Envelope Processing Research Articles

Study on High-Order Elliptical Gear Parametric Design, Automatic Modeling and Motion Simulation

In this paper, the high-order elliptical gear design principle and methods were studied based on Solidworks API to accomplish high-order elliptical gear parametrical design, machining simulation and automatic modeling. Elliptical gear pair simulation was carried out for verification. The high-order elliptical gear modeling method proposed was to use gear hob type of envelope processing method with the advantages of being able to process concaved pitch curve of high-order elliptical gear. The idea of this design process can also be extended to other types of non-circular gear design and modeling.

Human immunodeficiency virus type 1 envelope proteins traffic toward virion assembly sites via a TBC1D20/Rab1-regulated pathway

BackgroundThe cellular activity of many factors and pathways is required to execute the complex replication cycle of the human immunodeficiency virus type 1 (HIV-1). To reveal these cellular components, several extensive RNAi screens have been performed, listing numerous 'HIV-dependency factors'. However, only a small overlap between these lists exists, calling for further evaluation of the relevance of specific factors to HIV-1 replication and for the identification of additional cellular candidates. TBC1D20, the GTPase-activating protein (GAP) of Rab1, regulates endoplasmic reticulum (ER) to Golgi trafficking, was not identified in any of these screens, and its involvement in HIV-1 replication cycle is tested here.FindingsExcessive TBC1D20 activity perturbs the early trafficking of HIV-1 envelope protein through the secretory pathway. Overexpression of TBC1D20 hampered envelope processing and reduced its association with detergent-resistant membranes, entailing a reduction in infectivity of HIV-1 virion like particles (VLPs).ConclusionsThese findings add TBC1D20 to the network of host factors regulating HIV replication cycle.

Approaches to the study of neural coding of sound source location and sound envelope in real environments

The major functions of the auditory system are recognition (what is the sound) and localization (where is the sound). Although each of these has received considerable attention, rarely are they studied in combination. Furthermore, the stimuli used in the bulk of studies did not represent sound location in real environments and ignored the effects of reverberation. Another ignored dimension is the distance of a sound source. Finally, there is a scarcity of studies conducted in unanesthetized animals. We illustrate a set of efficient methods that overcome these shortcomings. We use the virtual auditory space method (VAS) to efficiently present sounds at different azimuths, different distances and in different environments. Additionally, this method allows for efficient switching between binaural and monaural stimulation and alteration of acoustic cues singly or in combination to elucidate neural mechanisms underlying localization and recognition. Such procedures cannot be performed with real sound field stimulation. Our research is designed to address the following questions: Are IC neurons specialized to process what and where auditory information? How does reverberation and distance of the sound source affect this processing? How do IC neurons represent sound source distance? Are neural mechanisms underlying envelope processing binaural or monaural?

Dolphins (Tursiops truncatus) use multiple auditory mechanisms for detecting tonal signals in natural and anthropogenic noise

The dolphin's ability to detect a 10 kHz tone masked by a variety of noise types was measured using a standard band-widening paradigm. Maskers included natural noise (rain, snapping shrimp, and ice squeaks), anthropogenic noise (pile saw and boat propeller cavitation) and statistical noise (Gaussian and comodulated noise). For most noise types, detection thresholds increased as noise bandwidth increased up to 1 kHz (the dolphin's critical bandwidth at 10 kHz). Masking patterns for narrow-band maskers were similar regardless of the masker type. However, for noise bandwidths greater than 1 kHz, masking patterns diverged by as much as 23 dB depending on the noise type. The power spectrum model provided reasonable predictions for Gaussian, rain, pile saw, and boat noise masking patterns. Additional experiments suggested that mechanisms related to temporal envelope processing (across-channel envelope comparison and within-valley listening) determined masking patterns for snapping shrimp and comodulated noise. Thresholds in ice squeak noise, which proved to be the most effective masker, were related to the dolphin's inability to discriminate the signal from the background noise rather than inability to detect the signal. These results suggest that the dolphin auditory system uses multiple mechanisms for signal detection in complex noise [Work supported by the ONR.]

Detection and rate discrimination of amplitude modulation in electrical hearing

Three experiments were designed to examine temporal envelope processing by cochlear implant (CI) listeners. In experiment 1, the hypothesis that listeners' modulation sensitivity would in part determine their ability to discriminate between temporal modulation rates was examined. Temporal modulation transfer functions (TMTFs) obtained in an amplitude modulation detection (AMD) task were compared to threshold functions obtained in an amplitude modulation rate discrimination (AMRD) task. Statistically significant nonlinear correlations were observed between the two measures. In experiment 2, results of loudness-balancing showed small increases in the loudness of modulated over unmodulated stimuli beyond a modulation depth of 16%. Results of experiment 3 indicated small but statistically significant effects of level-roving on the overall gain of the TMTF, but no impact of level-roving on the average shape of the TMTF across subjects. This suggested that level-roving simply increased the task difficulty for most listeners, but did not indicate increased use of intensity cues under more challenging conditions. Data obtained with one subject, however, suggested that the most sensitive listeners may derive some benefit from intensity cues in these tasks. Overall, results indicated that intensity cues did not play an important role in temporal envelope processing by the average CI listener.

A Signature in HIV-1 Envelope Leader Peptide Associated with Transition from Acute to Chronic Infection Impacts Envelope Processing and Infectivity

Mucosal transmission of the human immunodeficiency virus (HIV) results in a bottleneck in viral genetic diversity. Gnanakaran and colleagues used a computational strategy to identify signature amino acids at particular positions in Envelope that were associated either with transmitted sequences sampled very early in infection, or sequences sampled during chronic infection. Among the strongest signatures observed was an enrichment for the stable presence of histidine at position 12 at transmission and in early infection, and a recurrent loss of histidine at position 12 in chronic infection. This amino acid lies within the leader peptide of Envelope, a region of the protein that has been shown to influence envelope glycoprotein expression and virion infectivity. We show a strong association between a positively charged amino acid like histidine at position 12 in transmitted/founder viruses with more efficient trafficking of the nascent envelope polypeptide to the endoplasmic reticulum and higher steady-state glycoprotein expression compared to viruses that have a non-basic position 12 residue, a substitution that was enriched among viruses sampled from chronically infected individuals. When expressed in the context of other viral proteins, transmitted envelopes with a basic amino acid position 12 were incorporated at higher density into the virus and exhibited higher infectious titers than did non-signature envelopes. These results support the potential utility of using a computational approach to examine large viral sequence data sets for functional signatures and indicate the importance of Envelope expression levels for efficient HIV transmission.

Age Effects in Temporal Envelope Processing: Speech Unmasking and Auditory Steady State Responses

The purpose of this study was to determine whether temporal envelope processing is reduced in older listeners. Experiment 1 tested the hypothesis that older listeners exhibit reduced speech unmasking at higher modulation rates. Experiment 2 tested the hypothesis that auditory steady state response (ASSR) amplitudes are reduced in older listeners at high modulation rates. Two groups of observers with relatively normal hearing (younger, mean age = 25.0 years and older, mean age = 68.7 years) participated in two experiments. Experiment 1 examined speech unmasking in modulated noise as a function of masker modulation rate (16 and 32 Hz) and target speech rate (normal and 33% time compressed). Experiment 2 measured ASSR amplitudes as a function of modulation rate (32 and 128 Hz) and carrier frequency (500 and 2000 Hz). Experiment 1 indicated that older listeners show reduced speech unmasking for normal-rate speech and reduced recognition of rapid speech in steady noise. However, for rapid speech, there is no age effect for speech unmasking and no difference in the magnitude of masking release as a function of modulation rate. In general, effects of listener age and masker modulation rate on the magnitude of masking release are observed only for normal-rate speech. Experiment 2 showed that the ASSR amplitudes of older listeners are reduced for a 128-Hz modulation rate but not for a 32-Hz modulation rate, irrespective of carrier frequency. These results suggest that the reduced speech unmasking seen in older listeners for relatively slow modulation rates is not caused by deficits in envelope processing but rather is associated with the more constrained redundancy of the speech material available during the masker minima. Deficits in temporal envelope processing are evident in advanced age but only for relatively high envelope frequencies.

Age Effects in Temporal Envelope Processing: Speech Unmasking and Auditory Steady State Responses

Age Effects in Temporal Envelope Processing: Speech Unmasking and Auditory Steady State Responses

Role of the HIV gp120 Conserved Domain 1 in Processing and Viral Entry

The importance of the N-terminal region of HIV gp120 conserved domain 1 (gp120-C1) to envelope function has been examined by alanine-scanning mutagenesis and subsequent characterization of the mutagenic effects on viral entry; envelope expression, processing, and incorporation; and gp120 association with gp41. With respect to the wild-type gp120, mutational effects on viral entry fall into two classes: functional, as defined by >20% entry with respect to wild type, and impaired, as defined by <20% entry with respect to wild type. Based on Western blot analyses of cell lysates and virions, the entry impairment of W35A, V38A, Y39A, Y40A, G41A, V42A, and I52A is due primarily to disruption of envelope processing. The entry impairment of P43A and W45A is apparently due to a combination of effects on processing and incorporation into virions. In contrast, the entry impairment of V44A and F53A is primarily due to disruption of the gp120-gp41 interaction, which results in dissociation of gp120 from the virion. We present a model for gp120-C1 interactions with gp120-C5 and the gp41 disulfide loop in unprocessed gp160 and processed gp120/gp41.

Spectral weights and the transition between two auditory processes.

Evidence of broad auditory filters for processing temporal information was obtained with a molecular psychophysical technique. The standard in the 2IFC discrimination task consisted of n equal intensity sinusoids, with frequency separations ranging from 10 to 40 Hz. The signal was an intensity increment of the central sinusoid, which on average was 1000 Hz. Pitch cues were degraded by randomly selecting the center frequency over a 100 Hz range on each stimulus presentation. Single channel intensity cues were degraded with a roving‐level procedure. As tones were added symmetrically to the ends of the complex, thresholds increased until a certain bandwidth was reached, beyond which thresholds decreased. Previous results showed that transition bandwidths ranged from 100 Hz to more than 1000 Hz across individuals [B. G. Berg, J. Acoust. Soc. Am. 121, 3639–3645 (2007)]. This discontinuity presumably represents a change in the underlying auditory processes, with envelope cues at bandwidths narrower than the breakpoint and across channel level comparisons for wider bandwidths. Findings show that the pattern of spectral weight estimates before the breakpoint is consistent with an envelope processing model, whereas the weights for bandwidths greater than the transition point were consistent with an across‐channel comparison. [Work supported by ONR].

Role of the HIV gp120 Conserved Domain 5 in Processing and Viral Entry

The importance of the HIV gp120 conserved domain 5 (gp120-C5) to envelope function has been examined by alanine scanning mutagenesis and subsequent characterization of the mutagenic effects on viral entry and envelope expression, processing, and incorporation, as well as gp120 association with gp41. With respect to the wild-type gp120, mutational effects on viral entry fall into three classes: (1) functional (V489A, E492A, P493A, T499A, K500A, K502A, R503A, R504A, V505A, and V506A; (2) nonfunctional (I491A, L494A, V496A, and P498A); (3) enhanced (K490A, G495A, and Q507A). The nonfunctionality of the mutants is attributed to a combination of deleterious effects on processing, gp120-gp41 association, and membrane fusion. In the case of the nonfunctional mutant P498A, the introduction of the SOS mutation (A501C/T601C) results in substantially increased envelope processing and a gain of function. The effects of the mutants are interpreted with respect to the structures of gp41 and gp120. The extent of sensitivity of gp120-C5 to alanine substitutions underscores the importance of this domain to envelope function and suggests that gp120-C5 is an attractive and novel target for future drug discovery efforts.

Temporal envelope processing in the human auditory cortex: Response and interconnections of auditory cortical areas

Temporal envelope processing in the human auditory cortex has an important role in language analysis. In this paper, depth recordings of local field potentials in response to amplitude modulated white noises were used to design maps of activation in primary, secondary and associative auditory areas and to study the propagation of the cortical activity between them. The comparison of activations between auditory areas was based on a signal-to-noise ratio associated with the response to amplitude modulation (AM). The functional connectivity between cortical areas was quantified by the directed coherence (DCOH) applied to auditory evoked potentials. This study shows the following reproducible results on twenty subjects: (1) the primary auditory cortex (PAC), the secondary cortices (secondary auditory cortex (SAC) and planum temporale (PT)), the insular gyrus, the Brodmann area (BA) 22 and the posterior part of T1 gyrus (T1Post) respond to AM in both hemispheres. (2) A stronger response to AM was observed in SAC and T1Post of the left hemisphere independent of the modulation frequency (MF), and in the left BA22 for MFs 8 and 16 Hz, compared to those in the right. (3) The activation and propagation features emphasized at least four different types of temporal processing. (4) A sequential activation of PAC, SAC and BA22 areas was clearly visible at all MFs, while other auditory areas may be more involved in parallel processing upon a stream originating from primary auditory area, which thus acts as a distribution hub. These results suggest that different psychological information is carried by the temporal envelope of sounds relative to the rate of amplitude modulation.

Event-related potentials to pitch and rise time change in children with reading disabilities and typically reading children

Objective The purpose of the present study was to investigate whether children with reading disabilities (RD) process rise time and pitch changes differently to control children as a function of the interval between two tones. Methods Children participated in passive oddball event-related potential (ERP) measurements using paired stimuli. Mismatch negativity (MMN), P3a and late discriminative negativity (LDN) responses to rise time and pitch changes were examined. Results Control children produced larger responses than children with RD to pitch change in the P3a component but only when the sounds in the pair were close to each other. Compared to children with RD, MMN was smaller and LDN larger in control children in response to rise time change when the sounds in the pair were further apart. The non-overlap in ERP measures between the groups was 40–50%. Conclusions Problems in rapid processing of pitch change were reflected in a component associated with attention switching while amplitude envelope processing problems were reflected in components associated with stimulus detection or discrimination. Significance Children with RD process both rise time and pitch changes differently from control children thus providing evidence for the nature of amplitude envelope processing and rapid auditory processing deficits in dyslexia.

Role of envelope processing and gp41 membrane spanning domain in the formation of human immunodeficiency virus type 1 (HIV-1) fusion–competent envelope glycoprotein complex

Human immunodeficiency virus type 1 (HIV-1) entry into target cells is directed by the envelope (Env) glycoproteins, which are present on the surface of HIV-1 virion or infected cells in the form of trimers consisting of gp120/gp41 complexes. The surface subunit, gp120, initiates the entry process by interacting sequentially with the CD4 receptor and a co-receptor, thereby inducing a conformational change that allows the transmembrane (TM) gp41 subunit to mediate fusion between viral and target cell membranes. Cleavage of Env into its gp120 and gp41 components is necessary for activation of its fusogenic activity. Here, the gp41 TM glycoprotein was altered by either deleting an isoleucine residue (ΔI642) in a critical region of its ectodomain or by substituting its membrane spanning domain (MSD) by that of the influenza hemagglutinin (HA) glycoprotein (TM-HA) to examine the contribution of these regions to Env functions. Characterization of these mutant forms of gp41 revealed that they both affected the infectivity of pseudotyped virions, however, through distinct defects in Env functions. While deletion of Ile 642 drastically altered processing of Env, replacement of gp41 MSD by that of HA led to a marked fusion defect even though the TM-HA Env was efficiently processed and incorporated into viral particles. Interestingly, both ΔI642 and TM-HA Env were found to act as trans dominant-negative mutant of viral infectivity, presumably via their ability to form hetero-oligomers with wild type Env. Together, these results support a previously proposed model whereby all three gp120–gp41 monomers must be cleaved for the Env homo-trimer to function and suggest that the gp41 MSD plays a critical role in the formation of fusion-competent Env trimers.

Neural Rate and Timing Cues for Detection and Discrimination of Amplitude-Modulated Tones in the Awake Rabbit Inferior Colliculus

Neural responses to amplitude-modulated (AM) tones in the unanesthetized rabbit inferior colliculus (IC) were studied in an effort to establish explicit relationships between physiological and psychophysical measures of temporal envelope processing. Specifically, responses to variations in modulation depth (m) at the cell's best modulation frequency, with and without modulation maskers, were quantified in terms of average rate and synchronization to the envelope over the entire perceptual dynamic range of depths. Statistically significant variations in the metrics were used to define neural AM detection and discrimination thresholds. Synchrony emerged at modulation depths comparable with psychophysical AM detection sensitivities in some neurons, whereas the lowest rate-based neural thresholds could not account for psychoacoustical thresholds. The majority of rate thresholds (85%) were -10 dB or higher (in 20 log m), and 16% of the population exhibited no systematic dependence of average rate on m. Neural thresholds for AM detection did not decrease systematically at higher SPLs (as observed psychophysically): thresholds remained constant or increased with level for most cells tested at multiple sound-pressure levels (SPLs). At depths higher than the rate-based detection threshold, some rate modulation-depth functions were sufficiently steep with respect to the across-trial variability of the rate to predict depth discrimination thresholds as low as 1 dB (comparable with the psychophysics). Synchrony, on the other hand, did not vary systematically with m in many cells at high modulation depths. A simple computational model was extended to reproduce several features of the modulation frequency and depth dependence of both transient and sustained pure-tone responders.

Noise improves modulation detection by cochlear implant listeners at moderate carrier levels

Envelope detection and processing are very important for cochlear implant (CI) listeners, who must rely on obtaining significant amounts of acoustic information from the time-varying envelopes of stimuli. In previous work, Chatterjee and Robert [JARO 2(2), 159-171 (2001)] reported on a stochastic-resonance-type effect in modulation detection by CI listeners: optimum levels of noise in the envelope enhanced modulation detection under certain conditions, particularly when the carrier level was low. The results of that study suggested that a low carrier level was sufficient to evoke the observed stochastic resonance effect, but did not clarify whether a low carrier level was necessary to evoke the effect. Modulation thresholds in CI listeners generally decrease with increasing carrier level. The experiments in this study were designed to investigate whether the observed noise-induced enhancement is related to the low carrier level per se, or to the poor modulation sensitivity that accompanies it. This was done by keeping the carrier amplitude fixed at a moderate level and increasing modulation frequency so that modulation sensitivity could be reduced without lowering carrier level. The results suggest that modulation sensitivity, not carrier level, is the primary factor determining the effect of the noise.

Alanine Scanning Mutants of the HIV gp41 Loop

Based on mutagenesis and structural studies of human immunodeficiency virus (HIV) envelope proteins, the loop region of gp41 is thought to directly interact with gp120. The importance of the HIV gp41 loop region to envelope function has been systematically examined by alanine scanning of all gp41 loop residues and the subsequent characterization of the mutagenic effects on viral entry, envelope expression, envelope processing, and gp120 association with gp41. With respect to the wild-type gp41, mutational effects on viral entry fall into four classes as follows: 1) little or no effect (G594A, S599A, G600A, K601A, N611A, S615A, N616A, and L619A); 2) significantly reduced entry (I595A, L602A, I603A, V608A, and K617A); 3) abolished entry (L593A, W596A, G597A, T606A, W610A, W614A, S618A, and I622A); and 4) enhanced entry (T605A, P609A, S613A, E620A, and Q621A). The reduced functionality of many mutants was apparently due to either disruption of envelope processing (L593A and T606A), viral incorporation of the envelope (W610A, W614A, and I662A), or increased dissociation of gp120 (W596A, G597A, and S618A). The extreme sensitivity of the gp120-gp41 interaction to alanine substitutions (e.g. the G597A and S618A mutants are relatively conservative substitutions) suggests that this association is an attractive and novel target for future drug discovery efforts.

Auditory discrimination of binary sequences

Auditory sequence discrimination was investigated for stimuli generated with binary modulation coding schemes. Both amplitude- and frequency-shift keying (ASK and FSK) were used to convert 16-event binary patterns into a series of pulses. Discrimination was measured as a function of the number of binary events that differed between the standard and comparison sequences with temporal locations of the deviant pulses randomly selected on each trial. Across conditions, pulse duration ranged from 4 to 64 ms. In the ASK scheme, the carrier was wideband noise with off-key amplitudes scaled by a factor ranging from 0.0 to 0.5. Performance improved with increasing either pulse duration, amplitude shift, or the number of deviant pulses from one to eight. These trends are consistent with envelope processing by a modulation filterbank which discards phase information above low modulation rates. In the FSK scheme, binary patterns were coded by pulse-frequency differences centered at 1.25 kHz. As with ASK, FSK results showed performance improving with pulse duration and number of deviant pulses. FSK findings suggest that the low-pass results obtained with ASK envelope coding may reflect a general characteristic of sequence discrimination that is not restricted solely by auditory envelope processing. [Work supported by NIDCD.]

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.

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 secondorder 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 (≤7 Hz) decrease slightly by about 3–6 dB 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.