Papers by Christian Lorenzi
Over the last few decades, a variety of evidence has been presented to support the idea that, for... more Over the last few decades, a variety of evidence has been presented to support the idea that, for normal-hearing listeners, both temporal envelope (E) and temporal fine structure (TFS) cues play a role in speech identification. E cues in a few frequency bands seem to be sufficient for good speech identification in quiet, but TFS cues appear to play an important role when background sounds are present, especially for “glimpsing” speech in the temporal minima of fluctuating background sounds. There is also evidence that cochlear damage associated with mild to moderate hearing loss may severely degrade the ability to use TFS cues while preserving the ability to use E cues in speech stimuli. This is consistent with the relatively preserved ability of hearing-impaired listeners to identify speech in quiet when audibility is controlled for, and the substantial deficits observed for these listeners when speech is masked by uctuating background noise.
The Journal of the Acoustical Society of America, 2020
Natural soundscapes correspond to the acoustical patterns produced by biological and geophysical ... more Natural soundscapes correspond to the acoustical patterns produced by biological and geophysical sound sources at different spatial and temporal scales for a given habitat. This pilot study aims to characterize the temporalmodulation information available to humans when perceiving variations in soundscapes within and across natural habitats. This is addressed by processing soundscapes from a previous study [Krause, Gage, and Joo. (2011). Landscape Ecol. 26, 1247] via models of human auditory processing extracting modulation at the output of cochlear filters. The soundscapes represent combinations of elevation, animal, and vegetation diversity in four habitats of the biosphere reserve in the Sequoia National Park (Sierra Nevada, USA). Bayesian statistical analysis and support vector machine classifiers indicate that: (i) amplitude-modulation (AM) and frequency-modulation (FM) spectra distinguish the soundscapes associated with each habitat; and (ii) for each habitat, diurnal and seasonal variations are associated with salient changes in AM and FM cues at rates between about 1 and 100 Hz in the low (<0.5 kHz) and high (>1-3 kHz) audio-frequency range. Support vector machine classifications further indicate that soundscape variations can be classified accurately based on these perceptually inspired representations.
Trends in Hearing, 2019
There is increasing evidence that hearing-impaired (HI) individuals do not use the same listening... more There is increasing evidence that hearing-impaired (HI) individuals do not use the same listening strategies as normal-hearing (NH) individuals, even when wearing optimally fitted hearing aids. In this perspective, better characterization of individual perceptual strategies is an important step toward designing more effective speech-processing algorithms. Here, we describe two complementary approaches for (a) revealing the acoustic cues used by a participant in a /d/-/g/ categorization task in noise and (b) measuring the relative contributions of these cues to decision. These two approaches involve natural speech recordings altered by the addition of a “bump noise.” The bumps were narrowband bursts of noise localized on the spectrotemporal locations of the acoustic cues, allowing the experimenter to manipulate the consonant percept. The cue-weighting strategies were estimated for three groups of participants: 17 NH listeners, 18 HI listeners with high-frequency loss, and 15 HI liste...
Journal of the Association for Research in Otolaryngology, 2018
Robust neuronal discrimination in primary auditory cortex despite degradations of spectro-tempora... more Robust neuronal discrimination in primary auditory cortex despite degradations of spectro-temporal acoustic details: comparison between guinea pigs with normal hearing and mild age-related hearing loss-Manuscript Draft-Manuscript Number: JARO-D-17-00039R3 Full Title: Robust neuronal discrimination in primary auditory cortex despite degradations of spectro-temporal acoustic details: comparison between guinea pigs with normal hearing and mild age-related hearing loss
The Journal of the Acoustical Society of America, 2019
Frequency modulation (FM) is assumed to be detected through amplitude modulation (AM) created by ... more Frequency modulation (FM) is assumed to be detected through amplitude modulation (AM) created by cochlear filtering for modulation rates above 10 Hz and carrier frequencies (f c) above 4 kHz. If this is the case, a model of modulation perception based on the concept of AM filters should predict masking effects between AM and FM. To test this, masking effects of sinusoidal AM on sinusoidal FM detection thresholds were assessed on normal-hearing listeners as a function of FM rate, f c , duration, AM rate, AM depth, and phase difference between FM and AM. The data were compared to predictions of a computational model implementing an AM filter-bank. Consistent with model predictions, AM masked FM with some AM-masking-AM features (broad tuning and effect of AM-masker depth). Similar masking was predicted and observed at f c ¼ 0.5 and 5 kHz for a 2 Hz AM masker, inconsistent with the notion that additional (e.g., temporal fine-structure) cues drive slow-rate FM detection at low f c. However, masking was lower than predicted and, unlike model predictions, did not show beating or phase effects. Broadly, the modulation filter-bank concept successfully explained some AM-masking-FM effects, but could not give a complete account of both AM and FM detection.
The Journal of the Acoustical Society of America, 2018
The effect of the number of modulation cycles () on frequency-modulation (FM) detection threshold... more The effect of the number of modulation cycles () on frequency-modulation (FM) detection thresholds (FMDTs) was measured with and without interfering amplitude modulation (AM) for hearing-impaired (HI) listeners, using a 500-Hz sinusoidal carrier and FM rates of 2 and 20 Hz. The data were compared with FMDTs for normal-hearing (NH) listeners and AM detection thresholds (AMDTs) for NH and HI listeners [Wallaert, Moore, and Lorenzi (2016). J. Acoust. Soc. , 3088-3096; Wallaert, Moore, Ewert, and Lorenzi (2017). J. Acoust. Soc. , 971-980]. FMDTs were higher for HI than for NH listeners, but the effect of increasing was similar across groups. In contrast, AMDTs were lower and the effect of increasing was greater for HI listeners than for NH listeners. A model of temporal-envelope processing based on a modulation filter-bank and a template-matching decision strategy accounted better for the FMDTs at 20 Hz than at 2 Hz for young NH listeners and predicted greater temporal integration of FM...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 25, 2018
Frequency modulation (FM) is a common acoustic feature of natural sounds and is known to play a r... more Frequency modulation (FM) is a common acoustic feature of natural sounds and is known to play a role in robust sound source recognition. Auditory neurons show precise stimulus-synchronized discharge patterns that may be used for the representation of low-rate FM. However, it remains unclear whether this representation is based on synchronization to slow temporal envelope (ENV) cues resulting from cochlear filtering or phase locking to faster temporal fine structure (TFS) cues. To investigate the plausibility of those encoding schemes, single units of the ventral cochlear nucleus of guinea pigs of either sex were recorded in response to sine FM tones centered at the unit's best frequency (BF). The results show that, in contrast to high-BF units, for modulation depths within the receptive field, low-BF units (<4 kHz) demonstrate good phase locking to TFS. For modulation depths extending beyond the receptive field, the discharge patterns follow the ENV and fluctuate at the modul...
The auditory system processes temporal information at multiple scales, and disruptions to this te... more The auditory system processes temporal information at multiple scales, and disruptions to this temporal processing may lead to deficits in auditory tasks such as detecting and discriminating sounds in a noisy environment. Here, a modelling approach is used to study the temporal regularity of firing by chopper cells in the ventral cochlear nucleus, in both the normal and impaired auditory system. Chopper cells, which have a strikingly regular firing response, divide into two classes, sustained and transient, based on the time course of this regularity. Several hypotheses have been proposed to explain the behaviour of chopper cells, and the difference between sustained and transient cells in particular. However, there is no conclusive evidence so far. Here, a reduced mathematical model is developed and used to compare and test a wide range of hypotheses with a limited number of parameters. Simulation results show a continuum of cell types and behaviours: chopper-like behaviour arises ...
PLOS Computational Biology, 2016
Sound waveforms convey information largely via amplitude modulations (AM). A large body of experi... more Sound waveforms convey information largely via amplitude modulations (AM). A large body of experimental evidence has provided support for a modulation (bandpass) filterbank. Details of this model have varied over time partly reflecting different experimental conditions and diverse datasets from distinct task strategies, contributing uncertainty to the bandwidth measurements and leaving important issues unresolved. We adopt here a solely datadriven measurement approach in which we first demonstrate how different models can be subsumed within a common 'cascade' framework, and then proceed to characterize the cascade via system identification analysis using a single stimulus/task specification and hence stable task rules largely unconstrained by any model or parameters. Observers were required to detect a brief change in level superimposed onto random level changes that served as AM noise; the relationship between trial-by-trial noisy fluctuations and corresponding human responses enables targeted identification of distinct cascade elements. The resulting measurements exhibit a dynamic complex picture in which human perception of auditory modulations appears adaptive in nature, evolving from an initial lowpass to bandpass modes (with broad tuning, Q*1) following repeated stimulus exposure.
The Journal of the Acoustical Society of America, Jun 1, 2016
Frequency modulation (FM) and amplitude modulation (AM) detection thresholds were measured at 40 ... more Frequency modulation (FM) and amplitude modulation (AM) detection thresholds were measured at 40 dB sensation level for young (22-28 yrs) and older (44-66 yrs) listeners with normal audiograms for a carrier frequency of 500 Hz and modulation rates of 2 and 20 Hz. The number of modulation cycles, N, varied between 2 and 9. For FM detection, uninformative AM at the same rate as the FM was superimposed to disrupt excitation-pattern cues. For both groups, AM and FM detection thresholds were lower for the 2-Hz than for the 20-Hz rate, and AM and FM detection thresholds decreased with increasing N. Thresholds were higher for older than for younger listeners, especially for FM detection at 2 Hz, possibly reflecting the effect of age on the use of temporal-fine-structure cues for 2-Hz FM detection. The effect of increasing N was similar across groups for both AM and FM. However, at 20 Hz, older listeners showed a greater effect of increasing N than younger listeners for both AM and FM. The ...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 3, 2014
The dichotomy between acoustic temporal envelope (ENV) and fine structure (TFS) cues has stimulat... more The dichotomy between acoustic temporal envelope (ENV) and fine structure (TFS) cues has stimulated numerous studies over the past decade to understand the relative role of acoustic ENV and TFS in human speech perception. Such acoustic temporal speech cues produce distinct neural discharge patterns at the level of the auditory nerve, yet little is known about the central neural mechanisms underlying the dichotomy in speech perception between neural ENV and TFS cues. We explored the question of how the peripheral auditory system encodes neural ENV and TFS cues in steady or fluctuating background noise, and how the central auditory system combines these forms of neural information for speech identification. We sought to address this question by (1) measuring sentence identification in background noise for human subjects as a function of the degree of available acoustic TFS information and (2) examining the optimal combination of neural ENV and TFS cues to explain human speech percepti...
Journal of the Association for Research in Otolaryngology, 2014
Noise reduction (NR) systems are commonplace in modern digital hearing aids. Though not improving... more Noise reduction (NR) systems are commonplace in modern digital hearing aids. Though not improving speech intelligibility, NR helps the hearing-aid user in terms of lowering noise annoyance, reducing cognitive load and improving ease of listening. Previous psychophysical work has shown that NR does in fact improve the ability of normal-hearing (NH) listeners to discriminate the slow amplitude-modulation (AM) cues representative of those found in speech. The goal of this study was to assess whether this improvement of AM discrimination with NR can also be observed for hearing-impaired (HI) listeners. AM discrimination was measured at two audio frequencies of 500 Hz and 2 kHz in a background noise with a signal-to-noise ratio of 12 dB. Discrimination was measured for ten HI and ten NH listeners with and without NR processing. The HI listeners had a moderate sensorineural hearing loss of about 50 dB HL at 2 kHz and normal hearing (≤20 dB HL) at 500 Hz. The results showed that most of the HI listeners tended to benefit from NR at 500 Hz but not at 2 kHz. However, statistical analyses showed that HI listeners did not benefit significantly from NR at any frequency region. In comparison, the NH listeners showed a significant benefit from NR at both frequencies. For each condition, the fidelity of AM transmission was quantified by a computational model of early auditory processing. The parameters of the model were adjusted separately for the two groups (NH and HI) of listeners. The AM discrimination performance of the HI group (with and without NR) was best captured by a model simulating the loss of the fastacting amplitude compression applied by the normal cochlea. This suggests that the lack of benefit from NR for HI listeners results from loudness recruitment.
Vision Research, 2000
The present endeavor is meant (a) to provide a direct comparison between first-and second-order t... more The present endeavor is meant (a) to provide a direct comparison between first-and second-order temporal modulation and, by so doing, (b) to eliminate all spatial clues that might have contaminated previous assessments of the second-order temporal modulation transfer function (TMTF). The second aim was achieved by means of the temporal modulation of a purely temporal white noise, a stimulus used frequently in psychoacoustics but not used as yet in visual stimulation. Luminance and contrast temporal modulation thresholds were measured with a 2AFC staircase procedure. In the first case, the mean luminance of a spatially homogeneous, 30°field was modulated sinusoidally over time (first-order modulation). In the second case, the luminance of the same or of a 60°field was randomized over time at a rate of 150 Hz and this temporal white noise (the carrier) was modulated sinusoidally over time (second-order modulation). First-order thresholds reproduce the classical (large field) flicker sensitivity. Second-order thresholds (measured for the first time with purely temporal stimuli) are at least 100 times higher than first-order ones, display a low-pass characteristic (at least up to 0.5 Hz) and yield a critical fusion frequency (measured at 100% modulation) of 10 Hz. The data are in accord with other estimates of the TMTF of the second-order system and thus confirm the effective neutralization of the spatial cues present in these previous studies.
Proceedings of the National Academy of Sciences, 2006
People with sensorineural hearing loss have difficulty understanding speech, especially when back... more People with sensorineural hearing loss have difficulty understanding speech, especially when background sounds are present. A reduction in the ability to resolve the frequency components of complex sounds is one factor contributing to this difficulty. Here, we show that a reduced ability to process the temporal fine structure of sounds plays an important role. Speech sounds were processed by filtering them into 16 adjacent frequency bands. The signal in each band was processed by using the Hilbert transform so as to preserve either the envelope (E, the relatively slow variations in amplitude over time) or the temporal fine structure (TFS, the rapid oscillations with rate close to the center frequency of the band). The band signals were then recombined and the stimuli were presented to subjects for identification. After training, normal-hearing subjects scored perfectly with unprocessed speech, and were ≈90% correct with E and TFS speech. Both young and elderly subjects with moderate...
The Journal of the Acoustical Society of America, 2003
The present study extends previous work from Lorenzi et al. ͓J. Acoust. Soc. Am. 110, 2470-2478 ͑... more The present study extends previous work from Lorenzi et al. ͓J. Acoust. Soc. Am. 110, 2470-2478 ͑2001͔͒ by investigating the respective contribution of two temporal cues ͑fast modulation sideband and slow envelope beat cues͒ to the detection and discrimination of ''second-order'' sinusoidal amplitude modulation ͑SAM͒. Second-order SAM detection and rate discrimination abilities were measured at low beat rates (f m Ј р128 Hz͒ with a ''carrier'' modulation rate fixed at a high value (f m ϭ256 Hz͒. The second-order SAM data were compared with first-order SAM detection and rate discrimination thresholds measured in similar conditions at rates f m between 1 and 256 Hz. The results showed that ͑1͒ through 64 Hz, first-and second-order SAM detection thresholds increased similarly when stimulus duration decreased from 2 s to 250 ms, whereas first-order SAM detection thresholds remained unaffected by changes in duration when f m у128 Hz, and ͑2͒ through 32 Hz, first-and second-order SAM rate discrimination thresholds were similar and substantially lower than first-order SAM rate discrimination thresholds measured at f m у128 Hz. These data demonstrate that the perception of second-order SAM is mainly based on the slow envelope beat cues. They also suggest a substantial contribution of the slow envelope beat cues appearing at the output of modulation filters tuned to or near f m to the perception of second-order SAM.
The Journal of the Acoustical Society of America, 2012
Previous studies have demonstrated that normal-hearing listeners can understand speech using the ... more Previous studies have demonstrated that normal-hearing listeners can understand speech using the recovered "temporal envelopes," i.e., amplitude modulation (AM) cues from frequency modulation (FM). This study evaluated this mechanism in cochlear implant (CI) users for consonant identification. Stimuli containing only FM cues were created using 1, 2, 4, and 8-band FM-vocoders to determine if consonant identification performance would improve as the recovered AM cues become more available. A consistent improvement was observed as the band number decreased from 8 to 1, supporting the hypothesis that (1) the CI sound processor generates recovered AM cues from broadband FM, and (2) CI users can use the recovered AM cues to recognize speech. The correlation between the intact and the recovered AM components at the output of the sound processor was also generally higher when the band number was low, supporting the consonant identification results. Moreover, CI subjects who were better at using recovered AM cues from broadband FM cues showed better identification performance with intact (unprocessed) speech stimuli. This suggests that speech perception performance variability in CI users may be partly caused by differences in their ability to use AM cues recovered from FM speech cues.
The Journal of the Acoustical Society of America, 2010
This study measured the role of spectral details and temporal envelope (E) and fine structure (TF... more This study measured the role of spectral details and temporal envelope (E) and fine structure (TFS) cues in reconstructing sentences from speech fragments. Four sets of sentences were processed using a 32-band vocoder. Twenty one bands were either processed or removed, leading to sentences differing in their amount of spectral details, E and TFS information. These sentences remained perfectly intelligible, but intelligibility significantly fell after the introduction of periodic silent gaps of 120-ms. While the role of E was unclear, the results unambiguously showed that TFS cues and spectral details influence the ability to reconstruct interrupted sentences.
The Journal of the Acoustical Society of America, 2008
We will review recent studies investigating the reception of phonetic features (voicing, manner a... more We will review recent studies investigating the reception of phonetic features (voicing, manner and place of articulation) in non-stationary background maskers. In each study, consonant identification was assessed in steady and amplitude-modulated speech-shaped noise at signal-to-noise ratios yielding about 50% correct in steady noise. The rate and depth of amplitude modulation applied to the noise masker were either fixed or systematically varied. Confusion matrices were compiled across listeners and the amount of release from masking (percent information received in non-steady minus steady noise) was calculated for each phonetic feature and experimental condition. Speech and noise mixtures were i) left intact (unfiltered), ii) lowpass filtered (<1.5 kHz), or iii) processed in order to degrade spectral (place of excitation in the cochlea) and/or temporal fine structure cues. Overall, the results indicate that release from masking typically reported in normal-hearing listeners (i.e., the substantial improvement in speech reception in fluctuating noise compared to steady noise) is not identical across phonetic features. This suggests that the ability to "glimpse" into background noise valleys involves multiple auditory processes constrained by both peripheral and central factors.
The Journal of the Acoustical Society of America, 2008
Recent work has suggested involvement of temporal fine structure (TFS) information in speech perc... more Recent work has suggested involvement of temporal fine structure (TFS) information in speech perception, especially in adverse listening conditions. However, little is known regarding discrimination of pattern of TFS modulation, an ability that would underlie robust contribution to speech processing. The present study evaluated the ability to discriminate among stochastic patterns of frequency modulation (FM). Contrasting modulators were different samples of lowpass noise that shared a common bandwidth and resulted in the same maximum frequency excursion. Performance levels declined in an orderly manner with modulator bandwidth, similar to results obtained when lowpass noise is used to modulate amplitude (i.e., AM) rather than fine structure. Modeling, however, indicated that the similarity was not simply a result of FM-to-AM conversion at the output of auditory filters. In additional conditions, discrimination of stochastic FM was measured in the presence of wideband noise which in some cases was sinusoidally amplitude modulated at either 4 or 20 Hz. With both unmodulated and modulated maskers, little effect on performance was noted, even with a signal carrier level as low as 15-20 dB above detection threshold. Absence of a substantial masking effect indicates availability of TFS cues for speech perception in noise. [Work supported by NIH.]
The Journal of the Acoustical Society of America, 2001
Modulation perception has typically been characterized by measuring detection thresholds for sinu... more Modulation perception has typically been characterized by measuring detection thresholds for sinusoidally amplitude-modulated ͑SAM͒ signals. This study uses multicomponent modulations. ''Second-order'' temporal modulation transfer functions ͑TMTFs͒ measure detection thresholds for a sinusoidal modulation of the modulation waveform of a SAM signal ͓Lorenzi et al., J. Acoust. Soc. Am. 110, 1030-2038 ͑2001͔͒. The SAM signal therefore acts as a ''carrier'' stimulus of frequency f m , and sinusoidal modulation of the SAM signal's modulation depth ͑at rate f m Ј ͒ generates two additional components in the modulation spectrum at f m Ϫ f m Ј and f m ϩ f m Ј. There is no spectral energy at the envelope beat frequency f m Ј in the modulation spectrum of the ''physical'' stimulus. In the present study, second-order TMTFs were measured for three listeners when f m was 16, 64, and 256 Hz. The carrier was either a 5-kHz pure tone or a narrow-band noise with center frequency and bandwidth of 5 kHz and 2 Hz, respectively. The narrow-band noise carrier was used to prevent listeners from detecting spectral energy at the beat frequency f m Ј in the ''internal'' stimuli's modulation spectrum. The results show that, for the 5-kHz pure-tone carrier, second-order TMTFs are nearly low pass in shape; the overall sensitivity and cutoff frequency measured on these second-order TMTFs increase when f m increases from 16 to 256 Hz. For the 2-Hz-wide narrow-band noise carrier, second-order TMTFs are nearly flat in shape for f m ϭ16 and 64 Hz, and they show a high-pass segment for f m ϭ256 Hz. These results suggest that detection of spectral energy at the envelope beat frequency contributes in part to the detection of second-order modulation. This is consistent with the idea that nonlinear mechanisms in the auditory pathway produce an audible distortion component at the envelope beat frequency in the internal modulation spectrum of the sounds.
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Papers by Christian Lorenzi