The detection of temporal gaps as a function of frequency region and absolute noise bandwidth.

Temporal gap detection was measured as a function of absolute signal bandwidth at a low-, a mid-, and a high-frequency region in six listeners with normal hearing sensitivity. Gap detection threshold decreased monotonically with increasing stimulus bandwidth at each of the three frequency regions. Given conditions of equivalent absolute bandwidth, gap detection thresholds were not significantly different for upper cutoff frequencies ranging from 600 to 4400 Hz. A second experiment investigated gap detection thresholds at two pressure-spectrum levels, conditions typically resulting in substantially different estimates of frequency selectivity. Estimates of frequency selectivity were collected at the two levels using a notched-noise masker technique. The gap threshold-signal bandwidth functions were almost identical at pressure-spectrum levels of 70 dB and 40 dB for the two subjects in experiment II, while estimates of frequency selectivity showed poorer frequency selectivity at the 70-dB level than at 40 dB. Data from both experiments indicated that gap detection in bandlimited noise was inversely related to signal bandwidth and that gap detection did not vary significantly with changes in signal frequency over the range of 600 to 4400 Hz. Over the range of frequencies investigated, the results indicated no clear relation between gap detection for noise stimuli and peripheral auditory filtering.     

Comodulation masking release as a function of bandwidth and test frequency

Comodulation masking release (CMR) was investigated as a function of signal frequency (0.5-4.0 kHz) and the total bandwidth of noise centered on the signal frequency. Taking noncomodulated noise of the same bandwidth as the reference condition, CMR for modulated noise increased with increasing bandwidth of the flanking noise outside the critical band centered on the signal tone; however, this growth asymptoted for broad total bandwidths. These bandwidth effects were expressed by scaling the width of the flanking bands beyond the critical band centered on the signal frequency, approximately according to a critical bandwidth scale. After this scaling, signal frequency had negligible effect on CMR magnitude. For the low modulation frequencies involved, a beneficial effect on CMR at high carrier frequencies would not be expected, and none was observed. Some further trends in the masked thresholds in comodulated and noncomodulated conditions, and the choice of appropriate reference condition are discussed.     

包络调制率和载波频率对听觉时间调制检测能力的影响

通过心理物理实验探讨了包络调制率(<300 Hz)和纯音载波频率(<8 kHz)对听觉时间调制检测能力的影响. 测试信号为以纯音为载波的正弦幅度调制信号, 采用二选一强迫选择法和自适应调整步长的心理物理实验方法, 测试得到不同载波频率条件下的时间调制传递函数. 实验结果表明, 包络调制率和载波频率均会对听觉的时间调制检测能力产生影响. 当载波频率低于2 kHz时, 人耳的检测能力与调制率呈单调递增趋势;当载波频率高于3.5 kHz时, 检测能力也会受到调制率的显著影响, 但没有显著的单调变化趋势. 当调制率在10-100 Hz之间时, 检测能力不随载波频率明显变化;当调制率在150-300 Hz之间时, 调制检测能力随着载波频率上升而下降, 在载波频率达到3.5 kHz时, 调制检测能力不随载波频率显著改变.     

Rabi frequency as a carrier frequency of radiation

An analytical formula with three-center terms has been proposed for the calculation of the dynamic spin susceptibility of electron-doped cuprates. The results of the calculation of the imaginary part of the susceptibility reproduce the main features of inelastic neutron scattering and resonant inelastic X-ray scattering. It has been shown that the high-frequency behavior of the dispersion of collective spin excitations is mainly determined by the parameters of the conduction band and hardly depends on the exchange coupling of copper spins. The spin and superconducting gap parameters, as well as correlation effects associated with the three-center terms, play the determining role in the formation of the spin response in the region Q ≈ (π, π).     

The effects of frequency region and level on the temporal modulation transfer function

Temporal modulation transfer functions (TMTFs) were measured using narrow-band AM and QFM noises with upper spectral edges from 0.6 to 4.8 kHz, and spectrum levels of 10 and 40 dB SPL. The cutoff frequency of the TMTF increases as the upper spectral edge is increased up to 4.8 kHz at low levels, and is constant at higher levels. Sensitivity increases with bandwidth if frequency region is constant. In a second experiment, these results were compared to predictions of a model incorporating peripheral and central limitations to modulation detection. To obtain an estimate of peripheral filtering, frequency selectivity was measured using the notched-noise method, with probe frequencies and levels chosen to parallel those in the first experiment. The TMTF data were then predicted using the model. Predicted cutoff frequencies as a function of the upper spectral edge of the test stimulus were lower than but parallel to those of the subjects at the lower stimulus level. The model predicted only a slight increase in cutoff frequency with level, and thus predicted an increase in cutoff frequency with frequency region at the higher level as well, in contrast to the measured data. These results suggest that there are peripheral and central limitations to temporal resolution, but the psychoacoustically derived auditory filter may be only an indirect measure of peripheral filtering, and/or a more complex model may be needed.     

NoSo and NoS pi detection as a function of masker bandwidth in normal-hearing and cochlear-impaired listeners

NoSo and NoS pi detection thresholds for a 500-Hz pure-tone signal were measured as a function of masking noise bandwidth in normal-hearing and cochlear hearing-impaired subjects. NoSo and NoS pi critical bands were derived from the bandlimited noise functions. A notched noise measure of the monaural critical band was also obtained for each ear. One hypothesis tested was that an asymmetrical monaural critical band would result in a relatively steep improvement of the NoS pi detection threshold as a function of decreasing masker bandwidth and would, therefore, be associated with a wider binaural critical band. This was hypothesized because the outputs of the left and right auditory filters would be more decorrelated the greater the interaural difference in the monaural critical band. However, as the noise bandwidth was narrowed, the decorrelation would lessen, resulting in a relatively steep improvement in NoS pi detection. Results indicated that the masking level difference (MLD) was smaller and that the monaural critical bands were generally wider in cochlear-impaired listeners. NoSo and NoS pi critical bands were somewhat larger in the cochlear hearing-impaired listeners having relatively wide monaural critical bands. There was a significant correlation between monaural critical band asymmetry and the NoS pi critical band; however, this correlation was insignificant when a control was employed for the critical band in the worse ear. Therefore, the present results did not support a strong association between monaural critical band asymmetry and the width of the NoS pi critical band.     

Comodulation masking release (CMR) as a function of masker bandwidth, modulator bandwidth, and signal duration

These experiments examine how comodulation masking release (CMR) varies with masker bandwidth, modulator bandwidth, and signal duration. In experiment 1, thresholds were measured for a 400-ms, 2000-Hz signal masked by continuous noise varying in bandwidth from 50-3200 Hz in 1-oct steps. In one condition, using random noise maskers, thresholds increased with increasing bandwidth up to 400 Hz and then remained approximately constant. In another set of conditions, the masker was multiplied (amplitude modulated) by a low-pass noise (bandwidth varied from 12.5-400 Hz in 1-oct steps). This produced correlated envelope fluctuations across frequency. Thresholds were generally lower than for random noise maskers with the same bandwidth. For maskers less than one critical band wide, the release from masking was largest (about 5 dB) for maskers with low rates of modulation (12.5-Hz-wide low-pass modulator). It is argued that this release from masking is not a "true" CMR but results from a within-channel cue. For broadband maskers (greater than 400 Hz), the release from masking increased with increasing masker bandwidth and decreasing modulator bandwidth, reaching an asymptote of 12 dB for a masker bandwidth of 800 Hz and a modulator bandwidth of 50 Hz. Most of this release from masking can be attributed to a CMR. In experiment 2, the modulator bandwidth was fixed at 12.5 Hz and the signal duration was varied. For masker bandwidths greater than 400 Hz, the CMR decreased from 12 to 5 dB as the signal duration was decreased from 400 to 25 ms.(ABSTRACT TRUNCATED AT 250 WORDS)     

Minimum audible movement angle in the horizontal plane as a function of stimulus frequency and bandwidth, source azimuth, and velocity.

Minimum audible movement angles (MAMAs) were measured in the horizontal plane for four normal-hearing adult subjects in a darkened anechoic chamber. On each trial, a single stimulus was presented, and the subject had to say whether it came from a stationary loudspeaker or from a loudspeaker that was moving at a constant angular velocity around him. Thresholds were established by adaptively varying stimulus duration. In experiment 1, MAMAs were measured as a function of center frequency (500-5000 Hz), velocity (10 degrees-180 degrees/s), and direction of motion (left versus right). There was no effect of direction of motion. MAMAs increased with velocity, from an average of 8.8 degrees of arc for a target moving at 10 degrees/s to an average of 20.2 degrees of arc for a target moving at 180 degrees/s. MAMAs were higher for a 3000-Hz tone than for tones of lower or higher frequencies, as has been previously reported [D. R. Perrott and J. Tucker, J. Acoust. Soc. Am. 83, 1522-1527 (1988)]. In experiment 2, minimum audible angles (MAAs) were measured with sequentially presented stationary tone pulses (500-5000 Hz), and were shown to exhibit the same dependence on signal frequency that the MAMAs showed (average MAA at 3000 Hz: 8.4 degrees; average MAA at the other frequencies: 3.4 degrees). In experiment 3, MAMAs and MAAs were measured as a function of stimulus bandwidth (centered at 3000 Hz) and listening azimuth (0 degrees vs 60 degrees). Average MAAs decreased monotonically as stimulus bandwidth increased from 0 Hz to wideband (from 8.4 degrees to 1.2 degrees at 0 degrees azimuth; from 11.3 degrees to 1.5 degrees at 60 degrees azimuth). As in experiment 1, MAMAs increased with stimulus velocity, from values comparable to the MAAs for the slowest-velocity (10 degrees/s) targets to 70 degrees of arc or more in the poorest condition (third-octave band of noise presented at a velocity of 180 degrees/s and an azimuth of 60 degrees). MAMAs obtained in the slower-velocity conditions depended in the same way on stimulus bandwidth and listening azimuth that MAAs depended on these variables. In no case was the MAMA ever smaller than the MAA. It is hypothesized that a minimum integration time is required to achieve optimal performance in a dynamic spatial resolution task. Average estimates of this minimum time based on the current data vary from 336 ms (for targets presented at midline) to 1116 ms (for narrow-band targets presented at 60 degrees azimuth).(ABSTRACT TRUNCATED AT 400 WORDS)     

Mechanisms underlying the detection of frequency modulation

Frequency modulation detection limens (FMDLs) were measured for carrier frequencies (f(c)) of 1000, 4000, and 6000 Hz, using modulation frequencies (f(m)) of 2 and 10 Hz and levels of 20 and 60 dB sensation level (SL), both with and without random amplitude modulation (AM), applied in all intervals of a forced-choice trial. The AM was intended to disrupt excitation-pattern cues. At 60 dB SL, the deleterious effect of the AM was smaller for f(m) = 2 than for f(m) = 10 Hz for f(c) = 1000 and 4000 Hz, respectively, while for f(c) = 6000 Hz the deleterious effect was large and similar for the two values of f(m). This is consistent with the idea that, for f(c) below about 5000 Hz and f(m) = 2 Hz, frequency modulation can be detected via changes in phase locking over time. However, at 20 dB SL, the deleterious effect of the added AM for f(c) = 1000 and 4000 Hz was similar for the two values of f(m), while for f(c) = 6000 Hz, the deleterious effect of the AM was greater for f(m) = 10 than for f(m) = 2 Hz. It is suggested that, at low SLs, the auditory filters become relatively sharp and phase locking weakens, so that excitation-pattern cues influence FMDLs even for low f(c) and low f(m).     

Spectral loudness summation as a function of duration

Loudness was measured as a function of signal bandwidth for 10-, 100-, and 1000-ms-long signals. The test and reference signals were bandpass-filtered noise spectrally centered at 2 kHz. The bandwidth of the test signal was varied from 200 to 6400 Hz. The reference signal had a bandwidth of 3200 Hz. The reference levels were 45, 55, and 65 dB SPL. The level to produce equal loudness was measured with an adaptive, two-interval, two-alternative forced-choice procedure. A loudness matching procedure was used, where the tracks for all signal pairs to be compared were interleaved. Mean results for nine normal-hearing subjects showed that the magnitude of spectral loudness summation depends on signal duration. For all reference levels, a 6- to 8-dB larger level difference between equally loud signals with the smallest (delta f = 200 Hz) and largest (delta f = 6400 Hz) bandwidth is found for 10-ms-long signals than for the 1000-ms-long signals. The duration effect slightly decreases with increasing reference loudness. As a consequence, loudness models should include a duration-dependent compression stage. Alternatively, if a fixed loudness ratio between signals of different duration is assumed, this loudness ratio should depend on the signal spectrum.     

Spectral modulation masking patterns reveal tuning to spectral envelope frequency

Auditory processing appears to include a series of domain-specific filtering operations that include tuning in the audio-frequency domain, followed by tuning in the temporal modulation domain, and perhaps tuning in the spectral modulation domain. To explore the possibility of tuning in the spectral modulation domain, a masking experiment was designed to measure masking patterns in the spectral modulation domain. Spectral modulation transfer functions (SMTFs) were measured for modulation frequencies from 0.25 to 14 cycles/octave superimposed on noise carriers either one octave (800-1600 Hz, 6400-12,800 Hz) or six octaves wide (200-12,800 Hz). The resulting SMTFs showed maximum sensitivity to modulation between 1 and 3 cycles/octave with reduced sensitivity above and below this region. Masked spectral modulation detection thresholds were measured for masker modulation frequencies of 1, 3, and 5 cycles/octave with a fixed modulation depth of 15 dB. The masking patterns obtained for each masker frequency and carrier band revealed tuning (maximum masking) near the masker frequency, which is consistent with the theory that spectral envelope perception is governed by a series of spectral modulation channels tuned to different spectral modulation frequencies.     

载流子扩散对CCD调制传递函数的影响

由于电荷耦合器件(CCD)具有许多优于其他成像器件的特点,因此其应用领域已被不断地扩展,调制传递函数(MTF)可作为客观评价其成像质量的有效方法。从载流子扩散对其传递函数影响出发,分析其数学模型, 并利用该模型进一步探讨光谱不均匀性,不同扩散长度及初始耗尽宽度对MTF的影响,最后给出了仿真试验结果。     

Amplitude modulation sensitivity as a mechanism increment detection

Detectability of a tonal signal added to a tonal masker increases with increasing duration ("temporal integration"), up to some maximum duration. Initially assumed to be some form of energy integration over time, this phenomenon is now often described as the result of a statistical "multiple looks" process. For continuous maskers, listeners may also use a mechanism sensitive to changes in stimulus intensity, possibly a result of inherent sensitivity to amplitude modulation (AM). In order to examine this hypothesis, change detection was investigated in the presence of AM maskers presented at either the same carrier frequency as the target signal or at a distant frequency. The results are compatible with the hypothesis that listeners detect intensity increments by using change-detection mechanisms (modeled here as the outputs of a bank of modulation filters) sensitive to envelope modulation at both low (4-16 Hz) and high (around 100 Hz) rates. AM masking occurred even when the masker was at a carrier frequency more than two octaves above that of the signal to be detected. This finding is also compatible with the hypothesis that similar mechanisms underlie sensitivity to AM (where across-frequency masking is commonly shown) and detection of intensity increments.     

Modulation gap detection: effects of modulation rate, carrier separation, and mode of presentation.

Modulation gap detection (MGD) is a procedure that measures the sensitivity to an interruption in the modulation pattern imposed upon one or more carrier frequencies. The MGD task was developed to test conditions where a temporal event traverses frequency, but without a concomitant interruption in the spectral continuity of the stimulus. This contrasts with across-frequency gap detection where there is an inherent spectral discontinuity associated with the temporal gap, and where there is a marked decline in performance when the markers of the temporal gap are widely separated in frequency. The purpose of this study was to test the hypothesis that a wideband temporal analysis will be facilitated if there exists a spectral continuity throughout the temporal event. Experiment 1 established the procedure of MGD and indicated that a modulation rate of 8 Hz was optimal for the task. Experiment 2 showed that performance declined markedly when the carrier frequencies of the modulation markers were widely separated in frequency. This finding indicates that spectral continuity across the temporal event is not a sufficient prerequisite for the auditory system to undertake a wideband temporal analysis. Experiment 3 revealed that dichotic MGD also results in poor performance, similar to that seen for widely separated carrier frequencies in the monaural case. This supports the hypothesis that the "channels" across which temporal events are poorly processed do not necessarily correspond to peripheral frequency channels.     

Spectral detection of resonance fluorescence as a generalized quantum measurement

Spectrally resolved detection of single atom resonance fluorescence in the limit of well-separated spectral lines is considered. By using a special type of correlation measurements over the fluorescent field, in which a filtered photon detection is followed by an unfiltered photon detection, we obtain a conditioned atomic state following the filtered photon detection. The properties of the atomic state following detection of the reflected photon are studied and interpreted on the basis of quantum interference between the dressed states. Measurement operators associated with the detection of the passed and reflected photons are derived and used to construct the master equation for the atomic density matrix subjected to continuous spectral detection, the filter tuning being arbitrary.     

The influence of carrier level and frequency on modulation and beat-detection thresholds for sinusoidal carriers

This paper is concerned with modulation and beat detection for sinusoidal carriers. In the first experiment, temporal modulation transfer functions (TMTFs) were measured for carrier frequencies between 1 and 10 kHz. Modulation rates covered the range from 10 Hz to about the rate equaling the critical bandwidth at the carrier frequency. In experiment 2, TMTFs for three carrier frequencies were obtained as a function of the carrier level. In the final experiment, thresholds for the detection of either the lower or the upper modulation sideband (beat detection) were measured for "carrier" frequencies of 5 and 10 kHz, using the same range of modulation rates as in experiment 1. The TMTFs for carrier frequencies of 2 kHz and higher remained flat up to a modulation rate of about 100-130 Hz and had similar values across carrier frequencies. For higher rates, modulation thresholds initially increased and then decreased rapidly, reflecting the subjects' ability to resolve the sidebands spectrally. Detection thresholds generally improved with increasing carrier level, but large variations in the exact level dependence were observed, across subjects as well as across carrier frequencies. For beat rates up to about 70 Hz (at 5 kHz) and 100 Hz (at 10 kHz), beat detection thresholds were the same for the upper and the lower sidebands and were about 6 dB higher than the level per sideband at the modulation-detection threshold. At higher rates the threshold for both sidebands increased, but the increase was larger for the lower sideband. This reflects an asymmetry in masking with more masking towards lower frequencies. Only at rates well beyond the maximum of the TMTF did detection for the lower sideband start to be better than that for the upper sideband. The asymmetry at intermediate frequency separations can be explained by assuming that detection always takes place in filters centered above the stimulus spectrum. The shape of the TMTF and the beat-detection data reflects a limitation in resolving fast amplitude variations, which must occur central to the inner-ear filtering. Its characteristic resembles that of a first-order low-pass filter with a cutoff frequency of about 150 Hz.     

Linear frequency modulation photoacoustic radar: optimal bandwidth and signal-to-noise ratio for frequency-domain imaging of turbid media

The development of the pulse compression photoacoustic (PA) radar using linear frequency modulation (LFM) demonstrated experimentally that spectral matching of the signal to the ultrasonic transducer bandwidth does not necessarily produce the best PA signal-to-noise ratio, and it was shown that the optical and acoustic properties of the absorber will modify the optimal bandwidth. The effects of these factors are investigated in frequency-domain (FD) PA imaging by employing one-dimensional and axisymmetric models of the PA effect, and a Krimholtz-Leedom-Matthaei model for the employed transducers. LFM chirps with various bandwidths were utilized and transducer sensitivity was measured to ensure the accuracy of the model. The theory was compared with experimental results and it was shown that the PA effect can act as a low-pass filter in the signal generation. Furthermore, with the PA radar, the low-frequency behavior of two-dimensional wave generation can appear as a false peak in the cross correlation signal trace. These effects are important in optimizing controllable features of the FD-PA method to improve image quality.