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Biomedical subjects

Christian Lorenzi

Publications and source records attributed to Christian Lorenzi.

At least 19 recordsLinked to original sources
PubMed2006

Speech perception problems of the hearing impaired reflect inability to use temporal fine structure.

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 approximately 90% correct with E and TFS speech. Both young and elderly subjects with moderate flat hearing loss performed almost as well as normal with unprocessed and E speech but performed very poorly with TFS speech, indicating a greatly reduced ability to use TFS. For the younger hearing-impaired group, TFS scores were highly correlated with the ability to take advantage of temporal dips in a background noise when identifying unprocessed speech. The results suggest that the ability to use TFS may be critical for "listening in the background dips." TFS stimuli may be useful in evaluating impaired hearing and in guiding the design of hearing aids and cochlear implants.

Adult↗
PubMed2006

Speech masking release in listeners with flat hearing loss: effects of masker fluctuation rate on identification scores and phonetic feature reception.

Consonant identification was measured for a stationary and amplitude-modulated noise masker in four listeners with flat cochlear hearing loss, and four age-matched normal-hearing listeners. The masker modulation rate was systematically varied between 2 and 128 Hz. Masking release (MR), that is better identification performance in fluctuating, than in stationary noise, was highest in a masker fluctuating at 8-16 Hz in all normal-hearing listeners. In comparison, MR was only observed in two out of the four impaired listeners. In these listeners, MR was poorer than normal, and peaked at lower rates, that is 2 or 8 Hz. MR corresponded to increased reception of information for voicing, place, and manner between 2 and 64 Hz in all normal-hearing listeners. In impaired listeners, increased reception of information was mainly observed for manner, and mainly reduced for place, but these differences were not significant. For all phonetic features, MR was observed at lower masker fluctuation rates (< or =32 Hz) than in normal-hearing listeners. This study therefore shows that cochlear damage affects MR, both quantitatively and qualitatively.

Aged↗
PubMed2006

The ability of listeners to use recovered envelope cues from speech fine structure.

Recent work has demonstrated that auditory filters recover temporal-envelope cues from speech fine structure when the former were removed by filtering or distortion. This study extended this work by assessing the contribution of recovered envelope cues to consonant perception as a function of the analysis bandwidth, when vowel-consonant-vowel (VCV) stimuli were processed in order to keep their fine structure only. The envelopes of these stimuli were extracted at the output of a bank of auditory filters and applied to pure tones whose frequency corresponded to the original filters' center frequencies. The resulting stimuli were found to be intelligible when the envelope was extracted from a single, wide analysis band. However, intelligibility decreases from one to eight bands with no further decrease beyond this value, indicating that the recovered envelope cues did not play a major role in consonant perception when the analysis bandwidth was narrower than four times the bandwidth of a normal auditory filter (i.e., number of analysis bands > or =8 for frequencies spanning 80 to 8020 Hz).

Adult↗
PubMed2006

No adaptation in the amplitude modulation domain in trained listeners.

The present study shows that on average, exposure to a 15 min, 5 kHz tone modulated sinusoidally in amplitude at 16 Hz with a 100% depth does not affect significantly amplitude modulation (AM) detection thresholds measured between 4 and 64 Hz when listeners are extensively trained to the AM detection task, with and without adaptor before data collection. These results are compatible with previous work given that a clear 6-dB adaptation effect was observed during the first pilot trials. However, the results reveal that adaptation effects are not robust, and suggest that the mechanisms underlying adaptation to AM must be reevaluated.

Acoustic Stimulation↗
PubMed2005

Evaluation of two computational models of amplitude modulation coding in the inferior colliculus.

Two computational models replicating amplitude-modulation encoding in the inferior colliculus (IC) are presented and compared. Neurons in this nucleus are modeled as point neurons using Mc Gregor equations, and receive depolarizing currents from action potentials delivered by stellate cells (chopper units) in the cochlear nucleus (CN). Stellate cells are modeled using modified Hodgkin-Huxley equations and receive inputs from a peripheral auditory model. The CN models of the two proposed architectures are characterized by an important dispersion of cellular characteristics, and therefore by various cellular best modulation frequencies (BMFs) ranging from 60 to 300 Hz. In contrast with the previous model proposed by [M.J. Hewitt, R. Meddis, A computer model of amplitude-modulation sensitivity of single units in the inferior colliculus, J. Acoust. Soc. Am. 95 (1994) 2145], each IC cell model receives convergent input from stellate cells with various BMFs. This approach assumes therefore minimal constraints on the model architecture and cell characteristics. The two models differ in terms of the neuronal structure of the IC, composed of 1 or 2 layers of point neurons acting as coincidence detectors. Each model is evaluated using two metrics: mean firing rate and modulation gain. Rate and temporal modulation transfer functions (r-MTFs and t-MTFs, respectively) are simulated and compared with physiological data. Simulations reveal that (i) an important dispersion of BMFs in the CN cells providing input to IC cells yields plausible IC cells responses to AM stimuli, (ii) the 2-layer IC structure yields the best approximation of IC responses measured in vivo.

Computational Biology↗
PubMed2005

Masking release for consonant features in temporally fluctuating background noise.

Consonant identification was measured for normal-hearing listeners using Vowel-Consonant-Vowel stimuli that were either unprocessed or spectrally degraded to force listeners to use temporal-envelope cues. Stimuli were embedded in a steady state or fluctuating noise masker and presented at a fixed signal-to-noise ratio. Fluctuations in the maskers were obtained by applying sinusoidal modulation to: (i) the amplitude of the noise (1st-order SAM masker) or (ii) the modulation depth of a 1st-order SAM noise (2nd-order SAM masker). The frequencies of the amplitude variation fm and the depth variation f'm were systematically varied. Consistent with previous studies, identification scores obtained with unprocessed speech were highest in an 8-Hz, 1st-order SAM masker. Reception of voicing and manner also peaked around fm=8 Hz, while the reception of place of articulation was maximal at a higher frequency (fm=32 Hz). When 2nd-order SAM maskers were used, identification scores and received information for each consonant feature were found to be independent of f'm. They decreased progressively with increasing carrier modulation frequency fm, and ranged between those obtained with the steady state and the 1st-order SAM maskers. Finally, the results obtained with spectrally degraded speech were similar across all types of maskers, although an 8% improvement in the reception of voicing was observed for modulated maskers with fm < 64 Hz compared to the steady-state masker. These data provide additional evidence that listeners take advantage of temporal minima in fluctuating background noises, and suggest that: (i) minima of different durations are required for an optimal reception of the three consonant features and (ii) complex (i.e., 2nd-order) envelope fluctuations in background noise do not degrade speech identification by interfering with speech-envelope processing.

Adult↗
PubMed2005

Deficits in speech perception predict language learning impairment.

Specific language impairment (SLI) is one of the most common childhood disorders, affecting 7% of children. These children experience difficulties in understanding and producing spoken language despite normal intelligence, normal hearing, and normal opportunities to learn language. The causes of SLI are still hotly debated, ranging from nonlinguistic deficits in auditory perception to high-level deficits in grammar. Here, we show that children with SLI have poorer-than-normal consonant identification when measured in ecologically valid conditions of stationary or fluctuating masking noise. The deficits persisted even in comparison with a younger group of normally developing children who were matched for language skills. This finding points to a fundamental deficit. Information transmission of all phonetic features (voicing, place, and manner) was impaired, although the deficits were strongest for voicing (e.g., difference between/b/and/p/). Children with SLI experienced perfectly normal "release from masking" (better identification in fluctuating than in stationary noise), which indicates a central deficit in feature extraction rather than deficits in low-level, temporal, and spectral auditory capacities. We further showed that speech identification in noise predicted language impairment to a great extent within the group of children with SLI and across all participants. Previous research might have underestimated this important link, possibly because speech perception has typically been investigated in optimal listening conditions using non-speech material. The present study suggests that children with SLI learn language deviantly because they inefficiently extract and manipulate speech features, in particular, voicing. This result offers new directions for the fast diagnosis and remediation of SLI.

Adolescent↗
PubMed2005

Modulation masking produced by second-order modulators.

Recent studies suggest that an auditory nonlinearity converts second-order sinusoidal amplitude modulation (SAM) (i.e., modulation of SAM depth) into a first-order SAM component, which contributes to the perception of second-order SAM. However, conversion may also occur in other ways such as cochlear filtering. The present experiments explored the source of the first-order SAM component by investigating the ability to detect a 5-Hz, first-order SAM probe in the presence of a second-order SAM masker beating at the probe frequency. Detection performance was measured as a function of masker-carrier modulation frequency, phase relationship between the probe and masker modulator, and probe modulation depth. In experiment 1, the carrier was a 5-kHz sinusoid presented either alone or within a notched-noise masker in order to restrict off-frequency listening. In experiment 2, the carrier was a white noise. The data obtained in both carrier conditions are consistent with the existence of a modulation distortion component. However, the phase yielding poorest detection performance varied across experimental conditions between 0 degrees and 180 degrees, confirming that, in addition to nonlinear mechanisms, cochlear filtering and off-frequency listening play a role in second-order SAM perception. The estimated magnitude of the modulation distortion component ranges from 5%-12%.

Adolescent↗
PubMed2005

Perception of the envelope-beat frequency of inharmonic complex temporal envelopes.

Listeners can hear slow sinusoidal variations in the depth of sinusoidally amplitude-modulated (SAM) stimuli. Here, the SAM stimulus of frequency f(m) acts as the carrier, and the slow variation in depth of frequency f'm (referred to as "second-order" amplitude modulation) corresponds to a beat in the temporal envelope. Recent studies have suggested that second-order amplitude modulation perception is based on a modulation-distortion component or the "venelope" (the Hilbert envelope of the ac-coupled Hilbert envelope), both occurring at the envelope-beat frequency f'm. This was tested by transposing to the modulation domain the matching paradigm used by Schouten et al. [J. Acoust. Soc. Am. 34, 1418-1424 (1962)]. Listeners estimated the envelope-beat frequency evoked by a 5-Hz, second-order SAM white noise with f(m) either an integer multiple of f'm or shifted in frequency to make the complex envelope inharmonic. The results indicate that the perception of the envelope-beat frequency was affected by these shifts when f(m) < or = 20 Hz. This suggests that, at least at low modulation frequencies, the perceived envelope beat is not determined by a modulation-distortion or venelope component, but rather relies on the time intervals between the main peaks of the first-order envelope.

Acoustic Stimulation↗
PubMed2004

Temporal envelope processing in the human left and right auditory cortices.

The goal of this study was to determine the temporal response properties of different auditory cortical areas in humans. This is achieved by recording the phase-locked neural activity to white noises modulated sinusoidally in amplitude (AM) at frequencies between 4 and 128 Hz, in the left and right cortices of 20 subjects. Phase-locked neural responses are recorded in four auditory cortical areas with intracerebral electrodes, and modulation transfer functions (MTFs) are computed from these responses. A number of MTFs are bandpass in shape, demonstrating a selective encoding of AM frequencies below 64 Hz in the auditory cortex. This result provides strong physiological support to the idea that the human auditory system decomposes the temporal envelope of sounds (such as speech) into its constituting AM components. Moreover, the results show a predominant response of cortical auditory areas to the lowest AM frequencies (4-16 Hz). This range matches the range of AM frequencies crucial for speech intelligibility, emphasizing therefore the role played by these initial stations of cortical processing in the analysis of speech. Finally, the results show differences in AM sensitivity across cortical areas and hemispheres, and provide a physiological foundation for claims of functional specialization of auditory areas based on previous population measures.

Acoustic Stimulation↗
PubMed2004

Voice onset time encoding in patients with left and right cochlear implants.

Stop-consonant discrimination was investigated in normal-hearing listeners and cochlear-implanted patients (CIP) by recording auditory evoked potentials (AEPs) to /b epsilon/ and /p epsilon/ syllables. This study demonstrates that: (i) AEPs show time-locked components that mimic the temporal structure of the stimuli, indicating that both patients and control subjects encode those syllables according to the temporal cue (voice onset time) characterizing the voiced/voiceless contrast; (ii) the side of implantation does not affect the general structure of AEPs and /b epsilon/-/p epsilon/ discrimination thresholds (measured separately with a psychophysical procedure); (iii) poor time-locking to the syllables' temporal structure is associated with poor discrimination. This suggests that EEG investigation of temporal-processing provides an objective index of speech perception in CIP and could be used in implanted children.

Acoustic Stimulation↗
PubMed2004

Identification of envelope-expanded sentences in normal-hearing and hearing-impaired listeners.

The present study examined the effects of temporal-envelope expansion on speech perception. Sentence identification performance was measured in normal-hearing and hearing-impaired listeners for stationary and fluctuating noise. Two expansion schemes were used to increase the depth of the slow (< 16 Hz) and fast (< 256 Hz) amplitude fluctuations of the stimuli. In the first scheme, the envelope of the stimuli was raised to the power 2. In the second scheme, the high- and low-level segments of the envelope were compressed and expanded, respectively. When envelope processing was applied to speech before the addition of noise, the first form of expansion generally degraded identification, while the second form generally improved identification. When envelope processing was applied to speech after the addition of noise, both forms of expansion improved or did not affect identification scores in both groups of listeners when applied to the slowest fluctuations. When applied to the broadest range of fluctuations, both forms of expansion degraded identification. However, in hearing-impaired listeners, the second form of expansion yielded an increase in performance for fluctuating noise. This complex pattern of results will be discussed in light of previous studies on envelope expansion.

Adult↗
PubMed2004

Serotonin transporter 5HTTLPR polymorphism and affective disorders: no evidence of association in a large European multicenter study.

The available data from preclinical and pharmacological studies on the role of the serotonin transporter (5-HTT) support the hypothesis that a dysfunction in brain serotonergic system activity contributes to the vulnerability to affective disorders (AD). 5-HTT is the major site of serotonin reuptake into the presynaptic neuron, and it has been shown that the polymorphic repeat polymorphism in the 5-HTT promotor region (5-HTTLPR) may affect gene-transcription activity. 5-HTT maps to chromosome 17 at position 17q11.17-q12, and the 5-HTTLPR polymorphisms have been extensively investigated in AD with conflicting results. The present study tested the genetic contribution of the 5-HTTLPR polymorphism in a large European multicenter case-control sample, including 539 unipolar (UPAD), 572 bipolar patients (BPAD), and 821 controls (C). Our European collaboration has led to efforts to optimize a methodology that attenuates some of the major limitations of the case-control association approach. No association was found with primary psychiatric diagnosis (UPAD and BPAD) and with phenotypic traits (family history of AD, suicidal attempt, and presence of psychotic features). Our negative findings are not attributable to the lack of statistical power, and may contribute to clarify the role of 5-HTTLPR polymorphism in AD.

Bipolar Disorder↗
PubMed2004

Detection of 1st- and 2nd-order temporal-envelope cues in a patient with left superior cortical damage.

This psychophysical study explores the extent to which the auditory cortex is necessary for various aspects of temporal-envelope perception, that is, perception of the slow temporal modulations in amplitude known to be crucial for sound identification. The ability to detect 1st- and 2nd-order sinusoidal amplitude modulation (AM) is evaluated in a single patient showing left-hemisphere damage encroaching the primary and secondary auditory cortices. Here, 1st- and 2nd-order AM refer to (1) sinusoidal variation in the amplitude of a 2 kHz pure tone, and (2) sinusoidal variation in the depth of a 64 Hz AM applied to the 2 kHz pure tone, respectively. The results replicate previous findings by showing that damage to the left auditory cortex results in a selective deficit in auditory sensitivity to the lowest 1St-order AM (i.e., 1st-order AM frequencies < 16 Hz). Moreover, a dissociation is apparent between the ability to detect 1st- and 2nd-order temporal-envelope cues. The patient shows poorer than normal ability to detect 2nd-order AM at low frequencies ranging from 4-23 Hz, but normal ability to detect the high (64 Hz) 1st-order AM carrying these 2nd-order modulations. This result indicates that damage to the left primary and secondary auditory cortices affects the ability to detect temporal variations in the local properties of sounds(such as AM depth). It is also consistent with the idea that, as in vision, central nonlinear mechanisms are involved in the computation of such local (or 2nd-order) temporal properties.

Acoustic Stimulation↗
PubMed2004

Effects of amplitude compression on first- and second-order modulation detection thresholds in cochlear implant listeners.

The aim of this study was to examine the effects of instantaneous non-linear amplitude mapping on the detection of single-component and multicomponent temporal envelopes. To address this issue, first- and second-order amplitude modulation detection thresholds were measured in four cochlear implant users with the intervention of the compression device of the implant processor. The compression device is set to produce either a strongly or a weakly logarithmic mapping of stimulus amplitude to electrical amplitude. 'First-order' modulation detection thresholds indicate the ability of listeners to detect sinusoidal amplitude modulation (SAM) applied to a white noise carrier; they are measured as a function of the rate of that modulation, fm. 'Second-order' modulation detection thresholds indicate the ability to detect sinusoidal modulation applied to the depth of a sinusoidally amplitude-modulated signal (here, a 16-Hz sinusoidally amplitude-modulated white noise); they are measured as a function of the rate of the modulation applied to the modulation depth (referred to as fm'). In each task, stimuli are transformed by the implant processor and are presented through one electrode at approximately the same level. The results show that, in cochlear implant listeners, both first- and second-order modulation detection thresholds measured at the lower rates (< or =7 Hz) decrease slightly by about 3-6dB when the stronger compression is used. No effect of compression is observed at higher rates. These results suggest that instantaneous logarithmic amplitude mapping has beneficial- but limited-effects on the detection of single-component and multicomponent temporal envelopes. These results are discussed in light of current models of temporal envelope processing.

Auditory Threshold↗
PubMed2003

Effect of a noise modulation masker on the detection of second-order amplitude modulation.

Amplitude modulation waveforms can contain complex patterns of modulation frequency and depth that are characteristic of many biologically relevant sounds. To investigate the mechanisms involved in the processing of such patterns, we measured detection thresholds for second-order amplitude modulation (AM), a sinusoidal AM in which AM depth varies with time at frequency f(m)'. Second-order AM generates sidebands in the modulation spectrum on either side of the frequency components introduced by the first-order AM. Previous masking studies suggested that a distortion product located at f(m)' contributes to the detection of second-order AM. This hypothesis was tested by masking the putative distortion product using a noise modulation masker centred on (1) the second-order modulation frequency (f(m)'=2 Hz) and (2) the first-order modulation frequency (f(m)=16 Hz). The second-order AM was applied to a 5-kHz pure-tone carrier. Increasing the depth of a 2-Hz-wide noise modulator masker centred on 2 Hz had little effect on detection thresholds for second-order AM, but increased detection thresholds for 2-Hz first-order AM six-fold. Increasing the depth of an 8-Hz-wide noise modulator masker centred on 16 Hz increased detection thresholds for both first- and second-order AM three-fold. These results show that the detection of the second-order AM, when f(m)' is 2 Hz, is not dependent on the detection of modulation at f(m)' but is dependent on the detection of modulation components centred on f(m).

Adult↗
PubMed2003

Effect of cochlear damage on the detection of complex temporal envelopes.

Recent studies have demonstrated that the detection of complex temporal envelopes relies - at least partially - on the perception of a distortion component generated by a peripheral (cochlear) and/or central (post-cochlear) non-linearity. In the present study, first- and second-order amplitude modulation (AM) detection thresholds were obtained in normally hearing (NH) and hearing-impaired (HI) listeners using a 2-kHz pure-tone carrier. In both groups of listeners, first-order AM detection thresholds were measured for AM rates fm ranging between 4 and 87 Hz, and second-order AM detection thresholds were measured for second-order AM rates fm' ranging between 4 and 23 Hz, using a fixed first-order 'carrier' AM rate fm of 64 Hz. When the sound pressure level was adjusted in order to yield equal detectability in both groups for the 64-Hz first-order carrier modulation, (i) first-order AM detection thresholds for the HI listeners were normal at fm=87 Hz, and better-than-normal at fm=4 and 16 Hz, and (ii) second-order AM detection thresholds were identical at all modulation rates in NH and HI listeners. Similar results were obtained when the audibility of the 2-kHz pure-tone carrier was equated for both groups, i.e. when listeners were tested at the same sensation level. These results demonstrate clearly that cochlear damage has no effect on the detection of complex temporal envelopes, and indicate that the distortion component must be generated by a more central non-linearity than cochlear compression, transduction, or short-term adaptation.

Acoustic Stimulation↗