AM Detection Research Articles

Development of Auditory Processing in 6- to 11-Yr-Old Children

The aim of this study is to provide developmental standards on a variety of temporal, spectral, and binaural psychoacoustic (auditory processing [AP]) tests in typically developing children, including immediate and delayed retest reliability, and comparisons between single listener performance on different tests. This study also informs choices on the selection of tests for clinical evaluation of hearing and listening (e.g., for auditory processing disorder). This is a laboratory-based study of AP threshold and variability of 75 children, aged 6 to 11 yrs, and 21 young adults with normal audiometry recruited from local schools and colleges. Data were gathered in clinic-like conditions, without training and across two sessions. Eleven individual (e.g., simultaneous masking and backward masking [BM], amplitude modulation [AM], and frequency modulation [FM] detection) and three derived (temporal integration, frequency resolution, masking level difference) measure tests were embedded within a suite of computer games, each employing a three-interval, three-alternative (odd-one-out) forced choice response paradigm and a staircase adaptive method. AP measures generally showed lower thresholds and reduced variance with increasing age. At 6 to 7 yrs, performance was markedly poorer than in the older groups; 35% of the children could not do the test of frequency discrimination (FD). However, on all the tasks, some children in the same group performed at near-adult levels. The distribution of performance between individuals varied widely across tasks, with clustered performance on tests of tone detection (with or without a simultaneous masker) and AM detection, and scattered performance on BM, FM detection, and FD. Threshold maturity was achieved at different rates across tests and by 10 to 11 yrs of age on all tests except FD. Masking level difference (MLD) performance did not change with age. Retest reliability was mostly high within test sessions but, again, was poorer for some of the younger children. Between test sessions separated by one to several weeks, reliability varied from poor (for FM detection) to high (for long tone detection in quiet, BM, and FD). Correlations between thresholds on different tests were generally low. Data suggest that the perception of different auditory stimuli occurs and develops using rather independent mechanisms, even for tasks that are closely related in procedure. While individual children can perform reliably on several distinct tasks, differences between individuals on the same tasks can be large. Because some of the youngest children perform reliably across time, at or near adult levels, immaturity between 6 and 11 yrs of age, as reflected in group statistics, reflects poor performance of some individual children rather than obligate, age-related deficits in AP. While several of the tests used were found to have potential clinical applicability, because of their reliability and ability to distinguish between individuals, it is currently unclear how performance on such tests relates to everyday listening skills.

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.

Detection of sinusoidal amplitude modulation in logarithmic frequency sweeps across wide regions of the spectrum

Many natural sounds such as speech contain concurrent amplitude and frequency modulation (AM and FM), with the FM components often in the form of directional frequency sweeps or glides. Most studies of modulation coding, however, have employed one modulation type in stationary carriers, and in cases where mixed-modulation sounds have been used, the FM component has typically been confined to an extremely narrow range within a critical band. The current study examined the ability to detect AM signals carried by broad logarithmic frequency sweeps using a 2-alternative forced-choice adaptive psychophysical design. AM-detection thresholds were measured as a function of signal modulation rate and carrier sweep frequency region. Thresholds for detection of AM in a sweep carrier ranged from −8 dB for an AM rate of 8 Hz to −30 dB at 128 Hz. Compared to thresholds obtained for stationary carriers (pure tones and filtered Gaussian noise), detection of AM carried by frequency sweeps substantially declined at low (12 dB at 8 Hz) but not high modulation rates. Several trends in the data, including sweep- versus stationary-carrier threshold patterns and effects of frequency region were predicted from a modulation filterbank model with an envelope-correlation decision statistic.

Effectiveness of hierarchical Bayesian source current estimation on EEG-based brain-computer interfaces

Naphthalene is a volatile aromatic hydrocarbon to which humans are exposed from a variety of sources including mobile air sources and cigarette smoke. Naphthalene produces dose-(concentration)dependent injury to airway epithelial cells of murine lung which is observed at concentrations well below the current occupational exposure standard. Toxicity is dependent upon the cytochrome P450 mediated metabolic activation of the parent substrate to unstable metabolites which become bound covalently to tissue proteins. Nearly 70 proteins have been identified as forming adducts with reactive naphthalene metabolites using in vitro systems but very little work has been conducted in vivo because reasonably large amounts (100 μCi) of 14C labeled parent compound must be administered to generate detectable adduct levels on storage phosphor screens following separation of labeled proteins by 2D gel electrophoresis. The work described here was done to provide proof of concept that protein separation by free flow electrophoresis followed by AMS detection of protein fractions containing protein bound reactive metabolites would provide adducted protein profiles in animals dosed with trace quantities of labeled naphthalene. Mice were administered 200 mg/kg naphthalene intraperitoneally at a calculated specific activity of 2 DPM/nmol (1 pCi/nmol) and respiratory epithelial tissue was obtained by lysis lavage 4 h post injection. Free flow electrophoresis (FFE) separates proteins in the liquid phase over a large pH range (2.5–11.5) using low molecular weight acids and bases to modify the pH. The apparatus separates fractions into standard 96-well plates that can be used in other protein analysis techniques. The buffers of the fractions have very high carbon content, however, and need to be dialyzed to yield buffers compatible with 14C-AMS. We describe the processing techniques required to couple FFE to AMS for quantitation of protein adducts.

Free flow electrophoresis separation and AMS quantitation of 14C–naphthalene–protein adducts

Naphthalene is a volatile aromatic hydrocarbon to which humans are exposed from a variety of sources including mobile air sources and cigarette smoke. Naphthalene produces dose- (concentration) dependent injury to airway epithelial cells of murine lung which is observed at concentrations well below the current occupational exposure standard. Toxicity is dependent upon the cytochrome P450 mediated metabolic activation of the parent substrate to unstable metabolites which become bound covalently to tissue proteins. Nearly 70 proteins have been identified as forming adducts with reactive naphthalene metabolites using in vitro systems but very little work has been conducted in vivo because reasonably large amounts (100 μCi) of (14)C labeled parent compound must be administered to generate detectable adduct levels on storage phosphor screens following separation of labeled proteins by 2 D gel electrophoresis. The work described here was done to provide proof of concept that protein separation by free flow electrophoresis followed by AMS detection of protein fractions containing protein bound reactive metabolites would provide adducted protein profiles in animals dosed with trace quantities of labeled naphthalene. Mice were administered 200 mg/kg naphthalene intraperitoneally at a calculated specific activity of 2 DPM/nmol (1 pCi/nmol) and respiratory epithelial tissue was obtained by lysis lavage 4 hr post injection. Free flow electrophoresis (FFE) separates proteins in the liquid phase over a large pH range (2.5-11.5) using low molecular weight acids and bases to modify the pH. The apparatus separates fractions into standard 96-well plates that can be used in other protein analysis techniques. The buffers of the fractions have very high carbon content, however, and need to be dialyzed to yield buffers compatible with (14)C-AMS. We describe the processing techniques required to couple FFE to AMS for quantitation of protein adducts.

Wavelength- and amplitude-modulated photoacoustics: comparison of simulated and measured spectra of higher harmonics

Photoacoustic (PA) spectra generated by current modulation of a distributed feedback diode laser (DFB-DL) were measured for the ammonia absorption line at 1.53 microm and calculated using absorption spectra taken from a database. The algorithm is based on a combined amplitude- and wavelength-modulation (AM-WM) scheme. The spectral characteristics of the DFB-DL were determined by comparing simulated spectra with Fourier transform infrared measurements. PA spectra were measured and simulated from the first to fourth harmonic and a variation of the modulation depth with modulation frequency was observed. It was found that combined AM-WM modulation may produce larger PA signals than separate AM or WM detection for the first harmonic.

Roughness detection in fricative-like noise and tone stimuli

Audio (spectral) and modulation (envelope) frequencies both carry information in a speech signal. While low modulation frequencies (2-20Hz) convey syllable information, higher modulation frequencies (80-400Hz) allow for assimilation of perceptual cues, e.g., the roughness of amplitude-modulated noise in voiced fricatives, considered here. Psychoacoustic 3-interval forced-choice experiments measured AM detection thresholds for modulated noise accompanied by a tone with matching fundamental frequency at 125Hz: (1) tone-to-noise ratio (TNR) and phase between tone and noise envelope were varied, with silence between intervals; (2) as (1) with continuous tone throughout each trial; (3) duration and noise spectral shape were varied. Results from (1) showed increased threshold (worse detection) for louder tones (40-50dB TNR). In (2), a similar effect was observed for the in-phase condition, but out-of-phase AM detection appeared immune to the tone. As expected, (3) showed increased thresholds for shorter tokens, although still detectable at 60ms, and no effect for spectral shape. The phase effect of (2) held for the short stimuli, with implications for fricative speech tokens (40ms-100ms). Further work will evaluate the strength of this surprisingly robust cue in speech.

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<i>Beet necrotic yellow vein virus</i> (<i>benyvirus</i>)

Temporal integration functions of AM detection and AM depth discrimination

Previous studies (Lee, 1994; Lee and Bacon, 1997) suggested that both AM rate and AM depth discrimination were influenced by the number of AM cycles, instead of by the duration of stimulus. AM detection and AM depth discrimination were measured as a function of the number of AM cycles for the modulation rates of 10, 20, 40, 80, 125, 160, and 320 Hz. The carrier was a broadband noise (10 kHz low pass), and the carrier was either gated with the modulator (gated carrier) or presented 250 ms earlier and 250 ms later than the modulator (continuous carrier). The overall level of each presentation was randomized within 6-dB range from 65 dB SPL. For the lower modulation rates (10, 20, 40, and 80 Hz), there was a significant improvement with the continuous carrier at smaller number of cycles (two and four modulation cycles) as compared to the gated carrier condition. For the higher modulation rates (125, 160, and 320 Hz), however, the thresholds were not affected by carrier type. These results suggest that there might be a different temporal integration process for lower and higher modulation rates. [This work was supported by NIDCD Grant No. R03 DC06605-02.]

Temporal integration functions of amplitude modulation detection and amplitude modulation depth discrimination

Previous studies (Lee and Green, 1994; Lee and Bacon, 1997) suggested that both AM rate and AM depth discrimination were influenced by the number of AM cycles, instead of the duration of stimuli. AM detection and AM depth discrimination (standard depth=0.1) were measured as a function of the number of AM cycles for modulation rates of 10, 20, 40, 80, 125, 160, and 320 Hz. Different numbers of modulation cycles were used for each modulation rate: 2, 4, or 8 for 10 Hz; 2, 4, 8, or 16 for 20 Hz; 2, 4, 8, 16, or 32 for 40 Hz; 2, 4, 8, 16, 32, or 64 for 80, 125, 160, and 320 Hz. The carrier was a broadband-noise (10 kHz lowpass), and the carrier was either gated with the modulator or presented 250 ms earlier and 250 ms later than the modulator. The overall level of each presentation was randomized within 6-dB range from 65 dB SPL. The results suggest that there might be different temporal integration processes for AM detection and AM depth discrimination. The pattern is different for lower and higher modulation rates. [Work was supported by NIDCD Grant No. R03 DC06605-01.]

Auditory abilities of experienced signal analysts

Signal analysts continuously monitor audio communication signals for classification and identification. Performance levels of experienced analysts generally exceed that of most automated signal-classification schemes. Auditory abilities of four experienced military signal analysts were evaluated with both basic psychoacoustic listening tasks and multidimensional scaling of utility signals. The goal of the study was to determine the aspects of analysts’ auditory abilities relevant to job performance. Listening tasks were frequency discrimination, AM detection and rate discrimination, rippled-noise detection, delay discrimination, and detection of delay modulation. Across tasks, analysts’ thresholds were generally within the range of normative data. Results did suggest that frequency discrimination for both simple and complex stimuli is not a crucial ability for signal analysts. Stimuli used in the scaling study were first processed through a six-channel filterbank with both envelope- and phase-modulation functions extracted from each channel. Modulation functions were then applied to narrow-band carries. For some stimuli, functions were filtered or transposed across channel center frequencies. Multidimensional scaling of processed utility signals indicated that signal classification depends on both lower-rate amplitude and phase modulation. This result may have some bearing on the design of algorithms used in automated signal classification. [Work supported by AFRL.]

Formula omitted] atom counting for nuclear astrophysics

The nuclide 44 Ti (T 1/2=59.2 yr) has recently become an important asset to nuclear astrophysics through the measurement of its cosmic radioactivity, yielding significant information on fresh 44 Ti nucleosynthesis in supernovae. We propose to use AMS to determine the production rate of 44 Ti by the main channel believed to be responsible for 44 Ti astrophysical production, namely 40 Ca( α, γ ). A preliminary experiment conducted at the Koffler 14UD Pelletron accelerator demonstrates a sensitivity of 1×10 −14 for the 44 Ti/ Ti ratio. The AMS detection was performed using 44 Ti − ions sputtered from a TiO 2 sample, reducing considerably the 44 Ca isobaric interference. The present limit corresponds effectively to 44 Ti production with resonance strength in the range 10–100 meV for a one-day 40 Ca (α,γ) activation. Several such resonances are known to be responsible for 44 Ti production in the astrophysical temperature range and should be amenable to experiment with the proposed method.

Room 302, 10/18/2000 9: 00 AM - 10: 30 AM (PD) Detection of Perioperative Ischemia is Improved by Troponin (TnI) Measurement

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Room A, 10/17/2000 9: 00 AM - 11: 00 AM (PS) Detection of Patent Foramen Ovale through Pulse Oxymetry with Provocative Maneuvers

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Toward a digital neuromorphic pitch extraction system

This paper presents the design of a biologically based signal processing system implemented using standard digital inferior colliculus (IC) technology. The four-stage AM detection system is a step toward a full-pitch detection system and based on known mammalian physiology. The system is operational and has been successfully realized in field programmable grid array (FPGA) technology. Details of the system architecture, its operating principles, and the design decisions necessary to realize successfully neuromorphic systems in digital technology are given.

Effects of carrier level on the processing of highly detectable envelope fluctuations

A modified 2AFC matching procedure was used to measure the modulation depth that yielded similar perceived envelope fluctuations for different carrier levels. In one case, the standard was a 60-dB SPL 1-kHz tone that was amplitude-modulated at 16 Hz, with a modulation depth that produced highly detectable envelope fluctuations. The comparison had the same carrier and modulation frequencies as the standard, and its level ranged from 15 to 85 dB SPL. The data indicate that the higher the carrier level, the less modulation was needed to produce the same perceived fluctuation depth. For broadband noise carriers, however, the data indicate that approximately the same modulation depth was needed to obtain subjectively similar envelope fluctuations for all carrier levels tested. These results are similar to those observed for detection of AM, and they suggest that the level effects seen for detection extend to suprathreshold AM processing, i.e., Weber’s law for broadband noise and a ‘‘near-miss’’ for sinusoidal carriers. [Work supported by NIDCD Grant No. DC00683.]

Temporal versus spectral cues in AM detection

Several recent studies have shown that modulation thresholds for detecting sinusoidal AM are approximately constant out to much higher modulation frequencies for tonal carriers than for broadband noise carriers. It has been suggested that with tonal carriers there is a range of modulation frequencies for which both temporal (envelope) cues and spectral cues are used for detection. The present study attempts to assess the relative importance of these cues. Modulation thresholds for AM, quasifrequency modulation (QFM), and beats were measured for modulation frequencies of 8–512 Hz and carrier frequencies of 2 and 5 kHz. The results indicate that at intermediate modulation frequencies, AM thresholds are approximately constant while those for QFM and for beats decrease with increasing modulation frequency. This indicates that the detection of AM is not based solely on temporal cues. The implications of these findings for envelope detection and modulation filter-bank models will be discussed. [Work supported by NIDCD Grant No. DC00683.]

A model of auditory image flow. II. Detection of amplitude and frequency modulation

In order to evaluate the cortical model proposed in Todd [these proceedings] it was applied to the phenomenon of modulation detection. It was assumed that a discrimination task involves the correlation of the spatio‐temporal power spectra of two image sequences, such as may occur in a typical 2A‐2IFC procedure. The correlation was computed by k(1−r), where r is the product moment correlation, for four different modulation frequencies, 4, 16, 64, and 256 Hz at four modulation depths for both AM and FM of a 1000‐Hz carrier of 1000‐ms duration against the image power spectrum of an unmodulated 1000‐Hz 1000‐ms tone. The obtained measures were then linearly regressed (with no intercept) as a function of the square of the modulation index. In all cases k(1−r) gave a good fit (R2>0.95) for both AM and FM. For each of the modulation frequencies the slope of the regression could be used to estimate the model thresholds. The model shows the correct behavior for AM and FM detection. This mechanism, it is suggested, may provide an account of modulation detection interference since low spatial‐frequency filters span several ERBs.

AMS detection of chlorine-36 using small tandems

The present paper proposes a new detection system which can be added to existing or future 3 MV AMS tandems to provide 36Cl measurements at AMS sensitivities. The principles are as follows: A small 3 MV terminal tandem accelerates ions in the 4+ charge state to an energy of ∼ 15 MeV. At this energy, the ions are mass analyzed, stripped a second time and post-acceleration analyzed to select only those mass-36 particles in the 7+ charge state. Following this selection, the ions are directed into a conventional ionization detector located within a high voltage terminal that is maintained at an electric potential of ∼ −3 MV. In this final acceleration stage, 21 MeV is added to the energy of the ions for a final energy of ∼ 36 MeV. Such a detection arrangement combines well-established ion chamber technology and straightforward Van de Graaff high voltage technology with modern data transmission techniques.