Amplitude Modulation Detection Research Articles

Ability of primary auditory cortical neurons to detect amplitude modulation with rate and temporal codes: neurometric analysis

Amplitude modulation (AM) is a common feature of natural sounds, and its detection is biologically important. Even though most sounds are not fully modulated, the majority of physiological studies have focused on fully modulated (100% modulation depth) sounds. We presented AM noise at a range of modulation depths to awake macaque monkeys while recording from neurons in primary auditory cortex (A1). The ability of neurons to detect partial AM with rate and temporal codes was assessed with signal detection methods. On average, single-cell synchrony was as or more sensitive than spike count in modulation detection. Cells are less sensitive to modulation depth if tested away from their best modulation frequency, particularly for temporal measures. Mean neural modulation detection thresholds in A1 are not as sensitive as behavioral thresholds, but with phase locking the most sensitive neurons are more sensitive, suggesting that for temporal measures the lower-envelope principle cannot account for thresholds. Three methods of preanalysis pooling of spike trains (multiunit, similar to convergence from a cortical column; within cell, similar to convergence of cells with matched response properties; across cell, similar to indiscriminate convergence of cells) all result in an increase in neural sensitivity to modulation depth for both temporal and rate codes. For the across-cell method, pooling of a few dozen cells can result in detection thresholds that approximate those of the behaving animal. With synchrony measures, indiscriminate pooling results in sensitive detection of modulation frequencies between 20 and 60 Hz, suggesting that differences in AM response phase are minor in A1.

Basic Auditory Processing Deficits in Dyslexia

A review of research that uses behavioral, electroencephalographic, and/or magnetoencephalographic methods to investigate auditory processing deficits in individuals with dyslexia is presented. Findings show that measures of frequency, rise time, and duration discrimination as well as amplitude modulation and frequency modulation detection were most often impaired in individuals with dyslexia. Less consistent findings were found for intensity and gap perception. Additional factors that mediate auditory processing deficits in individuals with dyslexia and their implications are discussed.

Detection of signal component modulations using modulation intensity distribution

Modulations in vibration signals that are generated by rotating machinery carry a lot of useful information about health condition. This paper proposes a technique for detection of modulations, called modulation intensity distribution (MID), which may be considered as a generalization of the spectral correlation density. It applies to most common types of modulations in mechanical systems thanks to an open module that can be tailored accordingly by the user. This leads to specific versions of the MID based on the RMS value, the spectral correlation or the kurtosis, which apply to the detection of amplitude modulations of either discrete or random carriers. The algorithm for calculation of the MID is described and tested on both simulated signal and experimental vibrations. The utility of MID in the diagnostic of rolling element bearing is demonstrated to be a natural extension of narrow band envelope analysis.

Multisensory integration of temporal processing in the auditory and somatosensory modalities: A psychophysical and EEG study.

Event Abstract Back to Event Multisensory integration of temporal processing in the auditory and somatosensory modalities: A psychophysical and EEG study. Justin Timora1* and Timothy Budd1 1 University of Newcastle, Australia Prior research examining multisensory integration has established the importance of the cross modal correspondence of temporal information. In the present study we examine the perceptual and neurophysiological impact of cross modal variations in amplitude modulation (AM) rate of acoustic and vibrotactile stimulation. To achieve this 33 participants completed separate psychophysical and EEG recording sessions where the cross modal correspondence of AM rate was varied. For the psychophysical session AM detection thresholds were estimated for 21 and 40 Hz auditory and vibrotactile stimuli where AM rate varied across modalities in one of three different cross modal correspondence (CMC) conditions, being either the SAME, DIFFERENT or NONE (i.e. unmodulated). For the EEG session identical stimulation conditions were presented and an FFT analysis carried out to determine whether EEG entrainment at each AM rate varied according to cross modal correspondence of temporal stimulation. The psychophysical results showed significant decreases in AM detection thresholds for conditions where the non-target modality was amplitude modulated at the same rate as the target modality (i.e. SAME), indicating reduced perceptual sensitivity when stimuli in both modalities were amplitude modulated. In contrast the results of the EEG analysis showed the opposite relationship, where EEG activity at the stimulation rate (i.e. entrainment) showed increases in EEG power for stimulus conditions where cross modal correspondence for AM stimulation was the same (i.e. SAME). These results suggest a potential dissociation between perception and EEG activity and are discussed in terms of the relationship between oscillatory neural activity and multisensory integration. Keywords: multisensory integration, multisensory processing, steady state, amplitude modulation, temporal processing Conference: ACNS-2012 Australasian Cognitive Neuroscience Conference, Brisbane, Australia, 29 Nov - 2 Dec, 2012. Presentation Type: Poster Presentation Topic: Sensation and Perception Citation: Timora J and Budd T (2012). Multisensory integration of temporal processing in the auditory and somatosensory modalities: A psychophysical and EEG study.. Conference Abstract: ACNS-2012 Australasian Cognitive Neuroscience Conference. doi: 10.3389/conf.fnhum.2012.208.00173 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 14 Oct 2012; Published Online: 17 Nov 2012. * Correspondence: Mr. Justin Timora, University of Newcastle, Newcastle, Australia, justin.timora@uon.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Justin Timora Timothy Budd Google Justin Timora Timothy Budd Google Scholar Justin Timora Timothy Budd PubMed Justin Timora Timothy Budd Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Monaural voiced speech segregation based on elaborate harmonic grouping strategies

In this paper, an enhanced algorithm based on several elaborate harmonic grouping strategies for monaural voiced speech segregation is proposed. Main achievements of the proposed algorithm lie in three aspects. Firstly, the algorithm classifies the time-frequency (T-F) units into resolved and unresolved ones by carrier-to-envelope energy ratio, which leads to more accurate classification results than by cross-channel correlation. Secondly, resolved T-F units are grouped together according to minimum amplitude principle, which has been verified to exist in human perception, as well as the harmonic principle. Finally, “enhanced” envelope autocorrelation function is employed to detect amplitude modulation rates, which helps a lot in reducing half-frequency error in grouping of unresolved units. Systematic evaluation and comparison show that performance of separation is greatly improved by the proposed algorithm. Specifically, signal-to-noise ratio (SNR) is improved by 0.96 dB compared with that of previous method. Besides, our algorithm is also effective in improving the PESQ score and subjective perception score.

The effect of temporal asymmetry on amplitude modulation detection using pure-tone carriers (L)

The effect of temporal asymmetry on amplitude modulation detection was studied using sawtooth modulators with rising (ramped) or falling (damped) temporal envelopes within each period of modulation. For pure-tone carriers, damped modulation was more detectable than ramped modulation for a 5-kHz carrier (by a threshold difference of 3.2 dB on average) but not for a 1-kHz carrier. The threshold difference obtained at 5 kHz between the ramped and damped modulators was consistent across modulation rates (8-128 Hz). This carrier frequency dependence suggests that the effect of temporally asymmetry on modulation detection originates from envelope-based, within-channel mechanisms.

Auditory processing deficits in individuals with primary open-angle glaucoma

Objective: The high energy demand of the auditory and visual pathways render these sensory systems prone to diseases that impair mitochondrial function. Primary open-angle glaucoma, a neurodegenerative disease of the optic nerve, has recently been associated with a spectrum of mitochondrial abnormalities. This study sought to investigate auditory processing in individuals with open-angle glaucoma. Design/Study sample: Twenty-seven subjects with open-angle glaucoma underwent electrophysiologic (auditory brainstem response), auditory temporal processing (amplitude modulation detection), and speech perception (monosyllabic words in quiet and background noise) assessment in each ear. A cohort of age, gender and hearing level matched control subjects was also tested. Results: While the majority of glaucoma subjects in this study demonstrated normal auditory function, there were a significant number (6/27 subjects, 22%) who showed abnormal auditory brainstem responses and impaired auditory perception in one or both ears. Conclusions: The finding that a significant proportion of subjects with open-angle glaucoma presented with auditory dysfunction provides evidence of systemic neuronal susceptibility. Affected individuals may suffer significant communication difficulties in everyday listening situations.

In Situ Gas-Phase Diagnostics for Titanium Nitride Atomic Layer Deposition

This report describes the performance of a technique for the simultaneous, rapid measurement of major gas phase species present during titanium nitride thermal atomic layer deposition involving tetrakis(dimethylamido) titanium (TDMAT) and ammonia. In this chemical system, the three primary gas phase species are the two reactants, TDMAT and ammonia, and the reaction product, dimethyl amine. For the measurement of these three species, a direct absorption method based on a broadband infrared source with two different mid-infrared bandpass filters and utilizing amplitude modulation and synchronous detection was developed. By splitting the optical beam exiting the deposition chamber and selecting appropriate filters, all three species could be monitored simultaneously. It is also demonstrated that the high time resolution of this technique permits the observation of differences in the delivery into and removal from the deposition chamber of both TDMAT and ammonia with different carrier gases.

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.

<I>In Situ</I> Gas Phase Measurements During Metal Alkylamide Atomic Layer Deposition

Metal alkylamide compounds, such as tetrakis(ethylmethylamido) hafnium (TEMAH), represent a technologically important class of metalorganic precursors for the deposition of metal oxides and metal nitrides via atomic layer deposition (ALD) or chemical vapor deposition. The development of in situ diagnostics for processes involving these compounds could be beneficial in, e.g., developing deposition recipes and validating equipment-scale simulations. This report describes the performance of the combination of two techniques for the simultaneous, rapid measurement of the three major gas phase species during hafnium oxide thermal ALD using TEMAH and water: TEMAH, water, and methylethyl amine (MEA), the only major reaction by-product. For measurement of TEMAH and MEA, direct absorption methods based on a broadband infrared source with different mid-IR bandpass filters and utilizing amplitude modulation and synchronous detection were developed. For the measurement of water, wavelength modulation spectroscopy utilizing a near-IR distributed feedback diode laser was used. Despite the relatively simple reactor geometry employed here (a flow tube), differences were easily observed in the time-dependent species distributions in 300 mL/min of a helium carrier gas and in 1000 mL/min of a nitrogen carrier gas. The degree of TEMAH entrainment was lower in 300 mL/min of helium compared to that in 1000 mL/min of nitrogen. The capability to obtain detailed time-dependent species concentrations during ALD could potentially allow for the selection of carrier gas composition and flow rates that would minimize parasitic wall reactions. However, when nitrogen was employed at the higher flow rates, various flow effects were observed that, if detrimental to a deposition process, would effectively limit the upper range of useful flow rates.

On the mechanisms involved in the recovery of envelope information from temporal fine structure

Three experiments were designed to provide psychophysical evidence for the existence of envelope information in the temporal fine structure (TFS) of stimuli that were originally amplitude modulated (AM). The original stimuli typically consisted of the sum of a sinusoidally AM tone and two unmodulated tones so that the envelope and TFS could be determined a priori. Experiment 1 showed that normal-hearing listeners not only perceive AM when presented with the Hilbert fine structure alone but AM detection thresholds are lower than those observed when presenting the original stimuli. Based on our analysis, envelope recovery resulted from the failure of the decomposition process to remove the spectral components related to the original envelope from the TFS and the introduction of spectral components related to the original envelope, suggesting that frequency- to amplitude-modulation conversion is not necessary to recover envelope information from TFS. Experiment 2 suggested that these spectral components interact in such a way that envelope fluctuations are minimized in the broadband TFS. Experiment 3 demonstrated that the modulation depth at the original carrier frequency is only slightly reduced compared to the depth of the original modulator. It also indicated that envelope recovery is not specific to the Hilbert decomposition.

Separable developmental trajectories for the abilities to detect auditory amplitude and frequency modulation

Amplitude modulation (AM) and frequency modulation (FM) are inherent components of most natural sounds. The ability to detect these modulations, considered critical for normal auditory and speech perception, improves over the course of development. However, the extent to which the development of AM and FM detection skills follow different trajectories, and therefore can be attributed to the maturation of separate processes, remains unclear. Here we explored the relationship between the developmental trajectories for the detection of sinusoidal AM and FM in a cross-sectional design employing children aged 8–10 and 11–12 years and adults. For FM of tonal carriers, both average performance (mean) and performance consistency (within-listener standard deviation) were adult-like in the 8–10 y/o. In contrast, in the same listeners, average performance for AM of wideband noise carriers was still not adult-like in the 11–12 y/o, though performance consistency was already mature in the 8–10 y/o. Among the children there were no significant correlations for either measure between the degrees of maturity for AM and FM detection. These differences in developmental trajectory between the two modulation cues and between average detection thresholds and performance consistency suggest that at least partially distinct processes may underlie the development of AM and FM detection as well as the abilities to detect modulation and to do so consistently.

The Cost and Benefit of Juvenile Training on Adult Perceptual Skill

Sensory experience during development can modify the CNS and alter adult perceptual skills. While this principle draws support from deprivation or chronic stimulus exposure studies, the effect of training is addressed only in adults. Here, we asked whether a brief period of training during development can exert a unique impact on adult perceptual skills. Juvenile gerbils were trained to detect amplitude modulation (AM), a stimulus feature elemental to animal communication sounds. When the performance of these juvenile-trained animals was subsequently assessed in adulthood, it was superior to a control group that received an identical regimen of training as adults. The juvenile-trained animals displayed significantly better AM detection thresholds. This was not observed in an adult group that received only exposure to AM stimuli as juveniles. To determine whether enhanced adult performance was due solely to learning the conditioned avoidance procedure, juveniles were trained on frequency modulation (FM) detection, and subsequently assessed on AM detection as adults. These animals displayed significantly poorer AM detection thresholds than all other groups. Thus, training on a specific auditory task (AM detection) during development provided a benefit to performance on that task in adulthood, whereas an identical training regimen in adulthood did not bring about this enhancement. In contrast, there was a cost, in adulthood, following developmental training on a different task (FM detection). Together, the results demonstrate a period of heightened sensitivity in the developing CNS such that behavioral training in juveniles has a unique impact on adult behavioral capabilities.

Taking advantage of behavioral changes during development and training to assess sensory coding mechanisms

The relationship between behavioral and neural performance has been explored in adult animals, but rarely during the developmental period when perceptual abilities emerge. We used these naturally occurring changes in auditory perception to evaluate underlying encoding mechanisms. Performance of juvenile and adult gerbils on an amplitude modulation (AM) detection task was compared with response properties from auditory cortex of age-matched animals. When tested with an identical behavioral procedure, juveniles display poorer AM detection thresholds than adults. Two neurometric analyses indicate that the most sensitive juvenile and adult neurons have equivalent AM thresholds. However, a pooling neurometric revealed that adult cortex encodes smaller AM depths. By each measure, neural sensitivity was superior to psychometric thresholds. However, juvenile training improved adult behavioral thresholds, such that they verged on the best sensitivity of adult neurons. Thus, periods of training may allow an animal to use the encoded information already present in cortex.

Effects of non‐simultaneous modulated maskers on amplitude‐modulation depth discrimination.

Wojtczak and Viemeister [J. Acoust Soc. Am. 118, 3198–3210 (2005)] demonstrated that detection thresholds for amplitude modulation (AM) can be increased in the presence of an AM forward masker. In the present study, the effects of forward‐masking on AM detection thresholds were extended to AM processing for easily detectable (suprathreshold) AM modulation depths by measuring the effects of nonsimultaneous AM maskers on AM modulation depth discrimination limens (AM DLs). Signal AM DLs were measured for a range of standard modulation depths. In one experiment the temporal delay between the masker and signal was varied. Consistent with the effects of AM forward maskers on AM detection thresholds [Wojtczak and Viemeister (2005)], the effects of the non‐simultaneous AM maskers on AM DLs were greatest for short masker‐signal delays. In another experiment, the masker‐signal delay was fixed, the signal modulation frequency was fixed, and the modulation frequency of the non‐simultaneous masker was varied. AM DLs for the signal were usually greatest when the signal modulation frequency was equal to the masker modulation frequency. The results of these experiments suggest that non‐simultaneous AM maskers can affect suprathreshold AM processing but non‐simultaneous AM maskers become less effective as the modulation depth of the standard increased.

Amplitude modulation detection by human listeners in sound fields.

The temporal modulation transfer function (TMTF) approach allows techniques from linear system analysis to be used to predict how the auditory system will respond to arbitrary patterns of amplitude modulation (AM). Although this approach forms the basis for a standard method of predicting speech intelligibility based on estimates of the acoustical modulation transfer function (MTF) between source and receiver, human sensitivity to AM as characterized by the TMTF has not been extensively studied under realistic listening conditions, such as in reverberant sound fields. Here, TMTFs (octave bands from 2–512 Hz) were obtained in three listening conditions simulated using virtual auditory space techniques: diotic, anechoic sound field, and reverberant room sound field. TMTFs were then related to acoustic MTFs estimated using two different methods in each of the listening conditions. Both diotic and anechoic data were found to be in good agreement with classic results, but AM thresholds in the reverberant room were lower than predictions based on acoustic MTFs. This result suggests that simple linear systems techniques may not be appropriate for predicting TMTFs from acoustical MTFs in reverberant sound fields, and may be suggestive of mechanisms that functionally enhance modulation during reverberant listening.

Relationship between amplitude modulation in psychophysical tasks and speech in listeners with normal and impaired hearing.

Previous work suggests that listeners with hearing loss may be unable to discriminate high-rate amplitude modulations, even when the modulation depth is above the modulation detection threshold [Grant et al., J. Acoust. Soc. Am. (1998)] 104, 1051–60. For listeners with normal hearing, high-rate amplitude modulations contribute to speech understanding when spectral information is degraded [Xu et al., 117, 3255–3267 (2005)]. In listeners with hearing loss, the ability to use amplitude modulation in speech may be limited to frequencies at which modulation frequency discrimination is possible. To test this, amplitude modulation detection and discrimination thresholds were measured in listeners with normal hearing and mild-to-moderate sensorineural loss. The signal was a broadband noise carrier sinusoidally amplitude modulated at rates of 10–640 Hz. Sentence and nonsense syllable recognition was measured for the same listeners. To restrict spectral information, speech was vocoded with a sinusoidal carrier modulated with three or six channels of envelope information. Envelope filter cutoff frequency was varied from 10–640 Hz. Compared to listeners with normal hearing, the listeners with hearing loss had more variable modulation frequency discrimination and that discrimination was related to their ability to use high-rate modulation information in speech recognition. [Work supported by NIH.]

Amplitude‐modulation detection in reproducible modulation maskers: Correlation between Behavioral and Physiological Responses.

The use of reproducible noise maskers in studies of detection has proven useful to extend our understanding of coding and processing of complex sounds. In an effort to reveal potential neural mechanisms for the detection of amplitude‐modulation (AM) in the presence of modulation maskers, tetrode recordings were made from inferior colliculus neurons of awake rabbits using reproducible stimuli. Both rabbit and human behavioral data have been collected for the same set of reproducible maskers. The target AM and maskers were applied to the envelope of a 5 kHz carrier signal. Neural responses were recorded to stimuli with the level of target AM slightly above masked threshold for both rabbit and human. Neural detection thresholds were estimated based on average discharge rate and several temporal metrics, such as synchrony to the target AM, temporal reliability, and rapid fluctuation in the peri‐stimulus time histogram (PSTH) of responses. The hit and false‐alarm rates for neural detection of AM were estimated for a set of 20 reproducible AM maskers. Preliminary results suggest that some neural responses, based on mean rate, synchrony to the target AM, or the slope of the PSTH, can explain the parallel rabbit behavioral results. [Work supported by NIH‐NIDCD R01‐001641.]

Amplitude modulation detection as a function of modulation frequency and stimulus duration: Comparisons between macaques and humans

Previous observations show that humans outperform non-human primates on some temporally-based auditory discrimination tasks, suggesting there are species differences in the proficiency of auditory temporal processing among primates. To further resolve these differences we compared the abilities of rhesus macaques and humans to detect sine-amplitude modulation (AM) of a broad-band noise carrier as a function of both AM frequency (2.5 Hz–2 kHz) and signal duration (50–800 ms), under similar testing conditions. Using a go/no-go AM detection task, we found that macaques were less sensitive than humans at the lower frequencies and shorter durations tested but were as, or slightly more, sensitive at higher frequencies and longer durations. Humans had broader AM tuning functions, with lower frequency regions of peak sensitivity (10–60 Hz) than macaques (30–120 Hz). These results support the notion that there are species differences in temporal processing among primates, and underscore the importance of stimulus duration when making cross-species comparisons for temporally-based tasks.

Relations between perceptual measures of temporal processing, auditory-evoked brainstem responses and speech intelligibility in noise

This study investigates behavioural and objective measures of temporal auditory processing and their relation to the ability to understand speech in noise. The experiments were carried out on a homogeneous group of seven hearing-impaired listeners with normal sensitivity at low frequencies (up to 1 kHz) and steeply sloping hearing losses above 1 kHz. For comparison, data were also collected for five normal-hearing listeners. Temporal processing was addressed at low frequencies by means of psychoacoustical frequency discrimination, binaural masked detection and amplitude modulation (AM) detection. In addition, auditory brainstem responses (ABRs) to clicks and broadband rising chirps were recorded. Furthermore, speech reception thresholds (SRTs) were determined for Danish sentences in speech-shaped noise. The main findings were: (1) SRTs were neither correlated with hearing sensitivity as reflected in the audiogram nor with the AM detection thresholds which represent an envelope-based measure of temporal resolution; (2) SRTs were correlated with frequency discrimination and binaural masked detection which are associated with temporal fine-structure coding; (3) The wave-V thresholds for the chirp-evoked ABRs indicated a relation to SRTs and the ability to process temporal fine structure. Overall, the results demonstrate the importance of low-frequency temporal processing for speech reception which can be affected even if pure-tone sensitivity is close to normal.