children aged 6–12 years. Brain activity was measured across frontal and temporal brain areas in both cerebral hemispheres whilst children passively listened to the auditory stimuli. In all three conditions, significant activation was observed bilaterally in channels targeting superior temporal regions when stimuli were contrasted against silence. Unlike previous findings in infants, we found no significant activation in the region of interest over superior temporal cortex in school-age children when normal speech was contrasted against either TR speech or SCN. Although no statistically significant lateralisation effects were observed in the region of interest, a left-sided channel targeting posterior temporal regions showed significant activity in response to normal speech only, and was investigated further. Significantly greater activation was observed in this left posterior channel compared to the corresponding channel on the right side under the normal speech vs SCN contrast only. Our findings suggest that neither TR speech nor SCN are suitable auditory baselines for functionally isolating speech-specific processing in an experimental set up involving fNIRS with 6–12 year old children.

The perception of speech rate for time manipulated and vocoded sentences

Naturally produced fast speech reduces certain acoustic-phonetic features that may limit intelligibility relative to linear time compression. However, how reduction affects judgments of speaking rate has not been systematically investigated. The purpose of this study was to examine the effects of linear time compression and spectral reduction on judgments of speaking rate. Listeners provided speech rate judgments of sentences. Conditions compared rate perceptions for naturally spoken sentences at slow and fast rates with linearly time-compressed/expanded versions of the same sentence, matched for duration. Conditions also examined rate judgments for noise vocoded sentences that varied in intelligibility and signal-correlated noise that examined rate judgments based only on temporal acoustic features. Our preliminary results demonstrate that linear time-compressed/expanded sentences were judged as faster than naturally produced sentences. This difference was also found for noise-vocoded versions of the sentences, as well as for signal-correlated noise. Additionally, vocoded stimuli were perceived as faster than naturally produced stimuli. These preliminary results suggest that acoustic-phonetic reductions in naturally produced speech do not appear to increase the perceived speaking rate relative to linear time manipulations. Significantly, temporal properties of speech rhythm appear responsible for coding perceptual aspects of speaking rate independently from factors related to linguistic processing.

Charge Persistence in InGaAs/InP Single-Photon Avalanche Diodes

We present a detailed characterization and modeling of the charge persistence effect that impacts InGaAs/InP single-photon avalanche diodes. Such phenomenon is due to holes that pile-up at the heterointerface outside the active area and has two main consequences: 1) higher noise (equivalent to higher dark count rate), not decreasing as expected at low temperature and 2) possible distortion of the acquired time-resolved waveforms (due to such signal-correlated noise). We propose a model that describes: 1) the generation of holes at the detector periphery in the InGaAs layer; 2) their accumulation at the heterointerface; 3) their subsequent diffusion toward the active area within the InGaAs layer; and 4) their resulting drift to the high field depleted InP region, where the unwelcome spurious avalanche is eventually triggered. We support our model by detailed experimental measurements and simulations. Finally, we propose simple approaches for designing detectors less sensitive to this type of noise.

Evaluating signal-correlated noise as a control task with language-related gamma activity on electrocorticography

ObjectiveOur recent electrocorticography (ECoG) study suggested reverse speech, a widely used control task, to be a poor control for non-language-related auditory activity. We hypothesized that this may be due to retained perception as a human voice. We report a follow-up ECoG study in which we contrast forward and reverse speech with a signal-correlated noise (SCN) control task that cannot be perceived as a human voice. MethodsTen patients were presented 90 audible stimuli, including 30 each of corresponding forward speech, reverse speech, and SCN trials, during ECoG recording with evaluation of gamma activity between 50 and 150Hz. ResultsSites of the lateral temporal gyri activated throughout speech stimuli were generally less activated by SCN, while some temporal sites seemed to process both human and non-human sounds. Reverse speech trials were associated with activities across the temporal lobe similar to those associated with forward speech. ConclusionsFindings herein externally validate functional neuroimaging studies utilizing SCN as a control for non-language-specific auditory function. Our findings are consistent with the notion that stimuli perceived as originating from a human voice are poor controls for non-language auditory function. SignificanceOur findings have implications in functional neuroimaging research as well as improved clinical mapping of auditory functions.

Single-trial analysis of the neural correlates of speech quality perception

Objective. Assessing speech quality perception is a challenge typically addressed in behavioral and opinion-seeking experiments. Only recently, neuroimaging methods were introduced, which were used to study the neural processing of quality at group level. However, our electroencephalography (EEG) studies show that the neural correlates of quality perception are highly individual. Therefore, it became necessary to establish dedicated machine learning methods for decoding subject-specific effects. Approach. The effectiveness of our methods is shown by the data of an EEG study that investigates how the quality of spoken vowels is processed neurally. Participants were asked to indicate whether they had perceived a degradation of quality (signal-correlated noise) in vowels, presented in an oddball paradigm. Main results. We find that the P3 amplitude is attenuated with increasing noise. Single-trial analysis allows one to show that this is partly due to an increasing jitter of the P3 component. A novel classification approach helps to detect trials with presumably non-conscious processing at the threshold of perception. We show that this approach uncovers a non-trivial confounder between neural hits and neural misses. Significance. The combined use of EEG signals and machine learning methods results in a significant ‘neural’ gain in sensitivity (in processing quality loss) when compared to standard behavioral evaluation; averaged over 11 subjects, this amounts to a relative improvement in sensitivity of 35%.

Do not throw out the baby with the bath water: choosing an effective baseline for a functional localizer of speech processing

Speech processing engages multiple cortical regions in the temporal, parietal, and frontal lobes. Isolating speech-sensitive cortex in individual participants is of major clinical and scientific importance. This task is complicated by the fact that responses to sensory and linguistic aspects of speech are tightly packed within the posterior superior temporal cortex. In functional magnetic resonance imaging (fMRI), various baseline conditions are typically used in order to isolate speech-specific from basic auditory responses. Using a short, continuous sampling paradigm, we show that reversed (“backward”) speech, a commonly used auditory baseline for speech processing, removes much of the speech responses in frontal and temporal language regions of adult individuals. On the other hand, signal correlated noise (SCN) serves as an effective baseline for removing primary auditory responses while maintaining strong signals in the same language regions. We show that the response to reversed speech in left inferior frontal gyrus decays significantly faster than the response to speech, thus suggesting that this response reflects bottom-up activation of speech analysis followed up by top-down attenuation once the signal is classified as nonspeech. The results overall favor SCN as an auditory baseline for speech processing.

Speech versus non-speech as irrelevant sound: Controlling acoustic variation

Functional differences between speech and non-speech within the irrelevant sound effect were investigated using repeated and changing formats of irrelevant sounds in the form of intelligible words and unintelligible signal correlated noise (SCN) versions of the words. Event-related potentials were recorded from 25 females aged between 18 and 25 while they completed a serial order recall task in the presence of irrelevant sound or silence. As expected and in line with the changing-state hypothesis both words and SCN produced robust changing-state effects. However, words produced a greater changing-state effect than SCN indicating that the spectral detail inherent within speech accounts for the greater irrelevant sound effect and changing-state effect typically observed with speech. ERP data in the form of N1 amplitude was modulated within some irrelevant sound conditions suggesting that attentional aspects are involved in the elicitation of the irrelevant sound effect.

Evaluating an acoustically quiet EPI sequence for use in fMRI studies of speech and auditory processing

Echoplanar MRI is associated with significant acoustic noise, which can interfere with the presentation of auditory stimuli, create a more challenging listening environment, and increase discomfort felt by participants. Here we investigate a scanning sequence that significantly reduces the amplitude of acoustic noise associated with echoplanar imaging (EPI). This is accomplished using a constant phase encoding gradient and a sinusoidal readout echo train to produce a narrow-band acoustic frequency spectrum, which is adapted to the scanner's frequency response function by choosing an optimum gradient switching frequency. To evaluate the effect of these nonstandard parameters we conducted a speech experiment comparing four different EPI sequences: Quiet, Sparse, Standard, and Matched Standard (using the same readout duration as Quiet). For each sequence participants listened to sentences and signal-correlated noise (SCN), which provides an unintelligible amplitude-matched control condition. We used BOLD sensitivity maps to quantify sensitivity loss caused by the longer EPI readout duration used in the Quiet and Matched Standard EPI sequences. We found that the Quiet sequence provided more robust activation for SCN in primary auditory areas and comparable activation in frontal and temporal regions for Sentences>SCN, but less sentence-related activity in inferotemporal cortex. The increased listening effort associated with the louder Standard sequence relative to the Quiet sequence resulted in increased activation in the left temporal and inferior parietal cortices. Together, these results suggest that the Quiet sequence is suitable, and perhaps preferable, for many auditory studies. However, its applicability depends on the specific brain regions of interest.

The bounds on flexibility in speech perception.

Dutch listeners were exposed to the English theta sound (as in bath), which replaced [f] in /f/-final Dutch words or, for another group, [s] in /s/-final words. A subsequent identity-priming task showed that participants had learned to interpret theta as, respectively, /f/ or /s/. Priming effects were equally strong when the exposure sound was an ambiguous [fs]-mixture and when primes contained unambiguous fricatives. When the exposure sound was signal-correlated noise, listeners interpreted it as the spectrally similar /f/, irrespective of lexical bias during exposure. Perceptual learning about speech is thus constrained by spectral similarity between the input and established phonological categories, but within those limits, adjustments are thorough enough that even nonnative sounds can be treated fully as native sounds.

Assessing the (Sub)Conscious Processing of Noise based on ERPs

Event Abstract Back to Event Assessing the (Sub)Conscious Processing of Noise based on ERPs Anne Porbadnigk1, 2*, Jan-Niklas Antons2, 3, Benjamin Blankertz1, 2, 4, Matthias S. Treder1, Robert Schleicher2, 3, Sebastian Möller2, 3 and Gabriel Curio2, 5 1 Berlin Institute of Technology, Machine Learning Laboratory, Germany 2 Berlin Institute of Technology, Bernstein Focus: Neurotechnology, Germany 3 Telekom Laboratories, Quality and Usabililty Lab, Germany 4 Fraunhofer FIRST, Intelligent Data Analysis Group, Germany 5 Charité, Department of Neurology and Clinical Neurophysiology, Germany In the field of telecommunications, the quality of audio signals is typically assessed based on subjective behavioral data. However, some differences in quality might be too subtle to be detected consciously, while still possibly affecting the long term contentment of users. Neuro-physiological measures have the potential to complement behavioral approaches as objective and accurate measures for auditory quality assessment. Here, we present results of an EEG study (N=11), in which we investigate the use of event-related potentials (ERPs) as such a quantitative measure. Subjects were presented with the phoneme /a/ that was either undisturbed (70% non-targets) or superimposed with four different degrees of signal-correlated noise. The ERP analysis revealed the ’neuronal effort’ involved in detecting noise: the harder it is to detect noise in a stimulus, the higher the latency and the lower the amplitude of the P300 component. This is in line with related work, as the P300 latency is thought to index classification speed [1]. It is important to note that all of these trials are hits and thus indistinguishable on a behavioral level. Remarkably, for two subjects, misses of marginally noisy targets result in an ERP pattern that shows a striking resemblance with hits (detected targets) of the same deviant class (see Fig.1). In order to assess the similarity, we employed a shrinkage LDA classifier [2] that was trained to distinguish between ERP patterns of hits and non-targets for a given subject. Notably, we found that the classifier was well able to also discriminate between misses and non-targets for these two subjects (see Fig.1) – even though the behavioral data suggests that the stimuli were perceived in the same way. We conjecture that the noise is missed on a conscious level during these trials, but still processed subconsciously. We conclude that ERPs have the potential to be used successfully as a quantitative measure for the assessment of auditory quality, providing complementary information to conventional behavioral methods. Fig. 1. T-scaled scalp plots showing similarities between hits and misses (subject Vpcad, deviant class T2, significance level at 2.33). Figure 1 Acknowledgements This work was supported by the BMBF, FKZ 01GQ0850.

A comparison of modulation indices for describing amplitude-compressed speech.

This presentation explores two approaches to characterizing changes to speech with amplitude-compression amplification. In the first, we considered changes to waveform morphology using the envelope difference index (EDI); [Fortune et al. (1994)] to quantify the effects on amplitude envelope in the time domain. In the second, the spectral correlation index (SCI); [Gallun & Souza (2008)] was used to compare signal envelopes in the frequency domain. In the SCI, similarity is represented by the correlation of the average modulation spectra at six octave-spaced amplitude modulation frequencies (1–32 Hz) in six octave-spaced carrier frequency regions (250–8000 Hz) for a pair of phonemes. Test stimuli were a set of 16 vowel-consonant-vowel (VCV) syllables spoken by four talkers. The VCVs were digitally processed to limit spectral information using a signal-correlated noise technique [Schroeder (1968)] then submitted to a compression amplification simulation in which parameters (compression ratio and release time) were selected to achieve a range of temporal alteration. Consonant identification scores for 10 normal-hearing listeners were obtained and related to the modulation indices. Although the SCI was more sensitive to changes in specific compression parameters, the EDI was more closely related to recognition. [Work supported by R01 DC0060014 and VA RR&D CDA-2 C4963W.]

Contextual influences: Perception of sentences in noise is facilitated similarly in young and older listeners by meaningful semantic context; neural correlates explored via functional magnetic resonance imaging (fMRI)

Meaningful semantic context has been demonstrated to improve comprehension of spoken sentences by young and old adults, especially in difficult listening conditions. Evidence for this benefit is based largely on data collected using SPIN sentences, highly structured sentences with a predictable or unpredictable final word. We asked young (14 participants, aged 18-25) and older adults (20 participants, aged 60-75) to report entire sentences which were less structured in nature and contained either a meaningful or anomalous global semantic context. Sentences were mixed with signal-correlated noise, at 9 signal-to-noise ratios (-6 to +2 dB), and also presented without noise. Comprehension by both groups benefited from meaningful context, without a clear overall difference in the amount of benefit obtained. We used fMRI to look at neural activity associated with deriving benefit from meaningful context. Whole-brain EPI data were acquired from young (16 participants, aged 19-26) adults using a sparse imaging design. Word-report data obtained in the scanner were used as intelligibility measures in data analysis. In addition to activity associated with meaningful context, we observe a large left inferior-frontal region in which BOLD signal correlated more strongly with the intelligibility of anomalous compared to coherent prose, presumably reflecting challenged semantic integration processes.

Dissociating speech perception and comprehension at reduced levels of awareness.

We used functional MRI and the anesthetic agent propofol to assess the relationship among neural responses to speech, successful comprehension, and conscious awareness. Volunteers were scanned while listening to sentences containing ambiguous words, matched sentences without ambiguous words, and signal-correlated noise (SCN). During three scanning sessions, participants were nonsedated (awake), lightly sedated (a slowed response to conversation), and deeply sedated (no conversational response, rousable by loud command). Bilateral temporal-lobe responses for sentences compared with signal-correlated noise were observed at all three levels of sedation, although prefrontal and premotor responses to speech were absent at the deepest level of sedation. Additional inferior frontal and posterior temporal responses to ambiguous sentences provide a neural correlate of semantic processes critical for comprehending sentences containing ambiguous words. However, this additional response was absent during light sedation, suggesting a marked impairment of sentence comprehension. A significant decline in postscan recognition memory for sentences also suggests that sedation impaired encoding of sentences into memory, with left inferior frontal and temporal lobe responses during light sedation predicting subsequent recognition memory. These findings suggest a graded degradation of cognitive function in response to sedation such that "higher-level" semantic and mnemonic processes can be impaired at relatively low levels of sedation, whereas perceptual processing of speech remains resilient even during deep sedation. These results have important implications for understanding the relationship between speech comprehension and awareness in the healthy brain in patients receiving sedation and in patients with disorders of consciousness.

Motor cortex maps articulatory features of speech sounds

The processing of spoken language has been attributed to areas in the superior temporal lobe, where speech stimuli elicit the greatest activation. However, neurobiological and psycholinguistic models have long postulated that knowledge about the articulatory features of individual phonemes has an important role in their perception and in speech comprehension. To probe the possible involvement of specific motor circuits in the speech-perception process, we used event-related functional MRI and presented experimental subjects with spoken syllables, including [p] and [t] sounds, which are produced by movements of the lips or tongue, respectively. Physically similar nonlinguistic signal-correlated noise patterns were used as control stimuli. In localizer experiments, subjects had to silently articulate the same syllables and, in a second task, move their lips or tongue. Speech perception most strongly activated superior temporal cortex. Crucially, however, distinct motor regions in the precentral gyrus sparked by articulatory movements of the lips and tongue were also differentially activated in a somatotopic manner when subjects listened to the lip- or tongue-related phonemes. This sound-related somatotopic activation in precentral gyrus shows that, during speech perception, specific motor circuits are recruited that reflect phonetic distinctive features of the speech sounds encountered, thus providing direct neuroimaging support for specific links between the phonological mechanisms for speech perception and production.

Learning-induced neural plasticity associated with improved identification performance after training of a difficult second-language phonetic contrast

Adult native Japanese speakers have difficulty perceiving the English /r–l/ phonetic contrast even after years of exposure. However, after extensive perceptual identification training, long-lasting improvement in identification performance can be attained. This fMRI study investigates localized changes in brain activity associated with 1 month of extensive feedback-based perceptual identification training by native Japanese speakers learning the English /r–l/ phonetic contrast. Before and after training, separate functional brain imaging sessions were conducted for identification of the English /r–l/ contrast (difficult for Japanese speakers), /b–g/ contrast (easy), and /b–v/ contrast (difficult), in which signal-correlated noise served as the reference control condition. Neural plasticity, denoted by exclusive enhancement in brain activity for the /r–l/ contrast, does not involve only reorganization in brain regions concerned with acoustic-phonetic processing (superior and medial temporal areas) but also the recruitment of additional bilateral cortical (supramarginal gyrus, planum temporale, Broca’s area, premotor cortex, supplementary motor area) and subcortical regions (cerebellum, basal ganglia, substantia nigra) involved with auditory–articulatory (perceptual–motor) mappings related to verbal speech processing and learning. Contrary to what one may expect, brain activity for perception of a difficult contrast does not come to resemble that of an easy contrast as learning proceeds. Rather, the results support the hypothesis that improved identification performance may be due to the acquisition of auditory–articulatory mappings allowing for perception to be made in reference to potential action.

Use of temporal information in recognition of amplitude-compressed speech by older adults

Amplitude compression alters the speech envelope and under some conditions can reduce the availability of temporal cues for speech recognition. This may be a particular problem for older listeners, who demonstrated temporal resolution deficits in some studies. Older and younger hearing-impaired listeners were tested on their recognition of VCV syllables processed using the signal-correlated noise (SCN) method [Schroeder, J. Acoust. Soc. Am. 44, 1735–1736 (1968)]. This method results in a time-varying speech envelope modulating a noise carrier, and preserves temporal cues while minimizing spectral information. Recognition scores were obtained for uncompressed SCN syllables and for the same speech tokens after digital processing with a syllabic compression algorithm. In control conditions, recognition was tested for VCVs that included both temporal and spectral information. Younger and older listener groups were matched for mean hearing thresholds up to 4 kHz. A high-pass masker was included to eliminate contributions from the basal end of the cochlea. When compared to younger listeners with similar hearing losses, the older listeners demonstrated poorer performance on the compressed SCN signals. These results suggest that the poorer temporal resolution abilities of older listeners may play a role in their understanding of amplitude-compressed speech.

Multichannel compression, temporal cues, and audibility.

Although multichannel compression systems are quickly becoming integral components of programmable hearing aids, research results have not consistently demonstrated their benefit over conventional amplification. The present study examined two confounding factors that may have contributed to this inconsistency in results: alteration of temporal information and audibility of speech cues. Recognition of linearly amplified and multichannel-compressed speech was measured for listeners with mild-to-severe sensorineural hearing loss and for a control group of listeners with normal hearing. In addition to the standard speech signal, which provided both temporal and spectral information, the listener's ability to use temporal information in a multichannel compressed signal was directly tested using a signal-correlated noise (SCN) stimulus. This stimulus consisted of a time-varying speech envelope modulating a two-channel noise carrier. It preserved temporal cues but provided minimal spectral information. For each stimulus condition, short-term level measurements were used to determine the range of audible speech. Multichannel compression improved speech recognition under conditions where superior audibility was provided by the two-channel compression system over linear amplification. When audibility of both linearly amplified and multichannel-compressed speech was maximized, the multichannel compression had no significant effect on speech recognition score for speech containing both temporal and spectral cues. However, results for the SCN stimuli show that more extreme amounts of multichannel compression can reduce use of temporal information.